Pentachromacy

Pentachromacy is the condition of possessing five independent channels for conveying color information. Organisms with pentachromacy are called "pentachromats". For these organisms, the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than five different pure spectral lights.

The normal explanation of pentachromacy is that the organism's retina contains five types of cone cells with different absorption spectra. In practice the number of such receptor types may be greater than five, since different types may be active at different light intensities.

Some birds (notably pigeons) and butterflies have five or more kinds of color receptors in their retinae, and are therefore believed to be pentachromats, [ [http://www.springerlink.com/content/q77725639466x474/ Wavelength discrimination in the ‘visible’ and ultraviolet spectrum by pigeons, Jacky Emmerton1, and Juan D. Delhis, Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology. Volume 141, Number 1. March, 1980] ] though psychophysical evidence of functional pentachromacy is not easy to come by. Lampreys may also be pentachromats. [ [http://www.fasebj.org/cgi/content/abstract/fj.06-8057comv1?ck=nck Functional characterization, tuning, and regulation of visual pigment gene expression in an anadromous lamprey -- Davies et al., 10.1096/fj.06-8057com -- The FASEB Journal] ] As with tetrachromacy, it is suggested that women carriers of genes for "both" mild forms of color blindness, deuteranomaly and protanomaly, are born with five different types of color-sensing cones though the red- and green-deficient cones are later lost.

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