Reduced top-down modulation in autism: The role of prior knowledge in the visual perception of fragmented pictures

Background:

It has been suggested that the cognitive profile of Autism Spectrum Conditions (ASC) involves reduced top-down processes; abnormalities in using prior knowledge and past experience in modulating cognitive processes (Frith, 2003). In previous studies we showed diminished use of prior knowledge in modulating attention, memory, and aspects of face perception in high-functioning individuals with ASC. Here we investigated the effect of prior knowledge on the visual perception of fragmented pictures (faces, objects). Past research has shown that in typical development, this process is achieved by an interaction between face/ object-specific processes and higher-level processes of attention, memory, and mental imagery (Dolan et al., 1997).

Objectives:

We tested the alternative hypotheses that in people with ASC, perceptual learning may be overall reduced, or, given known abnormalities in face processing, that perceptual learning may be specifically reduced for faces.

Methods:

Participants were shown fragmented images of faces and objects before and after they were shown the corresponding black-and-white image. When first seen, the fragments look like random blobs but after having seen the real photographs, TD viewers can easily recognize the blobs as, for example, a face. Using eye-tracking technology, we also studied differences in visual fixations on the face/ object versus background between the pre- and post-learning phases. Twelve individuals with high-functioning ASC and 12 TD individuals, matched in terms of age and ability levels, took part in this study. 

Results: Both groups recognized significantly more faces and objects after having seen the corresponding image. However, in the ASD group, the perceptual learning effect was significantly reduced only for the face stimuli.

Conclusions: Our data suggest reduced influence of prior experience on visual perception of social stimuli. We discuss our findings in the context of the hypothesis of reduced top-down modulations and implications for potential abnormalities at the neuro-functional level.