• The 25 Most Influential Psychological Experiments in History

Most Influential Psychological Experiments in History

While each year thousands and thousands of studies are completed in the many specialty areas of psychology, there are a handful that, over the years, have had a lasting impact in the psychological community as a whole. Some of these were dutifully conducted, keeping within the confines of ethical and practical guidelines. Others pushed the boundaries of human behavior during their psychological experiments and created controversies that still linger to this day. And still others were not designed to be true psychological experiments, but ended up as beacons to the psychological community in proving or disproving theories.

This is a list of the 25 most influential psychological experiments still being taught to psychology students of today.

1. A Class Divided

Study conducted by: jane elliott.

Study Conducted in 1968 in an Iowa classroom

A Class Divided Study Conducted By: Jane Elliott

Experiment Details: Jane Elliott’s famous experiment was inspired by the assassination of Dr. Martin Luther King Jr. and the inspirational life that he led. The third grade teacher developed an exercise, or better yet, a psychological experiment, to help her Caucasian students understand the effects of racism and prejudice.

Elliott divided her class into two separate groups: blue-eyed students and brown-eyed students. On the first day, she labeled the blue-eyed group as the superior group and from that point forward they had extra privileges, leaving the brown-eyed children to represent the minority group. She discouraged the groups from interacting and singled out individual students to stress the negative characteristics of the children in the minority group. What this exercise showed was that the children’s behavior changed almost instantaneously. The group of blue-eyed students performed better academically and even began bullying their brown-eyed classmates. The brown-eyed group experienced lower self-confidence and worse academic performance. The next day, she reversed the roles of the two groups and the blue-eyed students became the minority group.

At the end of the experiment, the children were so relieved that they were reported to have embraced one another and agreed that people should not be judged based on outward appearances. This exercise has since been repeated many times with similar outcomes.

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2. Asch Conformity Study

Study conducted by: dr. solomon asch.

Study Conducted in 1951 at Swarthmore College

Asch Conformity Study

Experiment Details: Dr. Solomon Asch conducted a groundbreaking study that was designed to evaluate a person’s likelihood to conform to a standard when there is pressure to do so.

A group of participants were shown pictures with lines of various lengths and were then asked a simple question: Which line is longest? The tricky part of this study was that in each group only one person was a true participant. The others were actors with a script. Most of the actors were instructed to give the wrong answer. Strangely, the one true participant almost always agreed with the majority, even though they knew they were giving the wrong answer.

The results of this study are important when we study social interactions among individuals in groups. This study is a famous example of the temptation many of us experience to conform to a standard during group situations and it showed that people often care more about being the same as others than they do about being right. It is still recognized as one of the most influential psychological experiments for understanding human behavior.

3. Bobo Doll Experiment

Study conducted by: dr. alburt bandura.

Study Conducted between 1961-1963 at Stanford University

Bobo Doll Experiment

In his groundbreaking study he separated participants into three groups:

  • one was exposed to a video of an adult showing aggressive behavior towards a Bobo doll
  • another was exposed to video of a passive adult playing with the Bobo doll
  • the third formed a control group

Children watched their assigned video and then were sent to a room with the same doll they had seen in the video (with the exception of those in the control group). What the researcher found was that children exposed to the aggressive model were more likely to exhibit aggressive behavior towards the doll themselves. The other groups showed little imitative aggressive behavior. For those children exposed to the aggressive model, the number of derivative physical aggressions shown by the boys was 38.2 and 12.7 for the girls.

The study also showed that boys exhibited more aggression when exposed to aggressive male models than boys exposed to aggressive female models. When exposed to aggressive male models, the number of aggressive instances exhibited by boys averaged 104. This is compared to 48.4 aggressive instances exhibited by boys who were exposed to aggressive female models.

While the results for the girls show similar findings, the results were less drastic. When exposed to aggressive female models, the number of aggressive instances exhibited by girls averaged 57.7. This is compared to 36.3 aggressive instances exhibited by girls who were exposed to aggressive male models. The results concerning gender differences strongly supported Bandura’s secondary prediction that children will be more strongly influenced by same-sex models. The Bobo Doll Experiment showed a groundbreaking way to study human behavior and it’s influences.

4. Car Crash Experiment

Study conducted by: elizabeth loftus and john palmer.

Study Conducted in 1974 at The University of California in Irvine

Car Crash Experiment

The participants watched slides of a car accident and were asked to describe what had happened as if they were eyewitnesses to the scene. The participants were put into two groups and each group was questioned using different wording such as “how fast was the car driving at the time of impact?” versus “how fast was the car going when it smashed into the other car?” The experimenters found that the use of different verbs affected the participants’ memories of the accident, showing that memory can be easily distorted.

This research suggests that memory can be easily manipulated by questioning technique. This means that information gathered after the event can merge with original memory causing incorrect recall or reconstructive memory. The addition of false details to a memory of an event is now referred to as confabulation. This concept has very important implications for the questions used in police interviews of eyewitnesses.

5. Cognitive Dissonance Experiment

Study conducted by: leon festinger and james carlsmith.

Study Conducted in 1957 at Stanford University

Experiment Details: The concept of cognitive dissonance refers to a situation involving conflicting:

This conflict produces an inherent feeling of discomfort leading to a change in one of the attitudes, beliefs or behaviors to minimize or eliminate the discomfort and restore balance.

Cognitive dissonance was first investigated by Leon Festinger, after an observational study of a cult that believed that the earth was going to be destroyed by a flood. Out of this study was born an intriguing experiment conducted by Festinger and Carlsmith where participants were asked to perform a series of dull tasks (such as turning pegs in a peg board for an hour). Participant’s initial attitudes toward this task were highly negative.

They were then paid either $1 or $20 to tell a participant waiting in the lobby that the tasks were really interesting. Almost all of the participants agreed to walk into the waiting room and persuade the next participant that the boring experiment would be fun. When the participants were later asked to evaluate the experiment, the participants who were paid only $1 rated the tedious task as more fun and enjoyable than the participants who were paid $20 to lie.

Being paid only $1 is not sufficient incentive for lying and so those who were paid $1 experienced dissonance. They could only overcome that cognitive dissonance by coming to believe that the tasks really were interesting and enjoyable. Being paid $20 provides a reason for turning pegs and there is therefore no dissonance.

6. Fantz’s Looking Chamber

Study conducted by: robert l. fantz.

Study Conducted in 1961 at the University of Illinois

Experiment Details: The study conducted by Robert L. Fantz is among the simplest, yet most important in the field of infant development and vision. In 1961, when this experiment was conducted, there very few ways to study what was going on in the mind of an infant. Fantz realized that the best way was to simply watch the actions and reactions of infants. He understood the fundamental factor that if there is something of interest near humans, they generally look at it.

To test this concept, Fantz set up a display board with two pictures attached. On one was a bulls-eye. On the other was the sketch of a human face. This board was hung in a chamber where a baby could lie safely underneath and see both images. Then, from behind the board, invisible to the baby, he peeked through a hole to watch what the baby looked at. This study showed that a two-month old baby looked twice as much at the human face as it did at the bulls-eye. This suggests that human babies have some powers of pattern and form selection. Before this experiment it was thought that babies looked out onto a chaotic world of which they could make little sense.

7. Hawthorne Effect

Study conducted by: henry a. landsberger.

Study Conducted in 1955 at Hawthorne Works in Chicago, Illinois

Hawthorne Effect

Landsberger performed the study by analyzing data from experiments conducted between 1924 and 1932, by Elton Mayo, at the Hawthorne Works near Chicago. The company had commissioned studies to evaluate whether the level of light in a building changed the productivity of the workers. What Mayo found was that the level of light made no difference in productivity. The workers increased their output whenever the amount of light was switched from a low level to a high level, or vice versa.

The researchers noticed a tendency that the workers’ level of efficiency increased when any variable was manipulated. The study showed that the output changed simply because the workers were aware that they were under observation. The conclusion was that the workers felt important because they were pleased to be singled out. They increased productivity as a result. Being singled out was the factor dictating increased productivity, not the changing lighting levels, or any of the other factors that they experimented upon.

The Hawthorne Effect has become one of the hardest inbuilt biases to eliminate or factor into the design of any experiment in psychology and beyond.

8. Kitty Genovese Case

Study conducted by: new york police force.

Study Conducted in 1964 in New York City

Experiment Details: The murder case of Kitty Genovese was never intended to be a psychological experiment, however it ended up having serious implications for the field.

According to a New York Times article, almost 40 neighbors witnessed Kitty Genovese being savagely attacked and murdered in Queens, New York in 1964. Not one neighbor called the police for help. Some reports state that the attacker briefly left the scene and later returned to “finish off” his victim. It was later uncovered that many of these facts were exaggerated. (There were more likely only a dozen witnesses and records show that some calls to police were made).

What this case later become famous for is the “Bystander Effect,” which states that the more bystanders that are present in a social situation, the less likely it is that anyone will step in and help. This effect has led to changes in medicine, psychology and many other areas. One famous example is the way CPR is taught to new learners. All students in CPR courses learn that they must assign one bystander the job of alerting authorities which minimizes the chances of no one calling for assistance.

9. Learned Helplessness Experiment

Study conducted by: martin seligman.

Study Conducted in 1967 at the University of Pennsylvania

Learned Helplessness Experiment

Seligman’s experiment involved the ringing of a bell and then the administration of a light shock to a dog. After a number of pairings, the dog reacted to the shock even before it happened. As soon as the dog heard the bell, he reacted as though he’d already been shocked.

During the course of this study something unexpected happened. Each dog was placed in a large crate that was divided down the middle with a low fence. The dog could see and jump over the fence easily. The floor on one side of the fence was electrified, but not on the other side of the fence. Seligman placed each dog on the electrified side and administered a light shock. He expected the dog to jump to the non-shocking side of the fence. In an unexpected turn, the dogs simply laid down.

The hypothesis was that as the dogs learned from the first part of the experiment that there was nothing they could do to avoid the shocks, they gave up in the second part of the experiment. To prove this hypothesis the experimenters brought in a new set of animals and found that dogs with no history in the experiment would jump over the fence.

This condition was described as learned helplessness. A human or animal does not attempt to get out of a negative situation because the past has taught them that they are helpless.

10. Little Albert Experiment

Study conducted by: john b. watson and rosalie rayner.

Study Conducted in 1920 at Johns Hopkins University

Little Albert Experiment

The experiment began by placing a white rat in front of the infant, who initially had no fear of the animal. Watson then produced a loud sound by striking a steel bar with a hammer every time little Albert was presented with the rat. After several pairings (the noise and the presentation of the white rat), the boy began to cry and exhibit signs of fear every time the rat appeared in the room. Watson also created similar conditioned reflexes with other common animals and objects (rabbits, Santa beard, etc.) until Albert feared them all.

This study proved that classical conditioning works on humans. One of its most important implications is that adult fears are often connected to early childhood experiences.

11. Magical Number Seven

Study conducted by: george a. miller.

Study Conducted in 1956 at Princeton University

Experiment Details:   Frequently referred to as “ Miller’s Law,” the Magical Number Seven experiment purports that the number of objects an average human can hold in working memory is 7 ± 2. This means that the human memory capacity typically includes strings of words or concepts ranging from 5-9. This information on the limits to the capacity for processing information became one of the most highly cited papers in psychology.

The Magical Number Seven Experiment was published in 1956 by cognitive psychologist George A. Miller of Princeton University’s Department of Psychology in Psychological Review .  In the article, Miller discussed a concurrence between the limits of one-dimensional absolute judgment and the limits of short-term memory.

In a one-dimensional absolute-judgment task, a person is presented with a number of stimuli that vary on one dimension (such as 10 different tones varying only in pitch). The person responds to each stimulus with a corresponding response (learned before).

Performance is almost perfect up to five or six different stimuli but declines as the number of different stimuli is increased. This means that a human’s maximum performance on one-dimensional absolute judgment can be described as an information store with the maximum capacity of approximately 2 to 3 bits of information There is the ability to distinguish between four and eight alternatives.

12. Pavlov’s Dog Experiment

Study conducted by: ivan pavlov.

Study Conducted in the 1890s at the Military Medical Academy in St. Petersburg, Russia

Pavlov’s Dog Experiment

Pavlov began with the simple idea that there are some things that a dog does not need to learn. He observed that dogs do not learn to salivate when they see food. This reflex is “hard wired” into the dog. This is an unconditioned response (a stimulus-response connection that required no learning).

Pavlov outlined that there are unconditioned responses in the animal by presenting a dog with a bowl of food and then measuring its salivary secretions. In the experiment, Pavlov used a bell as his neutral stimulus. Whenever he gave food to his dogs, he also rang a bell. After a number of repeats of this procedure, he tried the bell on its own. What he found was that the bell on its own now caused an increase in salivation. The dog had learned to associate the bell and the food. This learning created a new behavior. The dog salivated when he heard the bell. Because this response was learned (or conditioned), it is called a conditioned response. The neutral stimulus has become a conditioned stimulus.

This theory came to be known as classical conditioning.

13. Robbers Cave Experiment

Study conducted by: muzafer and carolyn sherif.

Study Conducted in 1954 at the University of Oklahoma

Experiment Details: This experiment, which studied group conflict, is considered by most to be outside the lines of what is considered ethically sound.

In 1954 researchers at the University of Oklahoma assigned 22 eleven- and twelve-year-old boys from similar backgrounds into two groups. The two groups were taken to separate areas of a summer camp facility where they were able to bond as social units. The groups were housed in separate cabins and neither group knew of the other’s existence for an entire week. The boys bonded with their cabin mates during that time. Once the two groups were allowed to have contact, they showed definite signs of prejudice and hostility toward each other even though they had only been given a very short time to develop their social group. To increase the conflict between the groups, the experimenters had them compete against each other in a series of activities. This created even more hostility and eventually the groups refused to eat in the same room. The final phase of the experiment involved turning the rival groups into friends. The fun activities the experimenters had planned like shooting firecrackers and watching movies did not initially work, so they created teamwork exercises where the two groups were forced to collaborate. At the end of the experiment, the boys decided to ride the same bus home, demonstrating that conflict can be resolved and prejudice overcome through cooperation.

Many critics have compared this study to Golding’s Lord of the Flies novel as a classic example of prejudice and conflict resolution.

14. Ross’ False Consensus Effect Study

Study conducted by: lee ross.

Study Conducted in 1977 at Stanford University

Experiment Details: In 1977, a social psychology professor at Stanford University named Lee Ross conducted an experiment that, in lay terms, focuses on how people can incorrectly conclude that others think the same way they do, or form a “false consensus” about the beliefs and preferences of others. Ross conducted the study in order to outline how the “false consensus effect” functions in humans.

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In the first part of the study, participants were asked to read about situations in which a conflict occurred and then were told two alternative ways of responding to the situation. They were asked to do three things:

  • Guess which option other people would choose
  • Say which option they themselves would choose
  • Describe the attributes of the person who would likely choose each of the two options

What the study showed was that most of the subjects believed that other people would do the same as them, regardless of which of the two responses they actually chose themselves. This phenomenon is referred to as the false consensus effect, where an individual thinks that other people think the same way they do when they may not. The second observation coming from this important study is that when participants were asked to describe the attributes of the people who will likely make the choice opposite of their own, they made bold and sometimes negative predictions about the personalities of those who did not share their choice.

15. The Schacter and Singer Experiment on Emotion

Study conducted by: stanley schachter and jerome e. singer.

Study Conducted in 1962 at Columbia University

Experiment Details: In 1962 Schachter and Singer conducted a ground breaking experiment to prove their theory of emotion.

In the study, a group of 184 male participants were injected with epinephrine, a hormone that induces arousal including increased heartbeat, trembling, and rapid breathing. The research participants were told that they were being injected with a new medication to test their eyesight. The first group of participants was informed the possible side effects that the injection might cause while the second group of participants were not. The participants were then placed in a room with someone they thought was another participant, but was actually a confederate in the experiment. The confederate acted in one of two ways: euphoric or angry. Participants who had not been informed about the effects of the injection were more likely to feel either happier or angrier than those who had been informed.

What Schachter and Singer were trying to understand was the ways in which cognition or thoughts influence human emotion. Their study illustrates the importance of how people interpret their physiological states, which form an important component of your emotions. Though their cognitive theory of emotional arousal dominated the field for two decades, it has been criticized for two main reasons: the size of the effect seen in the experiment was not that significant and other researchers had difficulties repeating the experiment.

16. Selective Attention / Invisible Gorilla Experiment

Study conducted by: daniel simons and christopher chabris.

Study Conducted in 1999 at Harvard University

Experiment Details: In 1999 Simons and Chabris conducted their famous awareness test at Harvard University.

Participants in the study were asked to watch a video and count how many passes occurred between basketball players on the white team. The video moves at a moderate pace and keeping track of the passes is a relatively easy task. What most people fail to notice amidst their counting is that in the middle of the test, a man in a gorilla suit walked onto the court and stood in the center before walking off-screen.

The study found that the majority of the subjects did not notice the gorilla at all, proving that humans often overestimate their ability to effectively multi-task. What the study set out to prove is that when people are asked to attend to one task, they focus so strongly on that element that they may miss other important details.

17. Stanford Prison Study

Study conducted by philip zimbardo.

Study Conducted in 1971 at Stanford University

Stanford Prison Study

The Stanford Prison Experiment was designed to study behavior of “normal” individuals when assigned a role of prisoner or guard. College students were recruited to participate. They were assigned roles of “guard” or “inmate.”  Zimbardo played the role of the warden. The basement of the psychology building was the set of the prison. Great care was taken to make it look and feel as realistic as possible.

The prison guards were told to run a prison for two weeks. They were told not to physically harm any of the inmates during the study. After a few days, the prison guards became very abusive verbally towards the inmates. Many of the prisoners became submissive to those in authority roles. The Stanford Prison Experiment inevitably had to be cancelled because some of the participants displayed troubling signs of breaking down mentally.

Although the experiment was conducted very unethically, many psychologists believe that the findings showed how much human behavior is situational. People will conform to certain roles if the conditions are right. The Stanford Prison Experiment remains one of the most famous psychology experiments of all time.

18. Stanley Milgram Experiment

Study conducted by stanley milgram.

Study Conducted in 1961 at Stanford University

Experiment Details: This 1961 study was conducted by Yale University psychologist Stanley Milgram. It was designed to measure people’s willingness to obey authority figures when instructed to perform acts that conflicted with their morals. The study was based on the premise that humans will inherently take direction from authority figures from very early in life.

Participants were told they were participating in a study on memory. They were asked to watch another person (an actor) do a memory test. They were instructed to press a button that gave an electric shock each time the person got a wrong answer. (The actor did not actually receive the shocks, but pretended they did).

Participants were told to play the role of “teacher” and administer electric shocks to “the learner,” every time they answered a question incorrectly. The experimenters asked the participants to keep increasing the shocks. Most of them obeyed even though the individual completing the memory test appeared to be in great pain. Despite these protests, many participants continued the experiment when the authority figure urged them to. They increased the voltage after each wrong answer until some eventually administered what would be lethal electric shocks.

This experiment showed that humans are conditioned to obey authority and will usually do so even if it goes against their natural morals or common sense.

19. Surrogate Mother Experiment

Study conducted by: harry harlow.

Study Conducted from 1957-1963 at the University of Wisconsin

Experiment Details: In a series of controversial experiments during the late 1950s and early 1960s, Harry Harlow studied the importance of a mother’s love for healthy childhood development.

In order to do this he separated infant rhesus monkeys from their mothers a few hours after birth and left them to be raised by two “surrogate mothers.” One of the surrogates was made of wire with an attached bottle for food. The other was made of soft terrycloth but lacked food. The researcher found that the baby monkeys spent much more time with the cloth mother than the wire mother, thereby proving that affection plays a greater role than sustenance when it comes to childhood development. They also found that the monkeys that spent more time cuddling the soft mother grew up to healthier.

This experiment showed that love, as demonstrated by physical body contact, is a more important aspect of the parent-child bond than the provision of basic needs. These findings also had implications in the attachment between fathers and their infants when the mother is the source of nourishment.

20. The Good Samaritan Experiment

Study conducted by: john darley and daniel batson.

Study Conducted in 1973 at The Princeton Theological Seminary (Researchers were from Princeton University)

Experiment Details: In 1973, an experiment was created by John Darley and Daniel Batson, to investigate the potential causes that underlie altruistic behavior. The researchers set out three hypotheses they wanted to test:

  • People thinking about religion and higher principles would be no more inclined to show helping behavior than laymen.
  • People in a rush would be much less likely to show helping behavior.
  • People who are religious for personal gain would be less likely to help than people who are religious because they want to gain some spiritual and personal insights into the meaning of life.

Student participants were given some religious teaching and instruction. They were then were told to travel from one building to the next. Between the two buildings was a man lying injured and appearing to be in dire need of assistance. The first variable being tested was the degree of urgency impressed upon the subjects, with some being told not to rush and others being informed that speed was of the essence.

The results of the experiment were intriguing, with the haste of the subject proving to be the overriding factor. When the subject was in no hurry, nearly two-thirds of people stopped to lend assistance. When the subject was in a rush, this dropped to one in ten.

People who were on the way to deliver a speech about helping others were nearly twice as likely to help as those delivering other sermons,. This showed that the thoughts of the individual were a factor in determining helping behavior. Religious beliefs did not appear to make much difference on the results. Being religious for personal gain, or as part of a spiritual quest, did not appear to make much of an impact on the amount of helping behavior shown.

21. The Halo Effect Experiment

Study conducted by: richard e. nisbett and timothy decamp wilson.

Study Conducted in 1977 at the University of Michigan

Experiment Details: The Halo Effect states that people generally assume that people who are physically attractive are more likely to:

  • be intelligent
  • be friendly
  • display good judgment

To prove their theory, Nisbett and DeCamp Wilson created a study to prove that people have little awareness of the nature of the Halo Effect. They’re not aware that it influences:

  • their personal judgments
  • the production of a more complex social behavior

In the experiment, college students were the research participants. They were asked to evaluate a psychology instructor as they view him in a videotaped interview. The students were randomly assigned to one of two groups. Each group was shown one of two different interviews with the same instructor. The instructor is a native French-speaking Belgian who spoke English with a noticeable accent. In the first video, the instructor presented himself as someone:

  • respectful of his students’ intelligence and motives
  • flexible in his approach to teaching
  • enthusiastic about his subject matter

In the second interview, he presented himself as much more unlikable. He was cold and distrustful toward the students and was quite rigid in his teaching style.

