In 1971 psychologists created one of the most important experiments in the history of psychology.

The experiment, known as the Stanford Prison Experiment, looked at the impact of situations on human behavior.

The researchers, led by Philip Zipbardo，wanted to know how situations could affect how people behave.

In particular, they wanted to know if good people would change their personalities and lose their values.

In the experiment, participants were divided into two groups.

One group became prison guards, and the other group became prison inmates（犯人）.

The experiment was set up in Stanford University's psychology building.

A group of 24 students was chosen to play the roles, 12 guards, and 12 prisoners.

The students came from a larger group of volunteers who wanted to participate in a psychology experiment.

Those who were chosen had no criminal background and had no significant(明显的) medical of psychological problems.

They agreed to participate in the experiment for a one to two-week period.

The prisoners had to remain in prison 24 hours a day during the experiment.

Guards worked in teams of three and were assigned to work in eight-hour shifts.

Unlike the prisoners, they were free to return to their homes between shifts.

Hidden cameras and microphones were used to observe the behaviors of both prisoners and guards.

The simulated prison(模拟监狱） included three small prison cells, 6 feet by 9 feet.

Each cell has three small beds and held three prisoners.

There was also a closet that served as a solitary confinement(单独囚禁）room.

This was used to isolate(隔离） prisoners who needed to be punished for bad behavior.

Guards were instructed not to physically harm(人身伤害） the prisoners in any way.

Prisoners were to be addressed (称呼）by their assigned numbers and never by name.

To prevent eye contact with the prisoners, guards wore mirrored sunglasses.

This was done to dehumanize the relationship between guards and prisoners.