Categorical perception of race.

Traditionally, research demonstrating categorical perception (CP) has assumed that CP occurs only in cases where natural continua are divided categorically by long-term learning or innate perceptual programming. More recent research suggests that this may not be true, and that even novel continua between novel stimuli such as unfamiliar faces can show CP effects as well. Given this, we ask whether CP is dependent solely on the representation of individual stimuli, or whether stimulus categories themselves can also cause CP. Here, we test the hypothesis that continua between individual faces that cross the categorical boundary between races show an enhanced CP effect. We find that continua running from a black face to a white face do, indeed, show stronger CP effects than continua between two black faces or two white faces. This suggests that CP effects are enhanced when continua run between two distinctly represented individual stimuli, and are further enhanced when those individuals are, in turn, members of different stimulus categories.