Link-specific adaptation in the luminance and chromatic channels

We present evidence that adaptation occurs in the separate links that connect the receptors to the luminance and the chromatic channels. The relative effectiveness of the L and M cone inputs to the luminance and red/green chromatic channels was determined by using, respectively, heterochromatic flicker photometry and a cancellation technique which maintained a pure yellow. The findings provide evidence for a link-specific adaptation model, wherein one receptor system provides two separate links to the luminance and chromatic channels and the outputs of an individual cone to these two postreceptoral channels can be separately attenuated or weighted at each of these links by colored adapting lights. One line of evidence for link-specific adaptation is that colored adapting fields selectively suppress L and M cone inputs to the red/green chromatic channel by a smaller factor than the luminance channel. A second line of evidence is that there is not only a magnitude difference but also a dynamic difference between adaptive processes operating in the luminance and chromatic channels: the luminance channel has a faster gain change and recovery from adaptation than does the chromatic channel. The results, together with other evidence, make it plausible that an important component of light adaptation in cone vision occurs at the cone-bipolar synapse.