This project explores how attention in normal individuals is mediated by the inter- action of the attention systems of the cerebral hemispheres. There is considerable evidence that the hemispheres differ in their attentional characteristics, but it is not known how the single "spotlight" of attention that we experience emerges from the interaction of the hemispheres. This project will help advance our understanding of the relationship between brain and mind, and will ultimately help us to understand the effects of brain damage on cognitive function. Interhemispheric interaction in visuo- spatial attention will be studied with brain event-related potentials (ERPs) and standard behavioral measures. Measurements of ERP components will permit the study of neural systems involved in various types of attentional processing. Measures of "hemispheric utilization bias", which is likely to be an important factor in interhemispheric interaction, will also be used. The proposed experiments examine different aspects of interhemispheric interaction in attention: the processing stages involved, the influence of task difficulty and stimulus probability, trial-to-trial switching, and the shifting of attention. Through this research, we aim to develop a model of how attention is mediated by interhemispheric interaction.