Famous Psychology Experiments Throughout History

Without experimentation, we would likely not know nearly as much as we do about how the human mind works. Over the last century and a half, several influential psychologists have conducted studies that have shaped our understanding of the field and spurred further research. Such experiments may seem unethical by today's standards, but over the years, they have served as important learning resources and are still nonetheless an important part of the history of the discipline. 

Famous Psychology Experiments

Psychological studies help researchers better understand human thought and behavior. You may have read about particularly famous psychological experiments in a psychology book, or watched a documentary on one of the many experiments from the past that are now considered controversial. Learning about these studies can help you better understand their findings—and how those findings have contributed to some of history’s most important psychological theories and developments. Below, we’ll explore some influential psychology experiments in chronological order.

1920 — The Little Albert experiment: Classical conditioning

The case of Little Albert was one that demonstrated classical conditioning in humans.

Dr. John B. Watson and a graduate student by the name of Rosalie Rayner wanted to perform a study to prove the existence of classical conditioning. An infant named Albert B. was deemed the perfect candidate for the project because he did not show fear or cry. 

In the experiment, the two researchers hypothesized that the fear of an animal could be conditioned by performing specific actions.

A white rat was one of the stimuli, and a steel bar was the second one. Initially, Albert showed no hesitation to try to touch the white rat. However, when he did, Dr. Watson struck the steel bar to create a loud noise, startling Little Albert.

Over time, he became fearful when being presented with the rat, but then the researchers wanted to learn whether this fear could be transferred.

Following a brief intermission, Albert was presented with other objects and animals. Albert happily played with blocks, which shows that an emotional transfer didn't occur with those objects in the room, but when faced with rabbits and dogs as well as inanimate objects like wool and fur coats, a negative reaction occurred.

Therefore, this famous psychology experiment shows that emotional responses—such as irrational fears—can be conditioned. In the case of Albert, he developed a conditioned fear response to furry objects. The researchers had some ethical concerns, but the experiment provided insight as to why fears, especially irrational ones, can be formed. 

1951 — The Asch experiment: Group conformity

The Asch Experiment, which is named after Dr. Solomon Asch, showed that when faced with social pressure, a person may alter their responses to align them with the responses of others in a group, despite being certain that they have the correct answer.

At Swarthmore College, Solomon Asch conducted a study involving 50 students and a vision test. This exam included three different-sized lines, labeled A, B, and C, requiring the longest one to be chosen. [2]

Asch had a group of impostors who all gave a wrong answer in the presence of “naive” participants, who were unaware the other individuals were impostors.

In these 12 trials, the findings showed that approximately 75% of the naive participants conformed to the group's wrong answer.

Additionally, there were six controlled trials (making 18 total) that only had real participants. There wasn't a preselected answer, and everyone participated normally. In these, fewer than 1% of participants gave an incorrect response.

In the main trials, the participants who willingly conformed and gave the wrong answer wanted to fit in with the others without being looked at negatively. This situation is known as a normative influence. Other than the thought of feeling humiliated, people also sometimes conform because they perceive the rest of the group as being more informed. This is named informational influence.

The Asch conformity study demonstrated the power of group pressure to influence others. While it isn't as unethical as the previous classic experiment, this one has still faced criticism.

Since the Asch Experiment took place in the 1950s, during the "Red Scare" period in the United States, it's been argued that a conformist mentality was already present because of the culture of the time and the fear of being labeled a communist. However, this social science experiment still reinforces the influence groups can have on individuals.

1961 — The Bobo doll experiment: Social influences on human behavior

One of the most famous social psychology experiments of all time, the Bobo doll experiment helped inform our understanding of the ways human behavior can develop. Conducted by Albert Bandura, a pioneer in the field of social psychology, the experiment involved the observation of young children from the nursery school at Stanford University. Bandura split participants into three groups that consisted of adults, who would model different behaviors, and children, who would observe it. He had adults in one group model aggressive behavior toward a Bobo doll and those in another group model non-aggressive behavior. Children in the third group were not exposed to any modeled behavior. 

When given the opportunity to play with the Bobo doll and aggressive toys, children in the group with the aggressive adults became physically aggressive with the doll. Children in the group with the non-aggressive adults, however, displayed lower levels of anger and aggression. The children also displayed differences in aggression based on sex, with males tending to exhibit more physically aggressive behavior than females. (Males and females were verbally aggressive to the same degree.)

Bandura’s study revealed that children can learn social behaviors by observing other people, specifically adults. The results of the experiment helped inform his social learning theory, which emphasizes the role of one’s social environment in the development of behavior. This theory represented a significant shift away from the once-dominant ideas of pure behaviorism.     

