Volitional scaling of anticipatory ocular pursuit velocity using precues.

Human subjects cannot normally perform smooth eye movements in the absence of a target. However, the repeated presentation of identical, transient target motion stimuli, preceded by warning cues, leads to the build up of anticipatory smooth pursuit (ASP) eye movements several hundred milliseconds prior to stimulus onset. The present study sought to investigate whether subjects are able to volitionally scale ASP speed, as well as select pursuit direction, in advance of target motion stimuli of random direction (left vs. right) and speed (10, 20, 30 and 40 degrees /s), given stationary precues predictive of both these target parameters. The subjects' success at this task is discussed in terms of their ability to volitionally scale the internal store of target velocity information postulated to drive ASP.