Human colour perception and its adaptation

Abstract. Information about colour is initially extracted by the visual system in terms of the activity within a small number of receptor types with different spectral sensitivities, and then recoded within channels that respond to different combinations of the receptor signals. Many insights have been gained about these post-receptoral transformations, yet their number and nature remain poorly defined. This review examines how the signals coding colour are organized within the human visual system, and how these signals are affected by the processes of adaptation. Sensitivity is controlled by two distinct classes of adaptation that adjust to different aspects of the stimulus; retinal mechanisms of light adaptation adjust for changes in the average colour across scenes, while cortical mechanisms of contrast adaptation adjust for changes in the distribution of colours. Together these exert a profound and pervasive influence on our colour perception. 1