Colourblind people: evolutionary advantage?

[Hagen]

I was reading up the article about traffic lights and Colourblind people when I recalled a story relayed to me by a friend. Yep a bad start already, I know. It was told to him by an ex-SADF soldier during the border war who said that he had been a spotter in helicopter patrols because, being Colourblind, he could pick out camouflage from background foliage more easily.

I've heard that traffic lights' red and greens are designed to be different shades so that you can tell them apart (not that I noticed) and vaguely remember reading from an online source about a study linking colour blind animals to some selective pressure.

So is there an advantage to being Colourblind? If so it a learned skill to help one function in a three tone world,or is it intrinsic to the biology? Or is it just more lies and Internet rumours?

Kind regards
Luke

[engineer_comp_geek]

The military has been known to mix colorblind people into teams of non-colorblind photo analysts, so there is an element of truth to what you heard.

That said, I don't know if I would call it an evolutionary advantage. A colorblind person's inability to distinguish certain colors sometimes allows their eyes to avoid getting fooled by certain types of camouflage. This doesn't give them some kind of super ability with respect to detecting camouflaged things though, and it only works in certain circumstances. Colorblind people will also miss things that a normally sighted person can easily see.

For example, let's say you paint a tank in two different colors (picking colors that a colorblind person has difficulty distinguishing). A normally sighted person would see the camouflage pattern and might mistake the tank for an underbrush pattern or whatever the camouflage is designed to be. A colorblind person however can't distinguish the two different colors, and can't see the camouflage pattern at all. They only see the tank. It's not that the colorblind person sees "better", it's that they can't see the part that fools the eyes of a sighted person.

Pick different colors though, and the colorblind person might be able to distinguish those and would be fooled by the camouflage pattern. Colorblind folks aren't universally better at avoiding camouflage.

For general spotting and scouting types of things, the military prefers people with full sight capabilities.

[engineer_comp_geek]

Forgot to answer the second part of the question. Your eyes have different types of cells called rods and cones. Rods see black and white (they give you your detail vision) and see in low light conditions. The cones see colors. Normal people have three types of cones. Colorblind people are missing one (or more) of the types of cones.

It's purely biological. You can't train yourself for it.

[Der Trihs]

Originally Posted by Hagen

So is there an advantage to being Colourblind?

It depends on circumstances. Different things will be obvious to people/creatures that have various forms of colorblindness that are harder to see with full range vision. I recall reading about a species of monkey that has several different kinds of color blindness as a normal feature of the species; apparently it helps them with hunting fruit & seeing threats, since what blends in for one monkey will be obvious to another.

[UFC Is Sux]

Originally Posted by Hagen

So is there an advantage to being Colourblind? If so it a learned skill to help one function in a three tone world,or is it intrinsic to the biology?

Not that I have ever been able to deduce. My Daltonism rendered me unqualified to do several types of very lucrative jobs, caused my poor mother to have to sew numbers into my clothing so I didn't walk out of the house looking like Bozo the Clown, and earned me many outraged honks and ire by other drivers at traffic lights. I failed my driving test twice in high school before I managed to figure out that the green light on a traffic signal is usually on the bottom. So no, can't see any advantage to it at all.

[kanicbird]

It would seem that people with a higher number of rods may have better night vision, so colorblindness may have a advantage.

[Colibri]

Originally Posted by Hagen

I was reading up the article about traffic lights and Colourblind people when I recalled a story relayed to me by a friend. Yep a bad start already, I know. It was told to him by an ex-SADF soldier during the border war who said that he had been a spotter in helicopter patrols because, being Colourblind, he could pick out camouflage from background foliage more easily.

This probably works mainly with human-devised camouflage patterns. Camouflage that occurs in nature is most likely selected to work for both animals with full color vision, such as birds, and those with poor color vision. So there is likely little if any advantage under natural conditions.

Some primates (Old World monkeys and apes, and a few New World Monkeys), unlike most mammals, have good color vision (although not as good as most vertebrates). This is most likely an adaptation for detecting brightly colored fruits.

