The research will address a series of hypotheses about how visual cortex is organized in primates by relating connection patterns revealed by the use of 4 or more distinguishable tracers in single cases. Results will be related to cortical areas defined by architecture or relative location, and in some instances by electrophysiological mapping and optical imaging techniques. Neurons labeled by each injection will be counted in each area, and the proportion of the area with labeled cells measured so that connection magnitudes and topographic foci can both be quantified. (1.) In one set of experiments, injections of different tracers into 4 or more locations in the superior colliculus will be used to reveal for the first time the total projection pattern from cortical areas and the retinotopy of the projections of individual areas to the superior colliculus. The results will address hypotheses that some areas contribute more to superior colliculus function than others, and that differences in functional roles are reflected in differences in the topographic precision of those projections. (2.) Under the premise that different parts of the same area will have similar connections, injections of tracers will be used to evaluate the hypothesis that V3v and V3d are parts of the same area,V3, rather than separate areas with V3v being VP or V3d being part of DM. (3.) Connection patterns will be used to evaluate our proposal that the "V4" region in primates actually consists of two separate areas and part of another. We predict that each of the three areas will have a different pattern of connections with other cortical areas. (4.) Visual area MT is interconnected with intraparietal cortex, but it' s not known if these connections are topographic, and if one or two IP areas, LIP and VIP, exist. Injections in 4 locations in MT will address this issue by determining if one or two topographic patterns of connections with IP cortex exist. The connection patterns with MT are also expected to be topographic with proposed areas FSTd and DM, establishing them as valid areas. We expect that the results of these experiments will greatly advance our understanding of the organization of visual cortex in primates, and produce more accurate models of the human visual system that will permit more appropriate interpretations of functional data.