Uncovering Distinct Drivers of Covert Attention in Complex Environments With Pupillometry

Spatial visual attention prioritizes specific locations while disregarding others. The location of spatial attention can be deployed without overt movements (covertly). Spatial dynamics of covert attention are exceptionally difficult to measure due to the hidden nature of covert attention. One way to implicitly index covert attention is via the pupillary light response (PLR), as the strength of PLR is modulated by where attention is allocated. However, this method has so far necessitated simplistic stimuli and targeted only one driver of covert attention per experiment. Here we report a novel pupillometric method that allows tracking multiple effects on covert attention with highly complex stimuli. Participants watched movie clips while either passively viewing or top-down shifting covert attention to targets on the left, right, or both sides of the visual field. Using a recent toolbox (Open-DPSM), we evaluated whether luminance changes in regions presumably receiving more attention contribute more strongly to the pupillary responses-and thereby reveal covert attention. Three established effects of covert attention on pupil responses were found: (1) a bottom-up effect suggesting more attention drawn to more dynamic regions, (2) a top-down effect suggesting more attention towards the instructed direction, and (3) an overall tendency to attend to the left side (i.e. pseudoneglect). Beyond the successful validation of our method, these drivers of covert attention did not modulate each other's effects, indicating independent contributions of bottom-up, top-down, and pseudoneglect to covert attention in stimuli as dynamic as the present. We further explain how to use Open-DPSM to track covert attention in a brief tutorial.