The Temporal Dynamics of Attentional Allocation during Counterfactual Learning

Counterfactual learning, the ability to learn from what could have happened under different circumstances, is a key cognitive mechanism supporting behavioral adaptation. While its neural and computational underpinnings are increasingly understood, the temporal dynamics of attention toward factual and counterfactual outcomes remain poorly characterized. Here, we investigate the biological mechanisms underlying this process using a reinforcement learning task combined with eye-tracking and pupillometry in 36 human participants. Participants completed a two-armed bandit task with full outcome feedback and exhibited a robust confirmation bias, learning more from outcomes that supported their previous choices. Gaze patterns revealed a consistent temporal sequence of fixations from factual to counterfactual outcomes, modulated in opposite directions by the valence of each outcome. Pupil dilation, a proxy for noradrenergic arousal, was influenced by the factual outcome and by the similarity between factual and counterfactual feedback, consistent with increased surprise during disconfirmatory events. These results provide a mechanistic account of how attentional and arousal systems jointly shape outcome evaluation. By integrating behavioral modeling with physiological markers, this work contributes to a broader understanding of the adaptive constraints on decision-making and offers new insight into how organisms evaluate hypothetical alternatives in learning contexts.