Saccades modulate the relationship between visual motion and smooth eye movement. Before a saccade, pursuit eye movements reflect a vector average of motion across the visual field. After a saccade, pursuit primarily reflects the motion of the target closest to the endpoint of the saccade. We tested the hypothesis that the saccade produces a spatial weighting of motion around the endpoint of the saccade. Using a moving pursuit stimulus that stepped to a new spatial location just before a targeting saccade, we controlled the distance between the endpoint of the saccade and the position of the moving target. We demonstrate that the smooth eye velocity following the targeting saccade weights the presaccadic visual motion inputs by the distance from their location in space to the endpoint of the saccade, defining the extent of a spatiotemporal filter for driving the eyes. The center of the filter is located at the endpoint of the saccade in space, not at the position of the fovea. The filter is stable in the face of a distracter target, is present for saccades to stationary and moving targets, and affects both the speed and direction of the postsaccadic eye movement. The spatial filter can explain the target-selecting gain change in postsaccadic pursuit, and has intriguing parallels to the process by which perceptual decisions about a restricted region of space are enhanced by attention. The effect of the spatial saccade plan on the pursuit response to a given retinal motion describes the dynamics of a coordinate transformation.

All ethologically-relevant behavior is dynamic, and biological in origin. To understand the neural underpinnings of motor behavior is then to quantify the limitations placed on organisms as they move through and interact with their environment. This thesis stands as an attempt to understand the way the brain processes information to prepare for movement, and how a network of neurons might give rise to that movement. I chose to investigate oculomotor tracking in non-human primates as a model behavior that allowed excellent spatial and temporal control over the stimulus. First, by carefully controlling the motion of a single target, and measuring the eyes' response to particular perturbations, I mapped out effective constraints on the way the brain processes target motion to guide smooth eye movements. The next set of experiments was motivated by the observation that no two tracking movements are alike, even when faced with identical stimuli. I establish the dynamic relationship between fluctuations in single neurons recorded in the frontal eye fields and concomitant behavioral fluctuations. Utilizing measurements of the covariation between simultaneously recorded neurons, I describe the properties of the network of cells which give rise said fluctuations, which is likely dominated by fluctuations in a small subset of the active population at any moment in time. Taken together, the work I've done first establishes that proper oculomotor tracking likely takes the form of a re-allocation of cortical resources, but one that may be dominated by the activity of a small number of cortical neurons.