Tracking Covert Attention in Complex Stimuli with Pupil Size Changes

Abstract

Covert attention, the ability to attend to spatial locations without making eye movements, is categorized into endogenous and exogenous types. The pupil light response (PLR) has been shown to be modulated by covert attention, with changes in pupil size reflecting the luminance of attended stimuli when the stimuli are simplistic. This study aimed to determine whether covert attention could be effectively studied using pupil size changes and the Open Dynamic Pupil Size Modeling (Open-DPSM) toolkit. Thirty-six participants viewed 32 movie clips. Behavioral data confirmed the successful manipulation of attention, with better performance on the attended side. Significant correlations between horizontal pupil bias and hit rate bias indicated that behavioral and physiological measures align with the instructed attentional deployment. Horizontal pupil bias differences in different attended conditions demonstrated endogenous covert attention. Finally, sides with stronger visual events exerted a higher influence on the PLR than the side with weaker events, demonstrating exogenous attention. Together, these findings suggest that the Open-DPSM toolkit can measure covert attention via the PLR in complex stimuli such as movies, demonstrating consistent effects of both endogenous and exogenous attention.