Residual Red-Green Discrimination in Dichromats*

Five deuteranopes and three protanopes, carefully selected as dichromats by common tests, have been extensively investigated by additional methods. Some of these subjects show selective chromatic adaptation over the longwave end of the spectrum, while all but one show clear evidence of an ability to name colors in a nonrandom way (which tends toward the normal) when presented with longwave spectral stimuli which have been carefully equated for brightness. Further matching tests show that some of the subjects can detect slight color differences between stimuli that fall on their confusion lines as plotted in a chromaticity chart, although they make these nearly metameric matches easily. Scores on the various tests of color deficiency used in the study do not correlate with one another. It is concluded that most dichromats retain a residual and variably weak functioning of the red-green chromatic system.