CORTICAL REPRESENTATION OF THE VISUAL IMAGE

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DESCRIPTION (from the investigator's abstract): The goal of our research is to uncover the cortical pathways that underlie motion processing and to evaluate how the signals conveyed in these pathways influence motion perception and smooth pursuit eye movements in primates. Understanding the mechanisms that transform perceptual signals into positive decisions and actions is one of the long-term goals of visual science. Recent advances in our understanding of visual motion processing indicate that two important classes of visual motion stimuli are not processed in the same way as conventional luminance motion stimuli. Yet both lead to vivid impression of motion. We will use an integrated approach to study (a) neural and (b) pursuit performance by using the same stimulus conditions in both, and by using measures of response performance that can be equated across neurons, perception and pursuit. (1) The three classes of motion targets, luminance, chromatic and non-Fourier, can be distinguished psychophysically by the nature of perceptual judgments made in response to them. We will exploit established psychophysical differences in perceptual processing of the different classes of motion targets to study the performance of the populations of neurons in V1 and extrastriate visual areas V2 and V4. We will measure threshold contours in color space and motion sensitivity for chromatic and luminance stimuli to assess neuronal performance. For non-Fourier stimuli we will measure the performance of neurons for detecting boundary orientation, as well as their performance in signaling the direction of the moving boundary. (2) Concurrently with the neurophysiological experiments, we will examine the efficacy of the three classes of motion stimulus in eliciting pursuit. We will use Gabor patches as visual targets, as these will enable us to have independent control over the spatial, temporal and chromatic properties of the stimulus. By adopting the use of spatiotemporally restricted targets we obtain the ability to make a direct comparison between pursuit performance and psychophysical performance. We anticipate that this approach will give us the unique opportunity of bringing all three aspects of sensorimotor integration together to aid our understanding of important pathways in the brain and help to develop a conceptual framework for future investigations.