Spontaneous fluctuations in pupil size are correlated with neural activity and behavior in many ways. This is generally attributed to a single underlying cause: arousal. This unitary account disregards other potential underlying causes. To address this gap, we propose a comprehensive framework of four mechanisms that jointly underlie the complex and context-dependent relationships between spontaneous pupil-size fluctuations, neural activity, and behavior. In addition to arousal, we consider optical effects, brightness constancy, and self-generated visual stimulation. Based on this framework, we argue that pupil fluctuations should be considered beyond arousal, as a functionally important, yet still poorly understood, component of visual processing.

Prestimulus pupil size is associated with near-threshold detection performance in both the visual and auditory domain, a relationship that is commonly attributed to arousal. However, given that larger...

Researchers are increasingly showing interest in the ways in which various cognitive processes are influenced by the size of the pupil. However, this realm of research is complicated by the pupil’s no...