Psychology has given us profound insights into human behavior, often through experiments that challenged our assumptions about who we are and why we act the way we do. These groundbreaking studies not only advanced academic knowledge—they transformed how we understand ourselves, design our institutions, and interact with one another. Here are five psychology experiments that fundamentally changed our world.
- Stanford Prison Experiment – Power of situations over character
- Pavlov’s Dogs – Classical conditioning and behavioral psychology
- Marshmallow Test – Delayed gratification and self-control
- Milgram’s Obedience Studies – Authority and moral courage
- Bobo Doll Experiment – Observational learning and media influence
1. The Stanford Prison Experiment: The Power of Situations Over Character
In 1971, psychologist Philip Zimbardo conducted one of the most controversial and influential studies in psychology history. He transformed the basement of Stanford University’s psychology building into a mock prison and randomly assigned student volunteers to play either guards or prisoners.
What happened next shocked the research team and the world. Within days, the “guards” began exhibiting increasingly authoritarian and abusive behavior, while the “prisoners” showed signs of extreme stress and helplessness. The experiment, planned for two weeks, had to be stopped after just six days due to the psychological harm being inflicted.
Why It Changed the World: This experiment revealed how powerful situational forces can override individual personality and values. It challenged the common belief that only “bad people” commit cruel acts, showing instead that ordinary people can engage in harmful behavior when placed in certain social roles and environments. This insight has influenced everything from military training protocols to corporate ethics programs, emphasizing the importance of institutional safeguards and accountability systems.
The study also sparked crucial debates about research ethics that led to stricter protections for human subjects in psychological research. While the experiment’s methodology has faced significant criticism in recent years, its cultural impact on how we understand authority, power, and human behavior remains undeniable.
2. Pavlov's Dogs: The Foundation of Behavioral Psychology
Ivan Pavlov wasn’t even studying psychology when he made one of its most important discoveries. The Russian physiologist was researching digestion in dogs when he noticed something peculiar: his dogs began salivating not just when food appeared, but when they heard the footsteps of the assistant who fed them.
Intrigued, Pavlov designed experiments where he paired a neutral stimulus—a bell—with food. After repeated pairings, the dogs began salivating at the sound of the bell alone, even without food present. This phenomenon became known as classical conditioning.
Why It Changed the World: Pavlov’s discovery laid the groundwork for behaviorism, one of psychology’s most influential schools of thought. His work demonstrated that behaviors could be learned through association, opening new pathways for understanding and modifying human behavior.
The applications have been transformative. Classical conditioning principles underpin treatments for phobias, anxiety disorders, and addiction. They’ve influenced advertising strategies, educational techniques, and even our understanding of emotional responses. From helping people overcome fears through exposure therapy to explaining why certain songs evoke powerful memories, Pavlov’s insights remain central to both clinical practice and everyday life.
3. The Marshmallow Test: Delayed Gratification and Life Success
In the late 1960s and early 1970s, psychologist Walter Mischel conducted a deceptively simple experiment at Stanford University’s Bing Nursery School. Children aged four to six were offered a choice: they could eat one marshmallow immediately, or wait about 15 minutes and receive two marshmallows as a reward.
The researchers observed a range of strategies among the children. Some covered their eyes, others sang songs or talked to themselves, while many simply gave in to temptation. But the real revelation came years later when Mischel followed up with these same children as they grew into adults.
Why It Changed the World: The follow-up studies found correlations between the ability to delay gratification and various measures of life success, including higher SAT scores, better stress management, and healthier body mass indexes. This research popularized the concept of self-control as a crucial life skill and sparked decades of research into executive function and willpower.
The marshmallow test influenced parenting practices, educational curricula, and policy discussions about childhood development. It highlighted the importance of teaching children emotional regulation and self-control strategies. However, more recent research has revealed important nuances—showing that environmental factors like trust and socioeconomic background significantly influence a child’s willingness to wait, adding complexity to our understanding of self-control and its relationship to life outcomes.
4. Milgram's Obedience Studies: The Banality of Evil
Troubled by how ordinary Germans participated in Nazi atrocities during World War II, psychologist Stanley Milgram designed an experiment to test how far people would go in obeying authority figures, even when doing so conflicted with their conscience.
Participants were told they were part of a learning study where they would act as “teachers” delivering electric shocks to “learners” (actually actors) for incorrect answers. An authority figure in a lab coat instructed them to increase the voltage with each mistake, eventually reaching levels marked “Danger: Severe Shock.” Despite hearing the learner’s (fake) screams and pleas, a shocking 65 percent of participants delivered what they believed were potentially lethal shocks simply because the authority figure told them to continue.
Why It Changed the World: Milgram’s findings were disturbing and revelatory. They demonstrated that ordinary people could engage in harmful actions not out of malice, but through obedience to authority—what philosopher Hannah Arendt called “the banality of evil.” This challenged comfortable notions that atrocities are committed only by monsters, revealing instead the dangerous potential that exists within normal social dynamics.
The research has profoundly influenced how we think about responsibility, authority, and moral courage. It’s shaped military ethics training, medical protocols for questioning questionable orders, and whistleblower protections in organizations. The study reminds us that ethical behavior often requires the courage to question and resist authority when necessary, not just to follow rules blindly.
5. The Bobo Doll Experiment: Observational Learning and Media Violence
In 1961, Albert Bandura conducted a series of experiments that would fundamentally change our understanding of how children learn. Young children watched adults interact with an inflatable “Bobo doll”—either playing peacefully, behaving aggressively by hitting and kicking the doll, or not interacting with it at all.
When the children were later placed in a room with the Bobo doll, those who had observed aggressive behavior were significantly more likely to imitate those actions, even inventing new aggressive behaviors not modeled by the adults. This occurred even when the children received no direct instruction or reinforcement for their actions.
Why It Changed the World: Bandura’s research introduced the concept of social learning theory, demonstrating that people—especially children—learn not just through direct experience but by observing and imitating others. This was revolutionary because it showed that learning could occur without reinforcement, challenging the dominant behaviorist theories of the time.
The implications have been enormous. The Bobo doll experiments fueled ongoing debates about violence in media, from television to video games, raising questions about how exposure to aggressive content affects behavior. They’ve influenced parenting strategies, emphasizing the importance of modeling desired behaviors rather than just telling children what to do. In education, the research underscored the power of demonstration and example in teaching.
Social learning theory also became foundational in understanding how behaviors, attitudes, and even prejudices spread through communities and cultures, shaping approaches to everything from public health campaigns to social justice movements.
The Lasting Impact of Psychology Research
These five experiments represent pivotal moments when psychology revealed uncomfortable truths about human nature and transformed our understanding of the mind. They showed us that we’re more influenced by our environments, more obedient to authority, more affected by observation, and more susceptible to conditioning than we might want to believe.
Yet this knowledge is empowering. By understanding these psychological principles, we can design better institutions, create more ethical systems, raise more resilient children, and make more conscious choices in our own lives. We can recognize when situational pressures might lead us astray, question authority when necessary, be mindful of what we model for others, and develop strategies for self-control and independent thinking.
The legacy of these experiments extends far beyond academia. They remind us that the scientific study of human behavior isn’t just about abstract knowledge—it’s about understanding ourselves well enough to build a better world. As psychology continues to evolve, building on these foundational insights while addressing their limitations and ethical concerns, we gain increasingly sophisticated tools for navigating the complexities of human nature.
Understanding these classic experiments isn’t just intellectually fascinating—it’s practically essential for anyone seeking to understand why people behave the way they do and how we might encourage the best in human nature while guarding against the worst.