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Colors like magenta (red and blue wavelengths together) are nonspectral, having no single wavelength they correspond to. They only exist as a mix, and we see a

Colors like magenta (red and blue wavelengths together) are nonspectral, having no single wavelength they correspond to. They only exist as a mix, and we see a pinkish color that you can't write down as a wavelength. Tetrachromats could plausibly see more nonspectral colors by activating their extra color receptor and one of the other ones. There would be no exact equivalent in trichromatic vision. It depends on what their brains decide to do with it- maybe they would just land on an existing color in between. But there's no reason it has to. So these colors are something that tetrachromats could maybe see while awake, but usually with lots of other colors mixed in. Asleep, maybe the brain starts to play with them and generates pure versions of them. Trichromats wouldn't be very likely to have these dreams because their brains don't have experience of tetrachromat nonspectral colors at all.

arketyp 7y ago
That has nothing to do with my argument. Why would tetrachromats be inclined to dream of colors they do not see in the real world any more than trichromats?
- roywiggins 7y ago
  My point is they would see those colors in the real world, but only in combination with other colors, so it wouldn't be that noticable. They wouldn't see pure versions of them much, if at all. The intensity in a dream might be much stronger, enough that it would seem like a qualitatively new color rather than "hmm, that blue has something different going on compared to other blues" they you might get in real life. You could put them in front of light source that generated pure wavelengths designed to selectively activate their extra cone and ask what they see when you start mixing pure blue or green into it. Maybe they'd recognize those colors from their dreams, maybe not. I don't know. But it's a mechanism that would explain how tetrachromats might dream colors that trichromats don't.
  - arketyp 7y ago
    But this assumes the gamut of trichromacy is more anchored in reality (woken life) than the gamut of tetrachromacy. In principle there is nothing different between a trichromat and a tetrachromat sense of color. They see one dimension of color more, just like humans see one dimension more than dogs.
    - roywiggins 7y ago
      The fourth cone in tetrachromats overlaps quite a lot with the other three (which is why most tetrachromats don't see more colors than trichromats). For people where the fourth cone is meaningfully distinguishable from the others, it doesn't seem weird to me that you wouldn't see many objects that are strongly activating just that extra cone and not the ones next to it (wavelength wise) because they're closer together. We don't see bright, "pure" magenta very much, and when we do it's usually because we've engineered it. Nobody is engineering pigments for tetrachromats to enjoy. If I'm right, people who are nearly (but not entirely) colorblind (anomalous trichromats) due to a shifted cone would likewise be able to dream in colors they are capable of seeing only dimly while awake, whereas dichromats wouldn't.
_nalply 7y ago
Ah! Now I have theory: We trichromats have a hue circle, and magenta is the point where the lower and higher wavelenghts are joined. However this simple model breaks down for tetrachromats. Perhaps they have two hue circles orthogonal to each other. This means, hue becomes two-dimensional. Really crazy to imagine such a thing. I imagine in school the teacher tells the poor girl: Mix the blue and yellow colors to get green, and the girl doesn't understand because she has a lot more complex color model than the teacher.
- roywiggins 7y ago
  Here's a badly-worked out theory. We see magenta as a separate color because we can distinguish it from green- it's not green, because Red and Blue don't activate our green cones. But we can't distinguish between spectral yellow and R+G because there's no yellow cone: the activations of all our cones are more or less identical in both cases. If you have a yellow cone, you'd conceivably be able to distinguish between both kinds of yellow: redgreen and yellow could look as different as green and redblue do. I'm not sure how that would look as a "wheel", perhaps a figure-eight with the crossing at yellow.
  - marvin 7y ago
    I think this is a very good explanation. You're emphasizing that a trichromat will experience the same activation of their cones to the wavelength of yellow light, and light containing the wavelengths of red and green mixed. So the spectra of these two colors will be different, but appear identical. Whereas a hypothetical tetrachromat with an additional cone type that activates to the yellow wavelength, will have obviously different activations of their cones for the "wavelength of yellow" and "wavelengths of red and green mixed". And hence experience them as different colors. I'm not familiar enough with the different definitions of color spaces to define how to model this. You could easily define it as a four-dimensional RGBY color space, but to my understanding the other color spaces are defined because they have better properties for combining different colors, or playing better with interpolation between colors. It would be a challenge to come up with a good four-dimensional color space that is a useful artistic and visual tool, given that there are very few people around to evaluate it! And also because all computer monitors are trichromatic, so it'd be a job in itself to set up a test system. I wish someone in the interview had asked some of these people how they experience photos on computers!

