Target selection for voluntary eye movements

Eye movements determine the location of the fovea in visual space. By selecting where to look next, eye movements control which objects are rendered in detail on the retina. The still snapshots acquired between saccadic movements and panned images taken during smooth pursuit are then pieced together to create the subjective experience of our visual environment. Eye movement decisions fill in the visual world by selecting informative objects and drawing them onto their position in visual space.; The experiments presented here address basic questions about how eye-movement targets are selected. Are time-evolving decision signals shared by the two eye movement systems? How are these systems coordinated to ensure that a single target is tracked? How is the competition between visual targets mediated? How does this process take place in neural hardware?; The first chapter presents the results of a psychophysical experiment that compared the performance of the pursuit and saccadic system on a visual discrimination task. Chapter 2 follows up this question with a task that asks whether pursuit and saccades obey the same tradeoff between speed and accuracy. In Chapter 3, a model is presented that describes the competitive mechanism that takes place between potential saccade targets, which can describe both the proportion of correct responses as well as the latency distributions of correct and error responses. Chapter 4 presents a single unit recording study that assesses how prior information and sensory information modulate the activity of neurons in the superior colliculus.; The results of these support the hypothesis that both pursuit and saccade decisions are coordinated by activity present in a time-evolving salience map. When multiple potential targets exist, decision signals race against one another in a winner-take-all competition to trigger the eye movement. The modeling study suggests that decision signals rise at a rate proportional to the strength of the evidence available, which can account for both the performance and timing of saccadic eye movements on a simple discrimination task. When we record from single units on this task, however, the neurons involved in saccade target selection reveal a more interesting and complicated picture of this mechanism.