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MonochromacyFrom Wikipedia, the free encyclopedia
Monochromacy, also known as "total color blindness"[1], is a complete inability to distinguish colors.[2] This is distinguished from more common forms of color blindness, in which the affected individual can perceive color differences, but cannot make the same distinctions between colors as can an unaffected person. Organisms with monochromacy are called monochromats. The perceptual effect of any arbitrarily chosen light from the visible spectrum can be matched by any pure spectral light. CausesIn vertebrates there are typically two kinds of receptors; rods, which primarily distinguish between levels of illumination, and cones, which are responsible for perception of color. There are different types of cones; each perceives only a single color. The normal explanation of monochromacy is that the organism's retina contains only a single kind of light receptor cell, or at least that only one kind is active at any particular level of illumination. Monochromacy is caused by either a defect or the complete absence of the retinal cones.[1] Some individuals possess diseases or injuries that lead to nyctalopia, or night blindness, where rod cells stop responding properly to light. TypesThere are two known types of monochromacy.[3][4] "Animals with monochromatic vision may be either rod monochromats or cone monochromats. These monochromats contain photoreceptors which have a single spectral sensitivity curve."[5] There is also a third, theoretical type that has never been identified.
Animals that are monochromatsIt used to be confidently claimed that most mammals other than primates were monochromats. In the last half-century, however, evidence of at least dichromatic color vision in a number of mammalian orders has accumulated. Two of the orders of sea mammals, the pinnipeds (which includes the seal, sea lion, and walrus) and cetaceans (which includes dolphins and whales) clearly are cone monochromats, since the short-wavelength sensitive cone system is genetically disabled in these animals. The same is true of the owl monkeys, genus Aotus. Both rod and cone monochromacy occur as very rare forms of color blindness in humans. Rod monochromacy, or maskun, is the more common of the two. The majority of people described as color blind, however, are either dichromats or anomalous trichromats. Monochromat capabilityAccording to Jay Neitz, a renowned color vision researcher at the Medical College of Wisconsin, each of the three standard color-detecting cones in the retina of trichromats– blue, green and red -- can pick up about 100 different gradations of color. But the brain can combine those variations exponentially, multiplying each new variety of cone by 100, so that the average human can distinguish about one million different hues. [6] Therefore, a monochromat would be able to distinguish about 100 different colors. [7] See alsoReferences
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