Inversion and configuration of faces.

If the mouth and eyes of a face are inverted, the altered construction appears grotesque when upright, but not when upside-down. Three studies of this "Thatcher illusion" employed faces that were grotesque when upright because: (a) their eyes and mouths had been inverted ("Thatcherized" faces), (b) their eyes and mouths had been moved (spatially distorted faces), or (c) they had grotesque posed expressions. Inversion reduced the apparent grotesqueness of both Thatcherized and spatially distorted faces, but not grotesque-expression faces. Moreover, Thatcherized and distorted faces, although not grotesque-expression faces, were judged as more similar to normal, smiling faces when face-pairs were inverted than when they were upright. Similarity ratings to inverted face-pairs were correlated with latencies of response to these pairs in a task that encouraged attention to components (e.g., mouths, eyes) rather than wholistic properties. Similarity ratings to upright face-pairs showed no such correlation, and this and other findings suggested that although similarity ratings to upright faces are based on wholistic information, similarity ratings to inverted faces are based largely on components. The Thatcher illusion reflects a disruption of encoding of wholistic information when faces are inverted.