Crowding and visual search in high functioning adults with autism spectrum disorder

Paul A Constable^1,2, Joshua A Solomon¹, Sebastian B Gaigg², Dermot M Bowler^2
1Department of Optometry, Applied Vision Research Centre, City University London, United Kingdom; ²Department of Psychology, Autism Research Group, City University London, United Kingdom

Purpose: Individuals with autism spectrum disorder have demonstrated faster reaction times when searching for objects in a visual scene. One possible explanation for this observation is that the influence of crowding may not be as strong within this group compared to typically developing individuals.
Subjects and methods: We recruited 16 participants with and without a diagnosis of autism spectrum disorder in the age range of 20–58 years. The main experiments focused on determining the critical spacing for the correct identification of an ellipse’s orientation in the periphery when flanked by two circles with 81% correctly identified. The second experiment was an attempt to replicate previous studies that had demonstrated superior visual search in autism using reaction time, set-size slopes and intercepts as measures of search efficiency and pre-attentive processes.
Results: There were no significant group differences in the critical spacings for the crowded ellipses in the periphery (P = 0.358) or in the elliptical discrimination thresholds (P = 0.477). In addition there were no significant differences between groups in reaction times (P = 0.083), accuracy (P = 0.658) and set-size slopes (P = 0.976), however the intercept for the set-size slope function was significantly lower for the comparison group (P = 0.016).
Conclusions: The individuals we tested demonstrated neither immunity to crowding nor any advantage in the visual search task. Therefore, we failed to confirm that enhanced discrimination underlies superiority in visual search in adults with high functioning autism spectrum disorder. This finding may be associated with the older age group investigated compared to previous studies and suggests that the underlying mechanism of superior visual search may not be a persistent feature of autism spectrum disorder.

Keywords: critical spacing, reaction time, discrimination, visual perception