Sherif carried out a Lab experiment with a repeated measures design. He used a visual illusion called the auto kinetic effect, where a spot of light is viewed in a dark room and the light appears to move. Participants are falsely told that the light does move. They had to estimate how far it had moved. First the participants made their judgements individually. Then they made their judgements in groups of 3. And then they made their judgments again individually.
When the participants were alone they developed their own personal norm. This varied widely between them. When they made their judgements in groups, their estimates converged and became alike. When the participants were retested their answers were more like the group estimates, rather than their original guesses.
Participants were influenced by estimates of other people, and a group norm developed. Estimates converged because participants used information from others to help them. They were affected by informational influence.