Visual comparison processes: Identity and similarity decisions

In the first experiment, in which two successively presented free-form visual patterns varied in their similarity to each other, subjects had to decide, in one condition, if the patterns were “identical” and in two other conditions if the patterns were “similar.” Qualitative individual differences in the effect of similarity on the time required to make a decision were found in the “identity” condition, and these differences interacted with the “similarity” conditions. The individual differences and the experimental effects are interpreted in terms of a two-process model of the visual comparison process—a holistic matching process that is sometimes accompanied by an analytic difference detection process. In the second experiment, the same subjects repeatedly categorized subsets of the free-form visual patterns on the basis of similarity. There appeared to be no individual differences in the subjects’ perceptions of similarity, but subjects’ perceptions did differ from the assumptions made by the experimenters when they established the response criteria for the first experiment.