| Visual attention refers to the selection of behaviorally relevant objects in the environment. Human BOLD-fMRI studies have revealed that this function is mediated by the interactions of a distributed network of cortical areas. In parallel, electrophysiological and histological studies of the macaque have examined the neuronal mechanisms underlying these visual attention processes. However, the techniques used in the macaque are inherently limited in their ability to integrate information over large cortical distances. As a result, little is known about the topographic and functional organization of visual processing areas in the macaque and their relative contribution to visual attention. Furthermore, substantial discrepancies have been noted in the properties of human and macaque visual processing areas, but it is yet unclear whether these discrepancies are the result of technique or reflect real interspecies differences. This dissertation addresses these issues by using BOLD-fMRI in awake behaving macaques to assess the functional and topographic properties of the entire macaque visual attention system.;The tasks performed were designed to elicit neural signals associated with multiple visual attention processes. Analysis of the results revealed several characteristics of the macaque visual attention system. First, we unveiled the topographic organization of multiple visual processing areas. Second, we found that most of these areas exclusively represented the contralateral hemifield. Third, we found that the magnitude of the activity in the visual processing areas was modulated by the locus of attention. These characteristics allowed us to describe the macaque visual processing areas in terms of both function and organization.;The results derived from these experiments have clarified controversies involving the topographic organization of the macaque visual processing network, and have revealed previously unknown functional properties of the underlying areas. In addition, we were able to use this information to define areas within previously undifferentiated regions of cortex. Finally, the results have also revealed that the visual attention systems in the two species may differ substantially in several aspects, and therefore caution is needed in applying macaque data to human models of visual attention. |