Originally Posted by Der Trihs

It depends on circumstances. Different things will be obvious to people/creatures that have various forms of colorblindness that are harder to see with full range vision. I recall reading about a species of monkey that has several different kinds of color blindness as a normal feature of the species; apparently it helps them with hunting fruit & seeing threats, since what blends in for one monkey will be obvious to another.

Male howler monkeys are dichromats (having two color receptors), and have the equivalent of one of the common types of human color blindness. Female howlers are trichromats (with three receptors) and see colors as well as humans. However, I am not aware that troops derive any particular advantage from this.

Originally Posted by kanicbird

It would seem that people with a higher number of rods may have better night vision, so colorblindness may have a advantage.

Color blindness affects the cones but does not necessarily result in an increased number of rods. Do you have a cite that color blind people in general have better night vision?

[Smeghead]

Unless being a sniper or whatever helps the colorblind person have more kids, it's hard to see how it could be any sort of evolutionary effect.

[Snnipe 70E]

Originally Posted by UFC Is Sux

Not that I have ever been able to deduce. My Daltonism rendered me unqualified to do several types of very lucrative jobs, caused my poor mother to have to sew numbers into my clothing so I didn't walk out of the house looking like Bozo the Clown, and earned me many outraged honks and ire by other drivers at traffic lights. I failed my driving test twice in high school before I managed to figure out that the green light on a traffic signal is usually on the bottom. So no, can't see any advantage to it at all.

My wife and I have a rule. If she does not pick out my clothes when we are going out she can not complain about what I am wearing. Before this arangement I often heard "you are not wearing that shirt with those pants are you".

And it is not an advantage in my profession. In doing water tests there are some test that I can not do because the titrating involves going into a color I can not see well, so I have to sort of guess.

[j666]

Originally Posted by Snnipe 70E

And it is not an advantage in my profession. In doing water tests there are some test that I can not do because the titrating involves going into a color I can not see well, so I have to sort of guess.

Which tests? All the titrations I remember go from clear to colored - even if you can't distinguish the color, can't you tell that the solution has darkened?

Is color-blindedness know to be genetic? Could it be a developmental issue?

[thelabdude]

My color blind brother in law was very successful as a hunter. He could spot brown rabbits or the light gray the deer adopted in Pennsylvania winters better than most of us.

Many predators have limited color vision. I am not sure how they determined it, but dogs largely see things as blue and yellow. This makes it easier to spot movement of something colored much like its background. It is easy to see how a meat eater might be better off with limited color vision. Color is more important to vegetarians.

Speculation: We have evolved little since our hunter, gatherer days. Would a population of them eat better with a range of color vision among them?

[Colibri]

Originally Posted by thelabdude

Many predators have limited color vision. I am not sure how they determined it, but dogs largely see things as blue and yellow. This makes it easier to spot movement of something colored much like its background. It is easy to see how a meat eater might be better off with limited color vision. Color is more important to vegetarians.

I am not aware of any correlation between carnivory and colorblindness/color vision. Dogs, like most other mammals, are dichromats, with two color receptors, which limits the range of colors they can distinguish. But deer and other mammalian herbivores also have poor color vision. Avian carnivores like hawks have color vision as good as that of most other birds.

Most vertebrates, including fish, reptiles, amphibians, and birds, are tetrachromats, with four color receptors. It is assumed that mammals lost this capacity in the early stages of their evolution because ancestral mammals were primarily nocturnal. Color vision is of limited utility at night. Even today, most mammals are primarily active at night.

As mentioned above, some primates, including Old World Monkeys, apes, and humans, and a few New World Monkeys, re-evolved a third color receptor. This is probably an adaptation for locating fruit, which was already brightly colored so birds could find it.

[Kobal2]

Originally Posted by thelabdude

Color is more important to vegetarians.

I'd dispute this assertion.
Roughly speaking, there are three main defense strategies for prey:
a) run awayyyyy
b) blend in
c) be highly visible to advertise other means of defence (or bluff them)

Ignoring a) where colour doesn't play much of a role, I'd say colour sight is pretty central in the process of differentiating between the green tree frog that prays very hard b) will work ; and the violent red, more poisonous than a Sicilian mother in law tree frog who went all in with c).

