Multisensory Attenuation of the Pupil Light Response in Autistic and Non-Autistic Children.

Autonomic responses to sensory stimuli are altered in autism, yet little is known about how multisensory input modulates these responses. This study examined whether auditory stimuli affect the pupil light reflex (PLR), a parasympathetically driven response to light, in autistic and non-autistic children. Pupillometry was used to measure responses to visual-only (V), auditory-only (A), and audiovisual (AV) stimuli in 72 children aged 8-14 years (34 non-autistic, 38 autistic). We hypothesized that auditory input would attenuate pupil constriction in non-autistic children in the AV condition and that this cross-modal modulation might differ in autism, reflecting altered sensory-autonomic functioning. Across groups, results revealed a consistent pattern: auditory stimuli elicited pupil dilation, visual stimuli evoked constriction and simultaneous AV stimuli led to attenuated constriction relative to visual-only trials. This attenuation lends support to prior findings of multisensory attenuation of the PLR. Time-binned analysis revealed a group effect during the 500-1000 ms post-stimulus window: autistic children showed significantly more positive baseline-corrected pupil responses across conditions (i.e., less constriction in V/AV and greater dilation in A), suggesting group differences in the dynamic trajectory of the pupil response. Contrary to expectations, autistic and non-autistic children did not differ significantly on peak constriction or constriction latency within visual conditions. Offering insight into how autistic individuals integrate sensory information and regulate arousal, these findings support the presence of cross-modal modulation of the PLR and suggest that auditory signals influence early-stage visual-autonomic processing similarly across groups.