In everyday life the deployment of attention in the visual field is thought to be under the joint control of voluntary and reflexive orienting systems. The focus of this proposal is to examine the processes and brain structures involved in coordinating and integrating these systems. Chronometric measures of detection reaction time and accuracy will be collected from healthy human subjects and neurologic patients with lesions in brain areas known to be involved in visual attention. The studies with healthy subjects will test the hypothesis that, under conditions of competition, voluntary control over reflexive orienting is achieved through inhibitory processes. The patient studies will identify the neural mechanisms responsible for mediating and coordinating between these two forms of orienting. Specifically, the patient studies will: a) Explore the role of Dorsolateral Prefrontal and Temporal-Parietal Junction cortex in exerting voluntary. control over the reflexive system; b) Define the role of the Extra-Geniculate Midbrain pathways in mediating reflexive orienting; and c) Explore in Hemispatial Neglect patients whether stimuli that are not consciously perceived activate the reflexive and voluntary systems differentially. The current project will further our knowledge of the automatic and controlled attentional systems and the brain structures that subserve them. In addition, it will develop a biological framework for the issue of automaticity and control.
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