We used high-field (3T) functional magnetic resonance imaging (fMRI) to label cortical activity due to visual spatial attention, relative to flattened cortical maps of the retinotopy and visual areas from the same human subjects. In the main task, the visual stimulus remained constant, but covert visual spatial attention was varied in both location and load. In each of the extrastriate retinotopic areas, we found MR increases at the representations of the attended target. Similar but smaller increases were found in V1. Decreased MR levels were found in the same cortical locations when attention was directed at retinotopically different locations. In and surrounding area MT+, MR increases were lateralized but not otherwise retinotopic. At the representation of eccentricities central to that of the attended targets, prominent MR decreases occurred during spatial attention.
Bibliographical noteFunding Information:
These experiments were supported by NEI grant #EY07980 to R. B. H. T. and HFS grants to R. B. H. T. and A. M. D. We thank Ewa Wojciulik and Jody Culham for collaborating on informative pilot experiments related to the present study. We thank Bruce Fischl, Anthony Wagner, and Arthur Liu for crucial assistance with the data analysis. We thank Greg Simpson, Jack Belliveau, and Marty Woldorff for helpful suggestions on stimulus design and attention-related issues. We thank Terrance Campbell, Tim Reese, and Bruce Rosen for MRI support and the Rowland Institute for specialized machining.