Adaptational effects of short wave cone signals on red-green chromatic detection.

The red-green chromatic detection mechanism that responds to the difference of L and M cone test signals was isolated in forced-choice experiments. Detection contours in an L, M cone space were measured with 2 Hz Gabor test signals comprising different amplitude ratios of antiphase flickering red and green lights, which formed the 1.2 degree center of a 7.2 degree uniform adapting field. To compare the effect of short wave cone adapting levels on the red-green detection sensitivity, thresholds were measured on pairs of adapting fields that were shown to be tritanopic metamers for our individual observers: violet and green adapting lights that produce equal quantal catches in M cones and in L cones but very differently stimulate S cones. The degree to which the adapting field stimulated S cones had little effect on the red-green detection sensitivity, although the red appearance of the adapting field varied considerably owing to the S cone stimulation. Thus, while the S cones may affect the red-green hue dimension, S cone signals appear to have little adaptational effect on red-green detection mediated by the difference of L and M cone test signals.