The Active Pupil 2.0: A feedback loop between perception, mental state, and pupil size

Vision scientists often speak of active vision to emphasize that vision is as much about action as it is about perception. When you notice an object from the corner of your eye, it attracts your attention; this is perception. You then look at the object to see it more clearly; this is action. As soon as you look at the object, you perceive something new, which triggers another action. And so on, in a never-ending feedback loop. Nowadays, the notion of active vision is well-accepted. But one important class of eye movement has been sorely neglected in this context: the pupillary response. This is what I want to study. My general hypothesis is that pupillary responses are part of a feedback loop between perception, mental state (specifically arousal), and pupil size. This leads to three new and specific predictions, which I will test using psychophysics, eye tracking, and pupillometry in healthy human participants. First, I predict that arousal-related changes in pupil size are adaptive: A large pupil has specific benefits for situations that induce high arousal. Second, I predict that pupil size in turn affects arousal: A large pupil sends a vigilance signal to the brain. Third, I predict that pupil size affects perception: A large pupil sends a darkness signal to the brain. This project will make a significant contribution to vision science, because few studies have addressed the important role of pupillary responses in vision. (Though pupil size is routinely used as a tool to measure arousal, visual defects, etc.) Furthermore, this project has direct practical implications: Pupillary responses are important for the ergonomics of display design (when to use white letters on a dark background?), and could be used in a human-computer interface for communicating with locked-in patients.