Does Thompson's Thatcher Effect Reflect a Face-Specific Mechanism?

Abstract

The Thatcher Illusion or Thatcher Effect (TE—Thompson 1980, Perception 9 483–484) reflects the difficulty in perceiving the local inversion of parts when the whole object, generally a face, is globally inverted. We tested the generality of the TE with a range of faces and non-face objects, and observed the TE with many non-face categories including cars, buildings, bikes, and letter strings. In terms of magnitude, the face TE is not exceptionally large compared to other object categories, and the magnitude of the TE can be predicted by performance on this task for upright stimuli, regardless of whether the object is a face or not. We did not observe evidence for a unique mechanism contributing to the TE for faces. We discuss factors that influence the magnitude of the TE, some common across domains and others more specific to a particular category.