Influence of expected reward on perceptual decision making

Perceptual decision making is influenced by reward expected from alternative choice options or actions, but the underlying neural mechanisms are currently unknown. More specifically, it is debated whether reward effects are mediated through changes in sensory processing or later stages of decision making, or both. To address this question, we conducted two experiments in which male and female human subjects made saccades to what they perceived to be the first or second of two identical, but asynchronously presented targets with different expected reward. We found similar shifts in target selection between the two experiments indicating that expected reward did not influence sensory processing and, instead, caused response bias. Moreover, the observed response bias was suboptimal and independent of an individual9s sensitivity to sensory signals. To elucidate underlying neural mechanisms, we simulated our experiments with a cortical network model based on alternative mechanisms for how reward could exert its influence. We found that our observations are most compatible with reward-dependent input to the output layer of the decision circuit. Together, our results suggest that during a temporal judgment task, reward information influences perceptual choice by changing later stages of decision making rather than early sensory processing.