Pupil Size Dynamics Predict Momentary Changes in Self-Reported Arousal.

Subjective arousal, or feelings of activation and alertness, can dynamically modulate affect, behavior, and cognition. Momentary changes in subjective arousal have typically been assessed with self-report in humans, which may alter those very feelings. Although researchers have traditionally used pupil size as a physiological index of arousal, links between pupil dynamics and momentary changes in subjective arousal remain unclear. Here, we combined continuous pupillometry with repeated self-report probes of changing arousal as individuals engaged in a modified Monetary Incentive Delay task. Across Virtual Reality (N = 28; 12 females, 16 males) and Functional Magnetic Resonance Imaging (N = 27; 15 females, 12 males) studies, tonic and phasic pupil measures jointly predicted subsequent self-reported arousal beyond stated incentive value and at a temporal lag of ∼1.5-3.5 s. Neural activity associated with pupil dynamics further predicted pupil size, self-reported arousal, and behavioral motivation in held-out data. Together, these convergent findings establish pupil size as a temporally precise marker of momentary fluctuations in self-reported arousal.