The Journal of Neuroscience, March 15, 2001, 21(6):2075-2084
Linked Target Selection for Saccadic and Smooth Pursuit Eye
Movements
Justin L.
Gardner and
Stephen G.
Lisberger
Howard Hughes Medical Institute, Department of Physiology, W. M. Keck Foundation Center for Integrative Neuroscience, and
Bioengineering Graduate Group, University of California, San Francisco,
California 94143
In natural situations, motor activity must often choose a single
target when multiple distractors are present. The present paper asks
how primate smooth pursuit eye movements choose targets, by analysis of
a natural target-selection task. Monkeys tracked two targets that
started 1.5° eccentric and moved in different directions (up, right,
down, and left) toward the position of fixation. As expected from
previous results, the smooth pursuit before the first saccade reflected
a vector average of the responses to the two target motions
individually. However, post-saccadic smooth eye velocity showed
enhancement that was spatially selective for the motion at the endpoint
of the saccade. If the saccade endpoint was close to one of the two
targets, creating a targeting saccade, then pursuit was selectively
enhanced for the visual motion of that target and suppressed for the
other target. If the endpoint landed between the two targets, creating
an averaging saccade, then post-saccadic smooth eye velocity also
reflected a vector average of the two target motions. Saccades with
latencies >200 msec were almost always targeting saccades. However,
pursuit did not transition from vector-averaging to target-selecting
until the occurrence of a saccade, even when saccade latencies were >300 msec. Thus, our data demonstrate that post-saccadic enhancement of pursuit is spatially selective and that noncued target selection for
pursuit is time-locked to the occurrence of a saccade. This raises the
possibility that the motor commands for saccades play a causal role,
not only in enhancing visuomotor transmission for pursuit but also in
choosing a target for pursuit.
Key words:
selective attention; visual motion processing; gain
control; movement initiation; vector averaging; winner-take-all
Copyright © 2001 Society for Neuroscience 0270-6474/01/2162075-10$05.00/0