Have humans seen all colors?

Factual Questions
21

Because high-frequency light isn’t really “blue” and low frequency light isn’t really “red”.

“Red” is a mental construct created when an L-type cone cell fires. “Blue” is a mental construct created when an S-type cone cell fires. “Purple” is a mental construct created when both L- and S-types fire simultaneously.

The brain has no way of perceiving the spectrum directly. All it can perceive is the L-, M-, and S-type cones firing at different rates. It doesn’t know which stimulus corresponds to high-frequency light and which corresponds to low, or whether any combination represents a pure wavelength or not. It just treats the three stimuli as coordinates in a completely arbitrary 3-dimensional color space.

22

Chronos and Sunspace,

I hadn’t thought about it that way. I did notice that red and violet are very rough doubles of each other, and I also noticed that thered absorbance curve has a little upturn in the violet direction.

I’d be cautious about calling it an octave phenomeon, though, unless I knew a lot more about the physics of opsins. A huge oversimplification of how octaves work in the ear holds that a sound of, say, 440 Hz is qualitatively the same note as 220, 110, etc because the 440 hz has peaks that end up coinciding with 220, 110, etc. I’m not sure if that same sort of Fourier stuff applies to the physics of knocking around an opsin molecule until it bends. If any biochemists know the answer to that, I’d be glad to hear it.

23

I guess it has just always bothered me that the intermediate mental construct doesn’t work in all cases. When L- and M-type cones fire simultaneously, you don’t get a sensation that’s an intermediate of L-only (red) and M-only (green). You get yellow. Yet with M and S you do (greenish blue) and with L and S you do (purple). Cue griping at the illogical workings of nature.

I guess those silly opponent-process neurons responsible for our perceiving yellow just give me a mental block there. Otherwise, what you’re explaining would seem perfectly intuitive.

24

Sound works in octaves because anything that produces sound produces it in multiple frequencies multiples called harmonics. It’s in the physics of how sound is generated. (When you bang a 1m table its wood will warp not just in a sine wave of wavelength 1m but 0.5m, 0.33m, 0.25m, and anything else that’ll fit.) This doesn’t hold true for light.

But anyway that’s an interesting observation. Why does violet (extreme blue) look a bit like purple (blue + red)? Maybe it doesn’t. Maybe we don’t look at rainbows often enough and it’s their artificial renditions that fool us.

25

Hey! I know how you guys can check out a light spectrum. No need for prisms or rainbows, just find a CD. Anyway, yeah, violet in the spectrum looks exactly like purple on my monitor.

To continue the thought: my monitor produces a blue that looks like the blue in the CD. And so does red. But when the monitor combines blue and red, it results in what is essentially a bluer blue.

26

Interestingly enough, while the idea of colored non-visible light is arrant nonsense*, there are colors that humans can see that don’t correspond to any wavelength of light or any mix of wavelengths. If you look at the response curves of the various types of cone cells, you can see that there is very significant overlap–any light that stimulates the M cones will stimulate the L cones to a high degree and vice versa. The S cones also have some overlap with the M and L cones. It is presumably possible for the M cone to be stimulated artificially without stimulating the L or S cones or for the L and S cones to be stimulated without stimulating the M cone, although this would never happen naturally (at least not due to light). In fact, any number of naturally impossible combinations of response levels could be achieved. I have no idea how the brain would process these signals. It’s possible that each combination of cone response levels would be perceived identically to some naturally occurring response pattern. It’s also possible (I suppose) that the mind would perceive some color that it couldn’t see without artificial stimulation. Does anyone know if this has been studied?

*Not actually. Some people can see light that is outside the visible spectrum for most people. There are no hard edges to the limits of human vision, and some people are just more sensitive than others. Additionally, the lens and cornea block UV light that would otherwise be detectable by the S cones. Furthermore, there is some evidence that certain people have tetrachromatic vision, meaning they have four types of color receptors rather than three. According to Wikipedia, this would probably allow them to better distinguish between colors in the normal visual spectrum, not to see outside the usual range of wavelengths. How the brain would process the additional information (what the colors would look like), I think, is completely speculative.

27

Fun with vitamin A.

28

H.P. Lovecraft would say no, but then again, you probably wouldn’t want to: The Colour Out of Space - Wikipedia

29

The question has been pretty well covered, but I’ll just add a bit:
1.) We can certasinly see the colors in the spectrum. There’s no reason to think there are any gaps in this regime. In fact, the roble,m is the opposite – several regions of the CIE Chromaticty diagram are perceived as the same color. We have a problem with resolution. Dave MacAdam did a lot of work on this, and the regions of confusion are called MacAdam Ellipses, after him.

