Abstract
Reward associated with a saccade-target location increases movement vigor — how soon and how fast the eyes move to their target. Because each eye-movement is preceded by a shift of attention to the saccadic target prior to saccade onset, we hypothesized that increased movement vigor may require a corresponding change in pre-saccadic attention, that is, an earlier and more pronounced increase in visual sensitivity at the target before saccade onset. To investigate this, we manipulated reward for movement speed in a dual-task paradigm designed to assess the time course of pre-saccadic attention. While observers fixated a black fixation point, a change in its color indicated the maximum reward possible in a trial (0, 1, or 10 cents). After a 200-ms delay, a saccade cue indicated to which of three stimulus locations observers had to make a saccade. To assess pre-saccadic attention, we embedded an oriented Gabor patch (50ms-200ms before saccade onset) in a stream of dynamic noise and, upon saccade landing, observers reported its orientation. After each trial, observers received feedback of reward payoffs as a function of movement speed (independent of perceptual performance). Movement vigor (total movement time relative to amplitude) was enhanced in high- as compared to low and no-reward conditions. Saccade direction mediated this effect, as reward affected vertical saccades more strongly than horizontal saccades. Moreover, individual differences in movement vigor predicted the magnitude of pre-saccadic sensitivity, an association that was particularly pronounced in the high-reward condition. These results point to an influence of reward on the visual system beyond motor control: To deal with changes of vigor in response to reward the active visual system may regulate visual sensitivity at the saccadic target as a function of the predicted outcome, just milliseconds before saccade onset.