After watching the videos, the subjects were asked to rate the lecturer on:

  • physical appearance

His mannerisms and accent were kept the same in both versions of videos. The subjects were asked to rate the professor on an 8-point scale ranging from “like extremely” to “dislike extremely.” Subjects were also told that the researchers were interested in knowing “how much their liking for the teacher influenced the ratings they just made.” Other subjects were asked to identify how much the characteristics they just rated influenced their liking of the teacher.

After responding to the questionnaire, the respondents were puzzled about their reactions to the videotapes and to the questionnaire items. The students had no idea why they gave one lecturer higher ratings. Most said that how much they liked the lecturer had not affected their evaluation of his individual characteristics at all.

The interesting thing about this study is that people can understand the phenomenon, but they are unaware when it is occurring. Without realizing it, humans make judgments. Even when it is pointed out, they may still deny that it is a product of the halo effect phenomenon.

22. The Marshmallow Test

Study conducted by: walter mischel.

Study Conducted in 1972 at Stanford University

The Marshmallow Test

In his 1972 Marshmallow Experiment, children ages four to six were taken into a room where a marshmallow was placed in front of them on a table. Before leaving each of the children alone in the room, the experimenter informed them that they would receive a second marshmallow if the first one was still on the table after they returned in 15 minutes. The examiner recorded how long each child resisted eating the marshmallow and noted whether it correlated with the child’s success in adulthood. A small number of the 600 children ate the marshmallow immediately and one-third delayed gratification long enough to receive the second marshmallow.

In follow-up studies, Mischel found that those who deferred gratification were significantly more competent and received higher SAT scores than their peers. This characteristic likely remains with a person for life. While this study seems simplistic, the findings outline some of the foundational differences in individual traits that can predict success.

23. The Monster Study

Study conducted by: wendell johnson.

Study Conducted in 1939 at the University of Iowa

Experiment Details: The Monster Study received this negative title due to the unethical methods that were used to determine the effects of positive and negative speech therapy on children.

Wendell Johnson of the University of Iowa selected 22 orphaned children, some with stutters and some without. The children were in two groups. The group of children with stutters was placed in positive speech therapy, where they were praised for their fluency. The non-stutterers were placed in negative speech therapy, where they were disparaged for every mistake in grammar that they made.

As a result of the experiment, some of the children who received negative speech therapy suffered psychological effects and retained speech problems for the rest of their lives. They were examples of the significance of positive reinforcement in education.

The initial goal of the study was to investigate positive and negative speech therapy. However, the implication spanned much further into methods of teaching for young children.

24. Violinist at the Metro Experiment

Study conducted by: staff at the washington post.

Study Conducted in 2007 at a Washington D.C. Metro Train Station

Grammy-winning musician, Joshua Bell

During the study, pedestrians rushed by without realizing that the musician playing at the entrance to the metro stop was Grammy-winning musician, Joshua Bell. Two days before playing in the subway, he sold out at a theater in Boston where the seats average $100. He played one of the most intricate pieces ever written with a violin worth 3.5 million dollars. In the 45 minutes the musician played his violin, only 6 people stopped and stayed for a while. Around 20 gave him money, but continued to walk their normal pace. He collected $32.

The study and the subsequent article organized by the Washington Post was part of a social experiment looking at:

  • the priorities of people

Gene Weingarten wrote about the social experiment: “In a banal setting at an inconvenient time, would beauty transcend?” Later he won a Pulitzer Prize for his story. Some of the questions the article addresses are:

  • Do we perceive beauty?
  • Do we stop to appreciate it?
  • Do we recognize the talent in an unexpected context?

As it turns out, many of us are not nearly as perceptive to our environment as we might like to think.

25. Visual Cliff Experiment

Study conducted by: eleanor gibson and richard walk.

Study Conducted in 1959 at Cornell University

Experiment Details: In 1959, psychologists Eleanor Gibson and Richard Walk set out to study depth perception in infants. They wanted to know if depth perception is a learned behavior or if it is something that we are born with. To study this, Gibson and Walk conducted the visual cliff experiment.

They studied 36 infants between the ages of six and 14 months, all of whom could crawl. The infants were placed one at a time on a visual cliff. A visual cliff was created using a large glass table that was raised about a foot off the floor. Half of the glass table had a checker pattern underneath in order to create the appearance of a ‘shallow side.’

In order to create a ‘deep side,’ a checker pattern was created on the floor; this side is the visual cliff. The placement of the checker pattern on the floor creates the illusion of a sudden drop-off. Researchers placed a foot-wide centerboard between the shallow side and the deep side. Gibson and Walk found the following:

  • Nine of the infants did not move off the centerboard.
  • All of the 27 infants who did move crossed into the shallow side when their mothers called them from the shallow side.
  • Three of the infants crawled off the visual cliff toward their mother when called from the deep side.
  • When called from the deep side, the remaining 24 children either crawled to the shallow side or cried because they could not cross the visual cliff and make it to their mother.

What this study helped demonstrate is that depth perception is likely an inborn train in humans.

Among these experiments and psychological tests, we see boundaries pushed and theories taking on a life of their own. It is through the endless stream of psychological experimentation that we can see simple hypotheses become guiding theories for those in this field. The greater field of psychology became a formal field of experimental study in 1879, when Wilhelm Wundt established the first laboratory dedicated solely to psychological research in Leipzig, Germany. Wundt was the first person to refer to himself as a psychologist. Since 1879, psychology has grown into a massive collection of:

  • methods of practice

It’s also a specialty area in the field of healthcare. None of this would have been possible without these and many other important psychological experiments that have stood the test of time.

  • 20 Most Unethical Experiments in Psychology
  • What Careers are in Experimental Psychology?
  • 10 Things to Know About the Psychology of Psychotherapy

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About the Author

After earning a Bachelor of Arts in Psychology from Rutgers University and then a Master of Science in Clinical and Forensic Psychology from Drexel University, Kristen began a career as a therapist at two prisons in Philadelphia. At the same time she volunteered as a rape crisis counselor, also in Philadelphia. After a few years in the field she accepted a teaching position at a local college where she currently teaches online psychology courses. Kristen began writing in college and still enjoys her work as a writer, editor, professor and mother.

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7 Famous Psychology Experiments

Picture of a piece of art used for psychological experiments

Many famous experiments studying human behavior have impacted our fundamental understanding of psychology. Though some could not be repeated today due to breaches in ethical boundaries, that does not diminish the significance of those psychological studies. Some of these important findings include a greater awareness of depression and its symptoms, how people learn behaviors through the process of association and how individuals conform to a group.

Below, we take a look at seven famous psychological experiments that greatly influenced the field of psychology and our understanding of human behavior.

The Little Albert Experiment, 1920

A John’s Hopkins University professor, Dr. John B. Watson, and a graduate student wanted to test a learning process called classical conditioning. Classical conditioning involves learning involuntary or automatic behaviors by association, and Dr. Watson thought it formed the bedrock of human psychology.

A nine-month-old toddler, dubbed “Albert B,” was volunteered for Dr. Watson and Rosalie Rayner ‘s experiment. Albert played with white furry objects, and at first, the toddler displayed joy and affection. Over time, as he played with the objects, Dr. Watson would make a loud noise behind the child’s head to frighten him. After numerous trials, Albert was conditioned to be afraid when he saw white furry objects.

The study proved that humans could be conditioned to enjoy or fear something, which many psychologists believe could explain why people have irrational fears and how they may have developed early in life. This is a great example of experimental study psychology.

Stanford Prison Experiment, 1971

Stanford professor Philip Zimbardo wanted to learn how individuals conformed to societal roles. He wondered, for example, whether the tense relationship between prison guards and inmates in jails had more to do with the personalities of each or the environment.

During Zimbardo’s experiment , 24 male college students were assigned to be either a prisoner or a guard. The prisoners were held in a makeshift prison inside the basement of Stanford’s psychology department. They went through a standard booking process designed to take away their individuality and make them feel anonymous. Guards were given eight-hour shifts and tasked to treat the prisoners just like they would in real life.

Zimbardo found rather quickly that both the guards and prisoners fully adapted to their roles; in fact, he had to shut down the experiment after six days because it became too dangerous. Zimbardo even admitted he began thinking of himself as a police superintendent rather than a psychologist. The study confirmed that people will conform to the social roles they’re expected to play, especially overly stereotyped ones such as prison guards.

“We realized how ordinary people could be readily transformed from the good Dr. Jekyll to the evil Mr. Hyde,” Zimbardo wrote.

The Asch Conformity Study, 1951

Solomon Asch, a Polish-American social psychologist, was determined to see whether an individual would conform to a group’s decision, even if the individual knew it was incorrect. Conformity is defined by the American Psychological Association as the adjustment of a person’s opinions or thoughts so that they fall closer in line with those of other people or the normative standards of a social group or situation.

In his experiment , Asch selected 50 male college students to participate in a “vision test.” Individuals would have to determine which line on a card was longer. However, the individuals at the center of the experiment did not know that the other people taking the test were actors following scripts, and at times selected the wrong answer on purpose. Asch found that, on average over 12 trials, nearly one-third of the naive participants conformed with the incorrect majority, and only 25 percent never conformed to the incorrect majority. In the control group that featured only the participants and no actors, less than one percent of participants ever chose the wrong answer.

Asch’s experiment showed that people will conform to groups to fit in (normative influence) because of the belief that the group was better informed than the individual. This explains why some people change behaviors or beliefs when in a new group or social setting, even when it goes against past behaviors or beliefs.

The Bobo Doll Experiment, 1961, 1963

Stanford University professor Albert Bandura wanted to put the social learning theory into action. Social learning theory suggests that people can acquire new behaviors “through direct experience or by observing the behavior of others.” Using a Bobo doll , which is a blow-up toy in the shape of a life-size bowling pin, Bandura and his team tested whether children witnessing acts of aggression would copy them.

Bandura and two colleagues selected 36 boys and 36 girls between the ages of 3 and 6 from the Stanford University nursery and split them into three groups of 24. One group watched adults behaving aggressively toward the Bobo doll. In some cases, the adult subjects hit the doll with a hammer or threw it in the air. Another group was shown an adult playing with the Bobo doll in a non-aggressive manner, and the last group was not shown a model at all, just the Bobo doll.

After each session, children were taken to a room with toys and studied to see how their play patterns changed. In a room with aggressive toys (a mallet, dart guns, and a Bobo doll) and non-aggressive toys (a tea set, crayons, and plastic farm animals), Bandura and his colleagues observed that children who watched the aggressive adults were more likely to imitate the aggressive responses.

Unexpectedly, Bandura found that female children acted more physically aggressive after watching a male subject and more verbally aggressive after watching a female subject. The results of the study highlight how children learn behaviors from observing others.

The Learned Helplessness Experiment, 1965

Martin Seligman wanted to research a different angle related to Dr. Watson’s study of classical conditioning. In studying conditioning with dogs, Seligman made an astute observation : the subjects, which had already been conditioned to expect a light electric shock if they heard a bell, would sometimes give up after another negative outcome, rather than searching for the positive outcome.

Under normal circumstances, animals will always try to get away from negative outcomes. When Seligman tested his experiment on animals who hadn’t been previously conditioned, the animals attempted to find a positive outcome. Oppositely, the dogs who had been already conditioned to expect a negative response assumed there would be another negative response waiting for them, even in a different situation.

The conditioned dogs’ behavior became known as learned helplessness, the idea that some subjects won’t try to get out of a negative situation because past experiences have forced them to believe they are helpless. The study’s findings shed light on depression and its symptoms in humans.

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The Milgram Experiment, 1963

In the wake of the horrific atrocities carried out by Nazi Germany during World War II, Stanley Milgram wanted to test the levels of obedience to authority. The Yale University professor wanted to study if people would obey commands, even when it conflicted with the person’s conscience.

Participants of the condensed study , 40 males between the ages of 20 and 50, were split into learners and teachers. Though it seemed random, actors were always chosen as the learners, and unsuspecting participants were always the teachers. A learner was strapped to a chair with electrodes in one room while the experimenter äóñ another actor äóñ and a teacher went into another.

The teacher and learner went over a list of word pairs that the learner was told to memorize. When the learner incorrectly paired a set of words together, the teacher would shock the learner. The teacher believed the shocks ranged from mild all the way to life-threatening. In reality, the learner, who intentionally made mistakes, was not being shocked.

As the voltage of the shocks increased and the teachers became aware of the believed pain caused by them, some refused to continue the experiment. After prodding by the experimenter, 65 percent resumed. From the study, Milgram devised the agency theory , which suggests that people allow others to direct their actions because they believe the authority figure is qualified and will accept responsibility for the outcomes. Milgram’s findings help explain how people can make decisions against their own conscience, such as when participating in a war or genocide.

The Halo Effect Experiment, 1977

University of Michigan professors Richard Nisbett and Timothy Wilson were interested in following up a study from 50 years earlier on a concept known as the halo effect . In the 1920s, American psychologist Edward Thorndike researched a phenomenon in the U.S. military that showed cognitive bias. This is an error in how we think that affects how we perceive people and make judgements and decisions based on those perceptions.

In 1977, Nisbett and Wilson tested the halo effect using 118 college students (62 males, 56 females). Students were divided into two groups and were asked to evaluate a male Belgian teacher who spoke English with a heavy accent. Participants were shown one of two videotaped interviews with the teacher on a television monitor. The first interview showed the teacher interacting cordially with students, and the second interview showed the teacher behaving inhospitably. The subjects were then asked to rate the teacher’s physical appearance, mannerisms, and accent on an eight-point scale from appealing to irritating.

Nisbett and Wilson found that on physical appearance alone, 70 percent of the subjects rated the teacher as appealing when he was being respectful and irritating when he was cold. When the teacher was rude, 80 percent of the subjects rated his accent as irritating, as compared to nearly 50 percent when he was being kind.

The updated study on the halo effect shows that cognitive bias isn’t exclusive to a military environment. Cognitive bias can get in the way of making the correct decision, whether it’s during a job interview or deciding whether to buy a product that’s been endorsed by a celebrity we admire.

How Experiments Have Impacted Psychology Today

Contemporary psychologists have built on the findings of these studies to better understand human behaviors, mental illnesses, and the link between the mind and body. For their contributions to psychology, Watson, Bandura, Nisbett and Zimbardo were all awarded Gold Medals for Life Achievement from the American Psychological Foundation. Become part of the next generation of influential psychologists with King University’s online bachelor’s in psychology . Take advantage of King University’s flexible online schedule and complete the major coursework of your degree in as little as 16 months. Plus, as a psychology major, King University will prepare you for graduate school with original research on student projects as you pursue your goal of being a psychologist.

Famous Experiments

The Most Influential Psychological Experiments in History

Solomon Asch Conformity Line Experiment Study

asch experiment

Bandura's Bobo Doll Experiment on Social Learning

Reviewed by Olivia Guy-Evans, MSc

John Money Gender Experiment: Reimer Twins

Reviewed by Saul Mcleod, PhD

Van Ijzendoorn & Kroonenberg: Cultural Variations in Attachment

Jean piaget, behaviorism, neuroscience.

Jean Piaget's theory of cognitive development suggests that children move through four different stages of intellectual development which reflect the increasing sophistication of children's thoughts. Child development is determined by biological maturation and interaction with the environment.

Learn More: Piaget's Stages of Cognitive Development

Behaviorism is a theory of learning that states all behaviors are learned through interaction with the environment through a process called conditioning. Thus, behavior is simply a response to environmental stimuli.

Learn More: Behaviorist Approach in Psychology

Sigmund Freud (1856 to 1939) was the founding father of psychoanalysis, a method for treating mental illness and a theory that explains human behavior. His theories are clinically derived, based on what his patients told him during therapy.

Learn More: Sigmund Freud's Influence on Psychology

An approach is a perspective that involves certain assumptions about human behavior: the way people function, which aspects of them are worthy of study, and what research methods are appropriate for undertaking this study. The five major psychological perspectives are biological, psychodynamic, behaviorist, cognitive, and humanistic.

Learn More: Major Perspectives in Modern Psychology

Neuroscience is the branch of science concerned with studying the nervous system. It is a multidisciplinary field integrating numerous perspectives from biology, psychology, and medicine. It consists of several sub-fields ranging from the study of neurochemicals to the study of behavior and thought.

Learn More: What is Neuroscience?

Frequent Asked Questions

Is psychodynamic same as psychoanalytic?

The words psychodynamic and psychoanalytic are often confused. Remember that Freud’s theories were psychoanalytic, whereas the term ‘psychodynamic’ refers to both his theories and those of his followers, such as Carl Jung, Anna Freud, and Erik Erikson.

Learn More: Psychodynamic Approach

What is developmental psychology?

Developmental psychology is a scientific approach which aims to explain how thinking, feeling, and behavior change throughout a person’s life. A significant proportion of theories within this discipline focus upon development during childhood, as this is the period during an individual’s lifespan when the most change occurs.

Learn More: Developmental Psychology

What is Freud’s psychosexual theory?

Sigmund Freud proposed that personality development in childhood takes place during five psychosexual stages, which are the oral, anal, phallic, latency, and genital stages.

During each stage, sexual energy (libido) is expressed in different ways and through different body parts.

Learn More: Freud’s Psychosexual Stages of Development

What Is object permanence in Piaget’s theory?

Object permanence means knowing that an object still exists, even if it is hidden. It requires the ability to form a mental representation (i.e. a schema) of the object.

The attainment of object permanence generally signals the transition from the sensorimotor stage to the  preoperational stage of development .

Learn More: What Is Object Permanence According To Piaget?

What is the difference between a psychology and sociology?

Psychology studies the mind of an individual to understand human behavior and social and emotional reactions, whereas sociology looks beyond individuals and examines societal institutions and groups of people.

Learn More: Similarities and Differences Between Sociology and Psychology

Explore Famous Experiments

eeg sleep

Dement and Kleitman (1957)

patient hm brain

Henry Gustav Molaison: The Curious Case of Patient H.M. 

held hein

Held and Hein (1963) Kitten carosel

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Harry Harlow Theory & Rhesus Monkey Experiments in Psychology

Western Electric Hawthorne Plant

Hawthorne Effect: Definition, How It Works, and How to Avoid It

hofling obedience

Hofling Hospital Experiment (1966)


Hodges and Tizard (1989): Attachment Research Study

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What Happened to Kitty Genovese

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Konrad Lorenz: Theory of Imprinting in Psychology

little hans2

Little Hans - Freudian Case Study

little albert

Little Albert Experiment (Watson & Rayner)

Little Peter 1924

Little Peter, Cover-Jones (1924)


Loftus and Palmer (1974): Car Crash Experiment

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Mary Ainsworth: Strange Situation Experiment & Attachment Theory

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Stanford Marshmallow Test Experiment

milgram study

Stanley Milgram Shock Experiment

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Phineas Gage: His Accident and Impact on Psychology


Pavlov’s Dogs Experiment and Pavlovian Conditioning Response


Piliavin (1969) Subway Study

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Serial Position Effect (Glanzer & Cunitz, 1966)

psychiatric hospital

Rosenhan (1973) Experiment - 'On being sane in insane places'

summer camp

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Visual Cliff Experiment (Gibson & Walk, 1960)

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Skinner Box: What Is an Operant Conditioning Chamber?

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Stanford Prison Experiment: Zimbardo's Famous Study

Explore Psychology

8 Classic Psychological Experiments

Categories History

Psychological experiments can tell us a lot about the human mind and behavior. Some of the best-known experiments have given us insights into topics such as conformity, obedience, attachment, and learning.

There are many famous (and sometimes infamous) psychological experiments that have helped shape our understanding of the human mind and behavior. Such experiments offered insights into how people respond to social pressure and how they develop associations that lead to fear. 

While many of these psychological experiments are well known even outside of psychology, it is important to recognize that many of them could not be performed today.

In many instances, these experiments would never receive institutional review board approval due to ethical concerns and the potential harm to participants.

In this article, learn more about some of the most famous psychological experiments and discover why some of them are considered so controversial.

Table of Contents

Pavlov’s Dog Experiments, 1897

While not set up as a psychological experiment, Ivan Pavlov’s research on the digestive systems of dogs had a tremendous impact on the field of psychology. During his research, he noticed that dogs would begin to salivate whenever they saw the lab assistant who provided them with food.

By pairing a previously neutral stimulus (a sound) with a naturally occurring stimulus that automatically produces a response (food), Pavlov discovered that he could condition the dogs to salivate when they heard the sound.

The discovery of the classical conditioning process played a pivotal role in the formation of the behavioral school of psychology and has continued to influence our understanding of how learning can occur through associations.

Little Albert Experiment, 1920

Anyone who has ever taken an introductory course in psychology is probably familiar with the Little Albert experiment. In the famous experiment conducted in the 1920s by behaviorists John B. Watson and Rosalie Rayner, an infant was exposed to a white rat to which he initially exhibited no fear. The researchers then presented the rat accompanied by a loud clanging noise. 

After repeated pairings, the child began to cry when the rat alone was presented. This fear was even generalized to objects that resembled the rat such as fluffy white toys.

Watson’s research played an important role in the development of the school of thought known as behaviorism . It also provided evidence of the power of classical conditioning , which involves learning by association. 

The findings also had implications for our understanding of how fears can form, including phobias and irrational fears that sometimes develop early in life or after a single frightening experience.

Asch Conformity Experiment, 1951

The Asch conformity experiments were a series of psychological experiments conducted by psychologist Solomon Asch during the 1950s. The purpose of the experiments was to determine how much a person’s opinions were influenced by the opinions of the rest of the group.

In the study, participants were told that they were taking a “vision test” along with several other participants. In reality, the other individuals in the room were actors who were following the instructions provided by the experimenters.

When shown several line segments, the participants were supposed to select the one that matched a sample line segment in length.

