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- H. Bartsch, M. Stetter, and
K. Obermayer. On the Influence of Threshold Variability in a Model of the
Visual Cortex.
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In Artificial Neural Networks - ICANN 99, pages 73-78, 1999.
(FTP Gzipped PostScript, 6 pages, 59 kb)
Orientation-selective neurons in monkeys and cats show contrast
saturation and contrast-invariant orientation tuning [albr82].
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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