On the influence of threshold variability in a model of the visual cortex

Orientation-selective neurons in monkeys and cats show contrast saturation and contrast invariant orientation tuning. Recently proposed models for orientation selectivity predict contrast invariant orientation tuning but no contrast saturation at high strength of recurrent intracortical coupling, whereas at lower coupling strengths the contrast response saturates but the tuning widths are contrast dependent. In the present work we address the following question: if and under which conditions the incorporation of a stochastic distribution of activation thresholds of cortical neurons leads to the saturation of the contrast response curve as a network effect. We find that contrast saturation occurs naturally if two different classes of inhibitory inter-neurons are combined. Low threshold inhibition keeps the gain of the cortical amplification finite, whereas high threshold inhibition causes contrast saturation