First, subjects will participate in an fMRI experiment (93-M-0170) designed to localize the cortical regions of interest (ROIs) that are involved with attentional processing for each subject. Second, TMS will be used to create transient virtual disruptions in frontal and parietal ROIs of normal volunteers while they perform a task requiring spatial attention. We hypothesize that, when TMS is used to interfere with attentional processing, subjects will show impaired performance in a task that requires them to filter out irrelevant visual information. In contrast, performance during TMS should not suffer in a control task in which no irrelevant information needs to be filtered out.