Timing the anticipatory recovery in smooth ocular pursuit during the transient disappearance of a visual target.

After the disappearance of a moving target and the loss of visual feedback regarding image motion, smooth pursuit eye velocity decays rapidly. If, however, there is an expectation the target will reappear further along its trajectory, there is a scaled recovery in eye velocity before target reappearance. The aim of this study was to examine whether the timing of the anticipatory recovery is influenced by the duration of transient target disappearance. We found that subjects (N=6) did not maintain eye velocity close to target velocity throughout the inter-stimulus interval (ISI). In general, after an initial reduction in eye velocity a significant increase was observed for most subjects before target reappearance, or a recovery that halted the decay. The timing of the recovery was not influenced by ISI even when this was predictable. There was, however, a significant effect of the initial visible ramp duration, indicating that the recovery was a consequence of the previous eye velocity trajectory and subsequent reacceleration. We suggest, therefore, that the recovery was timed to the moment of target disappearance rather than reappearance, and was the result of reactivation of a variable gain mechanism that acts on the visuomotor drive to ocular pursuit.