Multisensory Integration Inhibits Pupillary Light Reflex: Evidence from Pupil Oscillation

摘要: Multisensory integration is able to enhance stimulus saliency at the early stage of information processing hierarchy. Due to the saliency enhancement, concurrently presented audiovisual stimuli are shown to evoke a transient pupil dilation than its unisensory constituents, presumably reflecting an enhanced activation of the sympathetic pathway. Since pupil size is mediated by both the sympathetic and the parasympathetic pathways, it remains largely unknown whether multisensory integration modulates pupillary responses mediated by the parasympathetic pathway. To probe this issue, the present study measured the pupillary light reflex, which refers to the pupil constriction in response to brightness and is completely controlled by the parasympathetic pathway. We purposely evoked an oscillation of pupillary light reflex by periodically changing the luminance of the visual stimuli, and found this induced pupil oscillation was substantially attenuated when the bright but not the dark phase of a flickering stimulus was periodically and synchronously presented with a burst of tone (Experiments 1 and 2). Furthermore, the inhibited pupillary light reflex vanished when the visual stimuli were moved from the central field to the periphery (Experiment 3), while persisted when the visual stimuli appeared outside the attention focus in a demanding task (Experiment 4). These findings that multisensory integration inhibits pupillary light reflex in an eccentricity dependent but attention independent manner offer preliminary but robust evidence that the parasympathetic pathway can be modulated by multisensory integration.