Is pigmentation important for face recognition? Evidence from contrast negation.

It is extraordinarily difficult to recognize a face in an image with negated contrast, as in a photographic negative. The variation among faces can be partitioned into two general sources: (a) shape and (b) surface reflectance, here termed 'pigmentation'. To determine whether negation differentially affects the processing of shape or pigmentation, we made two sets of faces where the individual faces differed only in shape in one set and only in pigmentation in the other. Surprisingly, matching performance was significantly impaired by contrast negation only when the faces varied in pigmentation. This provides evidence that the perception of pigmentation, not shape, is selectively disrupted by negation and, by extension, that pigmentation contributes to the neural representation of face identity.