Reward boosts working memory encoding over a brief temporal window
Wallis G., Stokes MG., Arnold C., Nobre AC.
© 2015 Taylor & Francis. Selection mechanisms for WM are ordinarily studied by explicitly cueing a subset of memory items. However, we might also expect the reward associations of stimuli we encounter to modulate their probability of being represented in working memory (WM). Theoretical and computational models explicitly predict that reward value should determine which items will be gated into WM. For example, a model by Braver and colleagues in which phasic dopamine signalling gates WM updating predicts a temporally-specific but not item-specific reward-driven boost to encoding. In contrast, Hazy and colleagues invoke reinforcement learning in cortico-striatal loops and predict an item-wise reward-driven encoding bias. Furthermore, a body of prior work has demonstrated that reward-associated items can capture attention, and it has been shown that attentional capture biases WM encoding. We directly investigated the relationship between reward history and WM encoding. In our first experiment, we found an encoding benefit associated with reward-associated items, but the benefit generalized to all items in the memory array. In a second experiment this effect was shown to be highly temporally specific. We speculate that in real-world contexts in which the environment is sampled sequentially with saccades/shifts in attention, this mechanism could effectively mediate an item-wise encoding bias, because encoding boosts would occur when rewarded items were fixated.