Tetrachromat

A tetrachromat is an organism for which the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than four different pure spectral lights. The condition of being a tetrachromat is called tetrachromacy.

The normal explanation of tetrachromacy is that the organism's retina contains four types of higher-intensity light receptors (called cone cells in vertebrates as opposed to rod cells which are lower intensity light receptors) with different absorption spectra. In practice the number of such receptor types may be greater than four, since different types may be active at different light intensities.

Tetrachromacy has not yet been demonstrated in any mammalian species, though it is likely that it occurs in some birds, fish, amphibians, reptiles, arachnids and insects. Humans and other Old World primates normally have three types of cone cells and are therefore trichromats. However, at low light intensities the rod cells may contribute to color vision, giving a small region of tetrachromacy in the color space.

It has been suggested that women who are carriers for certain kinds of color blindness (protanomaly or deuteranomaly) may be born as full tetrachromats, having four different simultaneously functioning kinds of cones. The biological basis for this phenomenon is X-inactivation.

External links

* Jameson, Kimberly A.; Highnote, Susan M.; and Wasserman, Linda M. "Richer color experience in observers with multiple photopigment opsin genes." Psychonomic Bulletin & Review, 2001, 8 (2), 244-261 http://www.klab.caltech.edu/cns186/papers/Jameson01.pdf
* Thompson, Evan (2000). "Comparative color vision: Quality space and visual ecology." In Steven Davis (Ed.), Color Perception: Philosophical, Psychological, Artistic and Computational Perspectives, pp. 163-186. Oxford: Oxford University Press. http://www.yorku.ca/evant/ETVancouvercolour.pdf
* Holba, Á.; Lukács, B. "On tetrachromacy." http://www.rmki.kfki.hu/~lukacs/TETRACH.htm
* Tetrachromacy in female humans (student essay)
* Looking for Madam Tetrachromat By Glenn Zorpette. Red Herring magazine, 1 November 2000
* Ultraviolet vision
* The Human is a blocked tetrachromat A review of the spectral sensitivity of the human visual system. (Claims that the human lens is mostly responsible for blocking the violet frequencies)