Abstract
Studies of the face inversion effect suggest that the configuration of internal features may have special status for expert face-processing mechanisms. Experiments with prosopagnosic subjects have shown that lesions of the fusiform gyrus impair the discrimination of such configurations. However, whether this impairment is selective or part of a more pervasive difficulty with facial structure is unclear.
We studied five patients with acquired prosopagnosia. We used an oddity paradigm in which they had to determine which of three simultaneously viewed faces differed from two others under unlimited viewing duration. Faces could differ in one of six ways, in external contour (forehead or chin), feature configuration (horizontal eye position or vertical mouth position), or feature shape (eye or mouth width). Processing load and attentional requirements were varied by using blocks in which either all 6 changes were possible, only one change was possible, or two changes were possible.
Patients varied in their results. One patient with bilateral anterior temporal damage showed little perceptual deficit in any condition. A left-handed patient with right FFA/OFA damage had a selective deficit for eye position in the 1-change and 2-change conditions, but had general impairments in the 6-change condition. Another left-handed patient with bilateral anterior temporal damage and loss of the right FFA/OFA was impaired for eye shape and eye position in all conditions, with deficits for mouth shape under 2-change and 6-change conditions. A patient with bilateral occipitotemporal damage was impaired for all stimuli in all conditions. A similar pervasive deficit was surprisingly found in the last patient, with a small right amygdalohippocampectomy.
We conclude that eye position may be particularly vulnerable to perceptual deficits in prosopagnosia, but that more general difficulties in perceiving other aspects of facial structure can occur, particularly under conditions stressing attention to the whole face.
NIMH 1R01 MH069898, CIHR MOP-77615, Canada Research Chair and Michael Smith Foundation for Health Research Senior Scholarship (JB).