<p>The exploration-exploitation tradeoff describes the cognitive balance between exploring novel options and exploiting known strategies to optimize decision-making. The locus coeruleus-norepinephrine (LC-NE) system has been implicated in regulating this tradeoff, with phasic and tonic LC activity linked to exploitation and exploration, respectively. Pupillometry provides a noninvasive measure of LC activity, with pretrial pupil size reflecting tonic activity and task-evoked pupil responses indicating phasic activity. In this study, we investigated how pupillary dynamics track transitions between exploration and exploitation in a novel cognitive paradigm, the Complex Card Matching Task (CCMT). The CCMT was designed to elicit clear exploratory and exploitative behaviors while incorporating two difficulty levels to assess task-related cognitive demands. Our findings showed that exploration was consistently associated with larger pupil size than exploitation in both pretrial and task-evoked periods, suggesting heightened LC-NE activity during uncertain decision-making. Importantly, task difficulty moderated these effects during exploitation, with larger pupils observed in the Hard condition, reflecting the increased cognitive effort required to maintain complex rules to make a decision. By contrast, exploration was unaffected by difficulty, indicating a stable arousal signature of rule discovery across task demands. The pupil dynamics observed in the exploration-exploitation tradeoff highlight the complexity of this process, suggesting that while exploration involves a consistent baseline of elevated arousal, exploitation is more sensitive to task difficulty. The CCMT provided a clear distinction between exploration and exploitation, reinforcing its value for investigating cognitive flexibility and decision-making processes. Our findings contribute to understanding the neural and physiological mechanisms underlying the exploration-exploitation tradeoff.</p>