On the Basic Sensation Curves of the Three-Color Theory

A new method is described for the measurement of the basic sensation curves of the three-color theory of Young-Helmholtz.In order to determine the spectral distribution of the absorption of the blue receptors a weak blue spot P that mainly excites the blue receptors is projected on a field F; this field is illuminated by monochromatic light with a wave-length λ. Its energy per cm2E is increased up to the energy E(λ) where P becomes invisible. The leading idea is that the sensitivity of the blue receptors G(λ) for this light is inversely proportional to E(λ). This means that the visibility of P is better when the excitation of the blue receptors by F is small. Some restrictions are given in Section 2. In the discussion of this idea an essential assumption is that a difference in the excitation of cones or rods is never observable if the difference is smaller than 1 percent. Evidence for this law is given. When necessary, the discrimination of P by the green or red receptors is excluded by adding an appropriate amount of green light to the illumination of F. The absorption curve of the green and red receptors may be found when a green or a red spot P is used. In Section 3 the apparatus is described. In Section 4 the results of the measurements are given for the author’s left eye (deuteranomalous), for a normal trichromat, and for a dichromat. The green curve of the deuteranomalous eye lies between the normal green curve and the red curve. In Section 5 some conclusions are drawn from the measurements. It is shown that the so-called international sensitivity curve z, which has its maximum in the blue, represents the absorption curve of the blue receptors; the international curves x and y, however, must be transformed. A tentative transformation is given. Finally it is remarked that the results of our measurements are in complete variance with the so-called four-color theory.