Location- or feature-based targeting of peripheral attention.

Using event-related fMRI we determined the differential effects of feature- versus location-based cues for directing peripheral attention. Pairs of same-color targets appeared on the left and on the right. A predictive cue indicated whether the subsequent targeting of attention would be based on location (left versus right) or color (red versus blue). Subjects had to press a button when the relevant pair of targets (in the cued side of space or of the cued color) were identical in shape. The feature-based cue thus also led to a "global" expectancy of targets on either side of space whereas the location-based cue elicited a more "focal" expectancy limited to one side of space. The right inferior parietal lobule was more active when attention was targeted on the basis of location than of color. There was no difference between left-sided or right-sided attention in this region, indicating that it mediated the targeting to both sides of space. These results show that the right inferior parietal cortex plays a relatively selective role in mediating location-based and spatially focal modes of attentional deployment. Its relatively equal activation for leftward and rightward attentional shifts is also consistent with models of right hemispheric dominance of spatial attention.