Vastly differing variances in the ratio of red and green cones between female and male human observers

Three cone types provide the input signals into our color vision. Their respective spectral sensitivities peak at wavelengths of about 430 nm (S-cones), 530 nm (M-cones) and 560 nm (L-cones). L- and M-cones comprise the vast majority of cone types in color-normal human retinae. The ratio between these two cone types — called the L/M-ratio – is found to vary considerably between 1 and 10. We have recently developed a new method to determine the relative contribution of the three cone types to the perception of brightness in human observers (Teufel Wehrhahn, JOSA A, 17: 994–1006, 2000). This method provides a fast and robust procedure to determine cone contributions to perceived brightness and includes an estimate of L/M-ratios. Here we report that color normal female and male observers have very different distributions of L/M-ratios. Specifically female observers show a distribution of L/M-ratios with two peaks, situated at low and high L/M-ratios, respectively. This is opposed to color normal male human observers, whose distribution was found to have only one peak at medium L/M-ratios. We propose that this difference in distributions is due to a previously unknown genetic mechanism regulating the genesis of retinal cones