Pattern motion signals from V1 receptive fields Q Li, N K Logothetis, G A Keliris |
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Department Physiology of Cognitive Processes, Max Planck Institute Biological Cybernetics, Germany
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| Local measurements by small receptive fields (RFs) in V1 are thought to induce ambiguous and noisy one-dimensional motion estimation. This necessitates integration at higher brain stages for computation of global pattern motion. Electrophysiological evidence from monkeys viewing plaid stimuli is consistent with this hypothesis finding a small percentage of cells in V1 responding to pattern motion but the percentage is increasing in higher motion responsive areas MT and MST. We conjectured that a subset of V1 RFs residing on specific stimulus features could directly respond to the pattern motion thus biasing motion integration at higher stages. We used a novel stimulus to mimic V1 RF responses to plaids. It comprised of a mask with multiple transparent apertures (0.4°) over a moving plaid. The aperture locations were chosen in advance to be of two types: AP1 were chosen to “see” only single grating components at any given time while AP2 were chosen to “see” only grating intersections. We manipulated the percentage of these two types in different trials to test how they influence motion perception. We found that the motion perception of subjects changes sigmoidally from 100% transparent when all apertures are AP1 to 100% coherent when all apertures are AP2. |
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