The Role of Secondary Executive Function Demands in the Manifestation of Inhibitory Difficulties in Individuals with Autism

Background: Executive function is postulated as one of the core areas of impairment in individuals with an autism spectrum disorder (ASD).  Past laboratory-based research, however, has provided only limited support for this hypothesis.  Indeed, when measured in isolation, aspects of executive function such as working memory and inhibitory control have often been found to be intact in ASD cohorts.  It remains unclear, however, to what extent impairments may be more readily observed when concurrent demands are placed on multiple components of executive function.

Objectives: To evaluate whether ASD-related impairments in inhibitory control are exaggerated (and thus easier to detect) in the presence of additional demands on other aspects of executive function (i.e., working memory).

Methods: An eye movement task was used to assess inhibitory performance in 28 individuals with ASD (Mean age = 14.0 years) and an age-matched comparison group of 41 typically developing individuals (Mean age = 13.8 years). The eye movement task comprised two experimental conditions:  In the prosaccade (baseline) condition, participants were asked to make an eye movement towards a peripheral luminance change (i.e., a brightened box) – a fairly reflexive response.  In the antisaccade (inhibitory) condition, the same stimulus was again shown, but participants were asked to inhibit the reflexive saccade and instead generate a voluntary saccade in the opposite direction.  To evaluate the impact of secondary load on inhibitory performance, each participant completed the aforementioned eye movement tasks in the presence of low and high secondary working memory demands.

Results: A mixed model ANOVA approach was used with group (ASD & control) serving as a between-subjects variable and inhibitory condition (baseline and inhibitory) and memory load (low and high) serving as within-subjects variables. Significant main effects of saccade condition and memory load were evident.  As anticipated, participants generally responded slower in the inhibitory eye movement condition as compared to the baseline condition, F(1, 67) = 118.38, p < .05.  The presence of high secondary working memory demands also resulted in slowed overall performance as compared to the low memory load condition, F(1, 67) =  8.96, p < .05. Most importantly, the 3-way interaction between inhibitory condition, memory load, and group approached significance, F(1, 67) = 3.95, p = 0.05. Increasing concurrent working memory load had little or no effect on inhibitory performance for the non-ASD comparison group, t(40) = 0.65 , p = .52.  In contrast, we found that an increase in working memory demands resulted in poorer inhibitory performance (an 8.90% increase in response time) for the ASD group, t(27) = 1.94, p < .05.

Conclusions: The current findings suggest that ASD-related impairments in cognitive abilities may be most apparent in situations requiring the coordination of multiple aspects of executive function.