Beyond individual differences: are working memory and inhibition informative specifiers within ASD?

Findings on working memory (WM) and inhibition in children with autism spectrum disorders (ASD) are contradictory and earlier studies largely ignored individual differences. As WM and inhibition seem to be related, children who experience WM deficits might also experience inhibition deficits. Moreover, these children possibly form a distinct subgroup, differing on other variables, such as cognitive functioning, symptom severity, behavior, and attention deficit hyperactivity disorder (ADHD) characteristics. We studied a large sample of children with and without ASD (8-12 years, IQ > 80) with classic experimental tasks (n-back task, ASD n = 77, control n = 45; stop task, ASD n = 74, control n = 43), and explored individual differences. The ASD group made more errors on the n-back task with increasing WM load, and had longer stop signal reaction times on the stop task when compared with controls. However, only 6 % of the ASD group showed both WM and inhibition deficits, and 71 % showed no deficits. Parents of children with WM and/or inhibition deficits tended to report more conduct problems on the disruptive behavior disorder rating scale. ADHD characteristics did not influence performance. Some children used medication during testing, which seemingly influenced stop task performance, but excluding these data did not change the main findings. Large individual differences in cognitive functioning are present, even within children with ASD with average or above average intelligence. However, whether individual differences in specific cognitive domains, such as WM and inhibition are as informative as individual differences in diagnosis, comorbidity, and general cognitive functioning, calls for future research.