The Most Influential Psychology Experiments

Medically reviewed by Laura Angers Maddox, NCC, LPC
Updated April 24, 2024by BetterHelp Editorial Team

Human psychology is often called a "soft science" because conclusions in certain types of studies or psychology experiments may be up to greater interpretation in psychology than in hard sciences like chemistry or biology. However, all sciences are interconnected, and psychology is real science. 

Many influential psychologists throughout history have encouraged people to treat psychology more like other sciences. For example, when you think about chemistry, you might think about experiments. In psychology, professionals study human behavior. There are many experiments carried out in psychological studies as well, and psychiatrists are as much medical doctors as other types of doctors, often studying how the body and mind interact, but with a special focus on the mind. Understanding these studies can help you understand mental health more profoundly.

Learn how major psychology experiments shape modern psychology

Famous and influential psychology experiments

Psychology experiments provide valuable insights into the human mind, helping experts develop treatments, expound on theories, and better understand behavior. Some of the most widely discussed psychological phenomena—such as learned helplessness, the bystander effect, and the placebo effect—have been reproduced and observed through these studies. The following are several famous psychology experiments from the past century. 

Harlow’s monkey mother experiments – Importance of early attachments

While teaching at the University of Wisconsin, psychologist Harry Harlow began conducting experiments on young rhesus monkeys, separating them from their mothers. He then made two surrogate mothers for the infant monkeys—one made of wire and one of terry cloth. The wire mother provided the monkeys with milk through a bottle, while the cloth mother had no food. 

When the monkeys were placed in a cage with both mothers, they chose to spend most of their time with the cloth mother, only going to the wire mother to drink the milk. When frightened, they would also go to the cloth mother for comfort. Harlow then conducted trials in which monkeys were either brought up with the wire mother or the cloth mother, observing significant behavioral differences in the monkeys that only had the wire mother. 

Harlow’s experiment highlights the importance of early attachments, affection, and tactile connection. His findings had a substantial influence on John Bowlby, who went on to develop attachment theory. Despite its impact, due to the study’s design, it is considered one of the most unethical psychology experiments of the 20th century. 

The Stanford prison experiment – Situational Influences on human behavior

The Stanford Prison Experiment was a landmark study in psychology conducted by social psychology professor Philip Zimbardo in 1971 at Stanford University and is one of the most famous psychology experiments of the 1900s. The study was designed to investigate the psychological effects of power dynamics and social roles in a simulated prison environment and is one the most controversial experiments in psychology.

Zimbardo recruited 24 male college students to participate in the study. Each student participant was randomly assigned to play the role of either a prisoner or a guard. The participants were carefully screened for psychological and physical health before participating. The simulated prison was set up in the basement of the famous psychology department, with the cells, prison guards' quarters, and other facilities modeled on an actual prison.

The experiment was supposed to last for two weeks, but it was terminated after only six days due to the escalating abuse of power by the guards and the psychological distress experienced by the prisoners. The guards quickly became authoritarian and abusive, using physical punishment, psychological intimidation to exert their authority over the prisoners. The prisoners, in turn, became increasingly submissive and passive, often displaying signs of depression, anxiety, and helplessness.

If you or a loved one is experiencing abuse, contact the Domestic Violence Hotline at 1-800-799-SAFE (7233). Support is available 24/7.

The Stanford Prison Experiment is considered controversial for a number of reasons. Critics argue that the study was unethical and that the human subjects were subjected to undue stress and harm. Additionally, some psychologists have questioned the validity of the study, arguing that it lacked scientific rigor and was too heavily influenced by Zimbardo's own biases and expectations. The study remains a landmark in the history of the psychology of cognitive dissonance and continues to inspire further research into the psychology of power and social roles.

The Little Albert experiment – Conditioning emotional responses

The Little Albert experiment was a controversial study conducted by John B. Watson and his graduate student, Rosalie Rayner, in 1920. Watson and Rayner wanted to learn more about healthy childhood development and emotional development. The study used classical conditioning and aimed to investigate whether a conditioned emotional response could be established in a human infant.

Little Albert was an 11-month-old baby who was selected as the subject of the study. Initially, Albert was presented with various stimuli, including a white rat, a rabbit, a dog, and a monkey. Albert showed no fear or anxiety towards any of these stimuli.

In the second phase of the experiment, Watson and Rayner paired the presentation of the white rat with a loud noise, creating a conditioned response of fear in the infant. After a few pairings, Albert began to show fear and distress when presented with the rat alone, as well as the physical appearance of other white, furry objects. This fear response was then generalized to other stimuli, including a Santa Claus mask, a fur coat, and a white laboratory rat.

The Little Albert experiment has been criticized for ethical reasons. Many psychologists argue that the study was unethical because it caused unnecessary psychological harm to the infant. Moreover, the study's scientific validity has been questioned because the experiment lacked controls, and the results were not systematically measured.

