They spent only a tenth of their conversation talking about subjects unrelated to imprisonment. The rest of the time they talked about escape, the quality of the food, and the causes of their discontent.
Zimbardo wondered whether the structure of the prison situation played a part in turning prisoners and guards into mean and violent people.
With the help of several colleagues, Zimbardo created a fake, simulated prison in the basement of the Stanford psychology building.
There he could observe volunteer subjects in the roles of prisoners and guards.
When it was time for the experiment to begin, the prisoners were unexpectedly picked up at their homes by a city police officer in a squad car. They were searched, handcuffed, fingerprinted, blindfolded, and taken to the "prison." There the prisoners were stripped, given a uniform and number, and placed in a cell with two other prisoners. They were told the cell would be their home for the next 2 weeks.
When the guards arrived, they were informed that they had the authority to make up their own rules for maintaining law, order, and respect in the prison and were free to improvise new ones at any time during their 8-hour shifts on duty.
At first, it was an exciting game, but it quickly became an unpleasant way of living. An hour after the prisoners went to sleep the guards abruptly woke them and made them line up and repeat their ID numbers. The guards made the prisoners do push-ups until they were exhausted. When the prisoners revolted, they were placed in solitary confinement and even made to clean toilets with their bare hands.
The results were horrific because some guards treated others as if they were despicable animals, taking pleasure in cruelty, while the prisoners became dehumanised robots who thought only of escape, of their own individual survival and of their hatred for the guards.
Some of the prisoners became severely depressed, confused, or hysterical and had to be released after only a few days. Just to get out of the prison, all but three of the remaining prisoners were willing to forfeit all the money they had earned for participating.
Zimbardo points out that had these individuals been thinking like the college students they were, instead of the prisoners they were playing, they simply would have quit.
Therefore the experiment only lasted 6 days, rather than 2 weeks.
Many of the guards became tyrants, arbitrarily using their power and enjoying the control they had over others. Other guards were not as brutal, but they never intervened on behalf of the prisoners and never told the other guards to "ease off."
In addition, Zimbardo's aborted study illustrated that, given the proper environmental circumstances, individuals can create the very social forces that come to shape their behaviour. It was the subjects themselves who created the reality of their roles and therefore defined the power that the prison structure exerted over them.
The fact that prisoners are convicted criminals or those guards may be strict may have little to do with the brutalising effect of prisons on both prisoners and guards.