Seminar Friday, October 17


Elio Santos, Ph.D.
Post Doctoral Research Associate
Department of Biomedical Engineering


Anticipatory smooth eye movements elicited by cues


Anticipatory eye movements are important when tracking the motion of a target because they help overcome inevitable sensorimotor delays.  Understanding the processes that govern anticipatory eye movements can reveal how motion signals of a target and anticipatory signals are combined to produce a response that facilitates the tracking of moving objects.  In order to determine whether the perceptual qualities of cues affect anticipatory eye movements, different types of cues were compared.  Subjects pursued a disc that moved inside an inverted Y-shaped tube.  Three cues were tested: (1) Natural: barrier that blocked the untraveled path; (2) Arbitrary/local: bar at the top of the tube indicated the path by being on the same side. (3) Arbitrary/global: color of the tube (red or green) indicated the path.  (4) Symbolic cue: arrow pointing to the future direction of motion of the disc. Three experiments tested the sensitivities of the oculomotor system to cue properties, namely, effectiveness in overwriting past history of target motion, cue delay, cue removal, and cue validity.  The barrier cue produced faster anticipatory eye movements than the arbitrary cues, and overwrite the effects of past history of target motion (Experiment 1).  Delaying the presentation of the cue until the disc approached the choice point decreased anticipatory eye velocity for all cues (Experiment 2).  Removing the cues after the onset of target motion (so that only memory of the cue was available) had no effects with arbitrary cues, but reduced anticipatory pursuit substantially for the barrier cue.  When the validity of the barrier cue was reduced so that the moving disc crashed through the barrier, the cue became ineffective (Experiment 3).  The results of all three experiments indicate that the perceptual qualities of cues are important for anticipatory eye movements, even when the directional information conveyed is the same.  This suggest different mechanisms are involved.  One mechanism may depend on arbitrary associations that can be learned.  Another mechanism evoked by naturalistic cues, such as the barrier, may be responsible for producing higher anticipatory eye velocities.