Reward uncertainty shapes cognitive flexibility

Recent work has shown that dynamics in reward value is an important driver of the stability-flexibility tradeoff. However, these studies have only examined deterministic reward, while real-world reward is predominantly uncertain and volatile in nature. Therefore, this study aimed to test how reward uncertainty shapes cognitive flexibility. Uncertainty was manipulated by varying the validity of reward cues through stochastic probabilistic reward schedules. Participants performed a voluntary task switching paradigm with performance-contingent monetary reward at two levels. We used linear mixed models in a large (n=616) undergraduate student sample that enabled us to examine individual differences in how gender and personality influence reward-guided task selection. In line with previous work, we observed a reliable effect of reward transition on flexibility, with more flexible task choices when rewards changed from trial-to-trial and more stability when rewards were stable. Critically, this effect decreased linearly with increasing reward uncertainty. Better than expected high reward outcomes were associated with even greater flexibility than expected high outcomes, however, the reverse was not observed for worse than expected outcomes. At higher levels of reward uncertainty, female participants relied more on recent reward outcomes than cues. Overall, males were more influenced by reward transition than females. Perhaps counterintuitively, reward transition effects on flexibility were most apparent in participants with low levels of reward responsiveness. Our findings suggest that reward uncertainty is a key context that tunes the translation of outcomes into future choices.