arketyp 7y ago

That has nothing to do with my argument. Why would tetrachromats be inclined to dream of colors they do not see in the real world any more than trichromats?

roywiggins 7y ago
My point is they would see those colors in the real world, but only in combination with other colors, so it wouldn't be that noticable. They wouldn't see pure versions of them much, if at all. The intensity in a dream might be much stronger, enough that it would seem like a qualitatively new color rather than "hmm, that blue has something different going on compared to other blues" they you might get in real life. You could put them in front of light source that generated pure wavelengths designed to selectively activate their extra cone and ask what they see when you start mixing pure blue or green into it. Maybe they'd recognize those colors from their dreams, maybe not. I don't know. But it's a mechanism that would explain how tetrachromats might dream colors that trichromats don't.
- arketyp 7y ago
  But this assumes the gamut of trichromacy is more anchored in reality (woken life) than the gamut of tetrachromacy. In principle there is nothing different between a trichromat and a tetrachromat sense of color. They see one dimension of color more, just like humans see one dimension more than dogs.
  - roywiggins 7y ago
    The fourth cone in tetrachromats overlaps quite a lot with the other three (which is why most tetrachromats don't see more colors than trichromats). For people where the fourth cone is meaningfully distinguishable from the others, it doesn't seem weird to me that you wouldn't see many objects that are strongly activating just that extra cone and not the ones next to it (wavelength wise) because they're closer together. We don't see bright, "pure" magenta very much, and when we do it's usually because we've engineered it. Nobody is engineering pigments for tetrachromats to enjoy. If I'm right, people who are nearly (but not entirely) colorblind (anomalous trichromats) due to a shifted cone would likewise be able to dream in colors they are capable of seeing only dimly while awake, whereas dichromats wouldn't.

_nalply 7y ago

Ah! Now I have theory: We trichromats have a hue circle, and magenta is the point where the lower and higher wavelenghts are joined. However this simple model breaks down for tetrachromats. Perhaps they have two hue circles orthogonal to each other. This means, hue becomes two-dimensional. Really crazy to imagine such a thing. I imagine in school the teacher tells the poor girl: Mix the blue and yellow colors to get green, and the girl doesn't understand because she has a lot more complex color model than the teacher.

roywiggins 7y ago
Here's a badly-worked out theory. We see magenta as a separate color because we can distinguish it from green- it's not green, because Red and Blue don't activate our green cones. But we can't distinguish between spectral yellow and R+G because there's no yellow cone: the activations of all our cones are more or less identical in both cases. If you have a yellow cone, you'd conceivably be able to distinguish between both kinds of yellow: redgreen and yellow could look as different as green and redblue do. I'm not sure how that would look as a "wheel", perhaps a figure-eight with the crossing at yellow.
- marvin 7y ago
  I think this is a very good explanation. You're emphasizing that a trichromat will experience the same activation of their cones to the wavelength of yellow light, and light containing the wavelengths of red and green mixed. So the spectra of these two colors will be different, but appear identical. Whereas a hypothetical tetrachromat with an additional cone type that activates to the yellow wavelength, will have obviously different activations of their cones for the "wavelength of yellow" and "wavelengths of red and green mixed". And hence experience them as different colors. I'm not familiar enough with the different definitions of color spaces to define how to model this. You could easily define it as a four-dimensional RGBY color space, but to my understanding the other color spaces are defined because they have better properties for combining different colors, or playing better with interpolation between colors. It would be a challenge to come up with a good four-dimensional color space that is a useful artistic and visual tool, given that there are very few people around to evaluate it! And also because all computer monitors are trichromatic, so it'd be a job in itself to set up a test system. I wish someone in the interview had asked some of these people how they experience photos on computers!