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**Cavernio** · 01-13-2014, 01:56 PM

http://discovermagazine.com/2012/jul...r-human-vision
Some women can see extra colors as they have an extra functional cone (the cell that reacts to wavelengths depending on color) in the retina, 4 instead of 3.

The Wikipedia subsection of tetrachromacy in people:

Humans and closely related primates normally have three types of cone cells and are therefore trichromats (animals with three different cones). However, at low light intensities the rod cells may contribute to color vision, giving a small region of tetrachromacy in the color space.[11]

In humans, two cone cell pigment genes are located on the sex X chromosome, the classical type 2 opsin genes OPN1MW and OPN1MW2. It has been suggested that as women have two different X chromosomes in their cells, some of them could be carrying some variant cone cell pigments, thereby possibly being born as full tetrachromats and having four different simultaneously functioning kinds of cone cells, each type with a specific pattern of responsiveness to different wavelengths of light in the range of the visible spectrum.[12] One study suggested that 2–3% of the world's women might have the kind of fourth cone that lies between the standard red and green cones, giving, theoretically, a significant increase in color differentiation.[13] Another study suggests that as many as 50% of women and 8% of men may have four photopigments and corresponding increased chromatic discrimination in comparison to trichromats.[12] In June 2012, after 20 years of study of women with four cones (non-functional tetrachromats), neuroscientist Dr. Gabriele Jordan identified a woman (subject cDa29) who was able to detect a greater variety of colors than trichromatic ones, corresponding with a functional tetrachromat (or true tetrachromat).[14]

Variation in cone pigment genes is widespread in most human populations, but the most prevalent and pronounced tetrachromacy would derive from female carriers of major red/green pigment anomalies, usually classed as forms of "color blindness" (protanomaly or deuteranomaly). The biological basis for this phenomenon is X-inactivation of heterozygotic alleles for retinal pigment genes, which is the same mechanism that gives the majority of female new-world monkeys trichromatic vision.

In humans, preliminary visual processing occurs within the neurons of the retina. It is not known how these nerves would respond to a new color channel, that is, whether they could handle it separately or just combine it in with an existing channel. Visual information leaves the eye by way of the optic nerve; it is not known whether the optic nerve has the spare capacity to handle a new color channel. A variety of final image processing takes place in the brain; it is not known how the various areas of the brain would respond if presented with a new color channel.

Mice, which normally have only two cone pigments, can be engineered to express a third cone pigment, and appear to demonstrate increased chromatic discrimination,[15] arguing against some of these obstacles; however, the original publication's claims about plasticity in the optic nerve have also been disputed.[16]

Humans cannot perceive UV light directly since the lens of the eye blocks most light in the wavelength range of 300-400 nm; shorter wavelengths are blocked by the cornea.[17] Nevertheless, the photoreceptors of the retina are sensitive to near UV light and people lacking a lens (a condition known as aphakia) perceive near UV light as whitish blue or whitish-violet, probably because all three types of cones are roughly equally sensitive to UV light, but blue cones a bit more.

Personally, there's a range of color that I call yellow that most people call green. The opposite happens less often, where I call something green that someone else calls yellow. I don't think I'm one of these women who see extra colors though, that's an aside. Color blindness doesn't run in my family; my yellow or blue cone is probably 'calibrated' to a wavelength off enough from average such that it comes up enough for me to discern that I probably see that wavelength of color differently.

01-13-2014, 01:56 PM	#50
Cavernio sunshine and rainbows Join Date: Feb 2006 Age: 41 Posts: 1,987	Re: how bad is ur eyes be http://discovermagazine.com/2012/jul...r-human-vision Some women can see extra colors as they have an extra functional cone (the cell that reacts to wavelengths depending on color) in the retina, 4 instead of 3. The Wikipedia subsection of tetrachromacy in people: Humans and closely related primates normally have three types of cone cells and are therefore trichromats (animals with three different cones). However, at low light intensities the rod cells may contribute to color vision, giving a small region of tetrachromacy in the color space.[11] In humans, two cone cell pigment genes are located on the sex X chromosome, the classical type 2 opsin genes OPN1MW and OPN1MW2. It has been suggested that as women have two different X chromosomes in their cells, some of them could be carrying some variant cone cell pigments, thereby possibly being born as full tetrachromats and having four different simultaneously functioning kinds of cone cells, each type with a specific pattern of responsiveness to different wavelengths of light in the range of the visible spectrum.[12] One study suggested that 2–3% of the world's women might have the kind of fourth cone that lies between the standard red and green cones, giving, theoretically, a significant increase in color differentiation.[13] Another study suggests that as many as 50% of women and 8% of men may have four photopigments and corresponding increased chromatic discrimination in comparison to trichromats.[12] In June 2012, after 20 years of study of women with four cones (non-functional tetrachromats), neuroscientist Dr. Gabriele Jordan identified a woman (subject cDa29) who was able to detect a greater variety of colors than trichromatic ones, corresponding with a functional tetrachromat (or true tetrachromat).[14] Variation in cone pigment genes is widespread in most human populations, but the most prevalent and pronounced tetrachromacy would derive from female carriers of major red/green pigment anomalies, usually classed as forms of "color blindness" (protanomaly or deuteranomaly). The biological basis for this phenomenon is X-inactivation of heterozygotic alleles for retinal pigment genes, which is the same mechanism that gives the majority of female new-world monkeys trichromatic vision. In humans, preliminary visual processing occurs within the neurons of the retina. It is not known how these nerves would respond to a new color channel, that is, whether they could handle it separately or just combine it in with an existing channel. Visual information leaves the eye by way of the optic nerve; it is not known whether the optic nerve has the spare capacity to handle a new color channel. A variety of final image processing takes place in the brain; it is not known how the various areas of the brain would respond if presented with a new color channel. Mice, which normally have only two cone pigments, can be engineered to express a third cone pigment, and appear to demonstrate increased chromatic discrimination,[15] arguing against some of these obstacles; however, the original publication's claims about plasticity in the optic nerve have also been disputed.[16] Humans cannot perceive UV light directly since the lens of the eye blocks most light in the wavelength range of 300-400 nm; shorter wavelengths are blocked by the cornea.[17] Nevertheless, the photoreceptors of the retina are sensitive to near UV light and people lacking a lens (a condition known as aphakia) perceive near UV light as whitish blue or whitish-violet, probably because all three types of cones are roughly equally sensitive to UV light, but blue cones a bit more. Personally, there's a range of color that I call yellow that most people call green. The opposite happens less often, where I call something green that someone else calls yellow. I don't think I'm one of these women who see extra colors though, that's an aside. Color blindness doesn't run in my family; my yellow or blue cone is probably 'calibrated' to a wavelength off enough from average such that it comes up enough for me to discern that I probably see that wavelength of color differently.