14 Famous Experiments That Shaped Psychology

Human nature and consciousness have been instrumental in the development of the world as we know now. The advancements humans have made from studying behavior have led to laws, technology and creating intelligent artificial beings from carefully crafted systems tools.

What has made all of this possible?

Experimental science.

The study of consciousness has remained one of the corner stones for the science of behavior. Throughout history, our understanding of psychology, of humans and other living beings has evolved through bold experiments.

Many of these experiments, conducted by some of the most influential psychologists, shocked the public. Many challenged the ethics of research itself.

In this series, we explore 14 of them. Iconic as they are, the experiments tell us how humans learn aggression and express psychopathy, why we conform to social pressure, and how early experiences shape attachment and fear. They provide us with demonstrable facts about how deeply our environment, social dynamics, concepts about ourselves and intelligence affect us.

So, let’s begin.

1. Jane Elliott’s A Class Divided Experiment (Eye-Color Lesson) (1968)

In 1968, Martin Luther King Jr., a champion of race equality, was assassinated. To demonstrate just how deeply discrimination could affect education, Jane Elliott conducted a profound experiment.

Summary

Jane was an elementary school teacher at Riceville, Iowa. Her goal was that she wanted her third graders to understand the effects of discrimination. While many educators tend to do this through lectures, Elliot wanted to demonstrate it in a naturalistic setting over a period of two days.

So, she split her all-white class into two groups based on eye color. One day, blue-eyed children were told they were smarter and more deserving of privileges. The brown-eyed kids were made to feel inferior. The next day, she reversed the roles.

Findings and Impact of the Experiment

The transformation was immediate. One might not expect a child to become cruel or bossy, but the “superior” group did just that. However, those labeled “inferior” felt demoralized and performed worse academically.

Once the exercise ended, the children reunited and openly discussed how painful the discrimination felt.

This experiment showed through a spontaneous classroom activity how quickly prejudice can form and how deeply it affects self-esteem and behavior.

Moreover, the experiment further demonstrated in-group behavior as – at their respective times – same eye-colored students interacted more with each other (e.g sat next to students with the same eye color during class and lunch).

Elliott’s research informed modern diversity training. Her research is still taught in various universities as an example of how deeply discrimination affects how we view ourselves and treat others.

Much of her approach is used in diversity training today in major corporations. While further replications of her exercise were conducted, research confirmed that the exercise had partially success in reducing implicit bias in participants.

2. Solomon Asch’s Line Experiment (1951)

Imagine you’re in a room with seven other people, and everyone says a clearly wrong answer to a simple question.

Would you stick to the truth or go along with the group? Turns out that human psychology is far trickier than we originally thought.

Summary

American psychologist, Solomon Asch invited groups of seven to nine male college students to what he described as a visual perception experiment. In reality, all but one of the participants were confederates – actors working with the experimenter. When the genuine participant entered, the others were already seated in a row, and the test began.

The setup was simple.

The experimenter displayed two large cards: one with a single “standard” line, and the other with three “comparison” lines of different lengths. One comparison line was identical in length to the standard line, while the others were either slightly shorter or longer -ranging from three-quarters of an inch to nearly two inches off. Each person was asked, in turn, to say aloud which comparison line matched the standard.

At first, everything seemed straightforward. On the opening trials, everyone gave the correct answer. But by the third round, something unusual happened: the confederates all deliberately chose the wrong line. Across 18 trials, this occurred 12 times, with occasional correct answers mixed in to avoid suspicion. The question was whether the lone real participant would trust his own eyes or conform to the group.

Findings and Impact of the Experiment

The results were surprising to say the least: about one-third of participants conformed to the group’s incorrect choice at least once. When asked privately, nearly everyone answered correctly.

Asch’s findings highlighted how powerful social pressure can be. It could even lead people to conform despite knowing that the answer they are being pressured to give isn’t the right one. All of that is possible without the possibility of being punished or reprimanded.

This has implications for decision-making, peer influence, and group dynamics.

