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Topic: Trichromatic color vision

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	Color vision - Wikipedia, the free encyclopedia
		Color vision is the capacity of an organism or machine to distinguish objects based on the wavelength of the light they reflect or emit.
		Perception of color is achieved in mammals through color receptors containing pigments with different spectral sensitivities.
		Color perception mechanisms are highly dependent on evolutionary factors, of which the most prominent is satisfactory recognition of food sources.
	en.wikipedia.org /wiki/Color_vision (878 words)

	Trichromat - Wikipedia, the free encyclopedia
		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.
		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.
		Some species of insects (such as honeybees) are also trichromats, being sensitive to ultraviolet, blue and green instead of blue, green and red.
	en.wikipedia.org /wiki/Trichromatic (330 words)

	OLYMPUS MIC-D: Physics of Light and Color - Human Vision and Color Perception (Site not responding. Last check: 2007-09-16)
		Clear vision is prevented by a reduction in the amount of light that reaches the retina and by clouding of the image as though the person were seeing through a haze.
		Although the color is intended for the vehicles to be easily seen and responded to, the wavelength distribution is not highly visible at low light levels and appears nearly fl at night.
		Often, red-green color blindness is caused by a sex-linked trait that is recessive (affecting about 6 percent of the human male population on their X-chromosome) with double recessives occasionally found in females, but being a very rare occurrence.
	www.mic-d.com /curriculum/lightandcolor/humanvision.html (3828 words)

	Color vision - TheBestLinks.com - Colour vision, Birds, Chromosome, Color blindness, ... (Site not responding. Last check: 2007-09-16)
		Color vision is the visual ability to perceive and correctly interpret color (that is, different wavelengths of visible light) and especially lighting cues.
		In most primates there are three types of color receptors, known as cone cells, that are maximally receptive to yellow, green, and blue frequencies of light, and this allows for trichromatic color vision.
		Brightly colored oil-droplets inside the cones are used to shift the spectral sensitivity of the cell.
	www.thebestlinks.com /Colour_vision.html (686 words)

	Nat' Academies Press, (NAS Colloquium) Vision: From Photon to Perception (1999)
		The generalization that color vision is a more developed and acute capacity in primates than it is in other mammals came from a consideration of the natural history of mammals (1).
		Although there were plenty of earlier hints that the color vision of New World monkeys differs from that of normal human subjects (3,4), it was unexpected to find the biggest difference was the degree of intraspecies variation in color vision.
		The former have trichromatic color vision; the latter are dichromats.
	books.nap.edu /books/0309068347/html/21.html (5339 words)

	The Evolution of Color Vision
		As this is grist for the evolution of color vision mill, we're literally ripe for the addition of a fourth cone class.
		The color vision of primates is not strictly homologous to the color vision of fish, birds, turtles, etc. Much of the machinery used for primate color vision arose independently long after similar systems developed (without being lost) in other vertebrate lineages.
		Color vision is mediated by cones, so named because of the shape of the receptive part of the cells.
	www.talkorigins.org /faqs/vision.html (4843 words)

	Colorblindness - Preliminary Draft (Site not responding. Last check: 2007-09-16)
		Color blindness is a genetic disease that is different in severity and location and is a sex-linked trait.
		In red-green color blindness only one of the two pigments is expressed; whereas, in anomalous trichromacy two pigments are expressed, but the anomalous pigment is displaced to a spectral location closer to that of it’s normal partners.
		The most dramtic aspect of dichromatic color vision is the occurrence of a spectral neutral point, a restricted region of the spectrum which to the dichromat appears the same as a broad band light.
	srv2.lycoming.edu /~newman/courses/bio22298/disorderpapers/Colorblindness/preliminary.htm (1290 words)

	Science News: Additional genes may affect color vision. @ HighBeam Research (Site not responding. Last check: 2007-09-16)
		The standard model of color vision, proposed more than 200 years ago, postulates three kinds of photopigments in cone cells on the retina.
		In color blindness, which affects as many as 8 to 10 percent of men, a person may lose the ability to see all colors or merely the capacity to discriminate between certain hues.
		This finding contradicts the standard model of color vision "that has held sway for more than 2 centuries, in which the presence of three pigments is proposed to explain human trichromatic color vision," the Neitzes conclude.
	www.highbeam.com /library/doc0.asp?DOCID=1G1:16702752&refid=ip_encyclopedia_hf (691 words)

	The Primates: Primate Color Vision (Site not responding. Last check: 2007-09-16)
		Vision among vertebrates is a result of having specialized light receptor structures known as rods and cones at the back of the eye in the retina.
		Color sensitive cones would be of little use to nocturnal primates due to the fact that they require the relatively bright light of daytime to detect color.
		Once again, color may be a valuable clue for such species since the edibility of leaves from the same tree or shrub often varies with their maturity, which can be signaled by color.
	anthro.palomar.edu /primate/color.htm (1000 words)

