It is important to find answers to two questions concerning the visual discriminations of dichromatic persons, especially deuteranopes: (i) Do such persons show a loss of sensitivity to various wavelengths of the spectrum as compared with normal subjects? (ii) What colors do they see?

A number of experiments were performed on the first question.

First, luminosity curves were determined on three groups of subjects, consisting respectively of five protanopes, six deuteranopes, and seven normal individuals. As compared with normal subjects, protanopes show a loss of luminosity in the red, whereas deuteranopes show a loss in the blue-to-green region of the spectrum (See 10).

Second, we examined the luminosity curves of a subject whose right eye is classifiable (on the basis of color-mixture determinations) as normal and whose left eye is classifiable as dichromatic. (The hue discrimination curve for her dichromatic eye seemed comparable to the curve of the usual deuteranope except in the violet, where it manifested relatively good discrimination.) The luminosity function for this subject's dichromatic eye, determined by data on threshold and flicker, exhibits the same type of luminosity loss in the blue and green regions of the spectrum as was shown by our group of six deuteranopes.

Only unilaterally dichromatic subjects can tell us how colors seen by a dichromatic eye appear to a normal eye. In the color-blind eye, our unilaterally dichromatic subject sees wavelengths below and above her neutral ("grey") point (which occurs at 502 mµ) as, respectively, a blue equivalent to about 470 mµ and a yellow equivalent to about 570 mµ in her normal eye.

The results on (i) luminosity loss and (ii) the seeing of wavelengths above 502 mµ as yellow are considered theoretically. The seeing of yellow by deuteranopes and protanopes may be accounted for by an idea based on Leber-Fick transmation theory. It is proposed that the characteristic sensitivities of the red and green receptors become similar while no change takes place in their central brain connections. Losses may be introduced into the transformed sensitivity curves to indicate appropriate degrees of luminosity deficit for deuteranopes and protanopes.