The findings of Asch’s experiments opened up psychological research on social conformity. For example, Milgram’s obedience studies stemmed from Asch’s work (Milgram was Asch’s doctoral student), extending the analysis of group pressure to obedience to authority figures.

Furthermore, theories on minority influence, groupthink, and the bystander effect often reference Asch’s basic framework as a jumping‑off point for group behavior analysis.

3. Albert Bandura’s Bobo Doll Experiment (1961-1963)

Violence begets violence.

Matthew 26:52

Why is it the case that children who grow up experiencing violence are more comfortable with using violence as a means? In the early 1960s, Albert Bandura conducted one of the most famous experiments of psychology to answer this question.

Summary

Bandura aimed to explore whether children learn aggressive behavior simply by watching adults.

This study did not attempt to explore beliefs. It only focused on the behavior of these children after they observed violence and aggression.

Bandura and his team recruited 72 children from the Stanford University Nursery School, evenly split between boys and girls aged three to six. The children were divided into a control group that saw no adult model, and eight experimental groups where children observed either an aggressive or a nonaggressive adult, with further divisions by gender.

To ensure fairness, teachers and experimenters rated each child’s baseline aggression so the groups were balanced. Each child was tested individually. While the child sat at a table with engaging activities, an adult model was given toys that included a large inflatable Bobo doll.

In the nonaggressive condition, the model played quietly with Tinkertoys, ignoring the doll.

In the aggressive condition, the model attacked the doll – punching, kicking, striking it with a mallet, and shouting phrases like “Sock him in the nose!”

After ten minutes, the child was moved to another room, first allowed to play briefly with attractive toys before being told those were off-limits and redirected to a final playroom.

The last room contained both aggressive toys, like a Bobo doll and dart guns, and nonaggressive ones, like dolls and crayons. For twenty minutes, observers behind a one-way mirror recorded how much of the children’s play imitated the model’s aggressive behavior, how often they used aggression in new ways, and whether they avoided aggression altogether.

Findings and Impact of the Experiment

Children who saw aggression were far more likely to mimic those violent actions and words. The children’s actions also differed based on their gender. Boys showed more physical aggression than girls, particularly when observing a male model.

This study demonstrated that observational learning plays a key role in the development of behavior. One does not need to do violence to learn it. The experiment shifted psychology from focusing solely on rewards and punishments to recognizing that we imitate what we see – a principle still relevant to understanding media influence on children.

This prompted public concern and legislative action on media violence in the 1970s and beyond. U.S. congressional hearings cited Bandura’s work when considering TV and video game content ratings.

While the assertion that video games directly cause violence is not based on science, video games can play a significant role in increasing aggressive behavior and emotions.

Bandura’s experiment also led to a shift in teaching practices and academia. Social Learning Theory, born from the Bobo Doll findings, is central to modern teaching and parenting. After all, role modeling, peer observation, and reinforcement are foundational tools in shaping behavior.

We have much to thank for when it comes Albert Bandura’s work!

4. John Watson’s Little Albert – Conditioning Fear (1920)

John B. Watson has been considered to be the founder of the behaviorist school of psychology. His work focused mainly on the mechanisms of learning.

“Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select.”

John B. Watson

However, instead of how children learn violence, Watson and Rosalie Rayner devised one of the most famous psychological experiments to see how children learn fear.

Summary

Baseline Observations (9 months old)

Albert was first introduced to a white rat, rabbit, dog, monkey, masks, cotton wool, and burning newspapers. He showed no fear of these stimuli, reaching for them or ignoring them casually. The only thing that frightened him was a loud noise made by striking a steel bar behind his head, which made him cry and recoil.

Conditioning Begins (11 months, 3 days old)

When Albert reached for the white rat, the steel bar was struck to create a sudden noise. After just a few pairings, Albert began to whimper and turn away from the rat even without the noise. Soon, he cried and tried to escape at the mere sight of it.

