Contrast Gain Control in the Visual Cortex
Izumi Ohzawa, Gary Sclar, and Ralph D. Freeman (1982)
Contrast gain control in the cat visual cortex.
Nature 298: 266-268.
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The eye functions effectively over an enormous range of ambient
illumination, because retinal sensitivity can be adapted to prevailing
light levels. Higher order neurones in the visual pathway are presumably
more concerned with relative changes in illumination, that is, contrast,
because a great deal of information concerning absolute light level is
processed at the retinal level. It would therefore be of considerable
functional value if cells in the visual cortex could adapt their response
levels to a steady-state ambient contrast, in a manner analogous to the
sensitivity control mechanism of the retina. We have examined here the idea
that adaptation of neurones in the visual cortex to ambient contrast is
similar to adaptation in the retina to ambient illumination. The
experiments were performed by measuring contrast response functions
(response amplitude as a function of contrast) of striate neurones, while
systematically adapting them to different contrast levels. Our results show
that, for the majority of cortical neurones, response-contrast curves are
laterally shifted along a log-contrast axis so that the effective domains
of neurones are adjusted to match prevailing contrast levels. This contrast
gain control mechanism, which was not observed for lateral geniculate (LGN)
fibres, must be of prime importance to visual function.