The pupil provides a rich, non-invasive measure of the neural bases of perception and cognition. It can particularly inform about the role of arousal-linked neuromodulation, which alters both cortical processing and pupil size. But a multitude of factors influence pupil size, which complicates interpretation. We measured pupil signals accompanying changes in multistable perception, i.e. accompanying endogenously-generated perceptual changes in the face of inconclusive sensory input. Perceptual changes were marked by a complex pupil response that could be decomposed into two components: a dilation tied to task execution and plausibly reflecting arousal-linked noradrenaline, and an overlapping constriction tied to the perceptual transient and plausibly reflecting altered cortical responses. Constriction, but not dilation, amplitude depended on the timing of perceptual changes, possibly providing an index of neural adaptation. We conclude that pupil size reflects several dissociable processes during perceptual multistability, and that arousal-linked neuromodulation shapes action but not perception in these circumstances.
bioRxiv Subject Collection: Neuroscience