Covert and overt recognition in prosopagnosia.

Prosopagnosic patients suffer an inability to recognize familiar people by visual inspection of their faces. Despite the absence of overt recognition, though, some prosopagnosic patients continue to process the identities of familiar faces covertly. A longstanding controversy concerns whether the recognition deficit in prosopagnosia is specific for faces, or also affects other types of visual stimuli. We investigated whether the patient P.H., who has severe problems with within-class recognition of many types of visual stimuli, would show covert recognition for all stimuli which he cannot recognize overtly. Such a finding would be consistent with the idea that face recognition and recognition of other visually similar stimuli are performed by the same underlying functional mechanisms. We assessed this possibility with a forced-choice decision between correct and incorrect alternative names for familiar faces, cars and flowers, and with comparisons of P.H.'s ability to learn true versus untrue names to familiar faces, cars and flowers. Results indicated that P.H. does show covert recognition of cars and flowers, as well as faces. In addition, the covert effects observed in the forced-choice name decision and learning tasks used here were shown to have a potential common basis. Finally, the possibility of using covert knowledge as a basis for rehabilitation was explored. As was observed by Sergent and Poncet (1990) in their patient, P.H. could achieve some overt face recognition under very specific circumstances.