Upside-down faces: a review of the effect of inversion upon face recognition.

Several studies have found that face recognition is disproportionately impaired by stimulus inversion when compated to recognition of other classes of visual stimuli. This effect has been interpreted as evidence that face recognition benefits from a 'special' process which is not engaged by an inverted face. This paper reviews studies of the effect of inversion on face recognition in recognition memory tasks, matching tasks and upon cerebral hemisphere asymmetries. Evidence is drawn from developmental studies and from studies of brain-injured and normal adult subjects. It is concluded that the evidence that inverted faces are processed differently from upright faces is far from compelling, and therefore the effect of inversion provides little or no evidence of a unique process in face recognition. The inversion effect is interpreted in terms of expertise in face processing and the highly homogeneous nature of faces as a stimulus class.