CORTICAL PROCESSING OF VISUAL MOTION

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The long-term objective of research in this laboratory is to understand how neuronal processing in extrastriate visual cortex contributes to visual perception and visually guided behavior. The proposed research will focus primarily on an extrastriate pathway that is thought to be involved in the analysis of visual motion. This pathway originates in striate cortex, continues through extrastriate areas MT and MST, and terminates in visuomotor regions of the parietal lobe. Recent neurological observations suggest that a similar pathway specifically related to visual motion information is present in humans. Such similarities indicate that the proposed studies of rhesus monkeys are likely to contribute directly to our developing knowledge of human vision and its diseases. Experiments will be carried out in awake, behaving monkeys trained to perform relevant perceptual and visuomotor tasks. Behavioral experiments are proposed that will identify the cortical areas involved in the perception of pattern on the basis of relative motion cues. Physiological experiments will investigate the neuronal basis of perceptual capabilities that we have studied psychophysically. An important component of this effort is to identify transformations in the visual information encoded by single neurons at progressively higher levels of the motion pathway. In particular, we will examine the physiological transformations that permit extraction of motion signals from a masking visual noise, and that permit reliable judgements of speed of moving objects. In the course of our visual experiments, we have developed a new behavioral paradigm that holds great promise for acquiring insight into the sensorimotor linkage between the visual and oculomotor systems. The key issue to be studied is how primates "select" visual targets for eye movements from among the many competing stimuli present in the visual image. In the new behavioral paradigm the "selection" event is separated in time from both the onset of the targets and execution of the eye movement. It is therefore possible to search for neuronal correlates of this higher order "selection" event in isolation from the strictly sensory and motor aspects of the task. Such experiments will shed light on the physiological mechanisms by which attentional phenomena mediate the interactions between sensory and motor systems.