A case of abnormal trichromatic colour vision due to a shift in the spectrum of the green-sensation curve

Abstract

The authors have each separately dealt with the question of complete and incomplete colour-blindness caused by the absence of, or decrease in, the response to stimulation of the red or green perceiving apparatus which is functional in the case of vision. We have shown that a large number of cases of defective perception of colour are simply explained on this hypothesis. Abnormality of colour vision may also be due to a shift in, or an alteration in form of, one of the sensation curves. In the present paper we discuss the effect of one type of shift on the colour perception and give the results of a series of measurements which show that such a shift, without any alteration of form, does sometimes occur. In a paper which appeared in the ‘Proceedings of the Royal Society,’ one of us indicated how a shift, that is a displacement of the whole curve so that the maximum is displaced to a different wave-length, of one of the sensation curves could be detected by a simple spectrum test, which is as follows. When yellow light of wave-length 5760 Å. U. is mixed with blue light of wave-length 4610 in suitable proportions the mixed light looks to the normal eye exactly the same as the white light from the crater of the electric arc both in hue and brightness. If a person who has a shift in one of the sensation curves is shown this match it will not appear correct to him nor can it be made correct by any alteration in the proportions of the yellow and blue lights. There will, however, in every case be found a position of the slit through which the yellow light is obtained with which a satisfactory match can be obtained. In other words the wave-length of the light which is complementary to the blue will be different to that of normal vision.