The Bobo doll experiment – Learned social behaviors  

The Bobo doll experiment was a study conducted by Albert Bandura in 1961 to investigate the effects of observational learning on aggressive behavior in children. The study aimed to demonstrate how children learn and imitate aggressive behaviors through observation and modeling.

In the experiment, children between the ages of three and six were divided into three groups: a control group, one group that observed a model being physically aggressive toward a Bobo doll, and one group that observed a model being verbally aggressive toward the doll. The children were then placed in a playroom with a Bobo doll and aggressive toys, and their behavior was observed.

The results of the study showed that the children who observed the aggressive adults were more likely to imitate the same behaviors than those who did not. Furthermore, the children who observed the verbally aggressive model were also more likely to use aggressive language toward the doll. A landmark child development study, the Bobo doll experiment, demonstrated that children can learn new behaviors through observation and modeling, even if those behaviors are aggressive or violent.

The Finland basic income experiment – Increased well-being and employment

Universal Basic Income is the idea of giving everyone a fixed income regardless of whether they work. The idea is often considered a part of economics or government. Still, psychologists have questioned how people would behave in a society where they were not required to work.

Supporters believe that universal basic income would improve society by allowing individuals to do what they love rather than chase money. Thinkers going back to the ancient Greek philosopher Socrates have said that when individuals pursue their interests and natural skills, society is better off.

Critics believe it would damage society and lead to group conflict because no one would pursue higher-order jobs if they didn't work to live. They often point out necessary, non-automated, undesirable, and low-paying jobs that may not be filled if people were less incentivized by money because of a base income.

The first attempt to settle this argument occurred in Finland between 2017 and 2018. The study signed on 2000 participants who had been unemployed during the previous year and gave them an amount equivalent to the unemployment they had received.

The study found that those receiving a basic income had similar work habits to the control group that didn't. However, the group that received basic income had better health, drew less from other social programs, reported better well-being, and performed better in their jobs. It has long been known that having a job increases an individual's sense of value and well-being, and this was still the case when an individual was not required to work to survive. 

There is little room for critics to come up with ethical concerns. The influence of the study was positive, and the experiment's size and ambition serve as a model for other countries attempting similar experiments, including Germany.

The Visual Cliff Experiment – Depth perception in infants

The previous studies discussed in this article were conducted for a limited time by groups of researchers. However, some experiments were conducted once and immediately recognized as valuable. One such experiment is the Visual Cliff Experiment.

Designed by Eleanor Gibson and Richard Walk in 1960, the Visual Cliff Experiment tested how and when young children develop depth perception and understand their relationships with their surroundings.

It was long thought that children gradually developed and understood depth perception by falling off surfaces. Often, parents don't want their children to fall, so this theory led to concern and controversy. Walk and Gibson had doubts that children needed to fall to understand the depth beyond them and came up with a way to put it to the test.

The test utilized a sheet with a checker pattern. The sheet was laid over a trench about a foot deep, making the drop-off visible. Heavy glass was placed over both sides of the trench, making the trench visible but safe to cross. A crawling child was then placed on one side of the trench with a parent on the other, coaxing the child to cross. Observers could then see the age at which a child recognizes the perceived drop-off and becomes hesitant to cross and identified this age as six to ten months, which was earlier than previously thought. 

The children also reacted to the visual cliff in several different ways. Some turned around and tried to back over the cliff as though they were trying to descend a stair. Others reached out with a hand to test the depth of the visual cliff. The experiment helped establish that children of this age often fall not because they are unaware of depth but because their depth perception matures faster than the motor ability to navigate it.

Learn how major psychology experiments shape modern psychology

Counseling and support options for you

There are now thousands of psychological studies on many topics regarding mental health. Learning about these studies can help you further understand how the mind and body interact and which types of treatments are most effective for specific mental health challenges. If you're looking for guidance in choosing a type of psychological support, several resources are available to you. 

Online therapy can help

Many individuals appreciate the convenience, cost-effectiveness, and value of online therapy services, like those offered through platforms like BetterHelp. With BetterHelp, you can meet with a therapist from home, specify the specialty in which you'd like to receive support, and choose between phone, video, or live chat sessions. 

There have also been scientific studies on the effectiveness of online therapy. Even methods like online chat messaging therapy have been proven as effective as face-to-face sessions and can reduce symptoms of depression, anxiety, and other mental health conditions. You do not need to have a diagnosis to receive support, and millions of clients reach out for help each year. 


Past psychological experiments designed to learn about human behavior have led to many breakthroughs in treatment, but some of the famous psychology experiments were controversial, such as:

  • the Stanford Prison Experiment, in which ordinary people simulated prisoners and prison guards
  • the Bobo Doll Experiment studying aggressive behavior
  • the Little Albert Experiment, which used classical conditioning to elicit certain responses to stimuli

Experimental psychology serves a purpose, but the experiment should be designed to yield useful information without compromising the mental health of the participants.

If you're interested in learning more about psychology or talking to someone about your mental health, consider reaching out to a psychologist to get started. 

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