Imagine yourself in the following situation: you sign up for a psychology experiment, and on a specified date you and seven others whom you think are also subjects arrive and are seated at a table in a small room. You don't know it at the time, but the others are actually associates of the experimenter, and their behaviour has been carefully scripted. You're the only real subject.
The experimenter arrives and tells you that the study in which you are about to participate concerns people's visual judgments. She places two cards before you. The card on the left contains one vertical line. The card on the right displays three lines of different length.
The experimenter asks all of you, one at a time, to choose which of the three lines on the right card matches the length of the line on the left card. The task is repeated several times with different cards. The other "subjects" unanimously choose the wrong line. It is clear to you that they are wrong, but they have all given the same answer.
What would you do? Would you go along with the majority opinion, or would you trust your own eyes?
In 1951, the social psychologist Asch used this experiment to examine how the pressure from other people could affect one's perceptions. In total, about one third of the subjects who were placed in this situation agree with the majority.
Some of the subjects indicated after the experiment that they assumed the rest of the people were correct and that their own perceptions were wrong. Others knew they were correct but didn't want to be different from the rest of the group. Some even insisted they saw the line lengths as the majority did.
Asch concluded that it is difficult to maintain that you see something when no one else does. Pressure from other people can make you see almost anything.