Functional benefits of cognitively driven pupil-size changes

Abstract

Pupil-size changes are typically associated with the pupil light response (PLR), wherethey are driven by the physical entry of light into the eye. However, pupil-size changes are also influenced by various cognitive processes, where they are driven byhigher-level cognition. For example, the strength of the PLR is not solely affected byphysical properties of the light but also by cognitive factors, such as whether thesource of light is attended or not, which results in an increase or decrease in thestrength of the PLR. Surprisingly, although cognitively driven pupil-size changes havebeen the focus of extensive research, their possible functions are rarely discussed.Here we consider the relative (dis)advantages of small versus large pupils in different situations from a theoretical point of view, and compare these to empirical results showing how pupil size actually changes in these situations. Based on this, we suggest that cognitively driven pupil-size changes optimize vision either through preparation, embodied representations, or a differential emphasis on central or peripheral vision. More generally, we argue that cognitively driven pupil-size changes are a form of sensory tuning: a subtle adjustment of the eyes to optimize vision for the current situation and the immediate future.