In some cases, those who were in on the study would pick the obvious match. In other cases, however, the study confederates would unanimously pick the wrong line segment. 

The results of Asch’s experiments found that people tended to conform when other people unanimously picked the wrong answer.

Across the 12 trials he conducted, Asch found that around 33% of the naive participants conformed to the group and picked the wrong answer. In a control group, for comparison, less than 1% of the participants ever chose the wrong answer. 

The experiments revealed how group pressure can cause people to change their own behavior in order to fit in with the rest of the group.

Robbers Cave Experiment, 1954

In the Robbers Cave psychological experiment , researcher Muzafer Sherif and his colleagues used a summer camp setting to look at how factors such as competition and prejudice influenced conflict between groups. 

In the experiment, boys attending a summer camp were randomly assigned to two groups. The groups were then placed in situations where they had to compete with one another. Such competition led to conflicts, competition, and hostility between the two groups.

Later, the experiments attempted to reconcile the groups and eliminate the tensions that the previous competitive tasks had created. Bonding activities had little impact, but the researchers found that situations that required members of the two groups to work together in order to overcome a problem were effective at reducing tensions.

The study had implications for how different social groups create their own norms and hierarchies and then use those rules to exclude outsiders.

Harlow’s Rhesus Monkey Experiments, 1958

Psychologist Harry Harlow conducted a series of experiments during the 1950s and 1960s that demonstrated how important love and affection were in the course of child development. In his experiments, he placed infant monkeys in an environment where they had access to two different surrogate “mothers.”

One was a wire mother who held a bottle and provided food, while the other was a soft surrogate mother who was covered in a terry cloth fabric. 

While the cloth mother did not provide nourishment, the experiments demonstrated that the baby monkeys preferred the soft mother over the wire mother. When they were frightened and needed comfort, they would turn to the cloth mother for security.

Milgram Obedience Experiment, 1963

The Milgram experiment was one of the most famous and controversial psychological experiments ever performed. The experiments involved an experimenter ordering participants to deliver electrical shocks to other people.

While the people who were supposedly receiving the shocks were actors who pretended to be in pain, the participants fully believed that they were delivering painful, and even dangerous shocks. 

Milgram’s findings suggested that up to 65% of the participants were willing to deliver potentially fatal shocks to another person simply because an authority figure ordered them to do so. 

Based on these findings, Milgram proposed that people were willing to follow orders from an authority figure if they think that person will take responsibility for the results and is qualified to give orders. 

Bobo Doll Experiment, 1961-1963

In this experiment, Albert Bandura investigated the effects of observational learning by having young children witness acts of aggression and then observing them to see if they copied the behavior.

Children in the study observed adults act aggressively toward a Bobo doll, a large inflatable doll resembling a bowling pin. When hit or kicked, the doll tips sideways and then returns to an upright position.

Bandura found that children who watched an adult act aggressively were more likely to imitate those behaviors later when they were allowed to play in a room with the Bobo doll.

The study played an important role in our understanding of social learning theory and how kids learn by watching others. 

Stanford Prison Experiment, 1971

In this infamous social psychology experiment, Philip Zimbardo set up a mock prison in the basement of the Stanford University psychology department and randomly assigned a group of 24 college students to either be guards or prisoners. 

The study was originally supposed to last for two weeks but had to be stopped after six days because participants reportedly became so immersed in their roles that they began to experience upsetting psychological effects. The results were believed to demonstrate the power that social roles and expectations can exert over a person’s behavior. 

The experiment is widely described in psychology textbooks and even became the subject of a feature film in 2015. 

More recent analysis has suggested that the experiment had serious design flaws, among other problems. In addition to the already problematic ethics of the study, analysis of the study’s records suggests that the experimenters may have played a role in encouraging the abusive behavior displayed by the participants.

Impact of Psychological Experiments

The psychology experiments of the past have had an impact on our understanding of the human mind and behavior. While many of the experiments described here have problems in terms of their design and their ethics, they remain some of the most famous examples of research within the field of psychology.

Learning more about these classic experiments can help you better understand research that informed the development of psychology. It can also provide inspiration for your own psychology experiment ideas and provide information to explore in your psychology papers .

Bandura A, Ross D, Ross SA. Transmission of aggression through imitation of aggressive models . Journal of Abnormal and Social Psychology. 1961;63:575-82. doi:10.1037/h0045925

Gantt WH . Ivan Pavlov . Encyclopaedia Brittanica . Updated February 23, 2020.

Gonzalez-franco M, Slater M, Birney ME, Swapp D, Haslam SA, Reicher SD. Participant concerns for the Learner in a Virtual Reality replication of the Milgram obedience study. PLoS ONE. 2018;13(12):e0209704. doi:10.1371/journal.pone.0209704

Jeon, HL. The environmental factor within the Solomon Asch Line Test . International Journal of Social Science and Humanity. 2014;4(4):264-268. doi:10.7763/IJSSH.2014.V4.360 

Le Texier T. Debunking the Stanford Prison Experiment . American Psychologist . 2019;74(7):823-839. doi:10.1037/amp0000401

Sherif M, Harvey OJ, White BJ, Hood WR, Sherif CW. Intergroup conflict and cooperation: The Robbers Cave experiment (Vol. 10) . Norman, OK: University Book Exchange; 1961.

Zimbardo P, Haney C, Banks WC, Jaffe D. The Stanford Prison Experiment: A simulation study of the psychology of imprisonment. Stanford University, Stanford Digital Repository, Stanford; 1971.


The 11 Most Influential Psychological Experiments in History

The history of psychology is marked by groundbreaking experiments that transformed our understanding of the human mind. These 11 Most Influential Psychological Experiments in History stand out as pivotal, offering profound insights into behaviour, cognition, and the complexities of human nature.

In this PsychologyOrg article, we’ll explain these key experiments, exploring their impact on our understanding of human behaviour and the intricate workings of the mind.

Table of Contents

Experimental psychology.

Experimental psychology is a branch of psychology that uses scientific methods to study human behaviour and mental processes. Researchers in this field design experiments to test hypotheses about topics such as perception, learning, memory, emotion, and motivation.

They use a variety of techniques to measure and analyze behaviour and mental processes, including behavioural observations, self-report measures, physiological recordings, and computer simulations. The findings of experimental psychology studies can have important implications for a wide range of fields, including education, healthcare, and public policy.

Experimental Psychology, Psychologists have long tried to gain insight into how we perceive the world, to understand what motivates our behavior. They have made great strides in lifting that veil of mystery. In addition to providing us with food for stimulating party conversations, some of the most famous psychological experiments of the last century reveal surprising and universal truths about nature.

11 Most Influential Psychological Experiments in History

Throughout the history of psychology, revolutionary experiments have reshaped our comprehension of the human mind. These 11 experiments are pivotal, providing deep insights into human behaviour, cognition, and the intricate facets of human nature.

1. Kohler and the Chimpanzee experiment

Wolfgang Kohler studied the insight process by observing the behaviour of chimpanzees in a problem situation. In the experimental situation, the animals were placed in a cage outside of which food, for example, a banana, was stored. There were other objects in the cage, such as sticks or boxes. The animals participating in the experiment were hungry, so they needed to get to the food. At first, the chimpanzee used sticks mainly for playful activities; but suddenly, in the mind of the hungry chimpanzee, a relationship between sticks and food developed.

The cane, from an object to play with, became an instrument through which it was possible to reach the banana placed outside the cage. There has been a restructuring of the perceptual field: Kohler stressed that the appearance of the new behaviour was not the result of random attempts according to a process of trial and error. It is one of the first experiments on the intelligence of chimpanzees.

2. Harlow’s experiment on attachment with monkeys

In a scientific paper (1959), Harry F. Harlow described how he had separated baby rhesus monkeys from their mothers at birth, and raised them with the help of “puppet mothers”: in a series of experiments he compared the behavior of monkeys in two situations:

Little monkeys with a puppet mother without a bottle, but covered in a soft, fluffy, and furry fabric. Little monkeys with a “puppet” mother that supplied food, but was covered in wire. The little monkeys showed a clear preference for the “furry” mother, spending an average of fifteen hours a day attached to her, even though they were exclusively fed by the “suckling” puppet mother. conclusions of the Harlow experiment: all the experiments showed that the pleasure of contact elicited attachment behaviours, but the food did not.

3. The Strange Situation by Mary Ainsworth

Building on Bowlby’s attachment theory, Mary Ainsworth and colleagues (1978) have developed an experimental method called the Strange Situation, to assess individual differences in attachment security. The Strange Situation includes a series of short laboratory episodes in a comfortable environment and the child’s behaviors are observed.

Ainsworth and colleagues have paid special attention to the child’s behaviour at the time of reunion with the caregiver after a brief separation, thus identifying three different attachment patterns or styles, so called from that moment on. kinds of attachment according to Mary Ainsworth:

Secure attachment (63% of the dyads examined) Anxious-resistant or ambivalent (16%) Avoidant (21%) The Strange Situation by Mary Ainsworth

In a famous 1971 experiment, known as the Stanford Prison, Zimbardo and a team of collaborators reproduced a prison in the garages of Stanford University to study the behaviour of subjects in a context of very particular and complex dynamics. Let’s see how it went and the thoughts on the Stanford prison experiment. The participants (24 students) were randomly divided into two groups:

“ Prisoners “. The latter were locked up in three cells in the basement of a University building for six days; they were required to wear a white robe with a paper over it and a chain on the right ankle. “ Guards “. The students who had the role of prison guards had to watch the basement, choose the most appropriate methods to maintain order, and make the “prisoners” perform various tasks; they were asked to wear dark glasses and uniforms, and never to be violent towards the participants of the opposite role. However, the situation deteriorated dramatically: the fake police officers very soon began to seriously mistreat and humiliate the “detainees”, so it was decided to discontinue the experiment.

4. Jane Elliot’s Blue Eyes Experiment

On April 5, 1968, in a small school in Riceville, Iowa, Professor Jane Elliot decided to give a practical lesson on racism to 28 children of about eight years of age through the blue eyes brown eyes experiment.

“Children with brown eyes are the best,” the instructor began. “They are more beautiful and intelligent.” She wrote the word “melanin” on the board and explained that it was a substance that made people intelligent. Dark-eyed children have more, so they are more intelligent, while blue-eyed children “go hand in hand.”

In a very short time, the brown-eyed children began to treat their blue-eyed classmates with superiority, who in turn lost their self-confidence. A very good girl started making mistakes during arithmetic class, and at recess, she was approached by three little friends with brown eyes “You have to apologize because you get in their way and because we are the best,” said one of them. The girl hastened to apologize. This is one of the psychosocial experiments demonstrating how beliefs and prejudices play a role.

5. The Bobo de Bbandura doll

Albert Bandura gained great fame for the Bobo doll experiment on child imitation aggression, where:

A group of children took as an example, by visual capacity, the adults in a room, without their behaviour being commented on, hit the Bobo doll. Other contemporaries, on the other hand, saw adults sitting, always in absolute silence, next to Bobo.

Finally, all these children were brought to a room full of toys, including a doll like Bobo. Of the 10 children who hit the doll, 8 were those who had seen it done before by an adult. This explains how if a model that we follow performs a certain action, we are tempted to imitate it and this happens especially in children who still do not have the experience to understand for themselves if that behaviour is correct or not.

6. Milgram’s experiment

The Milgram experiment was first carried out in 1961 by psychologist Stanley Milgram, as an investigation into the degree of our deference to authority. A subject is invited to give an electric shock to an individual playing the role of the student, positioned behind a screen when he does not answer a question correctly. An authorized person then tells the subject to gradually increase the intensity of the shock until the student screams in pain and begs to stop.

No justification is given, except for the fact that the authorized person tells the subject to obey. In reality, it was staged: there was absolutely no electric shock given, but in the experiment two-thirds of the subjects were influenced by what they thought was a 450-volt shock, simply because a person in authority told them they would not be responsible for it. nothing.

7. little Albert

We see little Albert’s experiment on unconditioned stimulus, which must be the most famous psychological study. John Watson and Rosalie Raynor showed a white laboratory rat to a nine-month-old boy, little Albert. At first, the boy showed no fear, but then Watson jumped up from behind and made him flinch with a sudden noise by hitting a metal bar with a hammer. Of course, the noise frightened little Albert, who began to cry.

Every time the rat was brought out, Watson and Raynor would rattle the bar with their hammer to scare the poor boy away. Soon the mere sight of the rat was enough to reduce little Albert to a trembling bundle of nerves: he had learned to fear the sight of a rat, and soon afterwards began to fear a series of similar objects shown to him.

8. Pavlov’s dog

Ivan Pavlov’s sheepdog became famous for his experiments that led him to discover what we call “classical conditioning” or “Pavlovian reflex” and is still a very famous psychological experiment today. Hardly any other psychological experiment is cited so often and with such gusto as Pavlov’s theory expounded in 1905: the Russian physiologist had been impressed by the fact that his dogs did not begin to drool at the sight of food, but rather when they heard it. to the laboratory employees who took it away.

He researched it and ordered a buzzer to ring every time it was mealtime. Very soon the sound of the doorbell was enough for the dogs to start drooling: they had connected the signal to the arrival of food.

9. Asch’s experiment

It is about a social psychology experiment carried out in 1951 by the Polish psychologist Solomon Asch on the influence of the majority and social conformity.

The experiment is based on the idea that being part of a group is a sufficient condition to change a person’s actions, judgments, and visual perceptions. The very simple experiment consisted of asking the subjects involved to associate line 1 drawn on a white sheet with the corresponding one, choosing between three different lines A, B, and C present on another sheet. Only one was identical to the other, while the other two were longer or shorter.

The experimentation was carried out in three phases. As soon as one of the subjects, Asch’s accomplice gave a wrong answer associating line 1 with the wrong one, the other members of the group also made the same mistake, even though the correct answer was more than obvious. The participants questioned the reason for this choice and responded that aware of the correct answer, they had decided to conform to the group, adapting to those who had preceded them.

psychotherapy definition types and techniques | Psychotherapy vs therapy Psychologyorg.com

10. Rosenbaum’s experiment

Among the most interesting investigations in this field, an experiment carried out by David Rosenhan (1923) to document the low validity of psychiatric diagnoses stands out. Rosenhan admitted eight assistants to various psychiatric hospitals claiming psychotic symptoms, but once they entered the hospital they behaved as usual.

Despite this, they were held on average for 19 days, with all but one being diagnosed as “psychotic”. One of the reasons why the staff is not aware of the “normality” of the subjects, is, according to Rosenhan, the very little contact between the staff and the patients.

11. Bystander Effect (1968)

The Bystander Effect studied in 1968 after the tragic case of Kitty Genovese, explores how individuals are less likely to intervene in emergencies when others are present. The original research by John Darley and Bibb Latané involved staged scenarios where participants believed they were part of a discussion via intercom.

In the experiment, participants were led to believe they were communicating with others about personal problems. Unknown to them, the discussions were staged, and at a certain point, a participant (confederate) pretended to have a seizure or needed help.

The results were startling. When participants believed they were the sole witness to the emergency, they responded quickly and sought help. However, when they thought others were also present (but were confederates instructed to not intervene), the likelihood of any individual offering help significantly decreased. This phenomenon became known as the Bystander Effect.

The diffusion of responsibility, where individuals assume others will take action, contributes to this effect. The presence of others creates a diffusion of responsibility among bystanders, leading to a decreased likelihood of any single individual taking action.

This experiment highlighted the social and psychological factors influencing intervention during emergencies and emphasized the importance of understanding bystander behaviour in critical situations.

11 Most Influential Psychological Experiments in History

The journey through the “11 Most Influential Psychological Experiments in History” illuminates the profound impact these studies have had on our understanding of human behaviour, cognition, and social dynamics.

Each experiment stands as a testament to the dedication of pioneering psychologists who dared to delve into the complexities of the human mind. From Milgram’s obedience studies to Zimbardo’s Stanford Prison Experiment, these trials have shaped not only the field of psychology but also our societal perceptions and ethical considerations in research.

They serve as timeless benchmarks, reminding us of the ethical responsibilities and the far-reaching implications of delving into the human psyche. The enduring legacy of these experiments lies not only in their scientific contributions but also in the ethical reflections they provoke, urging us to navigate the boundaries of knowledge with caution, empathy, and an unwavering commitment to understanding the intricacies of our humanity.

What is the most famous experiment in the history of psychology?

One of the most famous experiments is the Milgram Experiment, conducted by Stanley Milgram in the 1960s. It investigated obedience to authority figures and remains influential in understanding human behaviour.

Who wrote the 25 most influential psychological experiments in history?

The book “The 25 Most Influential Psychological Experiments in History” was written by Michael Shermer, a science writer and historian of science.

What is the history of experimental psychology?

Experimental psychology traces back to Wilhelm Wundt, often considered the father of experimental psychology. He established the first psychology laboratory in 1879 at the University of Leipzig, marking the formal beginning of experimental psychology as a distinct field.

What was the psychological experiment in the 1960s?

Many significant psychological experiments were conducted in the 1960s. One notable example is the Stanford Prison Experiment led by Philip Zimbardo, which examined the effects of situational roles on behaviour.

Who was the first experimental psychologist?

Wilhelm Wundt is often regarded as the first experimental psychologist due to his establishment of the first psychology laboratory and his emphasis on empirical research methods in psychology.

If you want to read more articles similar to  The 11 Most Influential Psychological Experiments in History , we recommend that you enter our  Psychology  category.

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I'm Waqar, a passionate psychologist and dedicated content writer. With a deep interest in understanding human behavior, I aim to share insights and knowledge in the field of psychology through this blog. Feel free to reach out for collaborations, queries, or discussions. Let's dig into the fascinating world of psychology together!

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John List

  • Big Brains: All Episodes

How John List Revolutionized Economics by Studying People in the Real World (Ep. 28)

Behind the scenes of policymakers reshaping our society, there are researchers supplying them with answers to our most pressing questions. University of Chicago economist John List is one of those people.

If you’ve played Candy Crush, flown on United Airlines, or taken an Uber or Lyft, you’ve been in one of Prof. John List’s experiments without even knowing it. List has revolutionized economics research through his pioneering use of field experiments. A field experiment is conducted in the real world instead of in a lab, testing theories on people in their day-to-day lives.

List’s experiments have changed the world by equipping policymakers with real-world data to address issues like climate change, the gender pay gap, and why inner-city schools fail. But now, he’s warning of a crisis that’s threatening the impact of scientific research: Many studies that claim to tell us something about the world fall apart when you test them on a larger scale. It’s something he calls ‘the scale-up problem.’

Subscribe to Big Brains on  Apple Podcasts ,  Stitcher  and  Spotify . (Episode published August 8, 2019)


  • Study uncovers gender gap in earnings of Uber drivers
  • Scholars take aim at false positives in research
  • Basing Laws on Nothing Is Easier Than Using Evidence— The Atlantic
  • How to Optimize Your Apology— Freakonomics Radio
  • When Not Paying Attention Pays Off— New York Times


John List:  When I step back and think about what I want to accomplish with my research career. It's quite simply to change the world.

Paul Rand:  Behind the scenes of policymakers passing legislation to reshape our society, there are researchers and academics supplying them with answers to our most pressing questions.  University of Chicago e conomist John List is one of those people.

John List: Now, how are you going to do it. The way that I think about doing it is I want to take on the biggest challenges that we face. And I want to use the economic lens and data to shed insights on those questions.

Paul Rand:  In the mid-90s, List revolutionized economics research through his pioneering use of field experiments. A field experiment is conducted in the real world instead of in a lab, testing theories on people in their day-to-day lives. If you’ve ever voted, flown United, taken an Uber or Lyft, you’ve been part of one of List’s experiments without even knowing it.

John List:  We need data. To make well-informed decisions. And the typical way that people have used data, is they wait for the world to give them the data. My way is to go out to the world and generate new data that can help inform important questions and give us important insights on how we should be acting.

Paul Rand:  List’s experiments have reshaped our world in ways that affect our everyday lives—by better equipping policymakers with data to address issues like discrimination, the gender pay gap, and how to raise charitable donations. But now, he’s warning of a crisis that’s threatening the impact of scientific research: many studies that claim to tell us something about the world fall apart when you try to test them on a larger scale.

John List:  You know you find a result there in your lab. But does that results scale up? And what interventional specialists have shown us over the last two decades is that a lot of times it doesn't.

Paul Rand:  List wants to change the world, but if the research turns out to be wrong on a large scale? Well… 

John List:  Houston we have problems.

Paul Rand:  From the University of Chicago, this is Big Brains, a podcast about the stories behind the pivotal research and pioneering breakthroughs reshaping our world. On this episode John List and the power of field experiments. I’m you’re host Paul Rand.

Paul Rand:  As far as accomplished economists go, John List is near the top. He’s served as the chairman of the economics department at The University of Chicago, worked in the White House on the Council of Economic Advisers from 2002-2003, and, most recently, was positioned as the chief economist at Uber and Lyft, all while continuing to teach and research. But List’s early years—and humble beginnings—are crucial to understanding how he came to redefine economics.

John List:  Sure, you're exactly right. It is very different than how my colleagues have come to be economists. So, I started in a little village called Sun Prairie Wisconsin as a kid. My father was a truck driver and my mother was a secretary. And it was sort of an ordinary kind of humble beginning in the sense that I was very loved, but education really wasn't that important when I was a kid. Now, what was important to me was sports and, in particular, I loved golf. When I went to college, I went on a partial golf scholarship. So first goal was to be a golf professional. That was it.

Paul Rand:  Great goal.

John List:  Yeah great goal, fun activity. I arrive the fall of 1987, and I learned two important things about myself. One was I'm not good enough to play professional golf.The second thing I learned that fall is that I really loved economics .And, we would golf every afternoon, and every afternoon I saw three or four econ professors out there golfing too. So I thought well.

Paul Rand:  Good gig.

John List:  Yeah. This is a pretty good gig. You can teach in the morning, you can golf in the afternoon. So, I said I want to do what those guys are doing.

