Face perception and within-category discrimination in prosopagnosia.

Prosopagnosics are impaired at face recognition, but unimpaired, or relatively less impaired, at common object recognition. It has been suggested that this dissociation results simply from the greater difficulty of face recognition compared to object recognition, or from the greater need to discriminate visually similar members of a single category in face recognition compared to object recognition. We tested these hypotheses using the performance of normal subjects in an 'old/new' recognition paradigm to establish the true relative difficulty of face and object recognition, and required both normal subjects and a prosopagnosic subject to discriminate both faces and visually similar exemplars of nonface object categories. In two different experiments, the prosopagnosic patient performed disproportionately poorly with faces. These results disconfirm the hypotheses described above, and imply that prosopagnosia is an impairment of a specialized form of visual recognition that is necessary for face recognition and is not necessary, or less necessary, for the recognition of common objects.