Although in some cases, as in the ambiguous face picture, there is a direct relationship between modifying hypotheses and perception, in other cases this is not so evident. For example, illusions persist even when we have full knowledge of them (. the inverted face, Gregory 1974). One would expect that the knowledge we have learned (from, say, touching the face and confirming that it is not 'normal') would modify our hypotheses in an adaptive manner. The current hypothesis testing theories cannot explain this lack of a relationship between learning and perception.
Researchers then gave all boys a two-day cooling-off period, and asked them to list characteristics of the two groups. The boys tended to characterize their own group highly favourably and the other group very negatively. The researchers then attempted to reduce the prejudice between the groups, and found that simply increasing their contact with each other made matters worse. In contrast, "Forcing the groups to work together to reach subordinate goals, or common goals, eased the prejudice and tension among the groups".  Thus, in this "integration" or conflict resolution phase, it was shown that superordinate goals reduce conflict significantly more effectively than communication or contact did.