Temporal Development of Asymmetric Reward-Induced Bias in Macaques

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Abstract
Time and expected outcome are two ubiquitous factors contributing to decision-making. However, it is unclear how they interact to influence motor responses. When two differential reward outcomes are expected at the end of a waiting period, behavioral bias is consistently induced, manifested as shorter latencies for motor responses associated with the preferred reward. To examine how this bias develops in time during the waiting period, we manipulated the duration of the waiting period in an asymmetric reward saccade task in monkeys. We found that the bias increases with the duration of waiting period. Surprisingly, the bias resulted from gradual suppression of saccades to nonpreferred targets rather than from facilitation of saccades to preferred targets. These results have important implications on the neural correlates of reward-induced bias.