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Atypical Eye Movement Characteristics during a Biological Motion Preference Task in Individuals with Autism Spectrum Disorder
Objectives: To examine differences in multiple eye gaze characteristics during a biological motion task in individuals with ASD and TD controls using eye tracking.
Methods: The study population included 40 TD (males = 65%, mean age [range] = 16.4 [6-63] years) and 121 ASD (76%, 14.6 [6-54] years) participants. Diagnosis of ASD was confirmed according to the Autism Diagnostic Observation Schedule (ADOS, 2nd edition). Participants were presented with a series of videos with point light displays representing biological motion on one side and non-biological motion on the other, and their eye movements were recorded. Each video lasted approximately 4 seconds. In total, 60 trials were presented with the biological-nonbiological side counterbalanced, and each trial preceded with a centering stimulus. Eye movements of each participant were characterized by: % total time gazing at the stimuli, % time gazing at biological versus non-biological motion, % time the first saccade was oriented towards biological motion, % time the first fixation was on biological motion, average latency of the first saccade and fixation on either type of stimuli.
Results: Each of the eye movement characteristics was modelled separately as a linear sum of participant’s age, gender and group. There was a significant effect of group on all characteristics (all p’s < 0.05), except “% time the first fixation was on biological motion”. In comparison to TD participants, the ASD participants at the population level were gazing less at the presented stimuli (difference = 8.8%) and biological motion (7.7%). Furthermore, the ASD participants were more frequently orienting their first saccade towards biological motion (2.6%) and had greater average latencies of the first saccade (112-132 msec) and fixation (105-118 msec) on either type of stimuli. The effect of group persisted the use of different data inclusion criteria (N = 3) to account for the presence of outliers, whereas the effects of age and gender varied across these criteria. The ASD participants demonstrated a subtle but significant preference for biological motion (mean = 54.5% versus 61.9% in the TD controls, comparisons against 50%: both p’s < 10-8). This preference (> 50%) was also observed in groups of the ASD participants with different severity levels (mild, moderate, severe) of the ADOS “restricted and repetitive behavior”, “social affect” and “total” symptom scores (all p’s < 0.05).
Conclusions: Individuals with ASD differ from TD controls on multiple properties of eye movements associated with biological motion preference. Age and gender appear to have little or no impact on these differences. However, individuals with ASD, like TD controls, exhibit preference for biological motion that appears across different symptom domains and levels of ASD. These findings have implications for the use of biological motion preference tasks as a biomarker for ASD.