Pupil Dynamics reflect Compensatory Control during Continuous Motor-Control following Cognitive Demand

Pupillometry is commonly used to assess workload and fatigue, but its interpretation in applied, continuous-control tasks remains unclear because pupil responses are strongly shaped by task context and often lack a theory-guided interpretive basis. The Compensatory Control Model and Locus Coeruleus-Norepinephrine system offer complementary frameworks for interpreting pupil dynamics in relation to regulatory effort and engagement under sustained cognitive demand. We aimed to examine how tonic and phasic pupil dynamics reflect compensatory regulation following sustained cognitive demand, and how these dynamics relate to subsequent performance during continuous motor control. Participants completed two sessions consisting of a low- versus high- demand working-memory task followed by a joystick-based continuous motor-control task. Linear mixed-effects models tested demand effects on pupil dynamics and behavior and evaluated trial- level pupil-performance associations. Prior high demand produced small and specific changes in motor-control performance. Task-evoked pupil response showed effects of engagement dependent on prior demand and small associations with movement timing and accuracy. Our results show that pupil dynamics sensitively reflect sustained cognitive demand, but their trial-level predictive value for subsequent continuous motor performance is limited.