Selective spatial attention in vision and touch: unimodal and multimodal mechanisms revealed by PET.

Two positron-emission tomography (PET) experiments explored the neural basis of selective spatial attention in vision and touch, testing for modality-specific versus multimodal activations due to attended side. In the first study, either light flashes or finger vibrations were presented bilaterally. Twelve healthy volunteers were scanned while sustaining covert attention on the left or right hemifield within each modality. The main effect for attending right minus left, across both modalities, revealed bimodal spatial attention effects in the left intraparietal sulcus and left occipitotemporal junction. Modality-specific attentional effects (again, for attending right vs. left) were found in the left superior occipital gyrus for vision, and left superior postcentral gyrus for touch. No significant activations were seen for attending left minus right. The second study presented only tactile stimuli, manipulating whether the eyes were open or closed, and including passive stimulation and rest baselines. The unimodal activation for tactile spatial attention in the left superior postcentral gyrus was replicated. The bimodal activation of the left intraparietal sulcus observed in the first study was now found for touch, but only when the eyes were open (hands visible), apparently confirming its multimodal nature. These results reveal mechanisms of sustained spatial attention operating at both modality-specific and multimodal levels.