Vp. Ferrera et Sg. Lisberger, ATTENTION AND TARGET SELECTION FOR SMOOTH-PURSUIT EYE-MOVEMENTS, The Journal of neuroscience, 15(11), 1995, pp. 7472-7484
Two rhesus monkeys were trained to track a small moving target in the
presence of a moving distracter. The target and distracter were distin
guished by their color. Smooth pursuit eye movements were quantified i
n terms of the latency of the eye movement and the open-loop eye accel
eration profile. Smooth pursuit latencies for single targets were on t
he order of 100 msec. When the target was paired with a distracter mov
ing in the same direction as the target, pursuit latencies decreased t
o roughly 85 msec. When the target was paired with a distracter moving
in the opposite direction, pursuit latencies increased to roughly 150
msec. The motion of the distracter had no significant effect on the e
ye acceleration profile. Experiments were performed to dissociate visu
al search for the target from pursuit initiation by providing a spatia
l cue rather than the color cue, These experiments showed that visual
search necessarily preceded pursuit initiation only when the distracte
r moved in the opposite direction relative to the target. In this case
, visual search contributed about 25 msec to the overall latency of pu
rsuit. Control experiments showed that the monkey need not attend to t
he distracter in order for it to influence the latency of pursuit. A n
etwork model was developed in which units that represent the motions o
f the target and distracter compete against one another. Attention ser
ves to bias the outcome of this competition toward the direction of th
e selected target. The performance of this network exhibits a striking
parallel to the effect of the distractor on smooth pursuit latency.