Influence of Autism Spectrum Disorder and Anxiety on Perceptual Load Capacity

Background: Perceptual load theory posits that there is a limited amount of information a person can perceive at any given time and information is processed automatically until reaching this capacity. Separate lines of research suggest that perceptual capacity may be enhanced in individuals with Autism Spectrum Disorder (ASD; Remington et al., 2009, 2012) and also in non-ASD populations with high trait anxiety (Berggren et al., 2015; Sadeh & Bredemeier, 2011).

Objectives: The present study represents a confluence of these two lines of research. We sought to examine whether enhanced perceptual capacity is unique to ASD, unique to anxiety disorders (with the ASD findings being a consequence of high comorbidity), or is attributable to a mechanism intrinsic to both of these conditions.

Methods: An established computerized paradigm (Remington et al., 2012; Berggren et al., 2015) was used to assess perceptual capacity limits in 56 high functioning male participants (28 with ASD). In the task, participants were shown visual arrays consisting of 1-6 letters (thus manipulating perceptual load). Participants were to respond as quickly as possible as to whether the target letter X or N was present in the array. On 50% of trials, an additional stimulus probe, a squiggle, was presented simultaneously with the letter display. Participants were also to monitor whether this probe was present or absent. Participants completed 4 blocks of 72 experimental trials each (total=288 trials).

Results: Detection sensitivity (d’) for the ‘squiggle’ detection task served as the primary dependent variable. Data were entered into hierarchical linear model analyses with group (ASD and non-ASD) and STAI anxiety scores as between-subject factors and array size (1, 2, 4, or 6) as a within-subject factor. As anticipated, there was a main effect of condition [F(3,165)=16.72, p<.001], indicating that performance declined at higher set sizes. The main effect of autism group trended towards significance [F(1,53)=3.32, p=0.07] with generally lower d’ scores for the ASD group. There were no main effects of anxiety, two-way, or three-way interactions between condition, group, and anxiety [all F<1]. When comparing highly elevated anxiety scores (>1.5SD above normative STAI score) with typical anxiety scores at array sizes 2 and 4, we found a significant interaction between array size and anxiety group [F(1,52)=5.89, p=.019] such that d’ declined significantly from array size 2 to 4 for individuals with typical anxiety scores but not for individuals with elevated scores.

Conclusions: Consistent with recent literature, these findings indicate that elevated levels of anxiety are associated with superior perceptual capacity. This was true across both the ASD and non-ASD groups. A main effect of ASD diagnosis was also evident such that individuals with ASD showed poorer overall performance. Although speculative, comorbid anxiety may have contributed to previous reports of enhanced performance in samples of individuals with ASD. Additional research is needed to fully understand the interplay between ASD, anxiety, and perceptual capacity.