Outgroup homogeneity effect in perception: An exploration with Ebbinghaus illusion

An outgroup homogeneity (OH) effect implies that outgroup members are perceived to be more similar than ingroup members. At present, however, it is not clear whether the OH effect is truly perceptual. Here, we used an Ebbinghaus illusion to demonstrate the OH effect in perception. Participants were presented with one central face that was surrounded by four surrounding faces. The central face was judged to be smaller as the size of the surrounding faces increased, thereby demonstrating an Ebbinghaus illusion. As predicted, however, this illusion was significantly greater when the faces allegedly belonged to an outgroup than when they allegedly belonged to an ingroup. This perceptual OH effect bore no significant relationship with cognitive OH measures. The perceptual versus cognitive OH effects might therefore be mediated by separate mechanisms.