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Tetrachromancy: Half of women see more colors than the rest of us

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    Tetrachromancy: Half of women see more colors than the rest of us

    Half of the Women See More Colors Than the Rest of the People Do
    By Stefan Anitei, Science Editor
    June 26th, 2007, 18:16 GMT
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    Normally, people have three types of cone cells for daylight, for detecting different colors. But some women can see extra colors as they have four types of cone cell receptors. They are called tetrachromats. Compared to them, we all are color blind.

    The first tetrachromat woman was discovered by researchers at Cambridge University in 1993. This is perhaps the most remarkable human mutation ever detected. The fact that all tetrachromats are female intrigued scientists. Now two scientists, working separately, want to investigate systematically for tetrachromats to clarify more about their existence and how they detect colors.

    All mammals descended from nocturnal tree dwellers, which were colorblind, but the line of primates had more advantages in developing color vision for finding fruit food. Human color vision is based on three forms of iodopsin (color pigments), each sensitive to a different light wavelength and is found in a different cone type. When a different cone type is stimulated, the brain reads it as a particular color.

    The three iodopsins respond to red, green and blue; all the other colors are their combinations. Like all pigments, iodopsins are proteins encoded by DNA genes. The genes encoding the "red" and "green" iodopsins are located on the X sex chromosome, while the "blue" iodopsin is on a non-sexual chromosome.

    That's why color-blindness mostly affects men: 8% of the Caucasian males; while under 0.5 % of Americana women present it. Women have X chromosomes: one from the mother and one the father, while men have just one X chromosome from the mother and an Y sex chromosome from the father (this one does not contain any iodopsin gene).

    X chromosomes can be a "green" iodopsine or a slightly shifted "green" iodopsine, and a "red" iodopsine and a shifted "red" iodopsine. That's why a woman can carry 5 types of iodopsins: these four plus "blue", while a man just three (a green type, a red one plus blue).

    A recent paper by Kimberly Jameson, Susan Highnote and Linda Wasserman of the University of California, San Diego, showed that up to 50 % of women carry 4 types of iodopsins and can employ their extra pigments in "contextually rich viewing circumstances".

    For example, when looking at a rainbow, these females can segment it into about 10 different colors, while trichromat (with three iodopsins) people can see just seven: red, orange, yellow, green, blue, indigo and violet. For tetrachromat women, green was found to be assigned in emerald, jade, verdant, olive, lime, bottle and 34 other shades.

    Still, the birds' abilities are even superior. Pigeons have five color receptors (and five types of cell receptors) and can process visual information up to 10 times faster than human beings. While we see a smooth TV image in real movement and color, they will see dull flickering lights.

    Tetrachromats species are encountered among birds, insects, jumping spiders, reptiles, and amphibians, but no mammal is known to posses this. Some of them detect UV light.


    Interesting. My wife and I are always arguing whether certain things are blue or green. I know neither of us are color blind. It would be cool if someone could set up a simple website with the color variations to test if you have the capability of seeing (and naming?) these extra colors.


      I don't know whether this is a real test or not. I see only uniform colors within the three circles:

      There are some that say that tetrachromancy cannot be tested on a standard monitor. Here is another test:

      and from


        well, I can't see any letters or numbers in the three circles. the colors are not uniform though.


          I recently caught part of a seminar about girls and, in addition to confirming a bunch of the Mars vs. Venus stuff, the speaker said that girls/women hear 2-4 times better than boys/men...which is girls think their parents are yelling at them all of the time when they aren't really yelling.

          I thought that was interesting.
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            Interesting. I live in a household with three boys and my husband and they detect color differently than I do. Nothing major, but mostly blues, greens and purples.
            Ugh, I've been kissed by a dog!
            Get some hot water, get some iodine ...
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