Apperceptive and associative forms of prosopagnosia.

Three prosopagnosic patients were given four face tests, two perceptual (an unknown face identification test and an age estimation test) and two also implying memory (a familiarity check test and a famous face recognition test). The patients' performance was assessed with reference to the score distribution of the normal population. A patient was found to fail both perceptual and mnestic tests, without any noticeable difference between them. Also the second patient had poor scores on both kinds of tests, but his impairment was significantly greater on the perceptual ones. The third patient, on the contrary, showed no perceptual deficit and only failed the mnestic tests. His inability to recognize the individuality of an item among members of the same category was strictly confined to faces and never present for other classes of stimuli (cars, coins, personal belongings). This finding is supportive of the thesis that in a few patients the deficit underlying prosopagnosia is face specific.