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Why are we not tetrachromats in twilight?

  1. Feb 21, 2013 #1
    I assume that we are not, because it should have got more mentions if we were.

    Man has 4 kinds of light receptors. Rods and 3 types of cones.

    All cats are grey in the dark, because no cones work in the dark, and there is only 1 type of rods.

    In bright light, man is trichromatic because rods are dazzled, and there are 3 types of cones.

    But twilight?

    The sensitivity of rods does not match that of any type of cones. The maximum sensitivity of rods is here
    described as 498 nm, which is further (36 nm) from the maximum green sensitivity at 534 nm than the difference between green maximum and red maximum (30 nm).

    In twilight, man should have 4 types of receptors functioning with very different spectral sensitivities. 3 types of cones, and rods.

    Why do the pictures of cones and rods not form a full tetrachromatic picture and perception of tetrachromatic hues in twilight?
  2. jcsd
  3. Feb 21, 2013 #2
    The experience of color is not solely dependent on the mechanism of the eye. Signals from the cones are "processed" into the personal experience of color in the brain:

    http://news.harvard.edu/gazette/1998/08.06/BrainsColorProc.html [Broken]

    Signals from the rods aren't lead to the color processing neurons and will always be experienced as shades of light and dark.

    Oliver Sacks examined, and wrote about, a man who lost the ability to experience color after a car accident damaged the color area of his brain. The story is online here:


    This man retained his ability to process information from the rods of his eyes but found life in a black and white world very distressing. But this is the answer to your question: The neurons that receive signals from rods are not capable of creating the experience of color.
    Last edited by a moderator: May 6, 2017
  4. Feb 23, 2013 #3


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    Last edited: Feb 23, 2013
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