Paul Rand:  Golf wasn’t the only sport List loved, he was also obsessed with baseball. And just like golf would lead him into economics, it was a collection of tiny memorabilia that would lead him on the path to developing his groundbreaking field experiments: baseball cards. 

John List:  That's right. That's right. So as a kid I would cut grass. That was my way of earning pocket change back in the 70s. After being paid, I would go down to the local convenience store called the PDQ and I would buy gum and baseball cards. And I amassed this huge collection. I loved the art of the baseball card. But what I loved more is the aspect of trading. But then, through the undergrad years, I also became a baseball card dealer.

Paul Rand:  Going to trade shows and so on. 

John List:  Absolutely. So what does that mean? What does it mean to be a baseball card dealer? What it means is pretty much every weekend that you're not golfing, you drive down to either Madison, Milwaukee, or Chicago. And you set up what's called a dealer's table which is a six foot long table in a big convention center. So, at the same time, I was learning about the principles of economics and economic theory. So I was always thinking, I wonder if those theories are actually right. And do they give you the correct depiction of what's happening in the baseball card market. So it's always in the back of my mind. I was doing experiments naturally. I would do things like, if a person would come to my table, I would try one form of bargaining with that person, and then when the next person would come, I would try a new form of bargaining, and then I would kind of see what is the best way to bargain.

Paul Rand:  List didn’t know it at the time, but he was laying the groundwork for his field experiments at those card shows. But what was so special about he was doing? 

John List:  So, in the fall of 1987, when I opened up my first economics textbook I turned to a page where it said: economists, essentially, can't do experiments because the world is too messy. Why is it messy? Because you have all kinds of people making all kinds of mistakes, zillions of prices, different products, markets, et cetera et cetera. They thought about it through the lens of a chemistry lab. Back in high school, when I did my chemistry experiments, rule number one was that test tubes had to be pristine. If they were not pristine, you would have a confounding variable i.e. the speck of dirt that would cause your interpretation of the experiment to be wrong. So they're certainly right, there are lots of specks of dirt in the field and in the world. So you can say, well how do you get around that problem? The area of field experiments gets around that problem through randomization. Randomization does not get rid of the dirt. The beauty behind randomization is when you randomly put some people in treatment and some people in control what it does is it balances the dirt across the treatment and control groups. And when you figure out what is the effect of my treatment in this scientific experiment, that dirt ends up differencing out and then it becomes a zero in expectations, and now I can learn something causal in the real world. So that's  kind of why I say they actually had it exactly reversed. 

Paul Rand:  So what was the reaction from the field when you began going on this direction was it, boy brilliant or you don’t know what you’re doing or, that doesn't make any sense?

John List:  Yeah it ranged from you're an idiot to what are you doing to just stay in the lab because we can learn everything we need to in the lab or just use naturally occurring data and make the assumptions. I think field experiments give you something unique though in that you're generating the data yourself. You're not waiting for the world to give you those data, and you can go beyond measurement and figure out the whys behind the data patterns. For example, why do people discriminate, why do people give to charitable causes, why do women earn less than men when they do the same job, why do inner city schools fail?

Paul Rand:  List continued to develop his method of economic field experiments. And, in the late ‘90s, he was finally given the opportunity to put his ideas into action.

John List:  I was an Assistant Professor at the University of Central Florida. And one day the Dean of the College of Business knocked on my door and he said, John I want you to help me raise money. So I said, well let me think about it. I’ve never raised money before, I've bought and sold sports cards in markets, but I've never raised money. And I went back to him and said, I'll help you on two conditions. One: you will allow me to help you raise money but doing it in a field experiment. And two: you will give me five thousand dollars in seed money to help me raise more money for you.

Paul Rand:  So did he think, you’re a pain in the ass for asking this or did he think, wow this is compelling.

John List:  A little bit of both, a little bit of both because he had to go back to his coffers. Here he thought he was going to get some free labor from an assistant professor so a little bit of both. But he agreed to it .

Paul Rand:  List’s field experiments in philanthropy yielded data about how, why and when people give that standard experiments just couldn’t provide. The answers he uncovered are now regularly used by charitable organizations. Like: the higher the announced seed money, the more people give, matching grants increase giving—even if the match is 1 to 1 or 3 to 1. But, List always brings things back to policymakers.

John List:  Now, after you establish those facts you can say, well, are you finding anything that can help policymakers and indeed we do. So one piece of advice that policymakers always need is how should we change the rules around charitable contributions in a way that will help the industry flourish. These are things like marginal tax rates, what are the charitable deductions that are allowed. So when they talk to us they say, you know we're thinking about changing the rules what do you think will happen if we do rule A B or C, and then we tell them exactly what the predictions from the data would be in terms of how it would affect overall charitable giving. Now a third kind of contribution is to say, why do people give? For centuries, you have great philosophers arguing that altruism is the most important underlying reason why people give.

Paul Rand:  You feel good when they give you.

John List:  Well, that's a little bit different. So the way that economists define altruism is, you give to help others. Now, you're onto something that is right though. The other kind of major model for why people might give is you just feel good about giving. That's called warm glow. Now, our data suggests that most givers are giving for that warm glow in what economists would say is sort of selfish because you give just so you feel good about the act of giving. Now to me, when I give talks to large groups of charitable organizations they get very upset with me when I stand in front of five hundred or thousannd people and say, look my data are saying that altruism is important, but not as important as warm glow. And I show them the data and they get upset because they say, why are you making things dirty in a way. Why as an economist do you have to bring in selfish motives et etc? And what I tell them is, I don't care why people give. I want to. 

Paul Rand:  Take the insight.

John List:  Exactly. I want to take the insight and kind of the fourth thing that our data can be used for is to help practitioners. I want to take the insight and say, if I want to grow the pool of, not only the number of donors, but the amount of money that they give, I have to know what makes a person give and what keeps them committed to a cause. Because if I don't know that, I'm not going to know how to fundraise appropriately.

Paul Rand:  List’s work with philanthropy made him a world-renowned economist, and it wasn’t long before for-profit companies started to notice. For the last few years, List has been working as the chief economist at Uber and Lyft, reshaping the way those firms operate while researching drivers and riders. What he’s learned about everything from the gender pay gap to how companies should apologize when they fall short, after the break.

John List:  So this story about me working with firms goes all the way back to when I arrived at Chicago. Steve Levitt published a book called Freakonomics which, all of the listeners, if you haven't read it.

Paul Rand:  You need to read it and listen to the program.

John List:  And listen to the program, exactly, exactly. So, when Freakonomics came out a bunch of firms started to call Steve. And Steve and I started to fly from firm to firm and talked to them about using economics, using behavioral economics and using field experiments to help their business. Now what we were after, of course, would be data. So then you fast forward to 2010, and I received a phone call from Amazon dot com. And it was Jeff Bezos on the other end. And Jeff wanted me to come out to Amazon and be their first Chief Economist.

Paul Rand:  Just calls you and says John I got an idea.

John List:  I've got an idea. I was very close to going and then there was one hiccup: the research that I did at Amazon would never see the light of day outside of the firm because they were trade secrets and they did not want me to use them in scientific publications. I was not ready to give up science at this time. And so I said, I'm sorry, you can give me whatever amount of money in stock options you want—I kind of regret that—but I'm not going to come. But I'll help you hire someone, and I did help them hire Pat Bajari. Who's still there, and he sends me Christmas cards and gives his net worth at the bottom of it. (laughs) So then, I receive a call from Travis Kalanick. 

Paul Rand:  Of Uber.

John List:  So Travis is the founder and CEO of Uber.

Paul Rand:  Did  y ou say hey bro.

John List:  Hey bro, exactly. You know Travis. So Travis tells me that they're on the market for a chief economist. And I said, you know well Travis unless I can use it to gain scientific insights and write scientific articles and publish the work, I'm still just not interested. He said, John we can take care of that for you. So I did that for nearly two years. And as you might guess, some things happened at Uber, and I ended up quitting May 15th of 2018 and I became the first chief economist at Lyft on May 21st of 2018. So at Uber and Lyft, I've taken on questions like who earns more money as a driver, men or women?

Paul Rand:  Turns out, men make about 7 percent more than women, and it’s because they drive faster and drive in more lucrative but sometimes less safe locations.

John List:  If the company messes up. What are the best ways to apologize to its customers?

Paul Rand:  List’s team showed that apologies had a literal cost for the company—discounts on future rides or coupons—were far more effective. It turns out that money does speak louder than words. 

John List:  I've worked a lot on tipping, how to think about inducing more people to tip, who gets tips, who gives tips.

Paul Rand:  According to the data, even though men make more, women do get more tips. Sometimes 10 to 20 percent more.

John List:  Really what I'm up to is, I'm trying to insert economic thinking at every decision node in the company.

Paul Rand:  The lessons and methods from List’s research in philanthropy and at Uber and Lyft can be applied far beyond those companies, to issues like climate change.

John:  I think a very important component of climate change is how the household is behaving. So, we’ve looked into how to induce households to adopt energy conserving technologies. And what we find is basically we can do two tricks to get households to adopt more energy conserving technologies. One is sort of a social norm treatment in that we tell them, you know, 70 percent of your neighbors have one of these gadgets in their home. Would you like one too? That gets people to adopt the first time. Now, if you want them to adopt deeper levels you have to use prices. And what I mean by prices is rebates and subsidies. So now we know if we want to get them to adopt the first one, we can use social nudges or social norms. If we want them to adopt a deeper level, we use price discounts. 

Paul Rand:  List has even tried to tackle questions like why inner-city schools fail.

John List:  That research is essentially going back to pre-K education. I think we pay way too much attention on trying to give kids cognitive skills and not enough attention at giving them executive function skills. After they leave my program if they develop executive function skills in my program they still have them in the eighth grade where if you push cognition that tends to deteriorate after they leave the program. What we also find is that the parental component is not largely ignored but it's not valued at the same level it should be. We think parents are the missing component in early childhood education, and we've designed incentive schemes to get parents more involved in their children's education from zero to five.

Paul Rand : When List tells you about his work, it seems as though he’s running hundreds of research studies at once. But lately, he’s been turning a lot of his attention to a credibility crisis in scientific research. List calls it the scale-up problem. That’s after the break.    

Paul Rand:  It’s a phrase we hear every time politicians are debating or defending a proposal, ”the research shows” or “the data is clear.” We rely on academics and researchers to provide our leaders with information to tackle the issues in our world—and we trust that information is as accurate as possible. But there’s been a growing concern that threatens the credibility of scientific research. List calls it the scale-up problem. 

John List:  As   an example, for the last 10 years, I've been doing an early childhood center in Chicago Heights so we can explore what's called the Education production function. So we're learning a lot about what works in Chicago Heights. But the question, of course, of the greatest import is after we find a result in Chicago Heights, if we scale that up to say all of Chicago or all of Illinois or all of the Midwest or all of the U.S. etc. should we expect to find the same impact from our program that we reported in Chicago Heights. We've never really gone after that question but that's the most important question that policymakers should have. They call it the voltage effect. And what that means is, if I find this really big effect in a small scale experiment if I go to a larger scale the effect ends up being one tenth, or one fifth of what it was in the original experiment. And to that I say Houston we have problems.

Paul Rand:  What do you do about that? 

John List:  So where we started as any good economist would is race to your office and write down a model. So, this is work with Dana Suskind, who was a previous guest on your show and happens to be my wife and one of my graduate students named Omar Al-Ubaydli. And the model is essentially a model of scientific knowledge creation. And we break down this credibility crisis or let's say the scale up effect into three bins. The first bin is what we call a false positive—I ran an experiment and I just got lucky in terms of I found a big effect but it was unlucky in the sense that it wasn't the truth. What we need to do is we need to make sure that we replicate that original experiment roughly three or four times . So, that’s different researchers replicating in your original work. And if you find the same result continuously, you can be very confident that it's a true result in that it should be scaled.Inference number two, kind of bin number two is: well, there could be incentives that the original researcher had that when he or she did the original experiment they might have done something that gave them an overly optimistic result. Let me give you an example of that. So, at Chicago Heights we hired roughly 20 to 40 teachers in our program. What researchers typically do is they put out an advertisement for teachers and a bunch of teachers apply and they take the 20 best teachers. It only makes sense. I'm starting a program, I want to give my program its best shot of being good, so I'm going to hire the 20 best teachers. But now when that result gets scaled up or when that program gets scaled up you might have to hire 20,000 teachers. And guess what, those first 20 are probably your best teachers and the next several thousand are not as good as the first 20. That's a reason for the scale up problem because when you did the original experiment your incentives were, try to get the biggest treatment effect. But at scale you can't choose just 20 teachers.Now, as researchers what can we do? You know what we can do is get a large pool of teachers and then randomly choose which ones are going to be in my original scientific experiment. Because if you randomly choose which ones come in as teachers, that looks a lot like what the population is going to be if we scale it up. So, those are the types of elementsthat as an original researcher you need to think, how do I want my results to be used and if I want them to be scaled up. I need to make those kinds of choices in the original research to make sure that my results will scale.

John List:  Economics to me is common sense. So I think economics that way can be viewed as a great window into the world and a great way to understand how people will respond to incentives for example. WhenI first started. To do field experiments. My main goal was to go to the real world. Generate data. That can test economic theory. Generate data. That can be potentially used by policymakers. 

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Social Psychology Experiments: 10 Of The Most Famous Studies

Ten of the most influential social psychology experiments explain why we sometimes do dumb or irrational things. 

social psychology experiments

Ten of the most influential social psychology experiments explain why we sometimes do dumb or irrational things.

“I have been primarily interested in how and why ordinary people do unusual things, things that seem alien to their natures. Why do good people sometimes act evil? Why do smart people sometimes do dumb or irrational things?” –Philip Zimbardo

Like famous social psychologist Professor Philip Zimbardo (author of The Lucifer Effect: Understanding How Good People Turn Evil ), I’m also obsessed with why we do dumb or irrational things.

The answer quite often is because of other people — something social psychologists have comprehensively shown.

Each of the 10 brilliant social psychology experiments below tells a unique, insightful story relevant to all our lives, every day.

Click the link in each social psychology experiment to get the full description and explanation of each phenomenon.

1. Social Psychology Experiments: The Halo Effect

The halo effect is a finding from a famous social psychology experiment.

It is the idea that global evaluations about a person (e.g. she is likeable) bleed over into judgements about their specific traits (e.g. she is intelligent).

It is sometimes called the “what is beautiful is good” principle, or the “physical attractiveness stereotype”.

It is called the halo effect because a halo was often used in religious art to show that a person is good.

2. Cognitive Dissonance

Cognitive dissonance is the mental discomfort people feel when trying to hold two conflicting beliefs in their mind.

People resolve this discomfort by changing their thoughts to align with one of conflicting beliefs and rejecting the other.

The study provides a central insight into the stories we tell ourselves about why we think and behave the way we do.

3. Robbers Cave Experiment: How Group Conflicts Develop

The Robbers Cave experiment was a famous social psychology experiment on how prejudice and conflict emerged between two group of boys.

It shows how groups naturally develop their own cultures, status structures and boundaries — and then come into conflict with each other.

For example, each country has its own culture, its government, legal system and it draws boundaries to differentiate itself from neighbouring countries.

One of the reasons the became so famous is that it appeared to show how groups could be reconciled, how peace could flourish.

The key was the focus on superordinate goals, those stretching beyond the boundaries of the group itself.

4. Social Psychology Experiments: The Stanford Prison Experiment

The Stanford prison experiment was run to find out how people would react to being made a prisoner or prison guard.

The psychologist Philip Zimbardo, who led the Stanford prison experiment, thought ordinary, healthy people would come to behave cruelly, like prison guards, if they were put in that situation, even if it was against their personality.

It has since become a classic social psychology experiment, studied by generations of students and recently coming under a lot of criticism.

5. The Milgram Social Psychology Experiment

The Milgram experiment , led by the well-known psychologist Stanley Milgram in the 1960s, aimed to test people’s obedience to authority.

The results of Milgram’s social psychology experiment, sometimes known as the Milgram obedience study, continue to be both thought-provoking and controversial.

The Milgram experiment discovered people are much more obedient than you might imagine.

Fully 63 percent of the participants continued administering what appeared like electric shocks to another person while they screamed in agony, begged to stop and eventually fell silent — just because they were told to.

6. The False Consensus Effect

The false consensus effect is a famous social psychological finding that people tend to assume that others agree with them.

It could apply to opinions, values, beliefs or behaviours, but people assume others think and act in the same way as they do.

It is hard for many people to believe the false consensus effect exists because they quite naturally believe they are good ‘intuitive psychologists’, thinking it is relatively easy to predict other people’s attitudes and behaviours.

In reality, people show a number of predictable biases, such as the false consensus effect, when estimating other people’s behaviour and its causes.

7. Social Psychology Experiments: Social Identity Theory

Social identity theory helps to explain why people’s behaviour in groups is fascinating and sometimes disturbing.

People gain part of their self from the groups they belong to and that is at the heart of social identity theory.

The famous theory explains why as soon as humans are bunched together in groups we start to do odd things: copy other members of our group, favour members of own group over others, look for a leader to worship and fight other groups.

8. Negotiation: 2 Psychological Strategies That Matter Most

Negotiation is one of those activities we often engage in without quite realising it.

Negotiation doesn’t just happen in the boardroom, or when we ask our boss for a raise or down at the market, it happens every time we want to reach an agreement with someone.

In a classic, award-winning series of social psychology experiments, Morgan Deutsch and Robert Krauss investigated two central factors in negotiation: how we communicate with each other and how we use threats.

9. Bystander Effect And The Diffusion Of Responsibility

The bystander effect in social psychology is the surprising finding that the mere presence of other people inhibits our own helping behaviours in an emergency.

The bystander effect social psychology experiments are mentioned in every psychology textbook and often dubbed ‘seminal’.

This famous social psychology experiment on the bystander effect was inspired by the highly publicised murder of Kitty Genovese in 1964.

It found that in some circumstances, the presence of others inhibits people’s helping behaviours — partly because of a phenomenon called diffusion of responsibility.

10. Asch Conformity Experiment: The Power Of Social Pressure

The Asch conformity experiments — some of the most famous every done — were a series of social psychology experiments carried out by noted psychologist Solomon Asch.

The Asch conformity experiment reveals how strongly a person’s opinions are affected by people around them.

In fact, the Asch conformity experiment shows that many of us will deny our own senses just to conform with others.

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The Most Famous Social Psychology Experiments Ever Performed

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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Emily is a board-certified science editor who has worked with top digital publishing brands like Voices for Biodiversity, Study.com, GoodTherapy, Vox, and Verywell.

famous field experiments

Social experiments often seek to answer questions about how people behave in groups or how the presence of others impacts individual behavior. Over the years, social psychologists have explored these questions by conducting experiments .

The results of some of the most famous social psychology experiments remain relevant (and often quite controversial) today. Such experiments give us valuable information about human behavior and how group influence can impact our actions in social situations.

At a Glance

Some of the most famous social psychology experiments include Asch's conformity experiments, Bandura's Bobo doll experiments, the Stanford prison experiment, and Milgram's obedience experiments. Some of these studies are quite controversial for various reasons, including how they were conducted, serious ethical concerns, and what their results suggested.

The Asch Conformity Experiments

What do you do when you know you're right but the rest of the group disagrees with you? Do you bow to group pressure?

In a series of famous experiments conducted during the 1950s, psychologist Solomon Asch demonstrated that people would give the wrong answer on a test to fit in with the rest of the group.

In Asch's famous conformity experiments , people were shown a line and then asked to select a line of a matching length from a group of three. Asch also placed confederates in the group who would intentionally choose the wrong lines.

The results revealed that when other people picked the wrong line, participants were likely to conform and give the same answers as the rest of the group.

What the Results Revealed

While we might like to believe that we would resist group pressure (especially when we know the group is wrong), Asch's results revealed that people are surprisingly susceptible to conformity .

Not only did Asch's experiment teach us a great deal about the power of conformity, but it also inspired a whole host of additional research on how people conform and obey, including Milgram's infamous obedience experiments.

The Bobo Doll Experiment

Does watching violence on television cause children to behave more aggressively? In a series of experiments conducted during the early 1960s, psychologist Albert Bandura set out to investigate the impact of observed aggression on children's behavior.

In his Bobo doll experiments , children would watch an adult interacting with a Bobo doll. In one condition, the adult model behaved passively toward the doll, but in another, the adult would kick, punch, strike, and yell at the doll.

The results revealed that children who watched the adult model behave violently toward the doll were likelier to imitate the aggressive behavior later on.​

The Impact of Bandura's Social Psychology Experiment

The debate over the degree to which violence on television, movies, gaming, and other media influences children's behavior continues to rage on today, so it perhaps comes as no surprise that Bandura's findings are still so relevant.

The experiment has also helped inspire hundreds of additional studies exploring the impacts of observed aggression and violence.

The Stanford Prison Experiment

During the early 1970s, Philip Zimbardo set up a fake prison in the basement of the Stanford Psychology Department, recruited participants to play prisoners and guards, and played the role of the prison warden.

The experiment was designed to look at the effect that a prison environment would have on behavior, but it quickly became one of the most famous and controversial experiments of all time.

Results of the Stanford Prison Experiment

The Stanford prison experiment was initially slated to last a full two weeks. It ended after just six days. Why? Because the participants became so enmeshed in their assumed roles, the guards became almost sadistically abusive, and the prisoners became anxious, depressed, and emotionally disturbed.

While the Stanford prison experiment was designed to look at prison behavior, it has since become an emblem of how powerfully people are influenced by situations.  

Ethical Concerns

Part of the notoriety stems from the study's treatment of the participants. The subjects were placed in a situation that created considerable psychological distress. So much so that the study had to be halted less than halfway through the experiment.

The study has long been upheld as an example of how people yield to the situation, but critics have suggested that the participants' behavior may have been unduly influenced by Zimbardo himself in his capacity as the mock prison's "warden."  

Recent Criticisms

The Stanford prison experiment has long been controversial due to the serious ethical concerns of the research, but more recent evidence casts serious doubts on the study's scientific merits.

An examination of study records indicates participants faked their behavior to either get out of the experiment or "help" prove the researcher's hypothesis. The experimenters also appear to have encouraged certain behaviors to help foster more abusive behavior.

The Milgram Experiments

Following the trial of Adolph Eichmann for war crimes committed during World War II, psychologist Stanley Milgram wanted to better understand why people obey. "Could it be that Eichmann and his million accomplices in the Holocaust were just following orders? Could we call them all accomplices?" Milgram wondered.

The results of Milgram's controversial obedience experiments were astonishing and continue to be both thought-provoking and controversial today.

What the Social Psychology Experiment Involved

The study involved ordering participants to deliver increasingly painful shocks to another person. While the victim was simply a confederate pretending to be injured, the participants fully believed that they were giving electrical shocks to the other person.

Even when the victim was protesting or complaining of a heart condition, 65% of the participants continued to deliver painful, possibly fatal shocks on the experimenter's orders.

Obviously, no one wants to believe that they are capable of inflicting pain or torture on another human being simply on the orders of an authority figure. The results of the obedience experiments are disturbing because they reveal that people are much more obedient than they may believe.

Controversy and Recent Criticisms

The study is also controversial because it suffers from ethical concerns, primarily the psychological distress it created for the participants. More recent findings suggest that other problems question the study's findings.

Some participants were coerced into continuing against their wishes. Many participants appeared to have guessed that the learner was faking their responses, and other variations showed that many participants refused to continue the shocks.

What This Means For You

There are many interesting and famous social psychology experiments that can reveal a lot about our understanding of social behavior and influence. However, it is important to be aware of the controversies, limitations, and criticisms of these studies. More recent research may reflect differing results. In some cases, the re-evaluation of classic studies has revealed serious ethical and methodological flaws that call the results into question.

Jeon, HL.  The environmental factor within the Solomon Asch Line Test .  International Journal of Social Science and Humanity.  2014;4(4):264-268. doi:10.7763/IJSSH.2014.V4.360 

Bandura and Bobo . Association for Psychological Science.

Zimbardo, G. The Stanford Prison Experiment: a simulation study on the psychology of imprisonment .

Le Texier T.  Debunking the Stanford Prison Experiment.   Am Psychol.  2019;74(7):823-839. doi:10.1037/amp0000401

Blum B.  The lifespan of a lie .  Medium .

Baker PC. Electric Schlock: Did Stanley Milgram's famous obedience experiments prove anything? Pacific Standard .

Perry G.  Deception and illusion in Milgram's accounts of the obedience experiments .  Theory Appl Ethics . 2013;2(2):79-92.

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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The Top 10 Science Experiments of All Time

These seminal experiments changed our understanding of the universe and ourselves..

Pavlov Dog

Every day, we conduct science experiments, posing an “if” with a “then” and seeing what shakes out. Maybe it’s just taking a slightly different route on our commute home or heating that burrito for a few seconds longer in the microwave. Or it could be trying one more variation of that gene, or wondering what kind of code would best fit a given problem. Ultimately, this striving, questioning spirit is at the root of our ability to discover anything at all. A willingness to experiment has helped us delve deeper into the nature of reality through the pursuit we call science. 

A select batch of these science experiments has stood the test of time in showcasing our species at its inquiring, intelligent best. Whether elegant or crude, and often with a touch of serendipity, these singular efforts have delivered insights that changed our view of ourselves or the universe. 

Here are nine such successful endeavors — plus a glorious failure — that could be hailed as the top science experiments of all time.

Eratosthenes Measures the World

Experimental result: The first recorded measurement of Earth’s circumference 

When: end of the third century B.C.

Just how big is our world? Of the many answers from ancient cultures, a stunningly accurate value calculated by Eratosthenes has echoed down the ages. Born around 276 B.C. in Cyrene, a Greek settlement on the coast of modern-day Libya, Eratosthenes became a voracious scholar — a trait that brought him both critics and admirers. The haters nicknamed him Beta, after the second letter of the Greek alphabet. University of Puget Sound physics professor James Evans explains the Classical-style burn: “Eratosthenes moved so often from one field to another that his contemporaries thought of him as only second-best in each of them.” Those who instead celebrated the multitalented Eratosthenes dubbed him Pentathlos, after the five-event athletic competition.

That mental dexterity landed the scholar a gig as chief librarian at the famous library in Alexandria, Egypt. It was there that he conducted his famous experiment. He had heard of a well in Syene, a Nile River city to the south (modern-day Aswan), where the noon sun shone straight down, casting no shadows, on the date of the Northern Hemisphere’s summer solstice. Intrigued, Eratosthenes measured the shadow cast by a vertical stick in Alexandria on this same day and time. He determined the angle of the sun’s light there to be 7.2 degrees, or 1/50th of a circle’s 360 degrees. 

Knowing — as many educated Greeks did — Earth was spherical, Eratosthenes fathomed that if he knew the distance between the two cities, he could multiply that figure by 50 and gauge Earth’s curvature, and hence its total circumference. Supplied with that information, Eratosthenes deduced Earth’s circumference as 250,000 stades, a Hellenistic unit of length equaling roughly 600 feet. The span equates to about 28,500 miles, well within the ballpark of the correct figure of 24,900 miles. 

Eratosthenes’ motive for getting Earth’s size right was his keenness for geography, a field whose name he coined. Fittingly, modernity has bestowed upon him one more nickname: father of geography. Not bad for a guy once dismissed as second-rate.

William Harvey Takes the Pulse of Nature

Experimental result: The discovery of blood circulation

When: Theory published in 1628

Boy, was Galen wrong. 

The Greek physician-cum-philosopher proposed a model of blood flow in the second century that, despite being full of whoppers, prevailed for nearly 1,500 years. Among its claims: The liver constantly makes new blood from food we eat; blood flows throughout the body in two separate streams, one infused (via the lungs) with “vital spirits” from air; and the blood that tissues soak up never returns to the heart. 

Overturning all this dogma took a series of often gruesome experiments. 

High-born in England in 1578, William Harvey rose to become royal physician to King James I, affording him the time and means to pursue his greatest interest: anatomy. He first hacked away (literally, in some cases) at the Galenic model by exsanguinating — draining the blood from — test critters, including sheep and pigs. Harvey realized that if Galen were right, an impossible volume of blood, exceeding the animals’ size, would have to pump through the heart every hour. 

To drive this point home, Harvey sliced open live animals in public, demonstrating their puny blood supplies. He also constricted blood flow into a snake’s exposed heart by finger-pinching a main vein. The heart shrunk and paled; when pierced, it poured forth little blood. By contrast, choking off the main exiting artery swelled the heart. Through studies of the slow heart beats of reptiles and animals near death, he discerned the heart’s contractions, and deduced that it pumped blood through the body in a circuit.

According to Andrew Gregory, a professor of history and philosophy of science at University College London, this was no easy deduction on Harvey’s part. “If you look at a heart beating normally in its normal surroundings, it is very difficult to work out what is actually happening,” he says. 

Experiments with willing people, which involved temporarily blocking blood flow in and out of limbs, further bore out Harvey’s revolutionary conception of blood circulation. He published the full theory in a 1628 book, De Motu Cordis [The Motion of the Heart]. His evidence-based approach transformed medical science, and he’s recognized today as the father of modern medicine and physiology.

Gregor Mendel Cultivates Genetics

Experimental result: The fundamental rules of genetic inheritance 

When: 1855-1863 

A child, to varying degrees, resembles a parent, whether it’s a passing resemblance or a full-blown mini-me. Why? 

The profound mystery behind the inheritance of physical traits began to unravel a century and a half ago, thanks to Gregor Mendel. Born in 1822 in what is now the Czech Republic, Mendel showed a knack for the physical sciences, though his farming family had little money for formal education. Following the advice of a professor, he joined the Augustinian order, a monastic group that emphasized research and learning, in 1843. 

Ensconced at a monastery in Brno, the shy Gregor quickly began spending time in the garden. Fuchsias in particular grabbed his attention, their daintiness hinting at an underlying grand design. “The fuchsias probably gave him the idea for the famous experiments,” says Sander Gliboff, who researches the history of biology at Indiana University Bloomington. “He had been crossing different varieties, trying to get new colors or combinations of colors, and he got repeatable results that suggested some law of heredity at work.”

These laws became clear with his cultivation of pea plants. Using paintbrushes, Mendel dabbed pollen from one to another, precisely pairing thousands of plants with certain traits over a stretch of about seven years. He meticulously documented how matching yellow peas and green peas, for instance, always yielded a yellow plant. Yet mating these yellow offspring together produced a generation where a quarter of the peas gleamed green again. Ratios like these led to Mendel’s coining of the terms dominant (the yellow color, in this case) and recessive for what we now call genes, and which Mendel referred to as “factors.” 

He was ahead of his time. His studies received scant attention in their day, but decades later, when other scientists discovered and replicated Mendel’s experiments, they came to be regarded as a breakthrough. 

“The genius in Mendel’s experiments was his way of formulating simple hypotheses that explain a few things very well, instead of tackling all the complexities of heredity at once,” says Gliboff. “His brilliance was in putting it all together into a project that he could actually do.”

Isaac Newton Eyes Optics

Experimental result: The nature of color and light

When: 1665-1666

Before he was that Isaac Newton — scientist extraordinaire and inventor of the laws of motion, calculus and universal gravitation (plus a crimefighter to boot) — plain ol’ Isaac found himself with time to kill. To escape a devastating outbreak of plague in his college town of Cambridge, Newton holed up at his boyhood home in the English countryside. There, he tinkered with a prism he picked up at a local fair — a “child’s plaything,” according to Patricia Fara, fellow of Clare College, Cambridge. 

Let sunlight pass through a prism and a rainbow, or spectrum, of colors splays out. In Newton’s time, prevailing thinking held that light takes on the color from the medium it transits, like sunlight through stained glass. Unconvinced, Newton set up a prism experiment that proved color is instead an inherent property of light itself. This revolutionary insight established the field of optics, fundamental to modern science and technology. 

Newton deftly executed the delicate experiment: He bored a hole in a window shutter, allowing a single beam of sunlight to pass through two prisms. By blocking some of the resulting colors from reaching the second prism, Newton showed that different colors refracted, or bent, differently through a prism. He then singled out a color from the first prism and passed it alone through the second prism; when the color came out unchanged, it proved the prism didn’t affect the color of the ray. The medium did not matter. Color was tied up, somehow, with light itself. 

Partly owing to the ad hoc, homemade nature of Newton’s experimental setup, plus his incomplete descriptions in a seminal 1672 paper, his contemporaries initially struggled to replicate the results. “It’s a really, really technically difficult experiment to carry out,” says Fara. “But once you have seen it, it’s incredibly convincing.” 

In making his name, Newton certainly displayed a flair for experimentation, occasionally delving into the self-as-subject variety. One time, he stared at the sun so long he nearly went blind. Another, he wormed a long, thick needle under his eyelid, pressing on the back of his eyeball to gauge how it affected his vision. Although he had plenty of misses in his career — forays into occultism, dabbling in biblical numerology — Newton’s hits ensured his lasting fame.

Michelson and Morley Whiff on Ether

Experimental result: The way light moves

Say “hey!” and the sound waves travel through a medium (air) to reach your listener’s ears. Ocean waves, too, move through their own medium: water. Light waves are a special case, however. In a vacuum, with all media such as air and water removed, light somehow still gets from here to there. How can that be? 

The answer, according to the physics en vogue in the late 19th century, was an invisible, ubiquitous medium delightfully dubbed the “luminiferous ether.” Working together at what is now Case Western Reserve University in Ohio, Albert Michelson and Edward W. Morley set out to prove this ether’s existence. What followed is arguably the most famous failed experiment in history. 

The scientists’ hypothesis was thus: As Earth orbits the sun, it constantly plows through ether, generating an ether wind. When the path of a light beam travels in the same direction as the wind, the light should move a bit faster compared with sailing against the wind. 

To measure the effect, miniscule though it would have to be, Michelson had just the thing. In the early 1880s, he had invented a type of interferometer, an instrument that brings sources of light together to create an interference pattern, like when ripples on a pond intermingle. A Michelson interferometer beams light through a one-way mirror. The light splits in two, and the resulting beams travel at right angles to each other. After some distance, they reflect off mirrors back toward a central meeting point. If the light beams arrive at different times, due to some sort of unequal displacement during their journeys (say, from the ether wind), they create a distinctive interference pattern. 

The researchers protected their delicate interferometer setup from vibrations by placing it atop a solid sandstone slab, floating almost friction-free in a trough of mercury and further isolated in a campus building’s basement. Michelson and Morley slowly rotated the slab, expecting to see interference patterns as the light beams synced in and out with the ether’s direction. 

Instead, nothing. Light’s speed did not vary. 

Neither researcher fully grasped the significance of their null result. Chalking it up to experimental error, they moved on to other projects. (Fruitfully so: In 1907, Michelson became the first American to win a Nobel Prize, for optical instrument-based investigations.) But the huge dent Michelson and Morley unintentionally kicked into ether theory set off a chain of further experimentation and theorizing that led to Albert Einstein’s 1905 breakthrough new paradigm of light, special relativity.

Marie Curie’s Work Matters

Experimental result: Defining radioactivity 

Few women are represented in the annals of legendary scientific experiments, reflecting their historical exclusion from the discipline. Marie Sklodowska broke this mold. 

Born in 1867 in Warsaw, she immigrated to Paris at age 24 for the chance to further study math and physics. There, she met and married physicist Pierre Curie, a close intellectual partner who helped her revolutionary ideas gain a foothold within the male-dominated field. “If it wasn’t for Pierre, Marie would never have been accepted by the scientific community,” says Marilyn B. Ogilvie, professor emeritus in the history of science at the University of Oklahoma. “Nonetheless, the basic hypotheses — those that guided the future course of investigation into the nature of radioactivity — were hers.”

The Curies worked together mostly out of a converted shed on the college campus where Pierre worked. For her doctoral thesis in 1897, Marie began investigating a newfangled kind of radiation, similar to X-rays and discovered just a year earlier. Using an instrument called an electrometer, built by Pierre and his brother, Marie measured the mysterious rays emitted by thorium and uranium. Regardless of the elements’ mineralogical makeup — a yellow crystal or a black powder, in uranium’s case — radiation rates depended solely on the amount of the element present. 

From this observation, Marie deduced that the emission of radiation had nothing to do with a substance’s molecular arrangements. Instead, radioactivity — a term she coined — was an inherent property of individual atoms, emanating from their internal structure. Up until this point, scientists had thought atoms elementary, indivisible entities. Marie had cracked the door open to understanding matter at a more fundamental, subatomic level. 

Curie was the first woman to win a Nobel Prize, in 1903, and one of a very select few people to earn a second Nobel, in 1911 (for her later discoveries of the elements radium and polonium). 

“In her life and work,” says Ogilvie, “she became a role model for young women who wanted a career in science.”

Ivan Pavlov Salivates at the Idea

Experimental result: The discovery of conditioned reflexes

When: 1890s-1900s

Russian physiologist Ivan Pavlov scooped up a Nobel Prize in 1904 for his work with dogs, investigating how saliva and stomach juices digest food. While his scientific legacy will always be tied to doggie drool, it is the operations of the mind — canine, human and otherwise — for which Pavlov remains celebrated today.

Gauging gastric secretions was no picnic. Pavlov and his students collected the fluids that canine digestive organs produced, with a tube suspended from some pooches’ mouths to capture saliva. Come feeding time, the researchers began noticing that dogs who were experienced in the trials would start drooling into the tubes before they’d even tasted a morsel. Like numerous other bodily functions, the generation of saliva was considered a reflex at the time, an unconscious action only occurring in the presence of food. But Pavlov’s dogs had learned to associate the appearance of an experimenter with meals, meaning the canines’ experience had conditioned their physical responses. 

“Up until Pavlov’s work, reflexes were considered fixed or hardwired and not changeable,” says Catharine Rankin, a psychology professor at the University of British Columbia and president of the Pavlovian Society. “His work showed that they could change as a result of experience.” 

Pavlov and his team then taught the dogs to associate food with neutral stimuli as varied as buzzers, metronomes, rotating objects, black squares, whistles, lamp flashes and electric shocks. Pavlov never did ring a bell, however; credit an early mistranslation of the Russian word for buzzer for that enduring myth. 

The findings formed the basis for the concept of classical, or Pavlovian, conditioning. It extends to essentially any learning about stimuli, even if reflexive responses are not involved. “Pavlovian conditioning is happening to us all of the time,” says W. Jeffrey Wilson of Albion College, fellow officer of the Pavlovian Society. “Our brains are constantly connecting things we experience together.” In fact, trying to “un-wire” these conditioned responses is the strategy behind modern treatments for post-traumatic stress disorder, as well as addiction.

Robert Millikan Gets a Charge

Experimental result: The precise value of a single electron’s charge

By most measures, Robert Millikan had done well for himself. Born in 1868 in a small town in Illinois, he went on to earn degrees from Oberlin College and Columbia University. He studied physics with European luminaries in Germany. He then joined the University of Chicago’s physics department, and even penned some successful textbooks. 

But his colleagues were doing far more. The turn of the 20th century was a heady time for physics: In the span of just over a decade, the world was introduced to quantum physics, special relativity and the electron — the first evidence that atoms had divisible parts. By 1908, Millikan found himself pushing 40 without a significant discovery to his name. 

The electron, though, offered an opportunity. Researchers had struggled with whether the particle represented a fundamental unit of electric charge, the same in all cases. It was a critical determination for further developing particle physics. With nothing to lose, Millikan gave it a go. 

In his lab at the University of Chicago, he began working with containers of thick water vapor, called cloud chambers, and varying the strength of an electric field within them. Clouds of water droplets formed around charged atoms and molecules before descending due to gravity. By adjusting the strength of the electric field, he could slow down or even halt a single droplet’s fall, countering gravity with electricity. Find the precise strength where they balanced, and — assuming it did so consistently — that would reveal the charge’s value. 

When it turned out water evaporated too quickly, Millikan and his students — the often-unsung heroes of science — switched to a longer-lasting substance: oil, sprayed into the chamber by a drugstore perfume atomizer. 

The increasingly sophisticated oil-drop experiments eventually determined that the electron did indeed represent a unit of charge. They estimated its value to within whiskers of the currently accepted charge of one electron (1.602 x 10-19 coulombs). It was a coup for particle physics, as well as Millikan. 

“There’s no question that it was a brilliant experiment,” says Caltech physicist David Goodstein. “Millikan’s result proved beyond reasonable doubt that the electron existed and was quantized with a definite charge. All of the discoveries of particle physics follow from that.”

Young, Davisson and Germer See Particles Do the Wave

Experimental result: The wavelike nature of light and electrons 

When: 1801 and 1927, respectively 

Light: particle or wave? Having long wrestled with this seeming either/or, many physicists settled on particle after Isaac Newton’s tour de force through optics. But a rudimentary, yet powerful, demonstration by fellow Englishman Thomas Young shattered this convention. 

Young’s interests covered everything from Egyptology (he helped decode the Rosetta Stone) to medicine and optics. To probe light’s essence, Young devised an experiment in 1801. He cut two thin slits into an opaque object, let sunlight stream through them and watched how the beams cast a series of bright and dark fringes on a screen beyond. Young reasoned that this pattern emerged from light wavily spreading outward, like ripples across a pond, with crests and troughs from different light waves amplifying and canceling each other. 

Although contemporary physicists initially rebuffed Young’s findings, rampant rerunning of these so-called double-slit experiments established that the particles of light really do move like waves. “Double-slit experiments have become so compelling [because] they are relatively easy to conduct,” says David Kaiser, a professor of physics and of the history of science at MIT. “There is an unusually large ratio, in this case, between the relative simplicity and accessibility of the experimental design and the deep conceptual significance of the results.”

More than a century later, a related experiment by Clinton Davisson and Lester Germer showed the depth of this significance. At what is now called Nokia Bell Labs in New Jersey, the physicists ricocheted electron particles off a nickel crystal. The scattered electrons interacted to produce a pattern only possible if the particles also acted like waves. Subsequent double slit-style experiments with electrons proved that particles with matter and undulating energy (light) can each act like both particles and waves. The paradoxical idea lies at the heart of quantum physics, which at the time was just beginning to explain the behavior of matter at a fundamental level. 

“What these experiments show, at their root, is that the stuff of the world, be it radiation or seemingly solid matter, has some irreducible, unavoidable wavelike characteristics,” says Kaiser. “No matter how surprising or counterintuitive that may seem, physicists must take that essential ‘waviness’ into account.”

Robert Paine Stresses Starfish

Experimental result: The disproportionate impact of keystone species on ecosystems

When: Initially presented in a 1966 paper

Just like the purple starfish he crowbarred off rocks and chucked into the Pacific Ocean, Bob Paine threw conventional wisdom right out the window. 

By the 1960s, ecologists had come to agree that habitats thrived primarily through diversity. The common practice of observing these interacting webs of creatures great and small suggested as much. Paine took a different approach. 

Curious what would happen if he intervened in an environment, Paine ran his starfish-banishing experiments in tidal pools along and off the rugged coast of Washington state. The removal of this single species, it turned out, could destabilize a whole ecosystem. Unchecked, the starfish’s barnacle prey went wild — only to then be devoured by marauding mussels. These shellfish, in turn, started crowding out the limpets and algal species. The eventual result: a food web in tatters, with only mussel-dominated pools left behind. 

Paine dubbed the starfish a keystone species, after the necessary center stone that locks an arch into place. A revelatory concept, it meant that all species do not contribute equally in a given ecosystem. Paine’s discovery had a major influence on conservation, overturning the practice of narrowly preserving an individual species for the sake of it, versus an ecosystem-based management strategy.

“His influence was absolutely transformative,” says Oregon State University’s Jane Lubchenco, a marine ecologist. She and her husband, fellow OSU professor Bruce Menge, met 50 years ago as graduate students in Paine’s lab at the University of Washington. Lubchenco, the administrator of the National Oceanic Atmospheric Administration from 2009 to 2013, saw over the years the impact that Paine’s keystone species concept had on policies related to fisheries management.

