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Retinal Regulation of Visual Contrast Sensitivity

Robert Shapley

Sensitivity to contrast is one of the most important attributes of the visual system of humans and other animals. This paper is about some of the reasons for the dependence of visual responses on contrast, and the neural machinery in the retina that makes it possible. Although it seems that perception of the brightness of objects is effortless, visual scientists have known for years that complex neuronal computations are required to perform the task. The perception of brightness is not simply a matter of counting photons. The primary determinant of brightness perception is local contrast—the local difference between luminances on either side of a boundary normalized by the (local) average luminance.