A nonlinear hypothesis for chromatic adaptation

Abstract Under different ordinary qualities of illumination, a given surface retains its chromatic appearance nearly undisturbed after the observer becomes adapted to the change in quality, although the visual stimuli may be quite different for the diverse qualities. This phenomenon, called “chromatic adaptation”, is customarily assumed to be equivalent to a proportional attenuation of responses that are linearly related to the physical stimuli. Analyses of data obtained recently by three independent experimenters using very different procedures indicate, however, that the hypothesis of a linear relation between the response and the stimulus fails systematically to account for the experimental results within reasonable limits of error. By combining the hypothesis of proportional attenuation and of various nonlinear relations between response and stimulus, most of the systematic errors in accounting for the experimental results can be eliminated. The most successful forms of the nonlinearities associated with the three color-receptor systems in various states of chromatic adaptation are found to be rather similar for the data of all three experiments. In general, the form of the nonlinearity thus deduced is different for each of the three color-receptor systems and, for each, is differently dependent upon the state of chromatic adaptation.