Generalization of Fear (11 months, 10 days old)

The researchers tested whether Albert’s fear spread to other objects. Indeed, he cried and withdrew when presented with a rabbit, a dog, a fur coat, cotton wool, and even a Santa Claus mask with a white beard. However, he played happily with his wooden blocks, showing that the fear was specific to furry textures.

Persistence of Fear (12 months old)

A month later, Albert was tested again. He continued to show fear toward the rabbit, dog, coat, and mask. However, the reactions were less intense. Watson also noted his frequent use of thumb-sucking as a way to calm himself during these trials.

End of the Study

Before extinction trials could be attempted, Albert’s mother removed him from the hospital, leaving the long-term outcome of his conditioned fears unknown. Watson and Rayner admitted that this could have a significantly negative impact on the personality of Albert. In modern times, this would be ethically impermissible.

Findings and Impact of the Experiment

The experiment was controversial, but it revealed that emotional responses can be classically conditioned in humans. Previously, it had only been studied in Pavlov’s experiment, with the dogs salivating to a bell.

Aside from this, the findings were foundational to later therapies such as systematic desensitization, exposure therapy, behavior modification, and elements of CBT. These approaches are widely used to treat phobias and anxiety disorders today.

The Little Albert experiment however gained notoriety as well. The Belmont Report of 1979 made sure that research like this and the Tuskegee Syphilis Study could not be ethically permitted. It is very possible that Albert could have been traumatized. Knowing the fact that trauma can affect the brain compromises the ethics of the study even further.

On the side of academic criticism, Ben Harris’s (1979) critique summed up problems with reporting, the lack of control trials and ethics.

Nevertheless, therapies incorporating psychological techniques that were outlined by Watson – such as exposure response prevention – do continue to benefit millions around the world who suffer from phobias.

5. Philip Zimbardo’s Stanford Prison Experiment – Power and Authority (1971)

The dynamics of power has been an interesting field of psychological investigation. From Plato, Nietzsche and Machiavelli to Foucault and Lacan, the question of how power arises as a part of human psychology has seen many answers.

But what would happen if regular people (who have not experienced political or much social power) are suddenly given immense control over others?

Summary

Arrests and Arrival (Day 1)

The study began with a surprise: the student “prisoners” were unexpectedly arrested at their homes by local Palo Alto police. They were handcuffed, searched, and booked at the police station before being blindfolded and taken to the mock prison in Stanford’s psychology building basement. On arrival, they were stripped, deloused, given smocks with ID numbers, nylon caps, and ankle chains. From the start, the aim was to dehumanize and strip them of individuality.

The First Rebellion (Day 2)

Tensions escalated quickly. By the second day, the prisoners staged a rebellion, barricading their cell doors with beds and shouting at the guards. The guards responded with fire extinguishers, forced prisoners out, stripped them naked, and placed ringleaders in solitary confinement. Guards began using psychological tactics, such as rewarding compliant prisoners with privileges while punishing others to create division.

Escalation of Control (Day 3)

The guards grew more authoritarian. They introduced frequent counts, enforced degrading tasks like push-ups, and restricted basic needs, including access to toilets. Some prisoners began showing emotional distress. One participant suffered a breakdown so severe that he had to be released from the study.

Psychological Warfare (Day 4)

Guards intensified their control, using humiliation and manipulation to maintain dominance. They forced prisoners to clean toilets with their bare hands and manipulated privileges to break solidarity. Prisoners responded with passive compliance or quiet acts of resistance. A hunger strike began, which the guards tried to crush by placing participants in solitary confinement and using other prisoners to pressure them into obedience.

Breaking Down (Day 5)

The psychological toll deepened. Several prisoners displayed signs of depression, crying, and acute stress. Others became passive and withdrawn, complying automatically with orders. Guards, meanwhile, became increasingly creative in inventing punishments, taking their roles far more seriously than anticipated.

