Influence of reward history on visual working memory representations

Reward is a strong determinant of human and non-human behavior, influencing the exploration of the world around us and our interactions with it. Interestingly, the impact of reward and reward-associated objects is not limited to strategic changes in approach behavior or attention deployment, but also extends to situations in which prioritizing processing of such objects is not necessarily advantageous for current goals. In spite of converging evidence for the automatic influence of reward on attentional deployment, less is known about the impact of reward on other cognitive processes. In this thesis I describe a first attempt to investigate the influence of reward in encoding and maintenance of visual representations in working memory. Throughout this thesis I argue that once objects have been associated with a positive outcome in past encounters, they are preferentially encoded and maintained in visual working memory (VWM) even when reward is no longer provided or when there is no consistent pairing between reward feedback and target identity. In Chapters 2 and 3 I demonstrate that reward associated objects interfere with the visual representations of less valuable items maintained in VWM. This interference was already present starting 10 ms from the offset of the memory display suggesting that valuable objects directly affected the encoding of less valuable items. This robust phenomenon was observed at different delays, both when reward-associated objects were task-relevant and when they were not, and was independent of object salience. However, the interference disappeared when task requirements for target selection increased suggesting that items with a positive reward history can effectively capture attention and interfere with VWM representations only when cognitive resources are not exhausted by the main task (Chapter 3). In the last study presented in this thesis I explored the possibility that reward could impact VWM beyond target selection and encoding, namely influencing the active maintenance process. To investigate this hypothesis I measured reward priming effects on event-related potential (ERP) indices of selective attention – the N2pc - and visual working memory maintenance – the CDA (contralateral delay activity). Results indicate that reward modulated CDA only, speaking for a discrete effect of reward on VWM maintenance. While the precise nature of such modulation is still unknown, these results suggest that reward history might influence the precision or the duration of visual representations maintained in VWM. Further studies are necessary to directly test this hypothesis, but these initial results suggest an interesting direction for future research in better characterizing the nature and extent of the influence of reward history on visual cognition.