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Do tetrachromatic women exist?
Lookup NU author(s)
Dr Gabriele Jordan
Dr Nicholas Atkinson
Jordan G, Atkinson N, Mollon JD
Conference Proceedings (inc. Abstract)
Twenty-Ninth European Conference on Visual Perception
St Petersburg, Russia
Year of Conference
20-25 August 2006
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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.
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