The Relationship between Saccadic Choice and Reaction Times with Manipulations of Target Value

Choosing the option with the highest expected value (EV; reward probability × reward magnitude) maximizes the intake of reward under conditions of uncertainty. However, human economic choices indicate that our value calculation has a subjective component whereby probability and reward magnitude are not linearly weighted. Using a similar economic framework, our goal was to characterize how subjective value influences the generation of simple motor actions. Specifically, we hypothesized that attributes of saccadic eye movements could provide insight into how rhesus monkeys, a well-studied animal model in cognitive neuroscience, subjectively value potential visual targets. In the first experiment, monkeys were free to choose by directing a saccade toward one of two simultaneously displayed targets, each of which had an uncertain outcome. In this task, choices were more likely to be allocated toward the higher valued target. In the second experiment, only one of the two possible targets appeared on each trial. In this task, saccadic reaction times (SRTs) decreased toward the higher valued target. Reward magnitude had a much stronger influence on both choices and SRTs than probability, whose effect was observed only when reward magnitude was similar for both targets. Across EV blocks, a strong relationship was observed between choice preferences and SRTs. However, choices tended to maximize at skewed values whereas SRTs varied more continuously. Lastly, SRTs were unchanged when all reward magnitudes were 1×, 1.5×, and 2× their normal amount, indicating that saccade preparation was influenced by the relative value of the targets rather than the absolute value of any single-target. We conclude that value is not only an important factor( )for deliberative decision making in primates, but also for the selection and preparation of simple motor actions, such as saccadic eye movements. More precisely, our results indicate that, under conditions of uncertainty, saccade choices and reaction times are influenced by the relative expected subjective value of potential movements.