Atypical categorical perception in autism: autonomy of discrimination?

A diminished top-down influence has been proposed in autism, to account for enhanced performance in low-level perceptual tasks. Applied to perceptual categorization, this hypothesis predicts a diminished influence of category on discrimination. In order to test this hypothesis, we compared categorical perception in 16 individuals with and 16 individuals without high-functioning autism. While participants with and without autism displayed a typical classification curve, there was no facilitation of discrimination near the category boundary in the autism group. The absence of influence of categorical knowledge on discrimination suggests an increased autonomy of low-level perceptual processes in autism, in the form of a reduced top-down influence from categories toward discrimination.