Abrupt End (Day 6)

Although the experiment was planned to run for two weeks, the emotional breakdowns among prisoners and the abusive behavior of guards forced Zimbardo to end it after only six days. By then, the line between reality and role-play had blurred: both guards and prisoners had internalized their assigned roles, revealing the disturbing ease with which ordinary people could adopt oppressive or submissive behaviors in a simulated prison environment.

Findings and Impact of the Experiment

The experiment demonstrated how situational forces, isolation of stimuli and deindividuation along with enforced roles can alter behavior. It showed how individuals bypassed personal morals due to the allure of power. As such, the experiment became a cornerstone for understanding deindividuation, obedience, institutional behavior, and the darker side of human nature.

A subject interesting for moral psychology and the dark tetrad trait of sadism.

Zimbardo’s testimony before Congress referenced the study when discussing prison reform and juvenile incarceration. As noted by the Stanford Report, the study’s footage and analysis have been used in law enforcement, military training, and criminal justice education to illustrate how unchecked authority and role expectations can lead to abuse.

Understandably so, much like the Little Albert experiment, the Stanford prison study also raised enduring debates about ethics in research. Some critics argue that informed consent was not taken prior to the experiment. So, the participants had no knowledge about the potentially devious effects of this study.

These issues were addressed generally in the Belmont Report.

6. Stanley Milgram’s Obedience Study – Following Orders (1961)

Stanley Milgram, intrigued by the question of how ordinary people could commit atrocities during wartime, conducted a study on obedience. The experiment, while being incredibly influential, gained a lot of notoriety.

Such was the controversy generated by Milgram’s and Zimbardo’s experiments that ethical considerations make it practically impossible for us to study behavior in a similar way today.

Summary

Stanley Milgram designed his 1963 study to investigate how far ordinary people would go in obeying authority, even when asked to harm another person. Forty men from New Haven, aged between 20 and 50 and representing a range of occupations, were recruited through newspaper ads and paid a small fee for participating. Each believed they were part of a study on learning and memory at Yale University.

Upon arrival, each participant met another “volunteer” (actually a confederate of the experimenter), and lots were drawn to decide who would be the “teacher” and who would be the “learner.” This draw was rigged so the true participant was always the teacher. The learner was then strapped into what looked like an electric chair in a separate room, with electrodes attached to his arm. The teacher watched this setup, reinforcing the realism of the situation.

The teacher was taken to another room and seated before a large shock generator, with switches ranging from 15 volts (“Slight Shock”) to 450 volts (“Danger: Severe Shock”). Before beginning, the participant received a small real shock (45 volts) to convince him of the machine’s authenticity.

The learning task required the teacher to read pairs of words aloud and then test the learner’s memory by offering multiple-choice answers. Whenever the learner gave a wrong response, the teacher was instructed to administer an electric shock, increasing the level by one switch each time. Unbeknownst to the teacher, no shocks were actually delivered – the learner was only acting. His responses were scripted: at first answering normally, but as shocks grew stronger, he began to complain, then pound on the wall at 300 volts, and finally stopped responding altogether after 315 volts.

If the teacher hesitated or questioned the procedure, the experimenter (dressed in a gray lab coat and standing nearby) used a series of verbal prods, such as: “Please continue,” or “The experiment requires that you continue.” If the teacher still resisted, stronger commands followed, with the final statement being, “You have no other choice, you must go on.“

The key measure of obedience was how far the participant went on the shock scale before refusing to continue.

Findings and Impact of the Experiment

Milgram’s work revealed the extraordinary power of authority in driving people to act against their conscience. This discovery has troubling ramifications for both the subjects for people in general. No one, not even Milgram himself, expected such a high percentage of compliance.

Milgram’s study fundamentally changed how psychologists understand compliance and is often cited in discussions of military, corporate, and political obedience.

There are a few lessons to be learned, as noted by Thomas Blass in his book, The Man Who Shocked the World: The Life and Legacy of Stanley Milgram.

First, the experiment demonstrated the strength of the tendency of people to obey. The presence of this tendency was acknowledged in a high obedience rate. A further nuanced, intrusive data collection might have yielded broader results. There were methodological lackings in the study.

Nevertheless, Milgram’s experiment demonstrated how people’s inclination to comply might lead them to behave against their moral convictions. Those kinds of violent acts do not require bad people to commit them.

Second, the experiment demonstrated the internal alterations that acted as mediating factors to enable harmful compliance.

Due to the debriefing of the rules and a controlled environment, possibly individuals were more inclined to obey a disembodied voice’s harsh commands than they otherwise would have been. As such, a change in internal states, including physiological reactions, can greatly alter behavior. This shows that legitimacy of authority is in a psychological context, lending credence to how important psychology really is. Certain characteristics can make authority seem absolute; certain stimuli including a reasonable control of autonomy, atmosphere, tone of voice giving prompts, colors.

The experiment provides circumstances where authority is highly suggested but not completely debriefed.

The controversy surrounding the experiment helped in bringing the importance of informed consent to the forefront of research. The World Medical Association produced the Declaration of Helsinki to advise medical researchers in protecting human patients’ well-being. The initial presentation took place during the General Assembly in 1964. The Declaration of Helsinki, unlike its precursor the Nuremberg Code, demands informed permission from study subjects.

Debriefing is a necessary part of psychological research to ensure the least amount of psychological distress.

7. Harry Harlow’s Monkey Experiments – The Need for Comfort (1958)

Prior to the latter half of the 20th century, it was believed that infants bonded with their mothers mainly for food and affection. Harry Harlow demonstrated how comfort affected the bonding of a child with his experiments on rhesus monkeys.

Summary

Harlow gave a total of eight infant rhesus monkeys two surrogate “mothers”, each.

One surrogate mother was made of wire (cold, rough and, as Harlow mentioned, ‘psychologically inept‘). The other surrogate mother was covered in a soft cloth.

Next, Harlow divided the eight infants into two groups with 4 infants each. Both groups were individually exposed to both surrogate mothers over a period of 165 days.

The Experimental Conditions

Harlow set up two experimental conditions.

In one group, he set the condition that the ‘wire’ mother lactated (provided the milk) while the ‘soft’ mother did not. In the other group, the soft mother lactated while the wire mother did not. He then recorded the number of hours each infant spent with each mother, in both conditions throughout the day.

The results were surprising, to say the least.

Monkeys in both the groups consumed the same amount of milk. They also had roughly the same amount of weight at the end of the experiment.

However, in both conditions, the infants overwhelmingly chose to significantly more time with the soft mother. Even when they were being fed by the wire mother, they clung to the cloth mother for comfort, especially when frightened.

The Control Groups

In another experiment, Harlow noted that monkeys who lived with surrogate mothers for x amount of time exhibited significantly different behaviors from another monkey living with surrogate mothers for y amount of time.

Findings and Impact of the Experiment

The main finding of the experiment was that social behavior could be altered depending on comfort associated with bonding.

In particular, Harlow showed that emotional security and warmth are essential for healthy attachment, not just physical sustenance. This research reshaped child-rearing advice and influenced theories of emotional development and attachment.

Harry Harlow’s research provided much required experimental and empirical evidence to psychoanalytic theory – especially with regards to object relations and attachment. His correspondence with John Bowlby, the British psychoanalyst who was one of the fathers of attachment theory, in particular is fascinating, to say the least.

8. Loftus and Palmer’s Memory Distortion Study (1974)

Our memories feel like video recordings of past events. Often, we think that they are very credible.

The truth is that they can be surprisingly unreliable.

Psychologists Elizabeth Loftus and John Palmer demonstrated just that.

Summary

Loftus and Palmer showed how unreliable memory could be in their groundbreaking study on eyewitness testimony.

Participants watched a film of a car accident and were later asked questions about what they saw. The twist was in the wording: one group was asked how fast the cars were going when they “hit,” another when they “smashed” into each other. The difference in wording led to dramatically different speed estimates, with the “smashed” group recalling much higher speeds.

