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Comment by gatherhunterer | Hacker News Reader

The title is misleading. The extra cone allows tetrachromats to appreciate individual colors that the normal optic system would “average” into a single hue. The visible spectrum is the same for tetrachromats: they cannot see infrared or ultraviolet wavelengths. These individuals see more color detail, not more colors.

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> These individuals see more color detail, not more colors.

If you're not able to differentiate between colors you're not able to see those colors.

Hell, your argument can be stretched to stating that there's no difference between monochromatic and trichromatic vision as long as the covered light spectrum is the same.

You misunderstand. Any trichromat could see those colors as well, they would just need to be much closer to the object in order to distinguish them. You are still thinking about them seeing more colors. They see more detail in color. Detail is not a matter of visibility but one of perspective. With a closer perspective you could see those colors as well.

I don't think that's true. Deuteranopic dichromats can't distinguish red and green by looking more closely.

Dichromatism is a disorder. Our brains expect a trichromatic signal and when it only receives dichromatic information the hues are “repeated” because a cone (usually the one responsible for green) is not available. In people with green-weak color blindness this makes green look like a “weak” reddish hue. Tetrachromats’ brains are still expecting a trichromatic signal but they get more information than is expected. That means that the image contains more information or detail but the colors are not nee colors.

What if trichromatism is also a disorder, that afflicts the vast majority of humans?

That’s not how brains or vision work. The brain is not “hard-coded” for trichromatism. Were that the case we would not be trichromats in the first place.

Our brains are rather complicated, interesting things- and probably do something like wire themselves up to whatever "sensors" are available.

> Any trichromat could see those colors as well, they would just need to be much closer to the object in order to distinguish them.

That’s patent nonsense.

Disagree. They are not be able to perceive a larger spectrum of wavelengths but they may perceive more colors. Just like a person without green cones would be able to perceive fewer colors.

By that logic, color blind people can see as many colors as us three-color seers, just in less "detail".

Would you also say that normal-sighted people "see more color detail" than those with deuteranopia? Sure, there's an experience of perceiving color when deuteranopes look at something green, but they still don't know what green is.

Depends on what you mean by more "color detail". Assuming that the activation curve of the 4th cone is sufficiently different, it's definitely possible to create two different spectra that a trichromat would be unable to distinguish between (regardless of how close they were or how long they stared at it) that a tetrachromat could easily distinguish between.

Can dogs just not distinguish between colors that we can, or are they actually missing out on parts of our visual spectrum?

Both. They can't differentiate between red/orange/yellow, can't differentiate greens from grays, but can see further into UV at the cost of not being able to see as deeply into red as you can.

If colorblindness is due to a lack of cones it seems the title isn't all that misleading.

> If colorblindness is due to a lack of cones

Some are, some aren't. Anomalous trichromacy (where one cone type is shifted) is still considered color blindness.

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