Trichromat
A
trichromat 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 three different pure spectral lights. The condition of being a trichromat is called
trichromacy.
The normal explanation of trichromacy is that the organism's
retina contains three types of
color receptors (called
cone cells in vertebrates) with different
absorption spectra. In practice the number of such receptor types may be greater than three, since different types may be active at different light intensities. In vertebrates with three types of cone cells, at low light intensities the
rod cells may contribute to colour vision, giving a small region of
tetrachromacy in the colour space.
Humans and other
Old World primates are usually trichromats, as are female
New World monkeys of most species, and both male and female
howler monkeys. Recent research suggests that trichromacy may also be quite general among
marsupials. Most other mammals are currently thought to be
dichromats, with only two types of cone (though the possibility of limited trichromacy at low light levels where the rods and cones are both active). Some species of
insects (such as
honeybees) are also trichromats, being sensitive to
ultraviolet, blue and green instead of blue, green and red.
*
Trichromatic theory of color vision* Arrese, CA; Oddy, AY; Runham, PB; Hart, NS; Shand, J; Hunt, DM (2005). "Cone topography and spectral sensitivity in two potentially trichromatic marsupials, the quokka (
Setonix brachyurus) and quenda (
Isoodon obesulus)."
Proceedings of the Royal Society of London Series B. 272(1595), 791-796.
* Calderone, JB; Jacobs, GH (2003). "Spectral properties and retinal distribution of ferret cones."
Visual Neuroscience. 20(1), 11-17.
* Calderone, JB; Reese, BE; Jacobs, GH (2003). "Topography of photoreceptors and retinal ganglion cells in the spotted hyena (
Crocuta crocuta)."
Brain Behavior and Evolution. 62(4), 182-192.
* Rowe, Michael H (2002). "Trichromatic color vision in primates."
News in Physiological Sciences. 17(3), 93-98. [
1]
*
The Straight Dope: "Are cats and dogs really color-blind? How do they know?"
