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 the field 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.
Pavlov’s Dog Experiments
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
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
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 had a tendency 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 picked 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
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
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 that held a bottle and provided food, while the other was a soft surrogate mother that 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
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
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 that resembles the shape of 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
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.