[DHMO]

Originally Posted by j666

Which tests? All the titrations I remember go from clear to colored - even if you can't distinguish the color, can't you tell that the solution has darkened?

Is color-blindedness know to be genetic? Could it be a developmental issue?

There are many tests in water-quality titration analysis where the end-point is determined by a change from color to no color, no color to color, and one color to another.

My brother, who has severe Red-Green color deficiency, had trouble in his high-school chemistry class when they were required to do a titration from a clear solution until a pale pink color appeared. His instructor walked past and noticed that his solution was bright red, and yet he was still titrating more reagent into the dish. He was completely oblivious to the color which was developed in the reaction.

I have relatively "normal" color vision, and was fascinated by his condition. It is my understanding that color deficiency is, in part, caused by a faulty gene (or set of genes) on the "X" chromosome, meaning that color deficiency tends to plague males more often than females. Color vision is obviously a complex biological process, controlled by many factors, but it does seem to have an hereditary component.

[Snnipe 70E]

Originally Posted by j666

Which tests? All the titrations I remember go from clear to colored - even if you can't distinguish the color, can't you tell that the solution has darkened?

Is color-blindedness know to be genetic? Could it be a developmental issue?

Yellow to shades of Red. Different shades of blue. None of the tritrations are clear from the start.

[j666]

Originally Posted by DHMO

My brother, who has severe Red-Green color deficiency, had trouble in his high-school chemistry class when they were required to do a titration from a clear solution until a pale pink color appeared. His instructor walked past and noticed that his solution was bright red, and yet he was still titrating more reagent into the dish. He was completely oblivious to the color which was developed in the reaction.

This is interesting; I had no idea someone might not see anything; I assumed they would just see a darkening grey.

I do know red-green color blindness was the classic example of recessive sex linked mutation, but I was wondering if any colorblindness might result from lack of adequate visual stimulation during development.

Originally Posted by Snnipe 70E

Yellow to shades of Red. Different shades of blue. None of the tritrations are clear from the start.

Huh. I guess I don't know that much about wet chemistry.


Thank you for the replies.

[kanicbird]

Originally Posted by Colibri

Color blindness affects the cones but does not necessarily result in an increased number of rods. Do you have a cite that color blind people in general have better night vision?

No not at all, just a thought that less cones should make room for more rods.

[Colibri]

Originally Posted by kanicbird

No not at all, just a thought that less cones should make room for more rods.

I'm not sure why you would think there are fewer cones in color-blind people. The problem usually is that one particular kind of receptor is defective, not that it is absent.

The Wikipedia article on color blindness provides some good background, and is worth reading if you are unfamiliar with its basis. There are several different kinds of color blindness in humans, owing to various genetic (usually) causes.

[thelurkinghorror]

Originally Posted by engineer_comp_geek

Rods see black and white (they give you your detail vision) and see in low light conditions.

Yes, but cones are the detail cells. Rods see coarsely. They are better at seeing contrast, though.

Originally Posted by kanicbird

It would seem that people with a higher number of rods may have better night vision, so colorblindness may have a advantage.

What matters is absolute number of cells, not rod/cone ratios. Losing a cone type will not increase your number of rods. In addition, losing your "red" cones will cause them to be replaced by "green" cones or vice versa; the absolute number of cones is not decreased. "Blue" cones are rather sparse on the retina, I'm not sure what happens with tritanopia but it's pretty rare.

Originally Posted by Colibri

Male howler monkeys are dichromats (having two color receptors), and have the equivalent of one of the common types of human color blindness. Female howlers are trichromats (with three receptors) and see colors as well as humans. However, I am not aware that troops derive any particular advantage from this.

I'm pretty certain it's: Howler monkeys are the only trichromats among NW monkeys. Most other species are dichromats. Some species have 3 types: dichromat males, dichromat females, and trichromat/polymorphic females who can see "humanlike" colors.

Color blindness affects the cones but does not necessarily result in an increased number of rods. Do you have a cite that color blind people in general have better night vision?

