Do tetrachromatic women exist?

Dr Gabriele Jordan; Dr Nicholas Atkinson

Do tetrachromatic women exist? Lookup NU author(s) Dr Gabriele Jordan Dr Nicholas Atkinson



Author(s)		Jordan G, Atkinson N, Mollon JD
Editor(s)
Publication type		Conference Proceedings (inc. Abstract)
Conference Name		Twenty-Ninth European Conference on Visual Perception
Conference Location		St Petersburg, Russia
Year of Conference		2006
Date		20-25 August 2006
Volume
Pages



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About 12% of women are carriers of an X-linked red/green hybrid gene that encodes a photopigment with a spectral sensitivity somewhere between those of the normal M and L cone photopigments. Owing to random X-chromosome inactivation (Lyon, 1961, Nature vol. 190), the retinal mosaic of such a carrier will contain more than three types of cone. We ask whether she can become a functional tetrachromat and exhibit enhanced colour discrimination. Our subjects perform a three-alternative temporal forced-choice task, in which two of the stimuli are monochromatic (590 nm) while the third is a mixture of two monochromatic lights (550 nm plus 670 nm). The stimulus fields are 2-deg, circular patches centred on the fovea and are presented in rapid succession in Maxwellian-view. Chromatic aberrations are masked by an annulus containing temporal chromatic noise. Subjects are asked to identify which of the triplet of stimulus fields is the mixture. In a random sequence, the program tests different combinations of (a) the red/green mixture ratio and (b) the radiance of the monochromatic field. For the normal, there is a combination of (a) and (b), equivalent to the Rayleigh match, where performance is at chance. A tetrachromat should not fail at any combination.