title: Psychophysical evidence for a non-linear representation of facial identity.
abstract: It has been proposed that faces are represented in the visual brain as points within a multi-dimensional "face space", with the average at its origin. We adapted a psychophysical procedure that measures non-linearities in contrast transduction (by measuring discrimination around different reference/pedestal levels of contrast) to examine the encoding of facial-identity within such a notional space. Specifically we had subjects perform identity discrimination at various pedestal levels of identity (varying from average/0% to caricature/125% identity) to derive "identity dipper functions". Results indicate that subjects are generally best at spotting identity change in neither average nor full-identity faces, but rather in faces containing an intermediate level of identity (which varies from face-to-face). The overall pattern of results is consistent with the neural encoding of faces involving a single modest non-linear transformation of identity that is consistent across faces and subjects, but that it scaled according to the distinctiveness of the face.
authors: UCL Institute of Ophthalmology, University College London, EC1V 9EL London, UK. s.dakin@ucl.ac.uk
authors: Steven C
authors: SC
authors: Dakin
authors: Diana
authors: D
authors: Omigie
mesh_terms: D004192:Discrimination, Psychological / Q000502:physiology; D005145:Face; D005260:Female; D006801:Humans; D008297:Male; D008960:Models, Psychological; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010469:Perceptual Distortion / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology