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Linearity and Normalization in Simple Cells of the Macaque Primary Visual Cortex

Linearity and Normalization in Simple Cells of the Macaque Primary Visual Cortex,Matteo Carandini,David J. Heeger,J. Anthony Movshon

Linearity and Normalization in Simple Cells of the Macaque Primary Visual Cortex   (Citations: 344)
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Simple cells in the primary visual cortex often appear to com- pute a weighted sum of the light intensity distribution of the visual stimuli that fall on their receptive fields. A linear model of these cells has the advantage of simplicity and captures a number of basic aspects of cell function. It, however, fails to account for important response nonlinearities, such as the decrease in response gain and latency observed at high con- trasts and the effects of masking by stimuli that fail to elicit responses when presented alone. To account for these nonlin- earities we have proposed a normalization model, which ex- tends the linear model to include mutual shunting inhibition among a large number of cortical cells. Shunting inhibition is divisive, and its effect in the model is to normalize the linear responses by a measure of stimulus energy. To test this model we performed extracellular recordings of simple cells in the primary visual cortex of anesthetized macaques. We presented large stimulus sets consisting of (1) drifting gratings of various orientations and spatiotemporal frequencies; (2) plaids com- posed of two drifting gratings; and (3) gratings masked by full-screen spatiotemporal white noise. We derived expressions for the model predictions and fitted them to the physiological data. Our results support the normalization model, which ac- counts for both the linear and the nonlinear properties of the cells. An alternative model, in which the linear responses are subject to a compressive nonlinearity, did not perform nearly as well.
Published in 1997.
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