Recent Advances in Color Vision.

Until a few years ago it was possible to account for nearly all the aspects of human color perception on the basis of the three-color theory, but such is no longer the case. This is largely due to improvements in the older methods of investigation and to the invention of new ones. Among the latter may be mentioned the microelectrode technique of Granit and the retinal direction effect of Stiles and Crawford. Modern requirements are met by a polychromatic theory, comprising 7 types of receptor, but there is no necessity for these to have such narrow spectral response curves as those exhibited by Granit's modulators. Modifications of the three- and four-color theories have been examined to see to what extent they can be made to fit in with experimental results. Particular notice has been taken of the possibility that there is polychromatism of the retinal receptors, but trichromatism of the nerve paths which connect these to the brain or even of the brain itself. The conclusion arrived at is that there must be polychromatism throughout the entire visual mechanism for color perception if a complete account is to be given of all the known facts.