Visual orienting can be either generated voluntarily via cognitive control or evoked externally (reflexively) via stimulus-driven processes. In addition, orienting may be either covert (attentional shifts) or overt (eye movements). We have proposed a tonic inhibition model of attention and orienting that details specific neural substrates for these processes and their interactions. Given the known disruption of the basal ganglia and frontal lobes in Parkinson's disease (PD), this population represents an ideal test of the model. This proposal will thus carry out a systematic investigation of orienting in PD, and will be the first study to comprehensively examine performance across both of these dimensions (i.e., voluntary vs. reflexive and covert vs. overt) in this population. In the first section we will compare voluntary and reflexive overt orienting in PD and control subjects. Based on our and others' previous research, we expect PD subjects to be deficient in voluntary eye movements but, under certain conditions, to be more efficient in reflexive eye movements. In a second section, we will examine the relative importance of deficient working memory vs. failure to inhibit irrelevant information in explaining poor voluntary performance in PD, both factors having been often proposed as possible explanations for poor performance on voluntary tasks. A third section of the proposal will compare voluntary and reflexive attention in PD and control subjects. No previous study in PD has examined reflexive spatial attention independent of voluntary spatial attention. The final section of the proposal will study the effect of different sensorimotor transformations on visuospatial attention in PD. We have previously found that simple or direct stimulus-response (S-R) mappings show a different attentional time course than do more complex, indirect S-R mappings. PD patients have difficulties with some visuomotor transformations. Hence, we will examine and compare the effects of S-R mappings on attentional paradigms in PD and control subjects. All proposed experiments would systematically manipulate medication status of the PD subjects to clarify the role of medication in alleviating orienting dysfunctions in PD. Despite its obvious importance, we are unaware of any overt or covert orienting studies that have examined this issue. Finally, the results of this proposal will have important implications for our understanding and modeling of the relation between attention and overt orienting.