Direct psychophysical estimates of the cone-pigment absorption spectra.

The absorption spectra of the long- and medium-wavelength-sensitive cone photopigments were derived by determining the spectra that best accounted for either the individual differences in the Stiles-Burch 10 degrees color matches [Opt. Acta 6, 1 (1959)] or the changes in color matches at high light levels due to photopigment bleaching [Vision Res. 20, 23 (1980)]. The estimates were made by finding the best-fitting coefficients for an 11th-order polynomial function of wavelength, with no requirement that the resulting sensitivities be consistent with the color-matching functions. The estimates are independent of the scaling effects of any inert screening filters and therefore directly reflect the photopigment sensitivities. The spectra implied by the differences in the matches are similar to the absorption spectra of Smith et al. [Vision Res. 16, 1087 (1976)], which were used as initial estimates. However, the peak sensitivity of the required long-wavelength-sensitive pigment is shifted toward slightly longer wavelengths.