I don't know either, but I could speculate it would have some effect on the Purkinje effect. I cannot fathom how this would actually appear, though, and whether colorblind people would be at an advantage or disadvantage here.

Originally Posted by j666

Is color-blindedness know to be genetic? Could it be a developmental issue?

The types were there is a missing red or green cone, or a shifted but not missing red or green cone are genetic. They are on the X chromosome and thus much more common in males, as females need to inherit two copies of the gene to have an effect. Blue cone defects are much rarer (<1% for both males and females) and have no sex differences because they are not on a sex chromosome (chromosome #7 IIRC).

[Broomstick]

Originally Posted by j666

Is color-blindedness know to be genetic? Could it be a developmental issue?

Almost always genetic.

Non-genetic colorblindness is, so far as I know, invariably the result of damage of some sort - strokes, damage to the retina, etc.

[j666]

Originally Posted by Broomstick

Almost always genetic.

Non-genetic colorblindness is, so far as I know, invariably the result of damage of some sort - strokes, damage to the retina, etc.

I believe that the visual system in human develops lot after birth in response to stimuli, so now I am wondering if that could affect color perception. If you kept an infant for six months in an environment with no red objects - no orange, no purple - would s/he be unable to process the color red, not because the cones were faulty, but because some associated brain cell was not properly wired? Would one have to also eliminate any light in the red wavelengths, if such a think could occur?

Anyone having a baby soon that we could borrow?

[Lemur866]

Originally Posted by j666

This is interesting; I had no idea someone might not see anything; I assumed they would just see a darkening grey.

Most "colorblind" people see colors, just not in the same way as other people. So they don't see everything in greyscale.

As has been said, a normal cone cell has three kinds of color receptors. For colorblind people the red-green receptor is damaged to a greater or lesser extent. So you can distinguish shades of blue and yellow very easily, but greens and reds are hard to tell apart from browns.

[Colibri]

Originally Posted by Lemur866

As has been said, a normal cone cell has three kinds of color receptors.

A nitpick: there are actually three different kinds of cone cells, one for each of the color receptors, rather than there being three kinds of receptors in each cone.

[thelurkinghorror]

Originally Posted by Lemur866

Most "colorblind" people see colors, just not in the same way as other people. So they don't see everything in greyscale.

e.g. a person who is missing either red or green cones (percept is similar enough) would see something similar to the right image here, vs. the left normal color vision.

As has been said, a normal cone cell has three kinds of color receptors. For colorblind people the red-green receptor is damaged to a greater or lesser extent. So you can distinguish shades of blue and yellow very easily, but greens and reds are hard to tell apart from browns.

Nitpick: There is no "red-green receptor," as at least 2 receptor types are required to distinguish between colors like red and green. The red-green continuum appears later in the visual system than the photoreceptors. But R/G can be disrupted, by removing either cone, and then it won't receive the necessary input to distinguish.

[barbitu8]

Those whose vision is better than 20/20 have this better vision due to more cones than normal. Is it because cones enable us to see more details?

[clairobscur]

Originally Posted by thelabdude

I am not sure how they determined it, but dogs largely see things as blue and yellow. ?

That should be quite easy to determine. For instance train the animal to find food in, say, a red container, then present it with two containers of different colors and see if it can pick the right one.


On a related note. Someone mentioned reptiles, etc... being quadrichromats. What color(s) can they tell apart? I mean, for instance do they see a "red1" and a "red2" where we can only see red?


Also, would it be possible (even if there is no actual example) for an animal to have *more* than 4 color receptors, or is it physically impossible for some reason? And if it possible, is there an upper limit, or could (in theory again) an animal be, say, dodecachromat?


Oh, and finally : is there any example of an human mutation with somehow slightly (or even radically) different cones? I'm making the assumption here that cones are "tuned" to a specific light frequency (which might be wrong) and envisioning a cone "tuned" to a somewhat lower or higher frequency than normal.

[Broomstick]

Originally Posted by clairobscur

On a related note. Someone mentioned reptiles, etc... being quadrichromats. What color(s) can they tell apart? I mean, for instance do they see a "red1" and a "red2" where we can only see red?