	Journal of Vision - Photopigment basis for dichromatic color vision in the horse, by Carroll, Murphy, Neitz, Ver Hoeve, ...
		This dictates that at photopic light levels the color vision capabilities must be limited to dichromacy, the only form of color vision that has been observed in nonprimate mammals (Jacobs, 1993).
		For a dichromat, when colors from the two ends of the spectrum are mixed, rather than getting an intermediate hue, the result is either achromatic (white or gray) or a desaturated version of one of the two basic hues (ie, a pastel blue or yellow).
		It is predicted to be similar to the experience of a red-green color blind human except the neutral (gray) regions are rotated (counterclockwise in Figure 3) compared to the human protanope or deuteranope.
	www.journalofvision.org /1/2/2/article.aspx (4121 words)

	HyperText Psychology - SENSES/Vision/color
		The trichromatic theory proposed by Helmholtz (1856) expanding on work by Thomas Young is a proposal that the eye must have three different types of receptors for color.
		The trichromatic theory assumes three, and only three types of color receptors, each more sensitive to a particualr color, i.e., red, or green, or blue.
		The study of color blindness is a good example of scientific method and the way in which theories are developed and tested.
	sun.science.wayne.edu /~wpoff/cor/sen/viscolor.html (281 words)

	Psychology 121, Study Questions, Chapter 6 (Site not responding. Last check: 2007-09-16)
		The results of the color matching experiments are (1) it takes at least _________ wavelengths, and (2) at most ___________ wavelengths to match any other wavelength, for people with normal color vision.
		Color perception is based on the ___________ of ____________ in the three color reception mechanisms.
		Trichromatic human color vision represents the best color vision, in terms of number of receptor types and range of wavelengths seen.
	people.ucsc.edu /~jgille/sqCh6.html (720 words)

	Perception \|
		A color that results when several component colors are combined in such a way that each component contributes a portion to the spectral composition of the combination.
		Colors, such as purple, that are not found in the spectrum.
		The theory that human color vision is trichromatic--that is, it depends on the responses of three types of cones.
	highered.mcgraw-hill.com /sites/0070579431/student_view0/chapter7/glossary.html (460 words)

	Color Blindness
		Color blindness is the difficulty someone has in recognizing or distinguishing one color from another.
		Color blindness may be detected during the routine ophthalmologic examination.
		The individual may not be able to see color with the lenses, but may be able to distinguish between colors better as a result of wearing them.
	www.innvista.com /health/ailments/eyeail/colorbl.htm (560 words)

	Primates trade smell for sight
		Yoav Gilad and his colleagues at the Max Planck Institute for Evolutionary Anthology in Germany and the Weizmann Institute in Israel have found a correlation between the loss of olfactory receptor (OR) genes, which are the molecular basis for the sense of smell, and the acquisition of full trichromatic color vision in primates.
		In trichromatic color vision, three retinal protein pigments, called opsins, absorb various wavelengths of light, which the brain processes to produce full-color images.
		The evolution of color vision, the authors propose, coincided with a growing complement of OR pseudogenes and a deterioration of the sense of smell.
	www.eurekalert.org /pub_releases/2004-01/plos-pts011204.php (502 words)

	Trichromatic theory (Site not responding. Last check: 2007-09-16)
		The trichromatic theory of color vision is based on the premise that there are three classes of cone receptors subserving color vision.
		Modern color scientists have put great effort into determining that there are indeed three classes of cones, that their outer segments contain spectrally selective photopigments and in determining the spectral absorbance of these photopigments.
		The trichromatic theory operates at the receptor level and the opponent processes theory applies to the subsequent neural level of color vision processing.
	www.yorku.ca /eye/trichrom.htm (217 words)

	Webvision: Color Perception
		Consequently, colour vision is described as being trivariant or trichromatic, and initial psychophysical studies demonstrated that colours could be matched by the use of three different primaries.
		Anomalous trichromats have all three cone photopigments, however, one cone photopigment is anomalous having a shifted peak sensitivity The types and prevalence of CVD is listed in Table 1.
		Rushton WAH (1963) A cone pigment in protanope.
	webvision.med.utah.edu /KallColor.html (4599 words)

	Background information
		Human night-time vision depends on sensitive rod photoreceptors, while human day-time color vision depends on the three types of cone photoreceptors.
		The three functions relating the matching intensities of the three primary lights to the wavelength of the spectral light are known as the color matching functions or CMFs.
		The missing values can be obtained by determining the locations of the confusion points of the three types of dichromats in the trichromatic chromaticity diagram (see Wyszecki and Stiles, 1982), but a better method is to measure the dichromat's cone spectral sensitivities directly.
	cvision.ucsd.edu /background.htm (608 words)

	Color Vision
		The chemical basis of vision depends upon the absorption of light (electromagnetic radiation) by special pigments in the eye.
		Colorblindness occurs when one or more of the cone pigments is defective. A colorblind person still has a range of color perception, but lacks the ability to discriminate a complete spectrum of colors.
		Purple is a color sensation produced by simultaneous stimulation of blue and red color receptors.
	www.cals.ncsu.edu /course/ent425/tutorial/colorvision.html (395 words)

