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I don't buy it. The different types of cones are all sensing the same physical property: wavelength. Each type of clone is more sensitive to some specific ran

I don't buy it. The different types of cones are all sensing the same physical property: wavelength. Each type of clone is more sensitive to some specific range of wavelengths (detail: the graphs of sensitivity vs wavelength for each type are approximately but not exactly bell curves).[0] TRICHROMATIC ------------ L M S <--long, medium, short cone cells R O Y G B I V 6 5 5 5 4 4 4 <--wavelength (read down) 5 9 7 1 7 4 0 0 0 0 0 5 5 0 So your visual system does the math to determine the scalar value of the color that is being perceived. If M cones are firing a lot and L and S cones only a little, it's a blue green. If L fires a little and M less so and S hardly at all, it's a red. Etc. Adding another type doesn't change the nature (dimensionality) of color, it merely changes two things: 1. the math you use to determine that scalar. and 2. your ability to distinguish between 650nm light and 651nm light (perhaps). Perhaps this will make it clear: imagine one million different types of cone cells, each with some distinct sensitivity range. That doesn't give you a million-dimension space. It would certainly give you the ability to tell the difference between 510nm light and 510.05nm light, though! 0: https://en.wikipedia.org/wiki/Cone_cell https://en.wikipedia.org/wiki/Cone_cell

schoen 10y ago
I think you're mistaken there simply because most colors are not a single wavelength. If colors were a single wavelength, then indeed something around 2 cones should already be sufficient to resolve any color in the range of their joint sensitivity, because there is enough information to deduce which single wavelength was responsible for their activation levels. But because we see things that are combinations of various wavelengths, adding more cones with different sensitivity always provides useful information for resolving which wavelengths are present at the same time at which intensity.
- daveloyall 10y ago
  I know that color spaces are a thing (I just don't yet understand WHY), and surely tetrachromatic people can distinguish more colors. So I'm sorta playing devil's advocate... I'm eager to have an 'aha!' moment over here. Does not this: Blue + Yellow = Green simply mean this? (475nm + 570nm) / 2 = 523nm (the average) Supposing that wavelength was the only property of light, yes, two ideal cones could determine exactly where on the spectrum some light belongs. However, there's intensity to be measured, too. Variable intensity means that if you just got two scalar values from two sensors... you haven't narrowed it down to a specific wavelength, because those same two values would arise for states. ..Right?
  - schoen 10y ago
    The blue + yellow = green is in subtractive mixing so it doesn't directly apply here, but taking red + green = yellow from additive mixing, there are two different things that could happen: * you can have a red light and a green light both shining together (like on your computer screen) * you can have a pure yellow light (like from a yellow laser, or the yellow part of a rainbow) These are physically different, as could be detected by a spectroscope. But for a normal trichromat human, perceiving either produces the same color sensation and we can't distinguish them using our eyes (because the excitation of the cones produced by either is roughly equivalent). (I should add that there can be still other combinations of wavelengths which, when they occur together at the same time, we would perceive as the same yellow.) If you add more cones, you could hope to distinguish these physically different phenomena, and have them somehow produce different sensations. However, we also apparently can't describe what those sensations would be like... https://en.wikipedia.org/wiki/Knowledge_argument#Thought_experiment https://en.wikipedia.org/wiki/Knowledge_argument#Thought_exp...
    - daveloyall 10y ago
      Aha!

schoen 10y ago

I think you're mistaken there simply because most colors are not a single wavelength. If colors were a single wavelength, then indeed something around 2 cones should already be sufficient to resolve any color in the range of their joint sensitivity, because there is enough information to deduce which single wavelength was responsible for their activation levels. But because we see things that are combinations of various wavelengths, adding more cones with different sensitivity always provides useful information for resolving which wavelengths are present at the same time at which intensity.

daveloyall 10y ago
I know that color spaces are a thing (I just don't yet understand WHY), and surely tetrachromatic people can distinguish more colors. So I'm sorta playing devil's advocate... I'm eager to have an 'aha!' moment over here. Does not this: Blue + Yellow = Green simply mean this? (475nm + 570nm) / 2 = 523nm (the average) Supposing that wavelength was the only property of light, yes, two ideal cones could determine exactly where on the spectrum some light belongs. However, there's intensity to be measured, too. Variable intensity means that if you just got two scalar values from two sensors... you haven't narrowed it down to a specific wavelength, because those same two values would arise for states. ..Right?
- schoen 10y ago
  The blue + yellow = green is in subtractive mixing so it doesn't directly apply here, but taking red + green = yellow from additive mixing, there are two different things that could happen: * you can have a red light and a green light both shining together (like on your computer screen) * you can have a pure yellow light (like from a yellow laser, or the yellow part of a rainbow) These are physically different, as could be detected by a spectroscope. But for a normal trichromat human, perceiving either produces the same color sensation and we can't distinguish them using our eyes (because the excitation of the cones produced by either is roughly equivalent). (I should add that there can be still other combinations of wavelengths which, when they occur together at the same time, we would perceive as the same yellow.) If you add more cones, you could hope to distinguish these physically different phenomena, and have them somehow produce different sensations. However, we also apparently can't describe what those sensations would be like... https://en.wikipedia.org/wiki/Knowledge_argument#Thought_experiment https://en.wikipedia.org/wiki/Knowledge_argument#Thought_exp...
  - daveloyall 10y ago
    Aha!