The Most Influential Psychology Experiments

Medically reviewed by Laura Angers Maddox, NCC, LPC
Updated August 7, 2023by BetterHelp Editorial Team

Human psychology is often called a "soft science" because conclusions in certain types of studies 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, experts 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 Influential Psychology Experiments Shape Modern Psychology

Much of what humanity understands about psychology comes from the theories of renowned scientists and philosophers. A lot of it also comes from the experience of clinical psychologists who have had professional interactions and conducted research studies with thousands of people throughout their careers. An even vaster amount of information has come from research, like the subsequent studies and psychological experiments. 

The Milgram Experiment

The events of the first half of the twentieth century, including the world wars, raised a few questions about and approaches to psychology.

Stanley Milgram was a 20th-century psychologist interested in what has become known as "the Nuremberg defense" or "superior orders." This legal plea was made at the Nuremberg Trials by perpetrators of war crimes during WWII who claimed they were not legally responsible for their actions because they had been ordered to carry them out. Many, including Milgram, wondered how far the average person would go because an authority figure had told them to.

To figure this out, Milgram, working at Yale at the time, recruited 40 participants for an experiment. The participants would be paired with another individual who they thought was another participant but was a colleague of Milgram. The volunteers were told that they were participating in an experiment to see if pain enhanced learning. 

Milgram's associate was hooked up to a shock generator controlled by the volunteer and asked to memorize words and their pairs. The volunteer was to name one of these pairs, and Milgram's colleague named the other word from the pair. If the associate pretending to be a study participant gave a wrong answer, the volunteer was asked to administer an electric shock that got progressively higher each time, with the highest marked "Danger - Severe Shock." Milgram's colleague would pretend to be tortured by the shocks. The experimenter, in a room with the volunteer and observing Milgram's colleague through a window, would use a series of increasingly dire prompts to convince the volunteer to continue administering shocks, even if the volunteer indicated that they wanted to stop.

65% of the volunteers continued the exercise to the highest possible setting, marked 450 volts. All the volunteers continued to the setting marked 300 volts. This study convinced Milgram that the average human is conditioned enough to listen to authority and that they will hurt another human because someone told them to.

The Milgram experiment wasn't only influential because of its role in understanding how we see authority. It was also influential because of the role it played in understanding experiments. Milgram conducted his experiments in the early 1960s, so some of the problems with his experiment wouldn't have passed institutional review boards today.

One example of a problem with this experiment is that all of Milgram's volunteers were male. Some people have since suggested that this might have influenced his results. However, it may be that all of his participants were male because war crimes had inspired the experiments, and all soldiers in combat roles at the time were men.

There are also potential ethical problems with Milgram's experiment, including that the volunteers were misinformed about the nature of the study. Milgram felt that this factor was the only way to get accurate results. Other potential issues include the fact that the volunteers may have been subjected to dangerous stress levels during the experiment. In addition, the fact that the volunteers were prompted to continue the experiment when they asked to leave may have violated the volunteers' right to leave a scientific study.

The Stanford Prison Experiment

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. The student participants were randomly assigned to two groups, either prisoners or guards. The participants were carefully screened for psychological and physical health before participating. The simulated prison was set up in the basement of the 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.

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.

Little Albert Experiment 

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.

Bobo Doll Experiment

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 towards a Bobo doll, and one group that observed a model being verbally aggressive towards the doll. The children were then placed in a playroom with a Bobo doll and other toys, and their behavior was observed.

The results of the study showed that the children who observed the aggressive model 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 towards the doll. The experiment demonstrated that children can learn new behaviors through observation and modeling, even if those behaviors are aggressive or violent.

The Basic Income Experiment

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. 

Like Milgram's experiment, The Finland Basic Income Experiment has ramifications and influences beyond its initial findings. 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

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.

The experiment has been replicated many times since, though now some experimenters use a sheet on a flat surface but with a pattern printed on it such that it creates the optical illusion of a trench. This process is often done not as a safety precaution but as a way of allowing the experiment to be carried out without using a floor modified to include a trench. The test has sometimes been utilized to determine how fast an infant learns essential skills.

Homosexuality Aversion Experiment

Homosexuality aversion experiments were a series of unethical experiments conducted in the mid-twentieth century that aimed to change an individual's sexual orientation from homosexual to heterosexual. The experiments were usually conducted using a combination of drugs, shock therapy, and behavioral conditioning.

The experiments were often conducted on unwilling or unknowing participants, and the methods used were highly controversial and unethical. Many of the participants suffered severe psychological distress. In the experiments, researchers would show nude or erotic images of men and women, the participants watched slides for as long as they felt comfortable. On images of men, they were given a shock after 8 seconds, images of women had no shock. 

Despite the lack of scientific evidence to support the effectiveness of these experiments, homosexuality aversion therapies continued to be used in some countries until the late twentieth century. In the 1970s, the American Psychological Association officially condemned such therapies, citing the lack of evidence to support their effectiveness and the potential harm they could cause.

Learn How Influential Psychology Experiments Shape Modern Psychology

Counseling Options 

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. 

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. 


Psychological studies from the past can showcase how psychologists practice therapy and research in the present and future. With over 41.7 million US adults in therapy, these studies can have the ability to change millions of lives. 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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