Face perception is category-specific: evidence from normal body perception in acquired prosopagnosia

Does the human visual system contain perceptual mechanisms specialized for particular object categories such as faces? This question lies at the heart of a long-running debate in face perception. The face-specific hypothesis posits that face perception relies on mechanisms dedicated to faces, while the expertise hypothesis proposes that faces are processed by more generic mechanisms that operate on objects we have extended experience with. Previous studies that have addressed this question using acquired prosopagnosia are inconclusive because the non-face categories tested (e.g., cars) were not well-matched to faces in terms of visual exposure and perceptual experience. Here we compare perception of faces and bodies in four acquired prosopagnosics. Critically, we used face and body tasks that generate comparable inversion effects in controls, which indicates that our tasks engage orientation-specific perceptual mechanisms for faces and bodies to a similar extent. Three prosopagnosics were able to discriminate bodies normally despite their impairment in face perception. Moreover, they exhibited normal inversion effects for bodies, suggesting their body perception was carried out by the same mechanisms used by controls. Our findings indicate that the human visual system contains processes specialized for faces.