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The divisive normalization model [Heeger, 1992] accounts successfully for a wide range of phenomena observed in single-cell physiological recordings from neurons in primary visual cortex (V1). Using mathematical analyses and simulation experiments, we investigated the role of the maintained-discharge (base firing rate) parameter in this model. We developed an implementation that can take grayscale images as inputs and applied it to the types of visual stimuli used in a comprehensive suite of published physiological studies. We found that three empirical phenomena are closely associated with the maintained-discharge parameter: (A) the existence of inhibitory regions in the receptive fields of simple cells in V1, (B) the supersaturation effect in the contrast sensitivity curves, and (C) the narrowing/widening of the spatial-frequency tuning curves when the stimulus contrast decreases. The model predicts two …