When asked later if they saw broken glass (which was never shown), participants in the “smashed” group were far more likely to say yes.

This shows how usage of certain leading words or prompts could elicit memory responses which share the bias in the question itself.

Findings and Impact of the Experiment

This study revealed that memory is reconstructive – it can be altered by post-event information or cues. It revolutionized legal practices by showing that eyewitness testimony is not always reliable.

Some improvements in the legal system have been directly influenced by this research. For instance, the New Jersey Supreme Court recommended that jurors be informed that eyewitness evidence isn’t always trustworthy, back in 2012, referring to the study. Moreover, the study also influenced police interview methods and courtroom procedures worldwide.

9. Festinger and Carlsmith’s Cognitive Dissonance Experiment (1957)

We like to think we’re rational beings. However, sometimes we change our beliefs just to align with our actions. This phenomenon, called cognitive dissonance, was famously demonstrated by Leon Festinger and James Carlsmith.

Summary

The participants of the study were asked to perform boring tasks (turning pegs for an hour), then offered either $1 or $20 to tell another person the activity was fun. Surprisingly, those paid only $1 later reported actually enjoying the task more than those paid $20.

Given that they were paid more, it would seem reasonable at first that those who received $20 would claim to have liked it more.

The trick, though, is this:

The $20 group had ample reason to lie: “It’s okay if I say it was fun because I got paid a lot.” Their action was justified by the large payoff; therefore, they didn’t need to adjust their ideas. In fact, they still found the work dull – much like the control group which wasn’t asked to recommend the activity to anyone. So, as such, they did not claim to like the activity with much vigor.

On the other hand, the $1 group did not have the same incentive (“I lied for just $1?”). Cognitive dissonance was the result of the smaller reward. This is reflected in the results as they showed greater enthusiasm while recommending the activity.

All in all, compared to the large reward group and the control group, the small reward group’s real attitude changed more.

Why? Receiving a small reward didn’t justify lying, so participants reduced the discomfort (dissonance) by trying to convince others that the activity they did was actually interesting – when it really wasn’t.

Findings and Impact of the Experiment

This classic experiment showed how we adjust our attitudes to match our circumstances. Festinger’s experiment helped shape theories in persuasion, self-justification, and marketing psychology.

Contrary to behaviorist expectations (that greater rewards strengthen attitudes), this study showed that smaller rewards often produced stronger internal change—since people needed to justify their behavior internally when external justification was weak. This shifted social psychology to more cognitive explanations.

Not only that, but cognitive dissonance theory has also influenced the field of advertising. It is a mainstay theory of consumer behavior which has stood the test of time.

10. The Hawthorne Effect (1920s–1950s)

The Hawthorne Effect is a psychological phenomenon entailing that when people know they’re being observed, they change their behavior. This was demonstrated after Landsberger revisited the results of a series of experiments earlier in the 20th century.

Summary

The experiments that led to this discovery were not conducted by the discoverer of the phenomenon, Henry Landsberger.

Rather, back in the 1920’s and 1930’s, the Hawthorne studies were conducted in a factory just outside Chicago. The original researchers, encouraged by Elton Mayo, wanted to know if better lighting would boost worker productivity.

It did – but strangely, productivity also rose when lighting was dimmed.

Further investigation was carried out to assess the impact of additional factors deemed crucial for productivity. The additional research was initially focused on physical aspects that contribute to monotony and weariness, and it was then carried out through four comprehensive experiments. However, in the end, the researchers concluded that there was some other factor at play – since the factors mentioned above did not significantly predict productivity in the workers.

Decades later, Henry Landsberger analyzed these results and coined the term Hawthorne Effect.

Findings and Impact of the Experiments

The Hawthorne Effect reminds psychologists and researchers to account for observation bias when designing studies. It’s also influenced workplace management, education, and medical research.

