Following my previous question: What color does the other cone in Tetrachromacy correspond to?

People with normal color vision posses 3 cones in their eye. But there are some rare cases when people can have 4 cones (Tetrachromacy). These people, some of them will notice the shades difference in the scene through their eye. And the rest won't notice it, because simply their 4th cone is activated in the close peak value with the the L-cone. Therefore eye will not find any difference and will encode only one color even if it's coming from 2 cones stimuli.

How do you check, to know how many cones you have in your eye ? If the case is, even people who posses 4 cones can't even notice the shades difference ?

  • $\begingroup$ Regarding your last question: article. $\endgroup$
    – rus9384
    Sep 23 '18 at 2:37

One of the two confirmed cases of tetrachromacy was confirmed genetically:

From this Popular Science article:

Based on Antico's genes, Jameson has determined that Antico's fourth cone absorbs wavelengths that are "reddish-orangey-yellow, but what it appears to Concetta is uncertain at the moment," she added. Since the tests aren't calibrated for this wavelength, empirically demonstrating tetrachromacy is still really difficult.

Color vision is connected to the X chromosome and mutations in the X chromosome cause less or more color vision. In the above case, the theory that people with 2 mutated X chromosomes could have four cones instead of three was tested.

This image from Scitable by Nature Education articles simulates regular vision on the left and tetrachromatic vision on the right:

enter image description here

As far as how to test to see how many cones you have, there are some online test that may or may not be very reliable. This Metro news article has a test produced by Professor Diana Derval, author of "DesigningLuxuryBrands: The Science of Pleasing Customers’ Senses. However, due to the limitations of computer screens it would not be reliable to test for tetrachromacy.

  • $\begingroup$ Thanks a lot! Very informative. And the reference, the reference also very interesting. $\endgroup$
    – raisa_
    Jul 10 '18 at 1:24
  • $\begingroup$ Well, this article says one can't check if [s]he is tetrachromat using LED displays. In the original image I could see 37 colors but I hardly have some kind of outstanding vision. This means it is not just not reliable test, but that any trichromat can finish as tetrachromat. And the article says that many of those who have 4 cone types may be trichromats. $\endgroup$
    – rus9384
    Sep 23 '18 at 2:33

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