Visfon Res. Vol. 13. pp. 20174031. Pcqwmon Press 1973. Printed in Great Britain. PIGMENTS IN ANOMALOUS TRICHROMATS W. A. H. RUSHTON, DIANE SPITZER POWELL and K. D. WHITE Institute of Molecular Biophysics, The Florida State University, Tallahassee, Florida 32306, U.S.A. (Received 2 February 1973; in revisedform 13 April 1973) LORD RAYLEIGH (188 1) found, when subjects were set to match a yellow light with a mixture of red and green, that a perfect match could always be made, but that about 5 per cent of males differed from the majority in the red/green ratio required. Those who require too much red are called “protanomalous”, those requiring too much green “deuteranomalous”. These subjects differ sharply from protanopes and deuteranopes to whom all wave lengths in the red-green spectral range appear the same in colour and can be matched by adjustment of intensity only. Rayleigh’s anomalous trichromats require both red and green in the mixture to match yellow, but they do not accept the proportions which satisfy normal subjects, protanomalous insisting upon a (red + green) mixture which the normal judges far too red; the deuteranomalous match being far too green. Much work has been done on the coiour vision in these common and interesting conditions notably by Wright and his colleagues (WRIGHT, 1946). It is frequently claimed that the pigments are normal but that the organization of nerve signals is not. For instance, that protanomalous have the normal “red” and “green” cones, but that the “red” cones are too few in number, or generate nerve signals that are too small, so that more red light than usual must be added to the mixture to produce “red signals” as large as “green signals”-which is conceived as the condition for matching “yellow signals”. This is not an example of clear thinking and it contradicts the Principle of Univariance to which we shall adhere. That may be stated as follows: “The intrinsic effect of light upon a visual pigment depends only upon the effective quantum catch by that pigment and does not depend upon what quanta are caught”, (see the first of these three papers, RUSHTON, POWELL and WHITE, 1973 hereafter referred to as RPW 1). Now, if a normal subject in making a Rayleigh match adjusts the red/green ratio and also the yellow intensity so that the quantum catch by each of the cone pigments involved is the same from the yellow field as from the (red + green) mixture, then each field will affect each pigment identically and neither pigment will be able to distinguish the one from the other. It is an experimental fact that from this position any movement of the red/green setting produces a colour mismatch which cannot be re-matched by any increased change in the red/ green setting or by any change of intensity of the yellow. Thus there is only one setting for the match, namely the one with which we started-when quanta are caught equally from the two fields on each of the cone pigments. Indeed, if the pigments cannot distinguish the fields, nothing else in the visual system can. Now if the anomalous trichromat has the normal cone pigments, then a Rayleigh match that was indistinguishable to normal pigments would be indistinguishable to him. This is 2017