On the Influence of Threshold
Variability in a Mean-field Model of the Visual Cortex
Hauke Bartsch, Martin Stetter and Klaus Obermayer
Abstract
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 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.