HIERARCHICAL PROCESSING IN THE MOTION SYSTEM

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The overall goals of research in this laboratory are twofold: exploring the basic mechanisms of visual information processing in primate visual cortex and investigating how this information processing serves as a substrate for visual perception and visually guided behavior. For several reasons, the "motion system" of dorsal extrastriate cortex in monkeys forms an excellent model system in which to ask such questions. First, the basic anatomy and physiology of areas on this pathway are well understood. Secondly, it is known from recent work in several laboratories that physiological events on this pathway are closely related to the perception of visual motion. Lastly, it seems very likely that a pathway with similar functions exists in human visual cortex as well, so that the information we obtain from the monkey will help us to understand human visual information processing and its disorders. A seemingly general rule of information processing in extrastriate cortex is the elaboration of complex response properties at later stages of processing. The research proposed in this grant will investigate this hierarchical processing in the motion system and ask what novel behavioral capabilities are supported by the complex properties of neurons in extrastriate area MST, which is arguably the highest-order area where neuronal signals are dominantly visual, as opposed to visuomotor. Experiments will be performed on the alert rhesus monkey, allowing simultaneous measurement of physiological and behavioral events. Two kinds of experiments will be performed, each directed towards one of the long- term objectives stated.above: l) Single-cell physiology experiments will probe the manner in which the response properties of neurons in two areas on the motion pathway, MT and MST, are built up from the signals of neurons with the simpler response properties of earlier levels. These experiments will employ novel visual stimuli to explore the interactions between receptive field (RF) subregions responsible for generating known RF properties. 2) Combined behavior and physiology experiments will elucidate how the complex response properties of neurons in MST relate to behavioral tasks dependent on the analysis of complex motion patterns. Monkeys will be trained to discriminate complex motion flow fields and to detect their "heading direction" on the basis of such fields. Neuronal sensitivity will be measured as the animal performs these tasks, and microstimulation experiments will determine if manipulation of neuronal signals affects task performance. Together, these two projects should reveal basic mechanisms of hierarchical information processing in the primate motion system and illuminate the behavioral role of the later stages of this processing.