Brightness and flicker luminosity in sex-linked dichromacy

Abstract

The luminosity functions based on heterochromatic brightness matching (HBM) and 15-Hz heterochromatic flicker photometry (HFP), each on a dark background, were compared for two protanopes and one deuteranope. At wavelengths greater than each observer’s achromatic point, there was very little difference between the two methods. At short wavelengths, the two types of curve diverged with less energy needed for HBM than for HFP. Using each observer’s own color matching functions, the data were replotted to show (1) the additivity of luminosity for two wavelengths and (2) the effect of colorimetric purity on the brightness: flicker ratio. Both types of analysis indicated a superadditive effect for HBM at short wavelengths. Several simple models combining receptoral or postreceptoral outputs, linearly or nonlinearly, failed to characterize completely dichromatic HBM on a dark background. The addition of a large white adapting field produced a two-lobed HBM luminosity curve that can be modeled approximately as an interaction of opponent and nonopponent processes.