Target selection for predictive smooth pursuit eye movements

Previous work has indicated that after exposure to a moving stimulus, people are able to produce predictive smooth eye movements prior to reappearance of the stimulus. Here, we investigated whether subjects are able to extract relevant velocity information from two simultaneously presented targets and use this information to produce a subsequent predictive response. A trial consisted of a series of two or five presentations of moving stimuli, preceded 500 ms earlier by an audio warning cue. In the first one or four presentations, subjects fixated during the presentation of two moving targets and in the final presentation they tracked a single moving target. During fixation, two moving targets were presented concurrently, originating from the fixation point and moving horizontally to the right at differing velocities (10, 20, 30 or 40 degrees /s), with each target being presented at the same velocity throughout a trial. In the tracking presentation, the fixation cross was extinguished and only a single target was presented, which the subjects were required to track with their eyes. To cue which of the two targets would be presented, the appropriate target was presented statically at the same time as the audio warning cue. A significant relationship was found between eye velocity 100 ms after the start of the tracking target (i.e. prior to visual feedback) and the cued target velocity. Thus, subjects were able to make predictive eye movements that were of appropriate velocity for the cued target, despite fixating and being uncertain which target was relevant, during previous exposure.