Covert recognition in acquired and developmental prosopagnosia

Background: Some patients with prosopagnosia have covert recognition, meaning that they retain some familiarity or knowledge of facial identity of which they are not aware. Objective: To test the hypothesis that prosopagnosic patients with right occipitotemporal lesions and impaired face perception lack covert processing, whereas patients with associative prosopagnosia and bilateral anterior temporal lesions possess it. Methods: Eight patients with prosopagnosia were tested with a battery of four face recognition tests to determine their ability to discriminate between famous and unknown faces. Results: Measures of overt familiarity revealed better residual discrimination in patients with acquired prosopagnosia than in those with the developmental form. With forced-choice methods using famous faces paired with unknown faces, no patient demonstrated covert familiarity. However, when the semantic cue of the name of the famous face was provided, covert processing was present in all five patients with acquired prosopagnosia, including the three with extensive right-sided lesions and impaired perceptual discrimination of facial configuration. Sorting unrecognized faces by occupation was also performed above chance in three of these five patients. In contrast, none of the three patients with developmental prosopagnosia bad covert processing, even though two demonstrated flawless performance on similar tests of name (rather than face) recognition. Overt familiarity correlated highly with the degree of covert recognition. Conclusions: Extensive right occipitotemporal lesions with significant deficits in face perception are not incompatible with covert face processing. Covert processing is absent in developmental prosopagnosia, because this condition likely precludes the establishment of a store of accurate facial memories. The presence of covert processing correlates with the degree of residual overt familiarity, indicating that these are related phenomena.