Color scaling of chromatic increments on achromatic backgrounds: Implications for hue signals from individual classes of cones

Abstract

AbstractThe hues of foveal monochromatic increments on concentric white backgrounds were measured as a function of the background retinal illuminance. For each background illuminance tested, the illuminance of the test spot was set 0.6 log unit above its increment threshold, and relative percentages of redness, yellowness, greenness, and blueness were estimated. The percentage of whiteness was also estimated in a separate judgement. At low background illuminances, the spectrum is dominated by blue at short and middle wavelengths and by red at long wavelengths. Higher background illuminances are marked by dramatic growth of yellow and green at middle wavelengths and red at short wavelengths. At still higher photopic levels, the pattern reverts back toward that seen at low background illuminances. The hue patterns at low and high adapting levels are characteristic of tritanopic vision, and are attributable to selective sensitivity losses in chromatic neural pathways that process short‐wavelength‐sensitive (S) cone responses. These results reinforce previous evidence that S cone activity produces a reddish purple hue at short wavelengths and (indirectly) a yellow hue at middle and long wavelengths, and that middle‐wavelength‐sensitive cone activity produces a slightly greenish blue.