	Trichromatic color vision with only two spectrally distinct photopigments - Nature Neuroscience
		Protanomaly is a common, X-linked abnormality of color vision.
		Like people with normal color vision, protanomalous observers are trichromatic, but their ability to discriminate colors in the red−green part of the spectrum is reduced because the photopigments that mediate discrimination in this range are abnormally similar.
		A single amino acid substitution was correlated with trichromacy in these subjects, suggesting that differences in pigment sequence may regulate the optical density of the cone.
	www.nature.com /cgi-taf/DynaPage.taf?file=/neuro/journal/v2/n10/abs/nn1099_884.html (237 words)

	The Evolution of Trichromatic Color Vision by Opsin Gene Duplication in New World and Old World Primates -- Dulai et ...
		Among the mammals, primates are unique in possessing trichromatic color vision.
		Variations of color vision in a New World primate can be explained by a polymorphism of retinal photopigments.
		Color vision of ancestral organisms of higher primates.
	www.genome.org /cgi/content/full/9/7/629 (5208 words)

	Trichromatic Color Vision in Primates -- Rowe 17 (3): 93 -- Physiology
		is the degree to which human color vision is not uniform (10).
		Nathans J. The evolution and physiology of human color vision: insights from molecular genetic studies of visual pigments.
		Neitz M and Neitz J. Molecular genetics of color vision and color vision defects.
	physiologyonline.physiology.org /cgi/content/full/17/3/93 (3970 words)

	physics - Trichromat
		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.
		Carnivores, especially nocturnal species, tend to be anomalous trichromats: they possess three distinct types of color receptors, but which respond to different wavelengths than those of primates.
		(The domestic dog, however, is a dichromat, having color vision similar to humans with deuteranopia.) Some species of insects (such as honeybees) are also trichromats, being sensitive to ultraviolet, blue and green instead of blue, green and red.
	www.physicsdaily.com /physics/Trichromat (246 words)

	Re: ARE DOGS COL0R BLIND?
		Color blindness is the inability to see certain colors.
		Color vision is controlled by cells in the retina of the eye called cones.
		Since it cannot see shades of red, the dog is said to have dichromatic (two color) vision compared to people who have trichromatic (three color) vision and can see the full spectrum of colors.
	www.madsci.org /posts/archives/mar97/855166408.Zo.r.html (225 words)

	1596supp
		Defend the statement that we are all partially color blind.
		Describe some key properties of anomalous trichromatic color vision, explaining the physiological mechanisms that underly them.
		Explain the molecular genetics of normal and anomalous color vision, starting with the key discoveries made as a graduate student by Jeremy Nathans.
	psy.ucsd.edu /~dmacleod/159/1596supp.htm (344 words)

	Natural Night Vision
		Based on the results, it was determined that the effectiveness and contribution of the ultraviolet photoreceptors was quite low in relation to the other two (blue and green photoreceptors).
		So an additional test was carried out by the researchers to see if these ultraviolet photoreceptors contributed to the hawkmoth’s color vision at all.
		The reward color was selected to be the ultraviolet-absorbing white stimulus instead of the ultraviolet-reflective.
	student.biology.arizona.edu /honors2003/group10/E4.html (229 words)

	Human Color Vision (Site not responding. Last check: 2007-09-16)
		This shows that even though the color stimuli of a object suggest one color, the human perception may perceive a completely different color, based on the sensitivity of the photo-receptors in the retina of the eye.
		Similarly, the stimuli produced by a fabric sample as shown in Figure 8 seems green to the human observer though the color stimuli seems to indicate otherwise.
		Because of the trichromatic nature of the human vision, it is very possible that two color stimuli, having different spectral power distribution will appear identical to the human eye.
	www.cs.unc.edu /~majumder/color/node12.html (355 words)

	Electroretinogram analysis of relative spectral sensitivity in genetically identified dichromatic macaques -- Hanazawa ...
		Trichromatic color vision in Old World primates originates from three types of retinal cone photoreceptors possessing differing
		for trichromatic color vision; the roles of lost and retained
		have trichromatic color vision homologous to that of humans (2)
	www.pnas.org /cgi/content/full/98/14/8124 (2592 words)

	Active Skim View of: Primate photopigments and primate color vision
		Active Skim View of: Primate photopigments and primate color vision
		From: (NAS Colloquium) Vision: From Photon to Perception
		The clear variations in the pigments of the New World monkeys suggested it would be profitable to correlate spectral positioning with sequence differences among several different phenotypic versions of the M and L cone pigments in these animals.
	www.nap.edu /nap-cgi/skimit.cgi?isbn=0309068347&chap=21-25 (371 words)

	color and color vision (Site not responding. Last check: 2007-09-16)
		Mixing of Colors: Learn about what happens when colors are combined.
		Opsin genes, cone photopigments, color vision and color blindness,
		Color and Vision Questions and Answers posed by the Munsell Color Science Laboratory, Rochester Institute of Technology
	www.yorku.ca /eye/color.htm (100 words)

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