Coordinated target selection for ocular orienting and tracking movements

Goal directed movements often require the coordination of multiple movement systems of the brain. For example, when we track the motion of a moving target with our eyes, we use two different movement systems: saccadic and pursuit. A saccade is a rapid movement of the eye that orients the eye to a target. A smooth pursuit is a tracking movement that moves the eye along with the target. These two movement systems have mostly separate neural circuitry. When multiple moving targets are available for tracking, the choice of tracking target must be coordinated between them. This thesis uses behavioral and neurophysiological techniques to analyze how saccades and pursuit coordinate target selection.; In a set of behavioral experiments, we find that target choice for saccades and smooth pursuit is temporally linked. Monkeys are allowed to track either one of two moving targets. We find that initial pursuit tracking occurs in a non-selective vector-average direction. Immediately after a targeting saccade pursuit becomes target selective. This temporal linkage between targeting saccades and target selective pursuit could be explained by two different models. In one, a central process tells both saccadic and pursuit systems which target is selected in parallel. An alternative, serial model, would have saccadic signals playing a direct causal role in selecting targets for the pursuit system. The behavioral data cannot distinguish between these two different hypothetical models.; In a set of neurophysiological experiments, we directly test the serial model. We evoke saccades through microstimulation of the frontal eye field to one of two moving targets before the time the monkey would naturally make a saccade. If the serial model is correct, then pursuit immediately after the evoked saccade should be selective for the target of the saccade. If, on the other hand, pursuit after the evoked saccade is still vector-averaging, we have evidence against the serial model. We find that pursuit after evoked saccades is just as selective for the saccade target as is pursuit after naturally occurring saccades. We conclude that target selection can be a serial process in which one movement system can select the target for another.