Psychophysical consequences of L/M cone ratio

Abstract

Human L/M cone ratio varies among individuals with normal color vision by at least 30:1. Here, we examine whether individuals' L/M ratio is related to their photopic red-green balance and mesopic rod hue bias for stimuli appearing either yellow (dark surround) or brown (bright surround), all of which involve postreceptoral processing of L and M cone signals.L/M ratio was determined by analysis of ERG recordings using specific L and M cone spectra revealed by individual genotyping and age-corrected lens density. Subjects determined photopic hue balances by adjusting R and G CRT phosphors at constant 21 cd/m² in a 2°-diameter foveal test disc presented with either black surround (yellow test) or 140 cd/m² white surround (brown test). Subjects determined mesopic hue balances by adjusting R and G CRT phosphors at constant 0.2 cd/m² in (a) foveal 2 test disc or (b) 7°-extrafoveal, 4°-diameter test disc, with either black surround (both foveal and extrafoveal) or 1.4 cd/m² white surround (foveal only). Rod influence was determined from the difference between R/G phosphor settings obtained 3–10 min after a flash bleach (minimizes rod influence) and after 15-min of dark adaptation (maximizes rod influence). Initial trends show L/M ratio correlations with multiple measures of red-green hue balance but assessment of the statistical significance and interpretation of these trends awaits completion of testing of additional observers. The results will identify similarities and differences in the neural pathways mediating rod hue biases and processing of dark vs. bright colors.