Prosopagnosia in a right hemispherectomized patient.

The first reported case of prosopagnosia in a right hemispherectomized woman, B.M., whose intellectual and cognitive functions were otherwise normal or only slightly impaired, is presented. She was totally unable to identify, and to experience a sense of familiarity with, faces of persons she knew, but she could evoke semantic information about them and retrieve their names from visual contextual cues. She was unaware that she was lacking face-recognition skills and that faces alone could be used to access the identity of individuals. The functional nature of her deficit was investigated through sensory, perceptual, memory, and learning tasks to determine the level at which her prosopagnosic disturbance occurred. She was defective at resolving low spatial-frequency information, but this was insufficient to explain the selectivity of her impairment. She was able to carry out cognitive operations specific to faces as long as facial identity did not have to be ascertained, and she performed as well as control subjects at deriving information about the gender, age, and emotion of faces. She was impaired at matching different views of the same faces, and multidimensional scaling analysis of dissimilarity judgements between faces indicated an inability to combine the component features into a configurational facial representation that would uniquely define each face. In contrast to recently reported cases of prosopagnosia, B.M. showed no sign of covert recognition of known faces in a learning task, and there was no indication that she could, even for a few seconds, store a faithful facial representation. The occurrence of prosopagnosia in this hemispherectomized patient confirms that this deficit can emerge without damage to the left hemisphere, and her unawareness of her deficit, which had remained unnoticed for several years, raises the possibility that other hemispherectomized patients may be prosopagnosic. The pattern of cognitive impairments displayed by B.M. indicates a perceptual basis to her disturbance and is discussed in relation to other cases of prosopagnosia.