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ABSTRACT DR. F. W. EDRIDGE-GREEN suggests that, if Prof. Hartridge's observations in _Nature_ of July 20 were correct, the stars should appear to change colour as their light falls upon
different cones of the fovea. Prof. Hartridge, in reply, says "Dr. Edridge-Greeryis quite right. On either the three-colour theory of Thomas Young, or on its modern counterpart, the
Wundt-Granit hypothesis, one would expect a point source, and therefore a star,to undergo subjective changes of colour as its image is caused to move over the retina. Some stars do change
colour, a fact usually explained on purely physical grounds ; I have also noticed changes of colour of local sources ; under conditions where physical explanations did not appear to apply
(_Nature_, July 20, p. 97). Why, it may be asked, are such colour variations so seldom seen when the eye is being used in normal vision ? The answer is not a simple one, since many factors
play a part. In the first place the retinal image, even of a point source, falls on a considerable area of retina. This is partly due to diffraction, and partly due to aberrations. In
consequence, many photo-receptors are usually stimulated at the same time. But further, colours which would normally be seen are eliminated by the anti-chromatic responses. In the third
place, there is a process which tends to smooth out differences in response. This is now under further investigation, because it is hindering progress. When a method has been found of
putting this process temporarily out of action, a new avenue of approach to the essential problem of vision will probably have been found." Access through your institution Buy or
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permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Colour Receptors in the Human Fovea. _Nature_ 158, 301 (1946). https://doi.org/10.1038/158301b0 Download citation * Issue Date: 31 August
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