The Change from Trichromatic to Dichromatic Vision in the Human Retina

Abstract

MANY years ago I noticed the confusion of yellow with white, and blue with black when test objects of small size are under critical examination¹. I thought, incorrectly, that this confusion was due to the chromatic aberration of the eye. Some years previously, König had, unknown to me, given the true explanation of the phenomenon, namely, that for objects of small size, examined by the fovea centralis, trichromatic vision is replaced by dichromatic vision². He thought that this change was strictly limited to the fovea centralis. Recently Willmer has come to the same conclusion³. Both König and Willmer are mistaken, however, for in a recent communication in Nature, I have produced evidence that the change occurs not only at the fovea centralis but practically all over the useful retina⁴. Further evidence on this point has now been obtained, together with many other facts, concerning the appearance of the colours of very small objects.