Before the Hawthorne studies, management theories emphasized financial incentives and efficient processes (think Taylorism and scientific management). The Hawthorne findings fundamentally reframed this view, highlighting that social and psychological factors – like feeling noticed or part of a team – play a powerful role in productivity. This shift birthed the Human Relations Movement, which focuses on group dynamics, interpersonal relationships, and emotional well-being at work

Moreover, practical steps like regular performance reviews, employee surveys, decision-making involvement, and fostering supportive workplace environments stem directly from the idea that employees perform better when they feel valued and closely observed.

11. The Kitty Genovese Case and the Bystander Effect (1964)

In a tragic real-world event, Kitty Genovese was murdered outside her apartment in New York while reportedly dozens of neighbors heard her cries for help. Few intervened or called the police.

This led psychologists John Darley and Bibb Latané to study what they called the bystander effect.

Summary

In lab experiments with college student recruits and simulating emergencies – in this case, a confederate having a seizure during a discussion over an intercom (the basic setup of the experiment), they found that the more people present, the less likely anyone is to help.

Basically, each person assumes someone else will act.

To break it down, when only one individual thought that they were listening to the cries of help (by the confederate), 85% of the people came to help. When they thought there were 2 or 3 others who listened as well, 62% of people attempted to aid.

However, knowing that 5 or more people were also listening to the cries of help, only 31% of the people helped.

Findings and Impact of the Experiment

The wide difference in behavior of the groups was explained through the fact that with more people present, the responsibility of corrective action diffuses.

It was proposed that this was why it took more than an hour after Genovese’s encounter with her murderer for help to actually arrive.

This insight changed emergency response training. CPR courses, for example, now teach rescuers to point directly to someone and say, “You call 911,” reducing diffusion of responsibility.

The creation of the 911 emergency system in the United States was one of the most significant and practical actions in response to the identification of the bystander effect. Policymakers saw the necessity for a centralized, single-point reporting system that removes diffusion of responsibility after being partially prompted by the reporting of the Kitty Genovese case.

The decision-making process was explained by Darley and Latané’s introduction of the Five-Step Model of bystander intervention, which consists of noticing, interpreting, admitting responsibility, choosing to help, and acting. Currently, this approach is essential to psychological research and intervention strategy creation.

12. Seligman’s Learned Helplessness Experiment (1967)

While studying classical conditioning in dogs, Martin Seligman made an unexpected discovery. Dogs exposed to unavoidable shocks eventually stopped trying to escape – even when later given the chance to avoid them.

The animals had learned that their actions were useless, leading to helpless behavior. Seligman later connected this to human depression: when people repeatedly face failure or uncontrollable stress, they may stop trying altogether, even when opportunities to improve arise.

Findings and Impact of the Experiment

Learned helplessness influenced therapies for depression and anxiety, shifting focus toward empowering individuals to regain control of their lives.

The model was improved by Abramson, Seligman, and Teasdale (1978) by adding attributional style, which states that people’s explanations of failure (internal, stable, or global) influence how long they feel hopeless and depressed.

Moreover, in context of psychotherapeutic practice, redefining setbacks through cognitive reconfiguration as transient, particular, and external has shown to have efficacy. This is particularly true of factors which people think are uncontrollable.

Moreover, learned helplessness gave birth to the concept of learned optimism, which is a positive psychology notion that fosters resilience. Currently, learned optimism has widespread applications, particularly with regards to health, social life and career prowess.

13. Rosenhan’s “Being Sane in Insane Places” (1973)

What if psychiatric diagnoses are influenced by context rather than clear symptoms? This would reveal some huge chinks in the way mental health is diagnosed and treated in psychiatric facilities accross the world.

Psychologist David Rosenhan tested this in his famous experiment back in 1973. The experiment garnered a significant amount of attention to how flawed the mental health system can sometimes be.

Summary

In his experiment, Rosenhan sent healthy “pseudo-patients” into psychiatric hospitals. They claimed only one symptom – hearing a voice saying “empty, hollow, thud” – but otherwise acted normally.

