Fast updating of stimulus history reveals weak internal representations of faces in autism.

Atypical perception has been widely reported in autism spectrum disorders, and deficits in face recognition, specifically, are argued to be closely associated with social impairment experienced by these individuals. However, it is still debated (a) whether deficits are perceptually based, and (b) what the role is of experience-based refinements of perceptual face representations in autism. We investigated the effect of short- and long-term experienced stimulus history on face processing. Autistic and non-autistic individuals performed same-different judgments in a serial discrimination task where two consecutive faces were drawn from a distribution of morphed faces. Use of stimulus statistics was measured by testing the gravitation of face representations towards, the mean of a range of morphed faces around which they were sampled (regression-to-the-mean). The results show that unlike non-autistic individuals, representations of own- and other-race faces were equally biased by stimulus statistics in autistic individuals. Moreover, autistic individuals used the most recently exposed faces without forming a strong internal representation based on the overall experienced faces, indicating a weaker internal model of the "typical" averaged face. This accumulated history of faces may underlie typical face specialization, and thus may account for the reduced specialization for own-race faces shown in autism. The results shed light on the way autistic people process and recognize faces, and on the basic mechanisms underlying atypical face perception.