Lubchenco and Menge credit Paine’s inquisitiveness and dogged personality for changing their field. “A thing that made him so charismatic was almost a childlike enthusiasm for ideas,” says Menge. “Curiosity drove him to start the experiment, and then he got these spectacular results.”

Paine died in 2016. His later work had begun exploring the profound implications of humans as a hyper-keystone species, altering the global ecosystem through climate change and unchecked predation.

Adam Hadhazy is based in New Jersey. His work has also appeared in New Scientist and Popular Science , among other publications. This story originally appeared in print as "10 Experiments That Changed Everything"

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famous field experiments

10 great psychology experiments

by Chris Woodford . Last updated: December 31, 2021.

S tare in the mirror and you'll find a strong sense of self staring back. Every one of us thinks we have a good idea who we are and what we're about—how we laugh and live and love, and all the complicated rest. But if you're a student of psychology —the fascinating science of human behaviour—you may well stare at your reflection with a wary eye. Because you'll know already that the ideas you have about yourself and other people can be very wide of the mark.

You might think you can learn a lot about human behaviour simply by observing yourself, but psychologists know that isn't really true. "Introspection" (thinking about yourself) has long been considered a suspect source of psychological research, even though one of the founding fathers of the science, William James, gained many important insights with its help. [1] Fortunately, there are thousands of rigorous experiments you can study that will do the job much more objectively and scientifically. And here's a quick selection of 10 of my favourites.

1: Are you really paying attention? (Simons & Chabris, 1999)

“ ...our findings suggest that unexpected events are often overlooked... ” Simons & Chabris, 1999

You can read a book or you can listen to the radio, but can you do both at once? Maybe you can listen to a soft-rock album you've heard hundreds of times before and simultaneously plod your way through an undemanding crime novel, but how about listening to a complex political debate while trying to revise for a politics exam? What about listening to a German radio station while reading a French novel? What about mixing things up a bit more. You can iron your clothes while listening to the radio, no problem. But how about trying to follow (and visualize) the radio commentary on a football game while driving a highway you've never been along before? That's much more challenging because both things call on your brain's ability to process spatial information and one tends to interfere with the other. (There are very good reasons why it's unwise to use a cellphone while you're driving—and in some countries it's illegal.)

Generally speaking, we can do—and pay attention—to only so many things at once. That's no big surprise. However human attention works (and there are many theories about that), it's obviously not unlimited. What is surprising is how we pay attention to some things, in some situations, but not others. Psychologists have long studied something they call the cocktail-party effect . If you're at a noisy party, you can selectively switch your attention to any of the voices around you, just like tuning in a radio, while ignoring all the rest. Even more striking, if you're listening to one person and someone else happens to say your name, your ears will prick up and your attention will instantly switch to the other person instead. So your brain must be aware of much more than you think, even if it's not giving everything its full attention, all the time. [2]

Photo: Would you spot a gorilla if it were in plain sight? Picture by Richard Ruggiero courtesy of US Fish and Wildlife Service National Digital Library .

Sometimes, when we're really paying attention, we aren't easily distracted, even by drastic changes we ought to notice. A particularly striking demonstration of this comes from the work of Daniel Simons and Christopher Chabris (1999), who built on earlier work by the esteemed cognitive psychologist Ulric Neisser and colleagues. [3] Simons and Chabris made a video of people in black or white shirts throwing a basketball back and forth and asked viewers to count the number of passes made by the white-shirted players. You can watch it here .

Half the viewers failed to notice something else that happens at the same time (the gorilla-suited person wandering across the set)—an extraordinary example of something psychologists call inattentional blindness (in plain English: failure to see something you really should have spotted). A related phenomenon called change blindness explains why we generally fail to notice things like glaring continuity errors in movies: we don't expect to see them—and so we don't. Whether experiments like "the invisible gorilla" allow us to conclude broader things about human nature is a moot point, but it's certainly fair to say (as Simons and Chabris argue) that they reveal "critically important limitations of our cognitive abilities." None of us are as smart as we like to think, but just because we fail and fall short that doesn't make us bad people; we'd do a lot better if we understood and recognized our shortcomings. [4]

2: Are you trying too hard? (Aronson, 1966)

No-one likes a smart-aleck, so the saying goes, but just how true is that? Even if you really hate someone who has everything—the good looks, the great house, the well-paid job—it tuns out that there are certain circumstances in which you'll like them a whole lot more: if they suddenly make a stupid mistake. This not-entirely-surprising bit of psychology mirrors everyday experience: we like our fellow humans slightly flawed, down-to-earth, and somewhat relatable. Known as the pratfall effect , it was famously demonstrated back in 1966 by social psychologist Elliot Aronson. [5]

“ ...a superior person may be viewed as superhuman and, therefore, distant; a blunder tends to humanize him and, consequently, increases his attractiveness. ” Aronson et al, 1966

Aronson made taped audio recordings of two very different people talking about themselves and answering 50 difficult questions, which were supposedly part of an interview for a college quiz team. One person was very superior, got almost all the questions right, and revealed (in passing) that they were generally excellent at what they did (an honors student, yearbook editor, and member of the college track team). The other person was much more mediocre, got many questions wrong, and revealed (in passing) that they were much more of a plodder (average grades in high school, proofreader of the yearbook, and failed to make the track team). In the experiment, "subjects" (that's what psychologists call the people who take part in their trials) had to listen to the recordings of the two people and rate them on various things, including their likeability. But there was a twist. In some of the taped interviews, an extra bit (the "pratfall") was added at the end where either the superior person or the mediocrity suddenly shouted "Oh my goodness I've spilled coffee all over my new suit", accompanied by the sounds of a clattering chair and general chaos (noises that were identically spliced onto both tapes).

Artwork: Mistakes make you more likeable—if you're considered competent to begin with.

What Aronson found was that the superior person was rated more attractive with the pratfall at the end of their interview; the inferior person, less so. In other words, a pratfall can really work in your favor, but only if you're considered halfway competent to begin with; if not, it works against you. Knowingly or otherwise, smart celebrities and politicians often appear to take advantage of this to improve their popularity.

3: Is the past a foreign country? (Loftus and Palmer, 1974)

Attention isn't the only thing that lets us down; memory is hugely infallible too—and it's one of the strangest and most complex things psychologists study. Can you remember where you were when the Twin Towers fell in 2001 or (if you're much older and willing to go back further) when JFK was shot in Dallas in 1963? You might remember a girl you were in kindergarten with 20 years ago, but perhaps you can't remember the guy you met last week, last night, or even 10 minutes ago. What about the so-called tip-of-the-tongue phenomenon where you're certain you know a word or fact or name, and you can even describe what it's like ("It's a really short word, maybe beginning with 'F'..."), but you can't bring it instantly to mind? [6] How about the madeleine effect, where the taste or smell or something suddenly sets off an incredibly powerful involuntary memory ? What about déjà-vu : a jarring true-false memory—the strong sense something is very familiar when it can't possibly be? [7] How about the curious split between short- and long-term memories or between "procedural memory" (knowing how to do things or follow instructions) and "declarative memory" (knowing facts), which breaks down further into "semantic memory" (general knowledge about things) and "episodic memory" (specific things that have happened to you). What about the many flavors of selective memory failure, such as seniors who can remember the name of a high-school sweetheart but can't recall their own name? Or sudden episodes of amnesia? Human memory is a massive—and massively complex—subject. And any comprehensive theory of it needs to be able to explain a lot.

“ ...the questions asked subsequent to an event can cause a reconstruction in one's memory of that event.. ” Loftus & Palmer, 1974

Much of the time, poor memory is just a nuisance and we all have tricks for working around it—from slapping Post-It notes on the mirror to setting reminders on our phones. But there's one situation where poor memories can be a matter of life or death: in criminal investigation and court testimony. Suppose you give evidence in a trial based on events you think you remember that happened years ago—and suppose your evidence helps to convict a "murderer" who's subsequently sentenced to death. But what if your memory was quite wrong and the person was innocent?

One of the most famous studies of just how flawed our memories can be was made by psychologists Elizabeth Loftus and John Palmer in 1974. [8] After showing their subjects footage of a car accident, they tested their memories some time later by asking "About how fast were the cars going when they smashed into each other?" or using "collided," "bumped," "contacted," or "hit" in place of smashed. Those asked the first—leading—question reported higher speeds. Later, the subjects were asked if they'd seen any broken glass and those asked the leading question ("smashed") were much more likely to say "yes" even though there was no broken glass in the film. So our memories are much more fluid, far less fixed, than we suppose.

Artwork: The words we use to probe our memories can affect the memories we think we have.

This classic experiment very powerfully illustrates the potential unreliability of eyewitness testimony in criminal investigations, but the work of Elizabeth Loftus on so-called "false memory syndrome" has had far-reaching impacts in provocative areas, such as people's alleged recollections of alien abduction , multiple personality disorder , and memories of childhood abuse . Ultimately, what it demonstrates is that memory is fallible and remembering is sometimes less of a mechanical activity (pulling a dusty book from long-neglected library shelf) than a creative and recreative one (rewriting the book partly or completely to compensate for the fact that the print has faded with time). [9]

4. Do you cave in to peer pressure? (Milgram, 1963)

Experiments like the three we've considered so far might cast an uncomfortable shadow, yet most of us are still convinced we're rational, reasonable people, most of the time. Asked to predict how we'd behave in any given situation, we'd be able to give a pretty good account of ourselves—or so you might think. Consider the question of whether you'd ever, under any circumstances, torture another human being and you'd probably be appalled at the prospect. "Of course not!" And yet, as Yale University's Stanley Milgram famously demonstrated in the 1960s and 1970s, you'd probably be mistaken. [10]

Artwork: The Milgram experiment: a shocking turn of events.

Milgram's experiments on obedience to authority have been widely discussed and offered as explanations for all kinds of things, from minor everyday cruelty to the appalling catalogue of repugnant human behavior witnessed during the Nazi Holocaust. Today, they're generally considered unethical because they're deceptive and could, potentially, damage the mental health of people taking part in them (a claim Milgram himself investigated and refuted). [26]

“ ...the conflict stems from the opposition of two deeply ingrained behavior dispositions: first, the disposition not to harm other people, and second, the tendency to obey those whom we perceive to be legitimate authorities. ” Milgram, 1963

Though Milgram's studies have not been repeated, related experiments have sought to shed more light on why people find themselves participating in quite disturbing forms of behavior. One explanation is that, like willing actors, we simply assume the roles we're given and play our parts well. In 1972, Stanford University's Philip Zimbardo set up an entire "pretend prison" and assigned his subjects roles as prisoners or guards. Quite quickly, the guards went beyond simple play acting and actually took on the roles of sadistic bullies, exposing the prisoners to all kinds of rough and degrading treatment, while the prisoners resigned themselves to their fate or took on the roles of rebels. [11] More recently, Zimbardo has argued that his work sheds light on atrocities such as the torture at the Abu Ghraib prison in 2004, when US army guards were found to have tortured and degraded Iraqi prisoners under their guard in truly shocking ways.

5. Are you a slave to pleasure? (Olds and Milner, 1954)

Why do we do the things we do? Why do we eat or drink, play football, watch TV... or do the legions of other things we feel compelled to do each day? How, when we take these sorts of behaviors to extremes, do we become addicted to things like drink and drugs, gambling or sex? Are they ordinary pleasures taken to extremes or something altogether different? Obsessions, compulsions, and addictive behaviors are complex and very difficult to treat, but what causes them... and how do we treat them?

Artwork: A rat will happily stimulate the "pleasure centre" in its brain.

“ It appears that motivation, like sensation, has local centers in the brain. ” James Olds, Scientific American, 1956.

The Olds and Milner ICSS (intracranial self-stimulation) experiment was widely interpreted as the discovery of a "pleasure center" in the brain, but we have to take that suggestion with quite a pinch of salt. It's fascinating, but also quite reductively depressing, to imagine that a lot of the things humans feel compelled to do each day—from work and eating to sport and sex—are motivated by nothing more than the need to scratch a deep neural itch: to repeatedly stimulate a "hungry" part of our brain. While it offers important insights into addictive behavior, the idea that all of our complex human pleasure-seeking stems from something so crudely behavioral—stimulus and reward—seems absurdly over-simple. It's fascinating to search for references to Olds and Milner's work and see it quoted in books with such titles as Your Money and Your Brain: How the New Science of Neuroeconomics Can Help Make You Rich . But it's quite a stretch from a rat pushing on a pedal to making arguments of that kind. [14]

6: Are you asleep at the wheel? (Libet, 1983)

Being a conscious, active human being is a bit like driving a car: looking out through your eyes is like staring through a windshield, seeing (perceiving) things and responding to them, as they see and respond to you. Consciousness, in other words, feels like a "top-down" thing; like the driver of a car, we're always in control, willing the world to bend to our way, making things happen according to ideas our brains we devise beforehand. But how true is that really? If you are a driver, you'll know that much of what you do depends on a kind of mental "auto-pilot" or cruise control. As a practiced driver, you barely have to think about what you're doing at all—it's completely automatic. We're only really aware of just how effort-full and attentive drivers need to be when we first start learning. We soon learn to do most of the things involved in driving without being consciously aware of them at all—and that's true of other things too, not just driving a car. Seen this way, driving seems impressive—but if you think again about the Simons and Chabris gorilla experiment, and consider its implications for sitting behind the wheel, you might want to take the bus in future.

Still, you might think, you're always, ultimately, in charge and in control: you're the driver , not the passenger, even if you are sometimes dozy at the wheel. And yet, a remarkable series of experiments by Benjamin Libet, in the 1980s, appeared to demonstrate something entirely different: far from consciously making things happen, sometimes we become conscious of what we've done after the fact. In Libet's experiments, he made people watch a clock and move their wrist when it reached a certain time. But their brain activity (which he was also monitoring) showed a peak a fraction of a second before their conscious decision to move, suggesting, at least in this case, that consciousness is the effect, not the cause. [15]

“ Many of our mental functions are carried out unconsciously , without conscious awareness. ” Benjamin Libet, Mind Time, 2004, p.2.

On the face of it, Libet's work seems to have extraordinary implications for the study of consciousness. It's almost like we're zombies sitting at the wheel of a self-driving car. Is the whole idea of conscious free will just an illusion, an accidental artefact of knee-jerk behavior that happens much more automatically? You can certainly try to argue it that way, as many people have. On the other hand, it's important to remember that this is a highly constrained laboratory experiment and you can't automatically extrapolate from that to more general human behavior. (Apart from anything else, the methodology of Libet's experiments has been questioned. [16] ) While you could try to argue that a complex decision (to buy a house or quit your job) is made unconsciously or subconsciously in whatever manner and we rationalize or become conscious of it after the fact, experiments like Libet's aren't offering evidence for that. Sometimes, it's too much of a stretch to argue from simple, highly contrived, very abstract laboratory experiments to bigger, bolder, and more general everyday behavior.

On the other hand, it's quite likely that some behavior that we believe to be consciously pre-determined is anything but, as William James (and, independently, Carl Lange) reasoned way back in the late 19th century. In a famous example James offered, we assume we run from a scary bear because we see the bear and feel afraid. But James believed the reasoning here is back to front: we see the bear, run, and only feel afraid because we find ourselves running from a bear! (How we arrive at emotions is a whole huge topic of its own. The James-Lange theory eventually spawned more developed theories by Walter Cannon and Philip Bard, who believed emotions and their causes happen simultaneously, and Stanley Shachter and Jerome Singer, who believe emotions stem both from our bodily reactions and how we think about them.) [17]

7: Why are you so attached? (Harlow et al, 1971)

“ Love is a wondrous state, deep, tender, and rewarding. Because of its intimate and personal nature it is regarded by some as an improper topic for experimental research. ” Harry Harlow, 1958.

Artwork: Animals crave proper comfort, not just the simple "reduction" of "drives" like hunger. Photo courtesy of NASA and Wikimedia Commons .

There's an obvious evolutionary reason why we get attached to other people: one way or another, it improves our chances of surviving, mating, and passing on our genes to future generations. Attachment begins at birth, but our attachment to our mothers isn't motivated purely by a simple need for nourishment (through breastfeeding or whatever it might be). One of the most famous psychological experiments of all time demonstrated this back in the early 1970s. The University of Wisconsin's Harry Harlow and his wife Margaret tested what happened when newborn baby monkeys were separated from their mothers and "raised," instead by crude, mechanical surrogates. In particular, Harlow looked at how the monkeys behaved toward two rival "mothers", one with a wooden head and a wire body that had a feeding bottle attached, and one made from soft, warm, comforting cloth. Perhaps surprisingly, the babies preferred the cloth mother. Even when they ventured over to the wire mother for food, they soon returned to the cloth mother for comfort and reassurance. [18]

The fascinating thing about this study is that it suggests the need for comfort is at least as important as the (more obviously fundamental) need for nourishment, so busting the cold, harsh claims of hard-wired behaviorists, who believed our attachment to our mothers was all about mechanistic "drive reduction," or knee-jerk stimulus and response. Ultimately, we love the loving—Harlow's "contact comfort"—and perhaps things like habits, routines, and traditions can all be interpreted in this light.

8: Are you as rational as you think? (Wason, 1966)

“ ... I have concentrated mainly on the mistakes, assumptions, and stereotyped behavior which occur when people have to reason about abstract material. But... we seldom do reason about abstract material. ” Peter Wason, 1966.

Like everyone else, you probably have your moments of wild, reckless abandon, but faced with the task of making a calm, rational judgment about something, how well do you think you'd do? It's not a question of what you know or how clever you are, but how well you can make a judgment or a decision. Suppose, for example, you had to hire the best applicant for a job based on a pile of résumés. Or what if you had to find a new apartment by the end of the month and you had a limited selection to pick among. What if you were on the jury of a trial and had to sit through weeks or evidence to reach a verdict? How well do you think you'd do? Probably, given all the information, you feel you'd make a fair job of it: you have faith in your judgment. And yet, decades of research into human decision-making suggests you'll massively overestimate your own ability. Overconfident and under-informed, you'll jump to hasty conclusions, swayed by glaring biases you don't even notice. In the words of Daniel Kahneman, probably the world's leading expert on human rationality, your brain opts to think "fast" (reaches a quick and dirty decision) when sometimes it'd be better off thinking "slow" (reaching a more considered verdict). [25]

A classic demonstration of how poorly we think was devised by British psychologist Peter Wason in 1966. The experimenter puts a set of four white cards in front of you, each of which has a letter on one side and a number on the other. Then they tell you that if a card has a vowel on one side, it has an even number on the other side. Finally, they ask you which cards you need to turn over to verify if that statement is true. Suppose the cards show A, D, 4, and 7. The obvious answer, offered by most people, is A and 4 or just A. But the correct answer is actually A and 7. Once you've turned over A, it serves no purpose to turn over D or 4: turning over D tells us nothing, because it's not a vowel, while turning over 4 doesn't provide extra proof or disprove the statement. By turning over 7, however, you can potentially disprove the theory if you reveal a vowel on the other side of it. Wason's four-card test demonstrates what's known as "confirmation bias"—our failure to seek out evidence that contradicts things we believe. [19]

Artwork: Peter Wason's four-card selection test. If a card has a vowel on one side, it has an even number on the other. Which cards do you need to turn over to confirm this?

As with the other experiments here, you could extrapolate and argue that Wason's abstract reasoning test is echoed by bigger and wider failings we see in ourselves. Perhaps it goes some way to explaining things like online "echo chambers" and "filter bubbles", where we tend to watch, read, and listen to things that reinforce things we already believe—intellectual cloth mothers, you might call them—rather than challenging those comfortable beliefs or putting them to the test. But, again, a simple laboratory test is exactly what it is: a simple, laboratory test. And other, broader personal or social conclusions don't automatically follow on from it. (Indeed, you might recognize the tendency to argue that way as a confirmation bias all of its own.)

9: How do you learn things? (Pavlov, 1890s)

Learning might seem a very conscious and deliberate thing, especially if you hate the subject you're studying or merely sitting in school. What could be worse than "rote" learning your times table, practising French vocabulary, or revising for an exam? We also learn a lot of things less consciously—sometimes without any conscious effort at all. Animals (other than humans) don't sit in classrooms all day but they learn plenty of things. Even one of the simplest (a sea-slug called Aplysia californica ) will learn to withdraw its syphon and gill if you give it an electric shock, as Eric Kandel and James Schwartz famously discovered. [20]

“ The animal must respond to changes in the environment in such a manner that its responsive activity is directed toward the preservation of its existence. ” Ivan Pavlov, 1926.

So how does learning come about? At its most basic, it involves making connections or "associations" between things, something that was probed by Russian psychologist Ivan Pavlov in perhaps the most famous psychology experiment of all time. Pavlov looked at how dogs behave when he gave them food. Normally, he found dogs would salivate (a response) when he brought them a plate of food (a stimulus). We call this an unconditioned response (meaning default, normal, or just untrained): it's what the dogs do naturally. Now, with the food a distant doggy memory, Pavlov rang a bell (a neutral stimulus) and found it produced no response at all (the dogs didn't salivate). In the next phase of the experiment, he brought the dogs plates of food and rang a bell at the same time and found, again, that they salivated. So again, we have an unconditioned response, but this time to a pair of stimuli. Finally, after a period of this training, he tested what happened when he just rang the bell and, to his surprise, found that they salivated once again. In the jargon of psychology, we say the dogs had become "conditioned" to respond to the bell alone: they associated the bell with food and so responded by salivating. We call this a conditioned (trained or learned) response: the dogs have learned that the sound of the bell is generally linked to the appearance of food. [21]

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Pavlov's work on conditioning was hugely influential—indeed, it was a key inspiration for the theory of behaviorism . Advanced by such luminaries as B.F. Skinner and J.B. Watson, this was the idea that animal behavior is largely a matter of stimulus and response and mental states—thinking, feeling, emoting, and reasoning—is irrelevant. But, as with all the other experiments here, it's a stretch to argue that we're all quasi-automated zombies raised in a kind of collective cloud of mind-control conditioning. It's true that we learn some things by simple, behavioural association, and animals like Aplysia may learn everything they know that way, but it doesn't follow that all animals learn everything by making endless daisy-chains of stimulus and response. [22]

10: You're happier than you realize (Seligman, 1975)

Money makes the world go round—or so goes the lyric of a famous song. But if you're American Martin Seligman, you'd probably think "happiness" was a better candidate for what powers the planet, or should. When I was studying psychology at college back in the mid-1980s, Professor Seligman came along to give a guest lecture—and it proved to be one of the most thought-provoking talks I would ever attend.

