Melting the Iceberg: Contrast Invariance in Visual Cortex

Neurons in visual cortex maintain their selectivity for stimulus orientation despite wide variations in stimulus contrast. Achieving this invariance is a challenge because of the iceberg effect: subthreshold responses are broader in selectivity than firing responses, and increasing contrast would bring them above threshold. An article in this issue of Neuron by Finn et al. explains how neurons solve this problem using simple mechanisms: contrast-gain control, additive noise, and firing threshold.