Task-Evoked Pupillary Response to Social Stimuli: Hypoactivation in Autism

Background: Previous research has demonstrated that individuals with autism spectrum disorders (ASD) present difficulties with attentional disengagement. Such perseverative attention may contribute to clinical symptoms of autism such as relative differences in sensitivity to social versus nonsocial sources of information. A marker of “attentional load,” or the degree of attentional resources allocated to a particular visual stimulus, is provided by the magnitude of changes in pupillary diameter. The present study investigated task-evoked pupillary responses (TEPR) in children with ASD when disengaging from social and nonsocial stimuli to determine whether allocation of attentional resources to social stimuli was decreased, possibly contributing to patterns of atypical social information processing.

Objectives: To assess the TEPR amplitude, a marker of attentional activation, when children with ASD and typically developing children (TYP) disengage from social and nonsocial stimuli.

Methods: In this study, 20 school age children with ASD (mean age = 145 months, SD = 24) and 22 age and IQ matched TYP children (mean age = 158 months, SD = 23) completed a modified gap-overlap task. The task presented a central social or nonsocial image of similar size and luminance, followed by a lateral nonsocial image. In the overlap condition, a lateral target appeared while children fixated on the central stimulus, requiring them to first disengage visual attention before reorienting to the periphery. For each of 40 overlap trials, pupillary diameter was examined at four separate epochs of 400 ms duration: (1) before and (2) after the onset of the central stimulus and (3) before and (4) after the participant disengaged and shifted attention to the lateral stimulus. Pupil diameter was measured with a Tobii 1750 eye tracker at a sampling rate of 50 Hz. Trials were deemed valid if a clear saccade from the central stimulus to the peripheral target was recorded between 80 and 1000 ms after the onset of the lateral stimulus. Diameter changes were calculated by pre-trial baseline subtraction to account for dark adaptation, accommodation, and fatigue.

Results: The two groups did not differ in their TEPR to the onset of either type of trial. The TYP group exhibited a pupillary dilation during disengagement from social stimuli. This differed significantly (p < .01) from the pupillary constriction shown by the ASD group in both social and nonsocial disengagement conditions and by the TD group in the nonsocial disengagement condition.

Conclusions: As measured by pupillary response, children with ASD failed to allocate attentional resources to disengage from social stimuli at the same rate as the TYP children. Hypoactivation to social stimuli may be one component process that contributes to deficits in orienting to salient social information in autism. Activation to nonsocial information may be a relative strength in autism and when paired with deficient activation to social information, may result in an overall pattern of increased attention to and experience with the nonsocial world.