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- H. Bartsch, M. Stetter, and
K. Obermayer. On the Influence of Threshold Variability in a Mean-Field
Model of the Visual Cortex.
.
In Emergent Neural Computational Architectures Based on
Neuroscience, pages 174-187. Springer, 2001.
(FTP Gzipped PostScript, 14 pages, 109 kb)
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 [hans97,bart97]. 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.
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