All were admitted with diagnoses of schizophrenia. Once inside, they behaved normally, yet the staff failed to recognize they were sane. Some were hospitalized for weeks.

In a follow-up, Rosenhan told hospitals he would send pseudo-patients (but didn’t); many real patients were wrongly suspected of being impostors.

Findings and Impact of the Experiment

This study exposed flaws in psychiatric diagnosis and treatment. It prompted reforms in mental health care and fueled debate over labeling and stigma in psychiatry. Once tagged, every behavior was filtered via the diagnosis, illustrating how clinical interpretation is highly biased by situational context.

Along with Robert Spitzer’s concerns, this study had a significant impact on DSM revision. DSM-III (1980) provided significantly more precise definitions of mental diseases, as well as specific recommendations for who should be included or excluded from each categorization. For example, in DSM-III, a hallucination had to be repeated multiple times; in DSM-IV (1994), hearing voices had to be experienced for more than a month before a diagnosis of schizophrenia could be established; and in DSM-5, this is extended to six months.

14. Ekman’s Universal Facial Expressions Study (1971)

Could it be that people from different cultures do not experience the same number of emotions?

Or a better question would be: are emotions shaped by culture, or are they biologically universal? Paul Ekman sought to find out whether emotions are truly universal or not.

Summary

Psychologist Paul Ekman conducted a cross-cultural study on identification of 6 basic emotions: happiness, anger, sadness, fear, surprise, and disgust.

He started by testing members of ‘literate’ civilizations, including those in the United States. He later visited a remote group – the Fore tribe in Papua New Guinea – who were not exposed to Western media in order to rule out cultural learning.

A picture of a facial expression was displayed to the participants. They were asked to select the picture that best suited brief, heartfelt narratives (such as “His child has died” or “He is about to fight”).

Findings and Impact of the Experiment

For participants in the U.S., Japan, Brazil, Chile and Argentina, an accuracy of 70-90% was observed. While conducting the experiment on the Fore tribe, Ekman noticed similar results. For happiness, recognition was well over 80%, while for anger, contempt, and sadness, it was between 70 and 80%. Although they were occasionally puzzled, fear and surprise were nonetheless identified at levels much above chance.

There was a second part to the study too, in which the researchers photographed the tribe members and asked Western participants to identify their emotions. The Western participants accurately identified the emotions accurately, usually more than 64% of the time. However, when it came to distinguishing surprise and fear – the accuracy dropped.

The study showed that even in isolated cultures with no exposure to Western media, people accurately recognized these emotions, and vice versa.

Ekman’s work demonstrated that core human emotions could be biologically hardwired, transcending culture. This finding has influenced everything from cross-cultural communication to modern lie detection techniques.

Ekman and Wallace Friesen developed the facial action coding system (FACS), an anatomically based system that decomposes facial expressions into specific muscle movements known as Action Units. FACS is still the gold standard for objectively coding and analyzing facial behavior, and it is widely used in psychology, animation, gaming, AI, and other fields.

Ekman’s discovery of microexpressions – brief, involuntary facial expressions – became a cornerstone in deception detection. He co-led the Wizards Project, which sought to uncover unusual individuals capable of detecting deceit with amazing precision. His approaches have influenced training for law enforcement, the TSA, and intelligence officials.

Wrapping Up the Series

While the list of experiments that have influenced modern thought and science is a much larger one, these 14 experiments form the backbone of modern psychology. In sum, they’ve shown that:

• Memory can be manipulated.
• Our beliefs adapt to match our actions.
• Observation alone can change behavior.
• Social dynamics often override individual responsibility.
• Repeated failure can lead to hopelessness.
• Mental illness diagnoses can be flawed.
• Emotions are universal and biologically ingrained.

Together, these famous experiments transformed therapy, legal systems, mental health care, education, and our understanding of human nature. They remind us that psychology is not static. Rather, human thought and behavior has potential for evolution and biases.

As psychologists continue to test traditional assumptions and shed new light on the mysteries of the mind, one can hope for many more discoveries to come!