ECVP 2004 Abstract

Cite as:
Jakab Z, Wenzel K, 2004, "Detecting tetrachromacy in human subjects" Perception 33 ECVP Abstract Supplement

Detecting tetrachromacy in human subjects

Z Jakab, K Wenzel

Human tetrachromacy is a rare condition in which the retina contains four different types of wavelength-selective photoreceptors (cones). There exist reports of both L-cone tetrachromacy, and M-cone tetrachromacy (two subtypes of the long-wave-sensitive or the middle-wave-sensitive cones in the same retina). We developed two psychophysical procedures, one for identifying L-cone tetrachromacy, and another to test for M-cone tetrachromacy. First we presented to subjects 720 nm and 760 nm monochromatic lights in the two halves of a vertically split circular field viewed through the aperture of a Pulfrich spectrophotometer. Subjects were asked to adjust the intensity of the 720 nm light to achieve a perfect match; we expected that L-cone tetrachromats would always sense a residual hue difference between the two lights. In testing for M-cone tetrachromacy, we looked for a peak of discriminability (corresponding to the sensitivity crossover of two slightly different M-cone subtypes) in the middle portion of the spectrum while the subjects' L-cones and M-cones were desensitised by a mixture of 380 nm and 720 nm lights. Eighty colour-normal subjects were examined; one L-cone tetrachromat and one M-cone tetrachromat were identified. Further examination of these subjects is in progress.

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