Saccade Vigor Reflects Rise of Decision Variables during Deliberation
During deliberation, as we quietly consider our options, the neural activities representing the decision variables that reflect the goodness of each option rise in various regions of the cerebral cortex. If the options are depicted visually, deliberation includes saccades that repeatedly focus gaze on each option, raising the possibility that saccade kinematics may be affected by the state of the decision variables. To test this idea, we engaged human subjects in a decision-making task in which they considered two effortful walking options. As they deliberated, they made saccades between the symbolic representations of the options. Their saccades had no bearing on the effort that they would later expend, yet saccade velocities increased gradually and differentially: the rate of rise was faster for saccades toward the option that they later indicated as their choice. Indeed, the rate of rise encoded the difference in the subjective value of the two options. Importantly, the subjects did not reveal their choice when deliberation ended. Rather, following a delay period, they did so by making another saccade. Remarkably, vigor for this saccade dropped to baseline and no longer encoded subjective value. Thus, saccade vigor appeared to provide a real-time window to an otherwise hidden process of option evaluation during deliberation.