Experience produces the atypicality bias in object perception.

When a morph face is produced with equal physical contributions from a typical parent face and an atypical parent face, the morph is judged to be more similar to the atypical parent. This discontinuity between physical and perceptual distance relationships, called the "atypicality bias" (Tanaka et al 1998, Cognition 68 199-220), has also been demonstrated with non-face objects (birds and cars; Tanaka and Corneille 2007 Perception & Psychophysics 69 619-627). We tested whether the atypicality bias can be induced for a novel set of artificial objects. Two categories of "blob" stimuli were generated, each composed of typical and atypical members. Morphs averaged from typical and atypical parent exemplars were used to test the presence of an atypicality bias before and after participants were familiarized with blob items. In experiment 1, participants were trained to discriminate between the two blob categories. An atypicality bias was evident after, but not prior to, category training. In experiment 2, participants rated the pleasantness of the blobs instead of learning to categorize them; an atypicality bias was present only after the ratings task. This finding suggests that relatively passive exposure to exemplars is sufficient to influence perceptions of similarity, and that the atypicality bias is a manifestation of this influence.