The Role of Uncertain Reward in Voluntary Task-switching as Revealed by Pupillometry and Gaze

Cognitive flexibility, the brain’s ability to adjust to changes in the environment, can be empirically examined via voluntary task-switching paradigms (VTS), for which greater proportion of switch trials (trials in which the participant switches to a qualitatively different task) indexes greater flexibility, whereas reduced switch rates index increased stability. Prior literature has shown an important correspondence for changing reward and flexibility: flexibility is highest when reward changes whereas flexibility is reduced when reward stays high relative to the previous trial. Recently, researchers have leveraged eye-tracking to investigate changes in pupil diameter associated with changing reward. The majority of these studies are under a deterministic reward schedule. Critically, few VTS studies have investigated pupil dilation in a probabilistic schedule, which is striking given the brain uses a probabilistic approach to resolve uncertainty in real-world scenarios. The purpose of this study was to examine the role of uncertain reward in a VTS paradigm. Participants were shown a cue shape under a deterministic reward schedule (Experiment 1) or a probabilistic reward schedule (Experiment 2), followed by a letter-number judgment task, and a feedback phase where participants were informed about correct or incorrect responses. We used pupil dilation as a neuropsychological correlate of arousal and accumulated fixations on a region (i.e. dwell time) to measure oculomotor capture. Results during the cue phase showed that pupil dilation under a deterministic schedule, but not probabilistic, tracked arousal from the magnitude of reward. Moreover, under deterministic cues, but not probabilistic, dwell time was increased for the eventual choice and dwell-time was reduced under high reward. Taken together, results show that the underlying mechanisms of pupil dilation and gaze, depend to some extent on cue certainty. Turning to feedback results, across both experiments, whereas pupil dilation was highest following Error feedback, average dwell time on Error feedback text was lowest, suggesting individuals are aroused following error-related feedback but look away, perhaps to protect their affective motivation or focus on the task. Overall results show that uncertain reward cues may alter pupil-linked arousal and attention as compared to certain reward, highlighting the role of uncertainty as an important modulator affecting attention and reward processing in environments that demand cognitive flexibility.