“ The time has finally arrived for a science that seeks to understand positive emotion, build strength and virtue, and provide guideposts for... 'the good life'. ” Martin Seligman, Authentic Happiness, 2003.

Though now widely and popularly known for his work in a field he calls positive psychology , Seligman originally made his name researching mental illness and how people came to be depressed. Taking a leaf from Pavlov's book, his subjects were dogs. Rather than feeding them and ringing bells, he studied what happened when he gave dogs electric shocks and either offered them an opportunity to escape or restrained them in a harness so they couldn't. What he discovered was that dogs that couldn't avoid the shocks became demoralised and depressed—they "learned helpnessness"—and eventually didn't even try to avoid punishment, even when (once again) they were allowed to. [23]

You can easily construct a whole (behavioural) theory of mental illness on the basis of Seligman's learned helplessness experiments but, once again, there's much more to it than that. People don't become depressed purely because they're in impossible situations where problems seem (to use the terminology) "internal" (their own fault), "global" (affecting all aspects of their life), and "stable" (impossible to change). Many different factors—neurochemical, behavioral, cognitive, and social—feed into depression and, as a result, there are just as many forms of treatment.

What's really interesting about Seligman's work is what he did next. In the 1990s, he realized psychologists were obsessed with mental illness and negativity when, in his view, they should probably spend more time figuring out what makes people happy. So began his more recent quest to understand "positive psychology" and the things we can all do to make our lives feel more fulfilled. The key, in his view, is working out and playing to what he calls our "signature strengths" (things we're good at that we enjoy doing). His ideas, which trace back to those early experiments on learned helpless in hapless dogs, have proved hugely influential, prompting many psychologists to switch their attention to developing a useful, practical "science of happiness." [24]

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For older readers, for younger readers, references ↑    see for example the classic discussion of consciousness in chapter 9: the stream of thought in principles of psychology (volume 1) by william james, henry holt, 1890. ↑    donald broadbent carried out notable early work on "selective attention" as this is called. see, for example, the role of auditory localization in attention and memory span by d.e. broadbent, j exp psychol, 1954, volume 47 number 3, pp.191–6. ↑     [pdf] gorillas in our midst: sustained inattentional blindness for dynamic events by daniel j simons, christopher f chabris, perception, 1999, volume 28, pp.1059–1074. ↑     the invisible gorilla and other ways our intuition deceives us by christopher chabris and daniel j. simons. harpercollins, 2010. ↑     [pdf] the effect of a pratfall on increasing interpersonal attractiveness by elliot aronson, ben willerman, and joanne floyd, psychon. sci., 1966, volume 4 number 6,pp.227–228. ↑     the 'tip of the tongue' phenomenon by roger brown and david mcneill, journal of verbal learning and verbal behavior, volume 5, issue 4, august 1966, pp.325–337. ↑     the cognitive neuropsychology of déjà vu by chris moulin, psychology press, 2017. ↑     reconstruction of automobile destruction: an example of the interaction between language and memory by elizabeth loftus and john palmer, journal of verbal learning & verbal behavior, volume 13 issue 5, pp.585–589. ↑     "that doesn't mean it really happened": an interview with elizabeth loftus by carrie poppy, the sceptical inquirer, september 8, 2016. ↑     behavioral study of obedience by stanley milgram, journal of abnormal and social psychology, 1963, volume 67, pp.371–378. ↑     a study of prisoners and guards in a simulated prison by craig haney, curtis banks, and philip zimbardo, naval research review, 1973, volume 30, pp.4–17. ↑     dr. robert g. heath: a controversial figure in the history of deep brain stimulation by christen m. o'neal et al, neurosurg focus 43 (3):e12, 2017. serendipity and the cerebral localization of pleasure by alan a. baumeister, journal of the history of the neurosciences, basic and clinical perspectives, volume 15, 2006. issue 2. the 'gay cure' experiments that were written out of scientific history by robert colvile, mosaic science, 4 july 2016. ↑     positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain by j. olds and p. millner, j comp physiol psychol, 1954 dec;47(6):419–27. ↑     the pleasure areas by h.j. campbell, methuen, 1973. ↑     mind time: the temporal factor in consciousness by benjamin libet, harvard university press, 2004. ↑     exposing some holes in libet's classic free will study by christian jarrett, bps research digest, 2008. ↑    for a decent overview, see the section "theories of emotion" in 58: emotion in psychology by openstaxcollege. ↑     the nature of love by harry f. harlow, american psychologist, 13, pp.673–685. for a more general account, see love at goon park: harry harlow and the science of affection by by deborah blum, basic books, 2002. ↑     reasoning by p.c. wason, in foss, brian (ed.). new horizons in psychology. penguin, 1966, p.145. ↑     eric kandel and aplysia californica: their role in the elucidation of mechanisms of memory and the study of psychotherapy by michael robertson and garry walter, acta neuropsychiatrica, volume 22, issue 4, august 2010, pp.195–196. ↑     conditioned reflexes; an investigation of the physiological activity of the cerebral cortex by i.p pavlov. dover, 1960. ↑     pavlov's dogs by tim tully, current biology, 2003, volume 13, issue 4, 18 february 2003, pp.r117–r119. ↑     learned helplessness: theory and evidence by steven maier and martin seligman, journal of experimental psychology: general, 1976, volume 105, number 1, pp3.–46. ↑     authentic happiness by martin seligman, nicholas brealey, 2003. ↑     thinking fast and slow by daniel kahneman, penguin, 2011. ↑     subject reaction: the neglected factor in the ethics of experimentation by stanley milgram, the hastings center report, vol. 7, no. 5 (oct., 1977), pp. 19–23. please do not copy our articles onto blogs and other websites articles from this website are registered at the us copyright office. copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties. text copyright © chris woodford 2021. all rights reserved. full copyright notice and terms of use . follow us, rate this page, tell your friends, cite this page, more to explore on our website....

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Field Experiments

For geologists, social scientists and environmental biologists, amongst others, field experiments are an integral part of the discipline.

This article is a part of the guide:

  • Research Designs
  • Quantitative and Qualitative Research
  • Literature Review
  • Quantitative Research Design

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  • 1 Research Designs
  • 2.1 Pilot Study
  • 2.2 Quantitative Research Design
  • 2.3 Qualitative Research Design
  • 2.4 Quantitative and Qualitative Research
  • 3.1 Case Study
  • 3.2 Naturalistic Observation
  • 3.3 Survey Research Design
  • 3.4 Observational Study
  • 4.1 Case-Control Study
  • 4.2 Cohort Study
  • 4.3 Longitudinal Study
  • 4.4 Cross Sectional Study
  • 4.5 Correlational Study
  • 5.1 Field Experiments
  • 5.2 Quasi-Experimental Design
  • 5.3 Identical Twins Study
  • 6.1 Experimental Design
  • 6.2 True Experimental Design
  • 6.3 Double Blind Experiment
  • 6.4 Factorial Design
  • 7.1 Literature Review
  • 7.2 Systematic Reviews
  • 7.3 Meta Analysis

As the name suggests, a field study is an experiment performed outside the laboratory, in the 'real' world. Unlike case studies and observational studies , a field experiment still follows all of the steps of the scientific process , addressing research problems and generating hypotheses.

The obvious advantage of a field study is that it is practical and also allows experimentation , without artificially introducing confounding variables .

A population biologist examining an ecosystem could not move the entire environment into the laboratory, so field experiments are the only realistic research method in many fields of science.

In addition, they circumvent the accusation leveled at laboratory experiments of lacking external or ecological validity , or adversely affecting the behavior of the subject.

Social scientists and psychologists often used field experiments to perform blind studies , where the subject was not even aware that they were under scrutiny.

A good example of this is the Piliavin and Piliavin experiment , where the propensity of strangers to help blood covered 'victims' was measured. This is now frowned upon, under the policy of informed consent , and is only used in rare and highly regulated circumstances.

Field experiments can suffer from a lack of a discrete control group and often have many variables to try to eliminate.

For example, if the effects of a medicine are studied, and the subject is instructed not to drink alcohol, there is no guarantee that the subject followed the instructions, so field studies often sacrifice internal validity for external validity .

For fields like biology, geology and environmental science, this is not a problem, and the field experiment can be treated as a sound experimental practice, following the steps of the scientific method .

A major concern shared by all disciplines is the cost of field studies, as they tend to be very expensive.

For example, even a modestly sized research ship costs many thousands of dollars every day, so a long oceanographical research program can run into the millions of dollars.

Pilot studies are often used to test the feasibility of any long term or extensive research program before committing vast amounts of funds and resources. The changeable nature of the external environment and the often-prohibitive investment of time and money mean that field experiments are rarely replicable , so any generalization is always tenuous.

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15 Famous Experiments and Case Studies in Psychology

15 Famous Experiments and Case Studies in Psychology

Chris Drew (PhD)

Dr. Chris Drew is the founder of the Helpful Professor. He holds a PhD in education and has published over 20 articles in scholarly journals. He is the former editor of the Journal of Learning Development in Higher Education. [Image Descriptor: Photo of Chris]

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psychology theories, explained below

Psychology has seen thousands upon thousands of research studies over the years. Most of these studies have helped shape our current understanding of human thoughts, behavior, and feelings.

The psychology case studies in this list are considered classic examples of psychological case studies and experiments, which are still being taught in introductory psychology courses up to this day.

Some studies, however, were downright shocking and controversial that you’d probably wonder why such studies were conducted back in the day. Imagine participating in an experiment for a small reward or extra class credit, only to be left scarred for life. These kinds of studies, however, paved the way for a more ethical approach to studying psychology and implementation of research standards such as the use of debriefing in psychology research .

Case Study vs. Experiment

Before we dive into the list of the most famous studies in psychology, let us first review the difference between case studies and experiments.

  • It is an in-depth study and analysis of an individual, group, community, or phenomenon. The results of a case study cannot be applied to the whole population, but they can provide insights for further studies.
  • It often uses qualitative research methods such as observations, surveys, and interviews.
  • It is often conducted in real-life settings rather than in controlled environments.
  • An experiment is a type of study done on a sample or group of random participants, the results of which can be generalized to the whole population.
  • It often uses quantitative research methods that rely on numbers and statistics.
  • It is conducted in controlled environments, wherein some things or situations are manipulated.

See Also: Experimental vs Observational Studies

Famous Experiments in Psychology

1. the marshmallow experiment.

Psychologist Walter Mischel conducted the marshmallow experiment at Stanford University in the 1960s to early 1970s. It was a simple test that aimed to define the connection between delayed gratification and success in life.

The instructions were fairly straightforward: children ages 4-6 were presented a piece of marshmallow on a table and they were told that they would receive a second piece if they could wait for 15 minutes without eating the first marshmallow.

About one-third of the 600 participants succeeded in delaying gratification to receive the second marshmallow. Mischel and his team followed up on these participants in the 1990s, learning that those who had the willpower to wait for a larger reward experienced more success in life in terms of SAT scores and other metrics.

This case study also supported self-control theory , a theory in criminology that holds that people with greater self-control are less likely to end up in trouble with the law!

The classic marshmallow experiment, however, was debunked in a 2018 replication study done by Tyler Watts and colleagues.

This more recent experiment had a larger group of participants (900) and a better representation of the general population when it comes to race and ethnicity. In this study, the researchers found out that the ability to wait for a second marshmallow does not depend on willpower alone but more so on the economic background and social status of the participants.

2. The Bystander Effect

In 1694, Kitty Genovese was murdered in the neighborhood of Kew Gardens, New York. It was told that there were up to 38 witnesses and onlookers in the vicinity of the crime scene, but nobody did anything to stop the murder or call for help.

Such tragedy was the catalyst that inspired social psychologists Bibb Latane and John Darley to formulate the phenomenon called bystander effect or bystander apathy .

Subsequent investigations showed that this story was exaggerated and inaccurate, as there were actually only about a dozen witnesses, at least two of whom called the police. But the case of Kitty Genovese led to various studies that aim to shed light on the bystander phenomenon.

Latane and Darley tested bystander intervention in an experimental study . Participants were asked to answer a questionnaire inside a room, and they would either be alone or with two other participants (who were actually actors or confederates in the study). Smoke would then come out from under the door. The reaction time of participants was tested — how long would it take them to report the smoke to the authorities or the experimenters?

The results showed that participants who were alone in the room reported the smoke faster than participants who were with two passive others. The study suggests that the more onlookers are present in an emergency situation, the less likely someone would step up to help, a social phenomenon now popularly called the bystander effect.

3. Asch Conformity Study

Have you ever made a decision against your better judgment just to fit in with your friends or family? The Asch Conformity Studies will help you understand this kind of situation better.

In this experiment, a group of participants were shown three numbered lines of different lengths and asked to identify the longest of them all. However, only one true participant was present in every group and the rest were actors, most of whom told the wrong answer.

Results showed that the participants went for the wrong answer, even though they knew which line was the longest one in the first place. When the participants were asked why they identified the wrong one, they said that they didn’t want to be branded as strange or peculiar.

This study goes to show that there are situations in life when people prefer fitting in than being right. It also tells that there is power in numbers — a group’s decision can overwhelm a person and make them doubt their judgment.

4. The Bobo Doll Experiment

The Bobo Doll Experiment was conducted by Dr. Albert Bandura, the proponent of social learning theory .

Back in the 1960s, the Nature vs. Nurture debate was a popular topic among psychologists. Bandura contributed to this discussion by proposing that human behavior is mostly influenced by environmental rather than genetic factors.

In the Bobo Doll Experiment, children were divided into three groups: one group was shown a video in which an adult acted aggressively toward the Bobo Doll, the second group was shown a video in which an adult play with the Bobo Doll, and the third group served as the control group where no video was shown.

The children were then led to a room with different kinds of toys, including the Bobo Doll they’ve seen in the video. Results showed that children tend to imitate the adults in the video. Those who were presented the aggressive model acted aggressively toward the Bobo Doll while those who were presented the passive model showed less aggression.

While the Bobo Doll Experiment can no longer be replicated because of ethical concerns, it has laid out the foundations of social learning theory and helped us understand the degree of influence adult behavior has on children.

5. Blue Eye / Brown Eye Experiment

Following the assassination of Martin Luther King Jr. in 1968, third-grade teacher Jane Elliott conducted an experiment in her class. Although not a formal experiment in controlled settings, A Class Divided is a good example of a social experiment to help children understand the concept of racism and discrimination.

The class was divided into two groups: blue-eyed children and brown-eyed children. For one day, Elliott gave preferential treatment to her blue-eyed students, giving them more attention and pampering them with rewards. The next day, it was the brown-eyed students’ turn to receive extra favors and privileges.

As a result, whichever group of students was given preferential treatment performed exceptionally well in class, had higher quiz scores, and recited more frequently; students who were discriminated against felt humiliated, answered poorly in tests, and became uncertain with their answers in class.

This study is now widely taught in sociocultural psychology classes.

6. Stanford Prison Experiment

One of the most controversial and widely-cited studies in psychology is the Stanford Prison Experiment , conducted by Philip Zimbardo at the basement of the Stanford psychology building in 1971. The hypothesis was that abusive behavior in prisons is influenced by the personality traits of the prisoners and prison guards.

The participants in the experiment were college students who were randomly assigned as either a prisoner or a prison guard. The prison guards were then told to run the simulated prison for two weeks. However, the experiment had to be stopped in just 6 days.

The prison guards abused their authority and harassed the prisoners through verbal and physical means. The prisoners, on the other hand, showed submissive behavior. Zimbardo decided to stop the experiment because the prisoners were showing signs of emotional and physical breakdown.

Although the experiment wasn’t completed, the results strongly showed that people can easily get into a social role when others expect them to, especially when it’s highly stereotyped .

7. The Halo Effect

Have you ever wondered why toothpastes and other dental products are endorsed in advertisements by celebrities more often than dentists? The Halo Effect is one of the reasons!

The Halo Effect shows how one favorable attribute of a person can gain them positive perceptions in other attributes. In the case of product advertisements, attractive celebrities are also perceived as intelligent and knowledgeable of a certain subject matter even though they’re not technically experts.

The Halo Effect originated in a classic study done by Edward Thorndike in the early 1900s. He asked military commanding officers to rate their subordinates based on different qualities, such as physical appearance, leadership, dependability, and intelligence.

The results showed that high ratings of a particular quality influences the ratings of other qualities, producing a halo effect of overall high ratings. The opposite also applied, which means that a negative rating in one quality also correlated to negative ratings in other qualities.

Experiments on the Halo Effect came in various formats as well, supporting Thorndike’s original theory. This phenomenon suggests that our perception of other people’s overall personality is hugely influenced by a quality that we focus on.

8. Cognitive Dissonance

There are experiences in our lives when our beliefs and behaviors do not align with each other and we try to justify them in our minds. This is cognitive dissonance , which was studied in an experiment by Leon Festinger and James Carlsmith back in 1959.

In this experiment, participants had to go through a series of boring and repetitive tasks, such as spending an hour turning pegs in a wooden knob. After completing the tasks, they were then paid either $1 or $20 to tell the next participants that the tasks were extremely fun and enjoyable. Afterwards, participants were asked to rate the experiment. Those who were given $1 rated the experiment as more interesting and fun than those who received $20.

The results showed that those who received a smaller incentive to lie experienced cognitive dissonance — $1 wasn’t enough incentive for that one hour of painstakingly boring activity, so the participants had to justify that they had fun anyway.

Famous Case Studies in Psychology

9. little albert.

In 1920, behaviourist theorists John Watson and Rosalie Rayner experimented on a 9-month-old baby to test the effects of classical conditioning in instilling fear in humans.

This was such a controversial study that it gained popularity in psychology textbooks and syllabi because it is a classic example of unethical research studies done in the name of science.

In one of the experiments, Little Albert was presented with a harmless stimulus or object, a white rat, which he wasn’t scared of at first. But every time Little Albert would see the white rat, the researchers would play a scary sound of hammer and steel. After about 6 pairings, Little Albert learned to fear the rat even without the scary sound.

Little Albert developed signs of fear to different objects presented to him through classical conditioning . He even generalized his fear to other stimuli not present in the course of the experiment.

10. Phineas Gage

Phineas Gage is such a celebrity in Psych 101 classes, even though the way he rose to popularity began with a tragic accident. He was a resident of Central Vermont and worked in the construction of a new railway line in the mid-1800s. One day, an explosive went off prematurely, sending a tamping iron straight into his face and through his brain.

Gage survived the accident, fortunately, something that is considered a feat even up to this day. He managed to find a job as a stagecoach after the accident. However, his family and friends reported that his personality changed so much that “he was no longer Gage” (Harlow, 1868).

New evidence on the case of Phineas Gage has since come to light, thanks to modern scientific studies and medical tests. However, there are still plenty of mysteries revolving around his brain damage and subsequent recovery.

11. Anna O.

Anna O., a social worker and feminist of German Jewish descent, was one of the first patients to receive psychoanalytic treatment.

Her real name was Bertha Pappenheim and she inspired much of Sigmund Freud’s works and books on psychoanalytic theory, although they hadn’t met in person. Their connection was through Joseph Breuer, Freud’s mentor when he was still starting his clinical practice.

Anna O. suffered from paralysis, personality changes, hallucinations, and rambling speech, but her doctors could not find the cause. Joseph Breuer was then called to her house for intervention and he performed psychoanalysis, also called the “talking cure”, on her.

Breuer would tell Anna O. to say anything that came to her mind, such as her thoughts, feelings, and childhood experiences. It was noted that her symptoms subsided by talking things out.

However, Breuer later referred Anna O. to the Bellevue Sanatorium, where she recovered and set out to be a renowned writer and advocate of women and children.

12. Patient HM

H.M., or Henry Gustav Molaison, was a severe amnesiac who had been the subject of countless psychological and neurological studies.

Henry was 27 when he underwent brain surgery to cure the epilepsy that he had been experiencing since childhood. In an unfortunate turn of events, he lost his memory because of the surgery and his brain also became unable to store long-term memories.

He was then regarded as someone living solely in the present, forgetting an experience as soon as it happened and only remembering bits and pieces of his past. Over the years, his amnesia and the structure of his brain had helped neuropsychologists learn more about cognitive functions .

Suzanne Corkin, a researcher, writer, and good friend of H.M., recently published a book about his life. Entitled Permanent Present Tense , this book is both a memoir and a case study following the struggles and joys of Henry Gustav Molaison.

13. Chris Sizemore

Chris Sizemore gained celebrity status in the psychology community when she was diagnosed with multiple personality disorder, now known as dissociative identity disorder.

Sizemore has several alter egos, which included Eve Black, Eve White, and Jane. Various papers about her stated that these alter egos were formed as a coping mechanism against the traumatic experiences she underwent in her childhood.

Sizemore said that although she has succeeded in unifying her alter egos into one dominant personality, there were periods in the past experienced by only one of her alter egos. For example, her husband married her Eve White alter ego and not her.

Her story inspired her psychiatrists to write a book about her, entitled The Three Faces of Eve , which was then turned into a 1957 movie of the same title.

14. David Reimer

When David was just 8 months old, he lost his penis because of a botched circumcision operation.

Psychologist John Money then advised Reimer’s parents to raise him as a girl instead, naming him Brenda. His gender reassignment was supported by subsequent surgery and hormonal therapy.

Money described Reimer’s gender reassignment as a success, but problems started to arise as Reimer was growing up. His boyishness was not completely subdued by the hormonal therapy. When he was 14 years old, he learned about the secrets of his past and he underwent gender reassignment to become male again.

Reimer became an advocate for children undergoing the same difficult situation he had been. His life story ended when he was 38 as he took his own life.

15. Kim Peek

Kim Peek was the inspiration behind Rain Man , an Oscar-winning movie about an autistic savant character played by Dustin Hoffman.

