The physical aspects of a theory of colour vision / by F.W. Edridge-Green.

  • Edridge-Green, F. W. (Frederick William), 1863-1953.
Date:
[1902?]
Catalogue details

Licence: In copyright

Credit: The physical aspects of a theory of colour vision / by F.W. Edridge-Green. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    Section A —Belfast, 1902.] The Physical Aspects of a Thaory of Colour Vision. By F. W. Edridge-Green, M.A, F.E.C.S. c The view which I wish to bring forward is that each optic nerve fibre is able lo couvey impulses correspondinj^ to all kinds of light; that is to say, a very similar condition exists in the impulses which are transmitted along the optic nerve to that which is accepted for waves of light previous to their entering the eye. The limitation of the number of colour sensations was thought to be necessary because it seemed physically impossible that a single fibre of the optic nerve could convey all waves of light. The facts of colour vision can only be satisfactorily explained on the assumption that each optic nerve fibre does convey impulses corresponding to all waves of light. It occurred to me that if there were a transforming apparatus in the eye we could explain the facts. The tele- phone shows how this may be accomplished in the case of sound. I saw that the retina was constructed in a mannor theoretically perfect from this point of view. The percipient layer of the retina is made up of two kinds of elements, the rods and the cones. The portion of the retina corresponding to the central portion of the field of vision contains only cones. External to this spot the cones are arranged with one or more rings of rods round them, the single ring being round those cones which are nearest to the central portion.^ In the rods there is a rose- coloured substance, the visual purple, which is very sensitive to light. This photo- chemical substance is found exclusively in the rods. I assumed that hght falling upon the eye liberated thje visual purple from the rods, just as heat would an ointment, and a photograph is formed. The decomposition of the visual purple by light chemically stimulates the ends of the cones, and a visital impulse is set up which is conveyed through the optic nerve fibres to the brain. I have examined the retinas of several monkeys after they had been kept in a dark room, and found that the visual purple was to be seen in the yellow spot, but situated between, and not in, the cones. This view gives a reason for a great many facts which were previously inexplicable. For instance, a bright light may fall upon the fovea (the centre of the yellow spot) without producing any sensation, and a perceptible interval elapses before we are able to see with the yellow spot, after the remainder of the retina, the fovea being the last point to convey a sensation of light. The first fact we should expect, the cones being insensitive to light; the .<*econd corresponds to the difiusion into the yellow spot of the visual purple. All the facts of colour mixing, contrast, and after-images can be explained by the hypothesis that the visual purple is the visual substance. A positive rose-coloured after-image can be obtained after white light or any spectral colour. The ordinary ] explanation of this, namely, that the action of the hypothetical red and violet ! fibres persists longer than those for green, cannot be true, because it is exceedingly ' difficult to obtain this after-image after spectral red, and very easy to see it after green. It would be against the whole principle of the theory that the red fibres should be excited most etficiently by green. But if we assume that the visual purple is the visual substance, then we have an easy explanation of the facts. The fibres of the optic nerve pass to the visual centre. I have assumed that the visual centre transmits to the mind impressions of white light, and that by it objects are seen monochromatically, as in a photograph. The visual centre is, therefore, acted upon by impulses caused by all rays of light, the colour-perceivin' centre being concerned with the quality of the impulse within the power of perceiving differences possessed by that centre, or portions of that centre. I will now apply this theory to colour-blindness, and it will be seen that it gives a simple explanation of the facts. Cases of colour-blindness may be divided into two classes, which are quite separate and distinct from each other, though both may be present in the same person. In the first class there is light as well as colour loss. In the second class the perception of light is the same as the normal sighted, but there is a a 15