Psychology, as a field, has often delved into the depths of human behavior and the workings of the mind.

While many studies have contributed to our understanding of human nature, some experiments have crossed boundaries and left ethical concerns in their wake. These ten psychological experiments stand out for their controversial methods, ethical violations, and lasting impacts on their participants.

1. The Stanford Prison Experiment (1971)

In this notorious study, Stanford University professor Philip Zimbardo randomly assigned Stanford students to the roles of prisoners and guards in a simulated prison environment.

The resulting psychological abuse inflicted by the “guards” on the “prisoners” led the experiment to be terminated after only six days, despite being initially planned for two weeks. This experiment raised serious ethical concerns regarding the well-being and psychological harm inflicted upon the participants.

2. Stanley Milgram’s Obedience Study (1963)

Stanley Milgram conducted a series of experiments to investigate obedience to authority figures.

Participants were instructed to administer increasingly strong electric shocks to a “learner” (an actor) whenever they answered a question incorrectly. The shocks were not real, but the participants believed they were causing immense pain.

This experiment revealed the extent to which individuals could be influenced to harm others under the influence of an authority figure, causing distress and ethical controversy.

3. The Little Albert Experiment (1920)

Carried out by psychologist John B. Watson, the Little Albert experiment aimed to condition fear in an infant.

A young boy, “Little Albert,” was repeatedly exposed to a white rat, and every time he reached for it, a loud noise was produced behind him, causing him to associate the fear response with the rat. This experiment not only raised concerns about ethical treatment of human subjects but also inflicted long-lasting psychological harm on Little Albert.

4. The Monster Study (1939)

In the Monster Study, Wendell Johnson and Mary Tudor subjected orphaned children to negative speech therapy to study the effects of labeling and stuttering.

The children were falsely categorized as stutterers and received negative feedback for their speech, leading them to develop significant speech problems and self-esteem issues. This experiment violated ethical guidelines and caused long-term emotional trauma in its participants.

5. Harlow’s Monkey Experiments (1950s-60s)

Harry Harlow conducted experiments on rhesus monkeys to understand the nature of love, attachment, and maternal separation.

Monkeys were separated from their mothers at birth and placed in isolation or with surrogate “mothers” made of wire and cloth. The prolonged isolation and deprivation of social interaction caused severe psychological and behavioral abnormalities in the monkeys, raising concerns about ethical treatment of animals and their well-being.

6. The Milgram’s Small World Experiment (1967)

This experiment conducted by social psychologist Stanley Milgram aimed to investigate the theory of “six degrees of separation.” Participants were asked to send a packet through personal contacts to reach a target individual.

The study revealed that individuals are often connected by a shorter chain of social contacts than expected. Although not as ethically controversial as Milgram’s obedience study, it brings the question of informed consent and privacy of personal networks.

7. The Aversion Project (1970s-90s)

The Aversion Project was a series of experiments carried out by the South African military on gay and lesbian soldiers.

The experimental treatments included chemical castration, electroconvulsive therapy, and hormone treatment to “cure” homosexuality. These unethical and inhumane experiments violated human rights and caused severe physical and psychological harm to participants.

8. The Bobo Doll Experiment (1961)

Conducted by Albert Bandura, the Bobo Doll Experiment aimed to understand the social learning of aggression in children.

Participants observed adults displaying aggressive or non-aggressive behavior towards a Bobo doll, and then were given the opportunity to interact with the doll themselves. The experiment found that children exposed to aggressive models were more likely to imitate their behavior.

Although the experiment provided valuable insights into social learning, concerns arose regarding exposing children to aggressive behavior and the potential long-term effects.

9. The Asch Conformity Experiment (1951)

Psychologist Solomon Asch conducted a series of experiments to study conformity within a group setting. Participants were shown lines of different lengths and were asked to identify the line that matched a given reference line.

The catch was that the other participants, who were actually confederates, deliberately chose the incorrect line. This experiment exposed the social pressure to conform and the power of influencing an individual’s perception, potentially leading to self-doubt and anxiety.

10. The Tuskegee Syphilis Study (1932-1972)

The Tuskegee Syphilis Study is one of the most infamous examples of unethical medical research. The study, conducted by the U.S. Public Health Service, withheld treatment for syphilis from African American men infected with the disease.

Participants were never informed about their condition or the available treatments, leading to the continued progression of the disease and unnecessary suffering. This experiment violated basic principles of research ethics, including informed consent and ensuring the well-being of participants.