Effects of categorical representation on visuospatial working memory in autism spectrum disorder

We tested whether individuals with autism spectrum disorder (ASD) are impaired in visuospatial working memory or in the use of the semantic system, in particular in categorization processes at the service of working memory. The performance of high-functioning individuals with ASD (N = 21) in a visual same–different task adapted from Lachmann and van Leeuwen [e.g., Lachmann, T., & van Leeuwen, C. (2010). Representational economy, not processing speed, determines preferred processing strategy of visual patterns. Acta Psychologica, 134(3), 290–298] was compared to those of typically developed controls (N = 25). In a categorical identity task, two successive patterns had to be judged as the same if they belonged to the same equivalence set (cf. Garner, W. R., & Clement, D. E. (1963). Goodness of pattern and pattern uncertainty. Journal of Verbal Learning and Verbal Behavior, 2, 446–452), including all possible rotation and reflection transformations (R&R category), and as different otherwise. In a physical identity task, only patterns that matched in both shape and orientation had to be responded to as the same; all others, including category matches, had to be classified as different. Equivalence sets had different sizes (ESS). Earlier studies showed an increase in reaction time (RT) with increasing ESS and, for the physical identity task, a response conflict for category matching. Both of these effects were interpreted as evidence for a categorical code by which individual patterns are mentally represented. Assuming that categorization processes are deficient in individuals with ASD, we expected no ESS effects and, in the physical identity task, absence of a response conflict for these individuals. In contrast, we found individuals with ASD to be generally as sensitive to ESS as controls, and they showed a response conflict in the physical identity task. Thus, categorical processing seems to be intact in ASD. However, a strong overall group effect was found in RTs: Individuals with ASD are considerably slower than controls.