Multisensory Signals Inhibit Pupillary Light Reflex: Evidence from Pupil Oscillation

摘要: Multisensory integration, which enhances the stimulus saliency at the early stage of processing hierarchy, is recently shown to produce a larger pupil size than its unisensory constituents. Theoretically, any modulation on pupil size ought to be associated with the sympathetic and parasympathetic pathways that are sensitive to lights. But it remains poorly understood how pupillary light reflex is changed in a multisensory context. The present study evoked an oscillation of pupillary light reflex by periodically changing the luminance of a visual stimulus at 1.25 Hz. It was found that such induced pupil oscillation was substantially attenuated when the bright but not the dark phase of the visual flicker was periodically and synchronously presented with a burst of tones. This inhibition effect persisted when the visual flicker was task-irrelevant and out of attentional focus, but disappeared when the visual flicker was moved from the central field to the periphery. These findings not only offer a comprehensive characterization of the multisensory impact on pupil response to lightness, but also provide valuable clues to the individual contributions of the sympathetic and parasympathetic pathways to multisensory modulation of pupil size.