The movie was released in 1988, a time when autism wasn’t widely known and acknowledged yet. So it was an eye-opener for many people who watched the film.

In reality, Kim Peek was a non-autistic savant. He was exceptionally intelligent despite the brain abnormalities he was born with. He was like a walking encyclopedia, knowledgeable about travel routes, US zip codes, historical facts, and classical music. He also read and memorized approximately 12,000 books in his lifetime.

This list of experiments and case studies in psychology is just the tip of the iceberg! There are still countless interesting psychology studies that you can explore if you want to learn more about human behavior and dynamics.

You can also conduct your own mini-experiment or participate in a study conducted in your school or neighborhood. Just remember that there are ethical standards to follow so as not to repeat the lasting physical and emotional harm done to Little Albert or the Stanford Prison Experiment participants.

Asch, S. E. (1956). Studies of independence and conformity: I. A minority of one against a unanimous majority. Psychological Monographs: General and Applied, 70 (9), 1–70. https://doi.org/10.1037/h0093718

Bandura, A., Ross, D., & Ross, S. A. (1961). Transmission of aggression through imitation of aggressive models. The Journal of Abnormal and Social Psychology, 63 (3), 575–582. https://doi.org/10.1037/h0045925

Elliott, J., Yale University., WGBH (Television station : Boston, Mass.), & PBS DVD (Firm). (2003). A class divided. New Haven, Conn.: Yale University Films.

Festinger, L., & Carlsmith, J. M. (1959). Cognitive consequences of forced compliance. The Journal of Abnormal and Social Psychology, 58 (2), 203–210. https://doi.org/10.1037/h0041593

Haney, C., Banks, W. C., & Zimbardo, P. G. (1973). A study of prisoners and guards in a simulated prison. Naval Research Review , 30 , 4-17.

Latane, B., & Darley, J. M. (1968). Group inhibition of bystander intervention in emergencies. Journal of Personality and Social Psychology, 10 (3), 215–221. https://doi.org/10.1037/h0026570

Mischel, W. (2014). The Marshmallow Test: Mastering self-control. Little, Brown and Co.

Thorndike, E. (1920) A Constant Error in Psychological Ratings. Journal of Applied Psychology , 4 , 25-29. http://dx.doi.org/10.1037/h0071663

Watson, J. B., & Rayner, R. (1920). Conditioned emotional reactions. Journal of experimental psychology , 3 (1), 1.


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Field Experiments in sociology

Table of Contents

Last Updated on February 24, 2023 by Karl Thompson

Field Experiments take place in  real-life settings such as a classroom, the work place or even the high street. Field experiments are much more common in sociology than laboratory experiments. In fact sociologists hardly ever use lab experiments because the artificial environment of the laboratory is so far removed from real life that most sociologists believe that the results gained from such experiments tell us very little about how respondents would actually act in real life.

It is actually quite easy to set up a field experiment. If you wanted to measure the effectiveness of different teaching methods on educational performance in a school for example, all you would need to do is to get teachers to administer a short test to measure current performance levels, and then get them to change one aspect of their teaching for one class, or for a sample of some pupils, but not for the others, for a period of time (say one term) and then measure and compare the results of all pupils at the end.

You need to know about field experiments for the research methods component of A-level sociology and the AQA exam board does seem to like setting exam questions on experiments!

Field experiments.png

The advantages of Field Experiments over Lab Experiments

Better external validity – The big advantage which field experiments obviously have better external validity than lab experiments, because they take place in normally occurring social settings.

Larger Scale Settings – Practically it is possible to do field experiments in large institutions – in schools or workplaces in which thousands of people interact for example, which isn’t possible in laboratory experiments.

The disadvantages of Field Experiments

It is not possible to control variables as closely as with laboratory experiments – With the Rosenthal and Jacobson experiment, for example we simply don’t know what else might have influenced the ‘spurting group’ besides ‘higher teacher expectations’.

The Hawthorne Effect (or Experimental Effect) may reduce the validity of results. The Hawthorne effect is where respondents may act differently just because they know they are part of an experiment. The Hawthorne Effect was a phrase coined by Elton Mayo (1927) who did research into workers’ productivity at the Western Electric Company’s Hawthorne plant. With the workers agreement (they knew that an experiment was taking place, and the purpose of the experiment), Mayo set about varying things such as lighting levels, the speed of conveyor belts and toilet breaks. However, whatever he did, the worker’s productivity always increased from the norm, even when conditions were worsened. He concluded that the respondents were simply trying to please the researcher. NB – The Hawthorne effect can also apply to laboratory experiments.

Practical Problems – Access is likely to be more of a problem with lab experiments. Schools and workplaces might be reluctant to allow researchers in.

Rosenthal and Jacobson’s 1968 Field Experiment

The aim of this research was to measure the effect of high teacher expectation on the educational performance of pupils.

Rosenthal and Jacobsen concluded that higher teacher expectations were responsible for this difference in achievement.

Limitations of the Experiment

Deception/ Lack of Informed Consent is an issue : In order for the experiment to work, R and J had to deceive the teachers about the real nature of the experiment, and the pupils had no idea what was going on.

Reliability is a problem : while the research design was relatively simple and thus easy to repeat (in fact within five years of the original study this was repeated 242 times) the exact conditions are not possible to repeat – given differences between schools and the type and mixture of pupils who attend different schools.

Seven Examples of Field Experiments in Sociology

Are Chinese Teaching Methods the Best?  – A Field Experiment in ‘tough teaching methods’ in the UK conducted in 2015.

Theory and Methods A Level Sociology Revision Bundle 

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Field Experiments

Last updated 22 Mar 2021

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Experiments look for the effect that manipulated variables (independent variables) have on measured variables (dependent variables), i.e. causal effects.

Field experiments are conducted in a natural setting (e.g. at a sports event or on public transport), as opposed to the artificial environment created in laboratory experiments. Some variables cannot be controlled due to the unpredictability of these real-life settings (e.g. the public interacting with participants), but an independent variable will still be altered for a dependent variable to be measured against.

Evaluation of field experiments:

- Field experiments generally yield results with higher ecological validity than laboratory experiments, as the natural settings will relate to real life.

- Demand characteristics are less of an issue with field experiments than laboratory experiments (i.e. participants are less likely to adjust their natural behaviour according to their interpretation of the study’s purpose, as they might not know they are in a study).

- Extraneous variables could confound results due to the reduced control experimenters have over them in non-artificial environments, which makes it difficult to find truly causal effects between independent and dependent variables.

- Ethical principles have to be considered, such as the lack of informed consent; if participants are not made aware of their participation in an experiment, privacy must be respected during observations and participants must be debriefed appropriately when observations come to an end.

- Precise replication of the natural environment of field experiments is understandably difficult, so they have poor reliability, unlike laboratory experiments where the exact conditions can be recreated.

- Field experiments are more susceptible to sample bias, as participants are often not randomly allocated to experimental conditions (i.e. participants’ groups are already pre-set rather than randomly assigned).

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3 Most Famous Psychology Experiments Everyone Should Know

by The Oxford Scholastica Team | 14 May, 2024 | Blog Articles , Psychology Articles

Hands grabbing prison bars

Have you ever wondered why good people do bad things? Or why anyone would ignore someone in need of help? How about why anyone would conform to an extreme idea that they don’t agree with?

Throughout the history of psychology, many experiments have attempted to answer these questions—some of which would never be allowed today for ethical reasons. Many of these have been very influential within the field of social psychology and are still taught today.

Keep reading to hear about three of the most shocking and well-known social experiments.

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1. The Stanford Prison Experiment

None of us would like to believe that we are capable of evil. However, Zimbardo’s infamous Stanford prison experiment showed that, actually, we all have this potential. It all depends on the situation.

Phillip Zimbardo was a researcher at Stanford University in America. In 1972, he recruited 24 mentally healthy, male, college students for an experiment taking place in a fake prison in the basement of Stanford. These participants were randomly allocated into 2 groups: prison guards and prisoners.

The guards received a uniform and mirrored sunglasses to wear for the job. Then, after being sent home, the prisoners were publicly arrested at their home on a Sunday morning. They were processed at a real police station before being transported to the ‘prison’.

No one could have predicted what would happen next.

The guards weren’t given any specific instructions on how to behave. Yet, very soon they began acting in extreme ways: they prevented prisoners from eating, took away their bedding, forced them to remove their clothes, and even punished them with chores such as cleaning toilets with their bare hands.

As well as this, the prisoners were submitting to the guards—even though they knew that they hadn’t actually done anything wrong and weren’t even in a real prison! After just thirty-six hours, a prisoner had to be extracted from the study as he had sunk into a deep depression with fits of rage and uncontrollable crying.

Just a few days later, other prisoners displayed similar symptoms. The guards also continued to abuse them. It was at this point that Zimbardo’s girlfriend told him he had to stop the experiment. It was shut down after just six days, despite Zimbardo intending it to run for fourteen.

This experiment demonstrates the power of the situation in influencing how we act. Good people, just like you or me, are capable of evil acts. But, the power of the situation doesn’t always have to be bad: it can also be a force for good.

Of course, we could never repeat this experiment for ethical reasons. This means that we need to assess how valid Zimbardo’s conclusions really are. For example, demand characteristics—how the guards assumed they should act—may have significantly shaped their behaviour.

2. The Bystander Effect

In 1964, Kitty Genovese was brutally murdered just outside her home. What makes this case so different is that thirty-eight witnesses were reported to be present at some point during this attack—all of whom failed to help her.

It was later shown that this didn’t quite happen how the newspapers had described. Few of the thirty-eight neighbours were actually aware of what was going on at the time. But, this still sparked a great interest in ‘the bystander effect’: the phenomenon that the more people there are present, the less likely someone is to help in an emergency situation.

Four years later, in 1968, John Darley and Bibb Latané went on to test this whether this effect held true. They put participants in a room, either alone or in groups with two other naïve participants or two confederates (researchers who pretend to be participants). They then filtered smoke into the room. The confederates remained passive as this happened.

The results of this followed the same shocking pattern as shown in the case of Kitty Genovese.

Participants were both least likely, and took longest, to report the smoke when with the passive confederates. Only 10% reported it when with them. This was slightly higher at 38% when they were in groups of three, but went all the way up to 75% when they were alone.

In the real world, this means that we are less likely to intervene in an emergency situation when surrounded by other people. And, we are even less likely when those people are also doing nothing.

It’s important to remember that this doesn’t make us bad people. The bystander effect happens for many reasons: we see other observers doing nothing and follow their cues, we believe we lack competency, or we simply expect someone else to take responsibility.

The best way to stop this happening is to know that the effect is there—so you are already one step closer to being the person who steps in to help out of a crowd of people.

3. Asch’s Conformity Experiment

Do you think you could be convinced to answer a question with the wrong answer, even when you knew the right one? Most of us would say no. However, Solomon Asch’s 1951 experiment suggests that both you and I probably can.

In this experiment, participants were simply asked to judge the size of a line compared to others. The answer to this was always very clear and unambiguous: in control trials participants gave the right answer 99% of the time. However, Asch placed participants in a group with confederates who all gave the wrong answer.

You might assume that participants would still give the answer they knew to be right. But, a surprising number of participants conformed to the group answer. Overall, they gave the wrong answer 37% of the time. This experiment is so surprising to us because we generally don’t realise how much our beliefs can be influenced by others. In our everyday lives, we conform to ideas not because we believe they are true, but simply to avoid standing out from the group.

As with all of these studies, it is important to consider how valid these findings are. And, the answer seems to be that they are: a meta-analysis by Bond & Smith (1996) found a significant level of conformity across cultures and over time.

However, a very clever adaptation of this experiment which did not use confederates failed to find this effect. 

Key takeaways from these famous psychology studies

These are three of the most influential and well-known experiments in the history of psychology.

Zimbardo taught us that good people are capable of doing bad things. Darley and Latané confirmed that we are less likely to help in an emergency when there are more people around. And, Asch showed how much we conform to group ideas.

If you enjoyed learning about the most interesting psychology experiments, consider signing up for our Psychology Summer School for high school students . At Oxford Scholastica, our Oxford Summer School programs give international students the chance to experience academic study at a higher level.

More interesting psychology studies and resources

  • Split brain experiments
  • Psychology of a murderer’s mind
  • The psychology of success
  • Spatial mapping
  • Books about psychological experiments

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10 Psychological Experiments That Could Never Happen Today

By meredith danko | sep 20, 2013.

The Chronicle of Higher Education

Nowadays, the American Psychological Association has a Code of Conduct in place when it comes to ethics in psychological experiments. Experimenters must adhere to various rules pertaining to everything from confidentiality to consent to overall beneficence. Review boards are in place to enforce these ethics. But the standards were not always so strict, which is how some of the most famous studies in psychology came about. 

1. The Little Albert Experiment

At Johns Hopkins University in 1920, John B. Watson conducted a study of classical conditioning, a phenomenon that pairs a conditioned stimulus with an unconditioned stimulus until they produce the same result. This type of conditioning can create a response in a person or animal towards an object or sound that was previously neutral. Classical conditioning is commonly associated with Ivan Pavlov, who rang a bell every time he fed his dog until the mere sound of the bell caused his dog to salivate.

Watson tested classical conditioning on a 9-month-old baby he called Albert B. The young boy started the experiment loving animals, particularly a white rat. Watson started pairing the presence of the rat with the loud sound of a hammer hitting metal. Albert began to develop a fear of the white rat as well as most animals and furry objects. The experiment is considered particularly unethical today because Albert was never desensitized to the phobias that Watson produced in him. (The child died of an unrelated illness at age 6, so doctors were unable to determine if his phobias would have lasted into adulthood.)

2. Asch Conformity Experiments

Solomon Asch tested conformity at Swarthmore College in 1951 by putting a participant in a group of people whose task was to match line lengths. Each individual was expected to announce which of three lines was the closest in length to a reference line. But the participant was placed in a group of actors, who were all told to give the correct answer twice then switch to each saying the same incorrect answer. Asch wanted to see whether the participant would conform and start to give the wrong answer as well, knowing that he would otherwise be a single outlier.

Thirty-seven of the 50 participants agreed with the incorrect group despite physical evidence to the contrary. Asch used deception in his experiment without getting informed consent from his participants, so his study could not be replicated today.

3. The Bystander Effect

Some psychological experiments that were designed to test the bystander effect are considered unethical by today’s standards. In 1968, John Darley and Bibb Latané developed an interest in crime witnesses who did not take action. They were particularly intrigued by the murder of Kitty Genovese , a young woman whose murder was witnessed by many, but still not prevented.

The pair conducted a study at Columbia University in which they would give a participant a survey and leave him alone in a room to fill out the paper. Harmless smoke would start to seep into the room after a short amount of time. The study showed that the solo participant was much faster to report the smoke than participants who had the exact same experience, but were in a group.

The studies became progressively unethical by putting participants at risk of psychological harm. Darley and Latané played a recording of an actor pretending to have a seizure in the headphones of a person, who believed he or she was listening to an actual medical emergency that was taking place down the hall. Again, participants were much quicker to react when they thought they were the sole person who could hear the seizure.

4. The Milgram Experiment

Yale psychologist Stanley Milgram hoped to further understand how so many people came to participate in the cruel acts of the Holocaust. He theorized that people are generally inclined to obey authority figures, posing the question , “Could it be that Eichmann and his million accomplices in the Holocaust were just following orders? Could we call them all accomplices?” In 1961, he began to conduct experiments of obedience.

Participants were under the impression that they were part of a study of memory . Each trial had a pair divided into “teacher” and “learner,” but one person was an actor, so only one was a true participant. The drawing was rigged so that the participant always took the role of “teacher.” The two were moved into separate rooms and the “teacher” was given instructions. He or she pressed a button to shock the “learner” each time an incorrect answer was provided. These shocks would increase in voltage each time. Eventually, the actor would start to complain followed by more and more desperate screaming. Milgram learned that the majority of participants followed orders to continue delivering shocks despite the clear discomfort of the “learner.”

Had the shocks existed and been at the voltage they were labeled, the majority would have actually killed the “learner” in the next room. Having this fact revealed to the participant after the study concluded would be a clear example of psychological harm.

5. Harlow’s Monkey Experiments

In the 1950s, Harry Harlow of the University of Wisconsin tested infant dependency using rhesus monkeys in his experiments rather than human babies. The monkey was removed from its actual mother which was replaced with two “mothers,” one made of cloth and one made of wire. The cloth “mother” served no purpose other than its comforting feel whereas the wire “mother” fed the monkey through a bottle. The monkey spent the majority of his day next to the cloth “mother” and only around one hour a day next to the wire “mother,” despite the association between the wire model and food.

Harlow also used intimidation to prove that the monkey found the cloth “mother” to be superior. He would scare the infants and watch as the monkey ran towards the cloth model. Harlow also conducted experiments which isolated monkeys from other monkeys in order to show that those who did not learn to be part of the group at a young age were unable to assimilate and mate when they got older. Harlow’s experiments ceased in 1985 due to APA rules against the mistreatment of animals as well as humans . However, Department of Psychiatry Chair Ned H. Kalin, M.D. of the University of Wisconsin School of Medicine and Public Health has recently begun similar experiments that involve isolating infant monkeys and exposing them to frightening stimuli. He hopes to discover data on human anxiety, but is meeting with resistance from animal welfare organizations and the general public.

6. Learned Helplessness

The ethics of Martin Seligman’s experiments on learned helplessness would also be called into question today due to his mistreatment of animals. In 1965, Seligman and his team used dogs as subjects to test how one might perceive control. The group would place a dog on one side of a box that was divided in half by a low barrier. Then they would administer a shock, which was avoidable if the dog jumped over the barrier to the other half. Dogs quickly learned how to prevent themselves from being shocked.

Seligman’s group then harnessed a group of dogs and randomly administered shocks, which were completely unavoidable. The next day, these dogs were placed in the box with the barrier. Despite new circumstances that would have allowed them to escape the painful shocks, these dogs did not even try to jump over the barrier; they only cried and did not jump at all, demonstrating learned helplessness.

7. Robbers Cave Experiment

Muzafer Sherif conducted the Robbers Cave Experiment in the summer of 1954, testing group dynamics in the face of conflict. A group of preteen boys were brought to a summer camp, but they did not know that the counselors were actually psychological researchers. The boys were split into two groups, which were kept very separate. The groups only came into contact with each other when they were competing in sporting events or other activities.

The experimenters orchestrated increased tension between the two groups, particularly by keeping competitions close in points. Then, Sherif created problems, such as a water shortage, that would require both teams to unite and work together in order to achieve a goal. After a few of these, the groups became completely undivided and amicable.

Though the experiment seems simple and perhaps harmless, it would still be considered unethical today because Sherif used deception as the boys did not know they were participating in a psychological experiment. Sherif also did not have informed consent from participants.

8. The Monster Study

At the University of Iowa in 1939, Wendell Johnson and his team hoped to discover the cause of stuttering by attempting to turn orphans into stutterers. There were 22 young subjects, 12 of whom were non-stutterers. Half of the group experienced positive teaching whereas the other group dealt with negative reinforcement. The teachers continually told the latter group that they had stutters. No one in either group became stutterers at the end of the experiment, but those who received negative treatment did develop many of the self-esteem problems that stutterers often show. Perhaps Johnson’s interest in this phenomenon had to do with his own stutter as a child , but this study would never pass with a contemporary review board.

Johnson’s reputation as an unethical psychologist has not caused the University of Iowa to remove his name from its Speech and Hearing Clinic .

9. Blue Eyed versus Brown Eyed Students

Jane Elliott was not a psychologist, but she developed one of the most famously controversial exercises in 1968 by dividing students into a blue-eyed group and a brown-eyed group. Elliott was an elementary school teacher in Iowa, who was trying to give her students hands-on experience with discrimination the day after Martin Luther King Jr. was shot, but this exercise still has significance to psychology today. The famous exercise even transformed Elliott’s career into one centered around diversity training.

After dividing the class into groups, Elliott would cite phony scientific research claiming that one group was superior to the other. Throughout the day, the group would be treated as such. Elliott learned that it only took a day for the “superior” group to turn crueler and the “inferior” group to become more insecure. The blue eyed and brown eyed groups then switched so that all students endured the same prejudices.

Elliott’s exercise (which she repeated in 1969 and 1970) received plenty of public backlash, which is probably why it would not be replicated in a psychological experiment or classroom today. The main ethical concerns would be with deception and consent, though some of the original participants still regard the experiment as life-changing .

10. The Stanford Prison Experiment

In 1971, Philip Zimbardo of Stanford University conducted his famous prison experiment, which aimed to examine group behavior and the importance of roles. Zimbardo and his team picked a group of 24 male college students who were considered “healthy,” both physically and psychologically. The men had signed up to participate in a “ psychological study of prison life ,” which would pay them $15 per day. Half were randomly assigned to be prisoners and the other half were assigned to be prison guards. The experiment played out in the basement of the Stanford psychology department where Zimbardo’s team had created a makeshift prison. The experimenters went to great lengths to create a realistic experience for the prisoners, including fake arrests at the participants’ homes.

The prisoners were given a fairly standard introduction to prison life, which included being deloused and assigned an embarrassing uniform. The guards were given vague instructions that they should never be violent with the prisoners, but needed to stay in control. The first day passed without incident, but the prisoners rebelled on the second day by barricading themselves in their cells and ignoring the guards. This behavior shocked the guards and presumably led to the psychological abuse that followed. The guards started separating “good” and “bad” prisoners, and doled out punishments including push ups, solitary confinement, and public humiliation to rebellious prisoners.

Zimbardo explained , “In only a few days, our guards became sadistic and our prisoners became depressed and showed signs of extreme stress.” Two prisoners dropped out of the experiment; one eventually became a psychologist and a consultant for prisons . The experiment was originally supposed to last for two weeks, but it ended early when Zimbardo’s future wife, psychologist Christina Maslach, visited the experiment on the fifth day and told him , “I think it’s terrible what you’re doing to those boys.”

Despite the unethical experiment, Zimbardo is still a working psychologist today. He was even honored by the American Psychological Association with a Gold Medal Award for Life Achievement in the Science of Psychology in 2012 .


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