Why do categorization effects occur in comparative judgment tasks?

Abstract

Three experiments were conducted to understand what eliminates the symbolic distance effect for reaction times (RTs) when subjects learn that items belong to categories. Artificial city locations were judged, and artificial states served as categories. In Experiment 1, whether or not categories were presented and the amount of categorization practice were manipulated. Only those subjects who had practice categorizing cities into states showed a reduced symbolic distance effect for different-state pairs. Analyses of serial position curves indicated that categorization produced faster RTs to different-as compared with their adjacent same-state pairs and it also produced faster RTs for same-state pairs closer to the category border. The border seems to serve as an anchor and facilitates RTs. In Experiments 2a and 2b, distance judgments were made by subjects who either had or had not categorized artificial cities into states. Subjects who learned categories gave larger estimates of distance between cities belonging to different states than to cities belonging to the same state. Categorization seemed to place cities from different states farther apart in psychological space, making their locations more discriminable. This, along with the use of the category border as an anchor, might explain why categorization effects occur in this location judgment task.