Attention to simultaneous unrelated auditory and visual events: behavioral and neural correlates.

The cognitive and neural bases of the ability to focus attention on information in one sensory modality while ignoring information in another remain poorly understood. We hypothesized that bimodal selective attention results from increased activity in corresponding sensory cortices with a suppression of activity in non-corresponding sensory cortices. In a functional magnetic resonance imaging (fMRI) study, we presented melodies and shapes alone (unimodal) or simultaneously (bimodal). Subjects monitored for changes in an attended modality while ignoring the other. Subsequently, memory for both attended and unattended stimuli was tested. Subjects remembered attended stimuli equally well in unimodal and bimodal conditions, and significantly better than ignored stimuli in bimodal conditions. When a subject focused on a stimulus, the blood-oxygen-level-dependent (BOLD) response increased in sensory cortices corresponding to that modality in both unimodal and bimodal conditions. Additionally, the BOLD response decreased in sensory cortices corresponding to the non-presented modality in unimodal conditions and the unattended modality in bimodal conditions. We conclude that top-down attentional effects modulate the interaction of sensory cortical areas by gating sensory input. This interaction between sensory cortices enhances processing of one modality at the expense of the other during selective attention, and subsequently affects memory encoding.