Structural encoding precludes recognition of face parts in prosopagnosia

The extent and the impact of spared processing of facial stimuli in the pro sopagnosic patient LH is examined using the inversion effect and the face c ontext effect. Our study asked how the deficit in individual face recogniti on is related to two perceptual abilities that are spared in this patient b ut between which there is interference when both are applied to the face st imulus, i.e. structural encoding of the face and parts-based matching proce dures. Three experiments studied this relationship with task demands and st imulus properties designed to trigger the parts-based processes. In the fir st experiment, human and animal faces are presented upright or inverted wit h good performance only for the inverted condition. In Experiment 2 normals show a clear face context effect (matching of upright faces easier than sc rambled or inverted ones) in the full face matching task whereas in the par ts matching task the face superiority effect disappears. In contrast, LH sh ows a face inferiority effect when matching full faces but also when matchi ng an isolated face part to a face part in a full face context. The results show that structural encoding of the face overrules parts-based procedures that could otherwise be helpful to tell individual faces apart.