2.) We can see from blue up through red on the spectrum, and some people can maybe see a bit beyond (especially if they’ve has artificial lenses implanted, I understand – they transmit a bit further than your natural lens) With very bright sources (like lasers) you can see a bit beyond the range you normally see, since otherwise the response there is normally too low. But I’m told that Really Far Red looks just like the furthest Red you normally see – your eye/brain system doesn’t see it as a different color. In other words, it falls into the same Macadam ellipse.

3.) Purple, on the other hand, lying along the line connecting the ends of the spectral locus on the Chromaticity Diagram, does appear to be a different color. Not in the same ellipse. To me, Indigo and Vioollet look more like darker blues, and purple is something else.

4.) Pink is definitely in the Chromatocity diagram – it lies along a line between the “white” center and a point in the red on the spectral locus. exactly where it lies depens upon how “red” it is, and how light it seems to be.

5.) Brown, on the other hand, is an interesting concept, and I confess that I have to look into it further. Since it’s made up of a mixture of colors, it ought to have a location on the Chromaticity Diagram. I’m tempted to say that a lot of browns are really very dark yellows (especially since my colonoscopy, which got to watch on color TV), but I find that answer not completely satisfying. Needs further study.

6.) certainly, people haven’t seen “all colors” if you mean visually perceiving all wavelengths of electromagnetic wavelengths, or even the EM wavelengths that can be perceived by living animals. Bees and, I think, horseshoe crabs can see further into the UV (and see it as a distinct color, unlike human viewers of UV). Pit Vipers can detect infrared. And the Mantis Shrimp has extraordinarily broad visual sensitivity.

7.) What about sensitivity to other properties of light? Bees and Horseshoe Crabs can detect polarized light. People have a very limited ability to do this (google “Haidinger’s Brush”). Some varities of Mantis Shrimp, it’s recently been learned, can detect circularly polarized light. The way they perceive the world must be vastly differrent from the way we do. Does “left hand circularly polarized red light” count as a different color from “right hand circularly polarized light”? How about to a Mantris Shrimp? Is it different from “Horizontally Linearly Polarized Light”?

30

Are there any languages that don’t have words for certain colors? I mean the common ones? Perhaps those people don’t see those colors

31

As a point of interest. I’ll reference the Mantis Shrimp. This animal possesses the most complex eyes know to science. Each eye is capable of stereo vision, can discern polarized light, and more. Read half way down the page.

32

Yep, lots. Pink is a rather rare color in most languages, while others have more words than English. Russian discriminates between light and dark blue I believe, and has separate words for them. People in other cultures can certainly see the colors, but have difficulty discriminating them.

As to the OP, some people do have “gaps.” Dichromats (2 cones) sometimes have a point in their spectrum where only one cone is responsive to light. The light of this specific range of wavelengths appears indistinguishable from white. That is the “neutral point.” This link is pretty good. Dogs are dichromats as are most non-primate animals.

33

That’s pretty amazing. But how do scientists figure it out? Who gives mantis shrimp their vision tests? How do you get them to cooperate? “OK, read the second row for me, please…”

34

Is this similar to asking if humans know about all the letters in the alphabet? Seems to me that we invented the alphabet, and we invented colors, so by definition there can’t really be anything outside of what we have…

35

Well, I would assume that from detailed physical analysis of the structure of the eye functionality can be determine to a certain degree. Also, while we can’t ask a mantis shrimp to cover his left eye and read the top line on the chart it would be basic to conduct experiments to determine sensitivity responses.

36

Yeah, if the food is always displayed behind the open door painted circularly-polarized ultraviolet, and they you present different series of closed doors with one painted circularly-polarized ultraviolet and the food always behind it instead of the ones painted circularly-polarized red or linearly-polarized ultraviolet, and the shrimp goes for the circularly-polarized ultraviolet door every time, I’d say that’s an indication. :slight_smile:

37

Cecil had a column on this: http://www.straightdope.com/columns/read/449/could-early-man-only-see-three-colors

38

That’s very cool. The “rules” at the end are fascinating - definitely worthy of further study!

39

Quoth Alex Dubinsky:

There are always harmonics, but except for very specific sorts of systems, they’re usually not integer multiples of the fundamental. That only happens for essentially 1-d systems, like a stretched string or a long tube (which, not coincidentally, are the sorts of systems we use to make musical instruments). But in a round drumhead, none of the harmonics are integer multiples, which is why drums don’t sound as “musical” as wind or string instruments.

40

So what are we seeing when we see fluorescent colors? Are they just perceived by our eyes as high intensity colors, as if to be phosphorescent?