Intermodal attention modulates visual processing in dorsal and ventral streams.

Attending to visual objects while ignoring information from other modalities is necessary for performing difficult visual discriminations, but it is unclear how selecting between sensory modalities alters processing within the visual system. We used an audio-visual intermodal selective attention paradigm with fMRI to study the effects of visual attention on cortical activity in the absence of competitive interactions between multiple visual stimuli. Complex stimuli (faces and words) activated higher visual areas even in the absence of visual attention. These stimulus-dependent activations (SDAs) covered foveal retinotopic cortex, extended ventrally to the anterior fusiform gyrus and dorsally to include multiple distinct foci in the intraparietal sulcus (IPS). Attention amplified the baseline response in posterior retinotopic regions and altered activity in different ways in the extrastriate dorsal and ventral pathways. The majority of the IPS was strongly and exclusively activated by visual attention: attention-related modulations (ARMs) encompassed and spread well beyond the focal SDAs. In contrast, in the fusiform gyrus only a small subset of the regions activated by unattended stimuli showed ARMs. Ventral cortex was also heterogeneous: we found a distinct ventrolateral region in the occipitotemporal sulcus (OTS) that was activated exclusively by attention, showing neither SDAs nor any significant stimulus preferences. Attention-dependent activations in the IPS and the OTS suggest that these regions play critical roles in intermodal visual attention.