1963 — The Milgram experiment: Obedience to authority

Attempting to explain the commission of war crimes during World War II, psychologist Stanley Milgram conducted a study on the influence of perceived authority on behavior. Milgram hypothesized that directions from people in power could lead individuals to behave in ways that were out of line with their values. 

To test this hypothesis, Milgram had “teachers”—participants who thought they were taking part in a study on cognition—deliver electrical shocks to the “learners”. The learners were actors, though, and no shocks were actually delivered. However, the participants fully believed that the shocks were real. 

During the study, the person administering the experiment—who was meant to serve as the authority figure—instructed the participants to provide increasingly powerful shocks to the learners as they answered questions incorrectly. When shocked, the actors exhibited signs of physical and psychological distress. Despite the evidence that they were harming the learners, the teachers often obeyed the experimenters when told to increase the voltage. Many eventually went to the highest setting. The Milgram experiments, though controversial, help illustrate the ways in which individuals conform to a perceived authority figure despite ethical concerns. 

1971 — The Stanford prison experiment: Social roles, power, and conformity

One of the most widely known and controversial psychological studies ever, the Stanford prison experiment was a week-long study that captured how people can conform to roles and potentially harm others due to their perceived power.

This study—funded by the U.S. Office of Naval Research—was conducted on campus by a team led by psychologist Dr. Philip Zimbardo. Here, a fictional prison was developed, and each of the 24 male students was provided the role of either a prisoner or a guard.

Despite instructing the guards not to physically harm the prisoners, the experiment became increasingly more oppressive and simulated real prison conditions.

The guards became dictatorial and cruel to the "inmates" and eventually engaged in abusive behavior. On the second day of the experiment, some prisoners staged a rebellion, and a few became so distressed that they quit the experiment early on. In contrast to the guards, many of the prisoners became submissive to the authority figures and reluctantly accepted any abuse.

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Even Dr. Zimbardo, who oversaw everything through surveillance, began to perceive himself more like a prison superintendent than a psychologist performing research. An outside observer was shocked when visiting the facilities, and Dr. Zimbardo concluded the experiment prematurely because of the events that occurred.

This experiment has consistently been under scrutiny for years. Although physical violence was not allowed, harm was done, and according to Zimbardo himself, the guards had permission to create oppression through boredom, frustration, and, to some extent, fear. He wanted to create a sense of powerlessness. The results of the experiment were outlined in the International Journal of Criminology and Penology, New York Times Magazine, and Naval Research Reviews.

While this trial has been considered unethical by many researchers, it may offer insight into social roles and how power (and lack thereof) can influence a person’s behavior. However, the extent to which it does so has been called into question, and the entire experiment has been criticized for various reasons and deemed to be poorly conducted overall.

1977 — The Halo Effect Experiment: Cognitive bias

As much as humans try to be unbiased, research on the halo effect shows that our perceptions of others can greatly influence our decision-making, both consciously and subconsciously.

Conducted by doctors Richard E. Nisbett and Timothy DeCamp Wilson from the University of Michigan, the famous halo effect experiment involved a large group of college students who were instructed to evaluate a man who spoke English with a very heavy European accent. They were to evaluate him based on his accent, physical appearance, and mannerisms when he was warm and friendly, as well as when he was cold and distant.

On appearance alone, approximately 70% of the students approved of how he looked when he behaved warmly, but when he was cold, nearly the same percentage of students disapproved of his looks. When the teacher was warm, the majority of students found his mannerisms to be appealing, but when he was cold, the majority found his mannerisms to be irritating. 

When the teacher was warm, the class was divided 50-50 on how his accent sounded, but when he was cold, a significant majority of the students found his accent to be irritating [5].

This experiment demonstrated that unrelated characteristics in people are judged based on how they perceive them globally. Cognitive bias is thought to be an everyday occurrence, and it can affect various aspects of life, such as our purchasing decisions, how we choose our favorite sports teams, and even job interviews. This experiment shows that humans can be easily influenced based on their perceptions.

Discussing your own fears and biases with a therapist

If you’re interested in exploring your own fears or biases, it may help to speak with a licensed therapist, whether in person or online. If you don’t feel comfortable with traditional in-office therapy, you might consider online therapy, which numerous peer-reviewed studies have shown to be effective. 

With online therapy, you can speak with a therapist from home via audio, video, or live chat at a time that works for you. Online therapy also tends to be more affordable than in-office therapy without insurance.