Paul van Donkelaar - US grants

Humans can very accurately follow moving visual targets using smooth pursuit eye movements. The objective of the proposed research is to gain a better understanding of the contribution of attention to this process. A new dual-task paradigm has been developed for this purpose. Subjects will be asked to follow a moving visual target with smooth pursuit eye movements while reacting to the appearance of a second peripheral target by pressing a button. Any systematic variations in the latency of the button pressing will be inferred to be due to alterations in the allocation of attention around the pursuit stimulus. By varying the timing of appearance, location, and eccentricity of the peripheral target relative to the pursuit stimulus it will be possible to examine how attention is distributed during pursuit responses. In addition, by changing the speed of the pursuit stimulus itself within this dual-task paradigm it will be possible to assess how attentional allocation changes as a function of the characteristics of the target being pursued. Finally, by manipulating where subjects direct their attention by the use of precues it will be possible to assess how perturbing the normal spatial allocation of attention influences smooth pursuit output. The overall results should provide a better understanding of how attention and smooth pursuit eye movements interact. This could prove useful in the design of systems and training of persons for situations in which smooth pursuit responses are typically elicited (e.g. pilots, assembly line workers). In addition, the paradigm itself could be used to understand in more detail the relationship between attentional deficits and declines in smooth pursuit output in schizophrenic individuals and children with attention deficit hyperactivity disorder.

The objective of this research is to gain a better understanding of the brain mechanisms underlying sensory-motor adaptation. Humans display a remarkable ability to adapt to a new situation, especially when available sensory information conflicts. Behaviorally, this adaptive ability has been well described. One way researchers have investigated this adaptation is by having subjects attempt to manually point at a visual target while wearing prism goggles. Initial reaching attempts are inaccurate because the prism systematically bends the light before it enters the eyes such that the target appears to shift left or right of its actual location. However, with repeated trials, the subject is able to adapt to the altered visual input and generate accurate responses. When the goggles are removed there is an aftereffect in which the reaching responses are inaccurate in the opposite direction to that observed during the prism exposure period. Based on these behavioral characteristics of prism adaptation, recent neurophysiological, clinical and human brain imaging studies have begun to identify the network of brain sites that contribute to this simple form of learning, but a more complete understanding of the potentially different contributions of the network's components is required. This goal will be accomplished by examining the degree to which adaptation is disrupted in normal, healthy human subjects when transcranial magnetic stimulation (TMS) is applied over the cerebellum, posterior parietal cortex, or premotor cortex during the training period. It is predicted that TMS delivered over each of these sites will have different effects on the degree of adaptation that occurs depending upon when the stimulation is given and the availability of visual feedback from the hand. In addition to expanding our basic understanding of the nature of sensorimotor adaptation and its underlying mechanisms, the proposed research may also be useful in contributing to the design of motor rehabilitation therapies.