Abstract
Prosopometamorphopsia (PMO) is a rare condition in which faces appear distorted (e.g. facial features are drooping or pinched together) while other visual categories remain largely or entirely undistorted. Whereas in prosopagnosia there is a face recognition deficit without perceptual distortions, in PMO there appear to be perceptual distortions without face recognition deficits. We tested three individuals with PMO on a battery of visual tasks which yielded a number of insights into face perception. First, we presented images of faces, objects, and simple geometric patterns. All three participants reported distortions to the faces but not to the objects or patterns. Second, we presented faces at four orientations and found that inverted and sideways faces generated distortions in two participants. Those distortions affected the same features at all orientations, which, despite evidence that inverted faces are processed qualitatively differently than upright faces, suggests that inverted and upright faces are both aligned to the same orientation-independent template. Third, we noted the importance of the vertical midline in the distortions. Two participants describe distortions that extend up to, but not past, the vertical midline. For the participant who sees the entire face distorted, we found that making faces symmetric across the vertical midline or occluding half of the face causes her distortions to disappear. Finally, similar to the synesthesia literature, we demonstrate the reality of PMO by showing that distortions can improve task performance. The participant who sees distortions for asymmetric but not symmetric faces performed significantly faster than controls on a visual search task with normal asymmetric faces as the targets and symmetric faces as distractors. Our results demonstrate that PMO is an understudied condition that provides a new avenue for exploring questions about face representation.