| Oculomotor tracking of moving objects is an important component of visually based cognition, planning, and decision-making. The eye has a fovea with high visual acuity that must be moved efficiently across a scene to see and understand it well. Ballistic or saccadic eye movements, by themselves, would greatly diminish the amount of time that the fovea fixates objects of interest. The brain intelligently coordinates saccades with smooth pursuit eye movements to maximize the amount of time that a moving target is foveated. In particular, the saccadic and smooth pursuit systems interact to often choose the same target, and to maximize its visibility through time. How does the brain coordinate these two types of eye movements to track objects that move in unpredictable directions and speeds? How do multiple brain regions interact, including frontal cortical areas, to decide the choice of a target among several competing moving stimuli? How can these insights be used to develop more effective machine tracking methods? Saccadic eye movements rapidly foveate peripheral visual or auditory targets, and smooth pursuit eye movements keep the fovea pointed toward an attended moving target. Analyses of tracking data in monkeys and humans reveal systematic deviations from predictions of the simplest model of saccade-pursuit interactions, which would use no interactions other than common target selection and recruitment of shared motoneurons. Instead, saccadic and smooth pursuit movements cooperate to cancel errors of gaze position and velocity, and thus to maximize target visibility through time. How are saccades calibrated to correctly foveate a target despite its continued motion during the saccade? A neural model is developed in this thesis to provide answers to such questions. The modeled interactions encompass motion processing areas MT, MST, FPA, DLPN and NRTP; saccade planning and execution areas FEF, SNr and Sc; the saccadic generator in the brain stem; and the cerebellum. Simulations illustrate the model's ability to functionally explain and quantitatively simulate anatomical, neurophysiological and behavioral data about saccade-pursuit target tracking. |
