HIERARCHICAL PROCESSING IN THE MOTION SYSTEM

University Of California Davis, Davis CA

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Abstract

DESCRIPTION (Adapted From The Applicant's Abstract): The broad goals of the research program in this laboratory are twofold: understanding the mechanisms of information processing in visual cortex, and connecting the information there with visual perceptual capabilities. The "motion system" of dorsal extrastriate cortex is a good model system for this purpose, because a wealth of data documents its anatomy, physiology, and utility in visual-motion-related behavior. Furthermore, it appears that this system exists in humans as well, from recent imaging work. Therefore, the insights we gain will probably directly further our understanding of human cortical information processing and its disorders. While we know much about the system, the basic processes by which motion information is processed and used remain mysterious. Specifically, we know that cortical areas MT and MST are connected in a serial arrangement, and that both are necessary for normal motion perception. The physiology of these areas suggests a dramatic transformation occurs between the two areas--MST represents much more complex motions than does MT. Work in this laboratory will employ two approaches to further elucidate the mechanisms and consequences of this hierarchy. First, we will employ dual electrode recording to measure the operation of circuit connections and test computational models of the way motion information is transformed. Two specific questions are under study. First, we know that multiple stimuli interact in MT in a mutually divisive manner, and we seek to establish the mechanism for this. Also, we are investigating the manner by which complex RFs in MST are assembled from the simpler ones in MT. Secondly, by recording neuronal activity in awake, behaving monkeys which are performing a complex motion task--discrimination of "heading" based on visual cues--we can infer how the signals in MST and MT are being used in the performance of the task. While we know that activity there is used in performance of the task, what we do not understand is how it is being used. To help with that question, quantitative measurements of neuronal sensitivity to heading stimuli, and of correlation with behavioral choice, will be made. These have in the past proven to be powerful tools for relating neuronal activity to perception.