Opponent-process additivity--III : Effect of moderate chromatic adaptation

Abstract

The luminance invariance and additivity of opponent-color equilibria were tested under conditions of chromatic adaptation to unique blue, green, yellow and to (nonunique) 650-nm red lights, varying from about 40 to 2000 td. Although the adapting lights produced large shifts in the loci of the red/green equilibrium colors away from their dark-adapted values, hardly any nonadditivity was produced by blue or green adaptation. For yellow adapting lights of 900 td or more, the red/green equilibria are luminance dependent, hence nonadditive. A small luminance dependence was produced by 40 td red adaptation. As a first approximation, the effects of moderate chromatic adaptation on the red/green opponent code can be described by a coefficient law; however, the fact that unique hues do not shift under moderate self-adaptation implies that the coefficient for at least one receptor type depends on the adapting input to other receptor types. The fact that yellow and red adaptation make the dark determined unique blue wavelength look reddish implies that the short-wavelength cones contribute a red input to the red/green opponent system. The yellow/blue system exhibited nonlinearities under chromatic adaptation which were qualitatively similar to the nonlinearities found under dark adaptation.