Background: Previous studies have shown atypical eye-movements in autism spectrum disorder (ASD), mostly in response to social stimuli. Studies of binocular coordination during reading suggest that ocular disparity is related to task difficulty. Binocular coordination may thus provide added insight into the mechanisms contributing to superior search abilities in individuals with ASD.
Objectives: To investigate the degree of binocular coordination in a visual search task and to relate frequency of aligned and disparate fixations to task performance in children with ASD.
Methods: Seventeen ASD and 11 age- and IQ-matched typically developing (TD) children participated, but three ASD and one TD participant had to be excluded for noncompliance. Binocular coordination was measured as the proportion of aligned and disparate (crossed or uncrossed) fixations. Search difficulty in the visual search task was manipulated by varying set size (6, 12, 24), distractor composition (heterogeneous, homogeneous) and target presence (present, absent)
Results: We found significant main effects of target presence, F(1,20)=7.67, p<.05, and set size, F(1,20)=4.29, p<.05, indicating that the proportion of aligned fixations decreased in conditions with greater task difficulty. In addition, there was a significant group by target presence interaction, F(1, 20)=4.84, p<.05, as the proportion of aligned fixations remained equivalent in target absent and present conditions for the ASD group, but increased in target present compared to absent for the TD group.
Conclusions: Consistent with findings by Juhasz et al. (Quart J Exp Psy, 2006), the proportion of disparate fixations increased with added demands on the visual system. Previous research has demonstrated that accelerated response time in target absent conditions drives the superior performance of individuals with ASD in visual search tasks. Our data suggest that target absence does not increase the task difficulty for individuals with ASD as it does for typically developing individuals.