Attentional mechanisms are required to select relevant and to filter out irrelevant information from cluttered visual scenes. In my laboratory we are studying the neural basis underlying these processes using functional brain imaging, behavioral performance measures, and electrophysiology in humans and non-human primates. Using these techniques, we have found that neural mechanisms of selective attention operate at multiple stages in the visual system, including cortical and subcortical stages. The modulatory effects of attention at each stage appear to be determined by the visual processing capabilities of that stage. These attention signals are not generated in the visual system, but in a distributed network of higher-order areas in frontal and parietal cortex that exerts top-down control via feedback projections.

In our most recent work, we have begun to complement the studies on attentional mechanisms in the human brain with studies in non-human primates using newly developed imaging techniques, which utilize fMRI to measure brain activity in awake monkeys performing visual tasks. The long-term goal of these studies is to use fMRI in monkeys in combination with fMRI-guided lesions and single-cell physiology to derive an animal model of visuo-spatial hemineglect, an attentional deficit.