Idiosyncratic pupil regulation in autistic children.

Recent neuroimaging and eye-tracking studies have suggested that children with autism exhibit more variable and idiosyncratic brain responses and eye movements than typically developing (TD) children. Here, we extended this research to pupillometry recordings. We successfully acquired pupillometry recordings from 111 children (74 with autism), 4.5-years-old on average, who viewed three 90 s movies, twice. We extracted their pupillary time-course for each movie, capturing their stimulus evoked pupillary responses. We then computed the correlation between the time-course of each child and those of all others in their group as well as between each autistic child and all children in the TD group. This yielded an average inter-subject correlation value per child, representing how similar their pupillary responses were to all others in their group or the comparison group. Children with autism exhibited significantly weaker inter-subject correlations than TD children in all comparisons. These differences were independent of previously reported differences in gaze inter-subject correlations and were largest in responses to a naturalistic movie containing footage of a social interaction between two TD children. The results demonstrate the utility of measuring the idiosyncrasy of pupil regulation, which can be performed with passive viewing of movies even by young children with co-occurring intellectual disability. These findings reveal that a considerable number of children with autism have significantly less stable, idiosyncratic pupil regulation than TD children, indicative of more variable, weakly regulated, underlying neural activity.