Retinal and cortical nonlinearities combine to produce masking in V1 responses to plaids |
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Authors: | Melinda Koelling Robert Shapley Michael Shelley |
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Institution: | (1) Department of Mathematics, Western Michigan University, 1903 Western Michigan Avenue, Kalamazoo, MI 49008, USA;(2) Center for Neural Science, New York University, 4 Washington Place, Room 809, New York, NY 10003, USA;(3) The Courant Institute, New York University, 251 Mercer Street, New York, NY 10012, USA |
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Abstract: | The visual response of a cell in the primary visual cortex (V1) to a drifting grating stimulus at the cell’s preferred orientation
decreases when a second, perpendicular, grating is superimposed. This effect is called masking. To understand the nonlinear
masking effect, we model the response of Macaque V1 simple cells in layer 4Cα to input from magnocellular Lateral Geniculate Nucleus (LGN) cells. The cortical model network is a coarse-grained reduction
of an integrate-and-fire network with excitation from LGN input and inhibition from other cortical neurons. The input is modeled
as a sum of LGN cell responses. Each LGN cell is modeled as the convolution of a spatio-temporal filter with the visual stimulus,
normalized by a retinal contrast gain control, and followed by rectification representing the LGN spike threshold. In our
model, the experimentally observed masking arises at the level of LGN input to the cortex. The cortical network effectively
induces a dynamic threshold that forces the test grating to have high contrast before it can overcome the masking provided
by the perpendicular grating. The subcortical nonlinearities and the cortical network together account for the masking effect.
Melinda Koelling is formerly from Center for Neural Science and Courant Institute, New York University. |
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Keywords: | Functional organization and circuitry Subcortical visual pathways Visual masking |
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