There is something basic about vision that we do not understand. Everyday experience tells us that we can perceive every detail of an object that our eyes can resolve, even if the object is complex. But neurophysiological evidence shows that the most detailed visual information is represented only at the early processing stages (areas V1 and V2), where neurons have small receptive fields that are fixed on the retinae. This means that a different set of neurons is activated every time the eyes move to a new fixation, which occurs continually 3-4 times per second. How can a stable percept of the object result from these scattered responses? This application proposes research to test a new theory that describes the emergence of object representations in the visual brain and its role in the deployment of attention. According to the theory, the remapping of receptive fields as found in LIP and extrastriate visual areas, and the remapping of figure-ground structure that was recently discovered in V1 and V2, have a common mechanism. The proposed experiments will use single-cell recordings in behaving non-human primates. By recording from parietal and extrastriate visual areas, two critical predictions of the theory will be tested. One is that remapping of receptive fields, as classically observed in connection with saccades, should also occur in response to object movements. Several areas where remapping has been found with the classic remapping paradigm will be tested, and results are expected to differ between areas. The second prediction is that the remapping signals recorded at high level (e.g., parietal area) and low level (e.g., area V2) should exhibit specific correlations. This will be tested by recordin simultaneously with two microelectrodes. If confirmed, this would be a step towards a comprehensive theory of visual processing that includes figure-ground organization, object-based attention, and perceptual stability.
The spatial deployment of attention is impaired in human patients with lesions of parietal and frontal cortex. The aim of the proposed research is to understand how the cortex structures visual information and how it creates a stable spatial representation that guides the deployment of attention. This will deepen the understanding of the visual deficits that are so devastating in patients with parietal and frontal lesions and will help in designing strategies for their diagnosis, prognosis and rehabilitation.
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