The pupillary light response reflects exogenous attention and inhibition of return

Here we show that the pupillary light response reflectsexogenous (involuntary) shifts of attention and inhibitionof return. Participants fixated in the center of a displaythat was divided into a bright and a dark half. Anexogenous cue attracted attention to the bright or darkside of the display. Initially, the pupil constricted whenthe bright, as compared to the dark, side of the displaywas cued, reflecting a shift of attention toward theexogenous cue. Crucially, this pattern reversed about 1 safter cue presentation. This later-occurring, relativedilation (when the bright side was cued) reflecteddisengagement from the previously attended location,analogous to the behavioral phenomenon of inhibitionof return. Indeed, we observed a reliable correlationbetween "pupillary inhibition" and behavioral inhibitionof return. Our results support the view that inhibition ofreturn results from habituation to (or short-termdepression of) visual input. We conclude that thepupillary light response is a complex eye movement thatreflects how we selectively parse and interpret visualinput