The 7 Most Famous Psychological Experiments of All-Time

1. Milgram Experiment. The Milgram Experiment, conducted by Yale University psychologist Stanley Milgram, tested how people become obedient to authority figures. The test measured participants’ willingness to administer shocks to other people, even when the shocks caused pain or damage, in conflict with their person conscience. The results were jarring: a very high percentage of people were willing to do almost anything as long as someone else “took responsibility” for the actions.

2. The Stanford Marshmallow Experiment. The Marshmallow Experiment was a study about delayed gratification in the 1970s that consisted of a child being offered a choice between one small reward (a marshmallow or cookie) immediately or two rewards if they waited for 15 minutes. Researchers discovered that children who were able to wait longer for more treats tended to have better life outcomes, measured by SAT scores, educational attainment, body mass index and other measures.

3. A Class Divided. The study, conducted in a third-grade Iowa classroom in 1968, was created to demonstrate to the effects of racism and prejudice to Caucasian students. The teacher divided her class into two separate groups: blue-eyed students and brown-eyed students. The blue-eyed students were told they were superior students and given extra privileges. The teacher singled out individual students in the brown-eyed group to stress negative characteristics of the minority group. 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. At the end of the experiment, the children were so relieved that they that they embraced one another and agreed people shouldn’t be judged on outward appearances. Subsequent experiments have had similar outcomes.

4. Hawthorne Experiment. The principle indicates that any subject that knows it is being observed will change its behaviour in response to their awareness of being observed. The original experiment was conducted at the Hawthorne Works in Cicero, Illinois when managers commissioned a study to see if their workers would become more productive in higher or lower levels of light. The workers’ productivity seemed to improve when changes were made, and slumped when the study ended. It was suggested that the productivity gain occurred as a result of the motivational effect on the workers of the interest being shown in them. The interpretation was labelled “The Hawthorne Effect.”

5. Bobo Doll Experiment. The experiment attempted to determine how environmental factors and social learning shaped a child’s development. Today you know it as “Nature vs. Nurture”. Albert Bandura conducted the Bobo Doll Experiment to prove that human behavior is largely based upon social imitation rather than inherited genetic factors.In his 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; and 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). The researchersfound that children exposed to the aggressive model were more likely to exhibit aggressive behavior towards the doll themselves, while the other groups showed little imitative aggressive behavior.

6. Car Crash Experiment. University of California at Irvine researchers Loftus and Palmer set out to show how deceiving memories can be. Participants watched video of a car accident and were asked to describe what happened as if they were eyewitnesses to the scene. They were divided into two groups and 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 researchers found the use of different verbs affected the participants’ memories of the accident, showing that memory can be easily distorted.

7. Seligman’s Experiment on Learned Helplessness. In 1965 Martin Seligman delved into research onto conditioning, the process by which animals and people associate one thing with another. The experiment involved a researcher ringing a bell and then administering a light shock to a dog. After a few times, the dog began to react to the shock before it happened. During the study, the researchers were 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 was electrified on one side of the fence but not the other side. Seligman placed each dog on the electrified side and administered a light shock. Unexpectedly, 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. The condition was described as “Learned Helplessness”.