Monochromat
Encyclopedia
Monochromacy, also known as "total color blindness", is a complete inability to distinguish colors. 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.
, 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 cone
s.
Some individuals possess diseases or injuries that lead to nyctalopia
, or night blindness, where rod cells stop responding properly to light.
s other than primate
s were monochromats. In the last half-century, however, evidence of at least dichromat
ic color vision in a number of mammalian orders
has accumulated. Two of the orders of sea mammals, the pinniped
s (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 dichromat
s or anomalous trichromat
s.
, a renowned color vision researcher at the Medical College of Wisconsin
, each of the three standard color-detecting cones in the retina of trichromat
s– 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. Therefore, a monochromat would be able to distinguish about 100 different colors.
Color blindness
Color blindness or color vision deficiency is the inability or decreased ability to see color, or perceive color differences, under lighting conditions when color vision is not normally impaired...
, 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
Visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
can be matched by any pure spectral light.
Causes
In vertebrates there are typically two kinds of receptors; rodsRod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...
, which primarily distinguish between levels of illumination, and cones
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
, which are responsible for perception of color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
. There are different types of cones; each perceives only a single color. The normal explanation of monochromacy is that the organism's retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
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 cone
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
s.
Some individuals possess diseases or injuries that lead to nyctalopia
Nyctalopia
Nyctalopia is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition...
, or night blindness, where rod cells stop responding properly to light.
Types
There are two known types of monochromacy. "Animals with monochromatic vision may be either rod monochromats or cone monochromats. These monochromats contain photoreceptors which have a single spectral sensitivity curve." There is also a third, theoretical type that has never been identified.- Rod monochromacy is the condition of having only rods in the retina. A rod monochromat is truly unable to see any color and can see only shades of grey.
- Cone monochromacy is the condition of having both rods and cones, but only a single kind of cone. A cone monochromat can have good pattern vision at normal daylight levels, but will not be able to distinguish hues. In humans, who have three different types of cones, there are three differing forms of cone monochromacy. There are three types named according to the single functioning cone class:
- Blue cone monochromacy, also known as S-cone monochromacy
- Green cone monochromacy, also known as M-cone monochromacy
- Red cone monochromacy, also known as L-cone monochromacy
- Cone monochromacy, type II, if its existence were established, would be the case in which the retina contains no rods, and only a single type of cone. Such an animal would be unable to see at all at lower levels of illumination, and of course would be unable to distinguish hues. In practice it is hard to produce an example of such a retina, at least as the normal condition for a species.
Animals that are monochromats
It used to be confidently claimed that most mammalMammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s other than primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s were monochromats. In the last half-century, however, evidence of at least dichromat
Dichromat
Dichromacy is the state of having two types of functioning color receptors, called cone cells, in the eyes. Organisms with dichromacy are called dichromats. Dichromats can match any color they see with a mixture of no more than two pure spectral lights...
ic color vision in a number of mammalian orders
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
has accumulated. Two of the orders of sea mammals, the pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...
s (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
Color blindness
Color blindness or color vision deficiency is the inability or decreased ability to see color, or perceive color differences, under lighting conditions when color vision is not normally impaired...
, however, are either dichromat
Dichromat
Dichromacy is the state of having two types of functioning color receptors, called cone cells, in the eyes. Organisms with dichromacy are called dichromats. Dichromats can match any color they see with a mixture of no more than two pure spectral lights...
s or anomalous trichromat
Trichromat
Trichromacy or trichromaticism is the condition of possessing three independent channels for conveying color information, derived from the three different cone types...
s.
Monochromat capability
According to Jay NeitzJay Neitz
Jay Neitz is professor of ophthalmology and a color vision researcher at the University of Washington in Seattle, Washington in the United States.- Cone cells and the numbers of colors an organism can see :...
, a renowned color vision researcher at the Medical College of Wisconsin
Medical College of Wisconsin
Medical College of Wisconsin is a private, freestanding medical school and graduate school located in Milwaukee, Wisconsin, United States. It was formerly affiliated with Marquette University....
, each of the three standard color-detecting cones in the retina of trichromat
Trichromat
Trichromacy or trichromaticism is the condition of possessing three independent channels for conveying color information, derived from the three different cone types...
s– blue
Blue
Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...
, green
Green
Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...
and red
Red
Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...
-- 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. Therefore, a monochromat would be able to distinguish about 100 different colors.
See also
- AchromatopsiaAchromatopsiaAchromatopsia , is a medical syndrome that exhibits symptoms relating to at least five separate individual disorders. Although the term may refer to acquired disorders such as color agnosia and cerebral achromatopsia, it typically refers to an autosomal recessive congenital color vision disorder,...
- Cone dystrophyCone dystrophyA cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision....
- Dichromacy
- Trichromacy
- Tetrachromacy