Functional Imaging of Crossmodal Spatial Representations and Crossmodal Sapatial Attention

This chapter reviews recent functional imaging studies using positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) to study crossmodal attention and integration. It first describes how these techniques have allowed the mapping of regions in the human brain that apparently respond to the stimulation of only one sensory modality (unimodal brain areas), versus those responding to stimulation in two or more different modalities (multimodal brain areas). It then considers the extent to which activation in these areas depends on the spatial location of the stimulus. The typical results highlight a hierarchical organization for stimulus processing in the human brain, with early cortical areas in sensory pathways appearing as unimodal and spatially specific. Higher-order areas respond to stimulation in multiple modalities, with some of these areas showing responses that are less dependent on the spatial location of the stimulitested. Such observations appear consistent with feedforward convergence as one potential mechanism for multisensory integration.