Evidence for a central component in adaptation to chromatic light.

Adaptation to environmental light allows our visual system to compensate for dynamic changes in the visual environment for avoiding everyday hazards (e.g., misreading traffic lights) and for accurate reaching. We investigated the hypothesis that adaptation to coloured light is achieved not only via photoreceptors in the retina and monocular contrast adaptation, but also by a binocular process that may occur at the level of the cerebral cortex. In the present study, to determine the role of higher-order cortical binocular processes in adaptation to coloured light, participants were adapted to chromatic light such that the duration of adaptation during monocular processing differed from that during binocular processing. A dichoptic device was used to adapt each eye independently. The extent of after-effects, measured as the distance between the neutral points before and after adaptation to coloured light, depended on the duration of adaptation not only at the monocular level but also at a higher cortical level downstream from binocular fusion. Thus, contrast adaptation to coloured light occurs on at least two levels; it is a result of monocular processes at one level and binocular processes at the other, and each type of process exhibits different temporal characteristics. The results of this study suggest a significant cortical role in adaptation to changes in lighting conditions or the optical environment, including the effects of age on the eye, and the necessity of further investigation to clarify the functional connection between chromatic adaptation by photoreceptors and chromatic adaptation by cortical systems.