Social categorization and perceptual judgment of size: when perception is social.

Social knowledge may affect not only people's thoughts and judgments but also their actual perceptions of physical magnitude. The physical magnitude of a stimulus is perceived in a relative way, comparing the magnitude of the target with surrounding context stimuli. Because similar objects invite comparison processes more easily than dissimilar objects ("similarity breeds comparability"), social knowledge can affect judgments of physical magnitude by determining what is perceived as (dis) similar. In Experiment 1, the authors show that social categorizations that are based on physical cues (e.g., gender) may affect the magnitude of perceptual contrast effects (the Ebbinghaus illusion). More important, in Experiment 2, the influence of social categorizations that have no physical bases is shown to affect the magnitude of perceptual contrast effects. Implications of these findings for theories of social knowledge effects are discussed.