Increased Baseline Pupil Size Linked to Uncertainty Avoidance in Decision Making

ABSTRACT Uncertainty is a key contributor to decision making, and humans show inconsistent attitudes towards it. Although excessive uncertainty‐avoidance or uncertainty‐seeking are hallmark symptoms of several mental conditions, the neural mechanism underlying uncertainty seeking and avoidance remains unclear. Here, we probed whether changes in pupil‐linked arousal are indicative of uncertainty avoidance in humans. Investigating baseline pupil size to capture endogenous fluctuations across two experiments ( N 1 = 24, N 2 = 21), we found that pretrial pupillary responses (as early as 700 ms prior to the onset of a trial) were closely related to uncertainty attitudes during multiarmed bandit tasks. Although increased baseline pupil size signalled avoidance in uncertainty‐related decisions, it did not foreshadow value processing per se. The specificity of our results suggests that uncertainty processing is dynamic and depends on (potentially noradrenergic) endogenous pupil fluctuations.