Abstract
Background: Movement disturbances are often associated with Autism Spectrum Disorder (ASD), including the movement of the eyes. However, oculomotor abnormalities in ASD have been typically studied in terms of the social aspects of visual exploration and engagement, either by analyzing gaze direction to points of social interest or by comparing gaze behavior to that of typically developing individuals when presented with specific stimuli. Methods: We analyzed a large eye-tracking data set obtained at the national autism research center of Israel from children watching three different short video clips with social content (n=274, 220 with ASD, ages 1-10 years). Inspired by a recent measure of “randomness” of movement found for pointing (Torres et al. 2016), we investigated the involuntary aspects of eye movements during video inspection, specifically the “randomness” of saccade timing assessed via gamma fitting of its time interval distribution, excluding intervals with large gaps or invalid data. Results: We found that the measure of saccade time “randomness” (1) was significantly higher in ASD compared to the TD children; (2) was positively correlated with severity (ADOS comparison score); and (3) was higher in ASD for all three video clips in different degrees. The results persisted even when children with reduced tracking quality (primarily ASD) were discarded, and the effects were highly significant and robust. A similar analysis with the peak saccade velocity showed a similar trend, which did not reach significance. Conclusion: Increased “randomness” of eye movements in ASD children watching video clips could be related to “neural variability” or noise, reduced executive control, or reduced engagement with the movies. These findings could contribute to the future development of oculomotor biomarkers as part of an integrative diagnostic tool for ASD.