I'm not sure - color vision in animals is highly variable. Bees, for example, don't see red but do see ultraviolet. Other animals, such as reptiles and birds, may have more photoreceptors for the human visiual spectrum.

Also, would it be possible (even if there is no actual example) for an animal to have *more* than 4 color receptors, or is it physically impossible for some reason? And if it possible, is there an upper limit, or could (in theory again) an animal be, say, dodecachromat?

There actually is a "dodecachromat", the mantis shrimp so the answer is yes to that one. So far as I know, that's currently the upper limit but whether that's an absolute or simply no other critter has had reason to evolve more I don't know.

Among other critters, there is apparently some evidence that some birds, such as pigeons, are pentachromats.

Oh, and finally : is there any example of an human mutation with somehow slightly (or even radically) different cones? I'm making the assumption here that cones are "tuned" to a specific light frequency (which might be wrong) and envisioning a cone "tuned" to a somewhat lower or higher frequency than normal.

Yes. The anomalous trichromats aren't missing specific cones, it's that certain of their cones are "tuned" to slightly different frequencies. Although these people are frequently lumped in with the colorblind, they are also sometimes referred to as the "colorweak". Such a person may, for example, perceive green as a distinct color when deeply saturated but may perceive pastel or tertiary shades as something else. For example, what a person with normal color vision perceives as "yellow-green" they might see as "yellow"/

[Colibri]

Originally Posted by clairobscur

On a related note. Someone mentioned reptiles, etc... being quadrichromats. What color(s) can they tell apart? I mean, for instance do they see a "red1" and a "red2" where we can only see red?

It's really impossible to understand how colors we can't perceive might look to an animal which can see them. How would you describe the sensation of "red" to a color-blind person?

Many tetrachromats such as birds can perceive into the ultraviolet. (In fact, it has been determined that some birds that look drab to us are brightly "colored" in the ultraviolet.) What ultraviolet might look like as a color is as unimaginable to us as red would be to a dog.

[thelurkinghorror]

Originally Posted by barbitu8

Those whose vision is better than 20/20 have this better vision due to more cones than normal. Is it because cones enable us to see more details?

Have a link? Sometimes LASIK leaves people with 20/10, but it doesn't affect the retina. The upper theoretical limit of your acuity is limited by the width of one cone (rods are wider), but they are already packed in there, I don't know if the amount of new cones you can add would be enough to make a difference?

Originally Posted by clairobscur

On a related note. Someone mentioned reptiles, etc... being quadrichromats. What color(s) can they tell apart? I mean, for instance do they see a "red1" and a "red2" where we can only see red?

Colibri covered it, but for example see spectral sensitivity curves. A new cone would work best if it is in a area of "low coverage," e.g. ultraviolet to the left, between S/M in middle, or infrared to the right. Most suspected human tetrachromats would have a fourth cone close to the L, M, so no mindblowing changes.

Fun fact, Colibri's namesake, the hummingbirds, (or at least among the whole Trochilidae family) sometimes have two foveae, or areas of the retina with high acuity and lots of cones and color vision.

Originally Posted by Broomstick

I'm not sure - color vision in animals is highly variable. Bees, for example, don't see red but do see ultraviolet. Other animals, such as reptiles and birds, may have more photoreceptors for the human visiual spectrum.

There are also some flowers that look identically dull to humans but look vividly different to a bee, sometimes looking like a "bullseye."

Yes. The anomalous trichromats aren't missing specific cones, it's that certain of their cones are "tuned" to slightly different frequencies. Although these people are frequently lumped in with the colorblind, they are also sometimes referred to as the "colorweak". Such a person may, for example, perceive green as a distinct color when deeply saturated but may perceive pastel or tertiary shades as something else. For example, what a person with normal color vision perceives as "yellow-green" they might see as "yellow"/

Also, the differences in an anomalous trichromat is small enough that the brain can compensate for the shift, which cannot be done if the cone is completely missing. So anomalous people may only rarely notice a difference or defect in extremely limited conditions.

[Broomstick]

Originally Posted by thelurkinghorror

Also, the differences in an anomalous trichromat is small enough that the brain can compensate for the shift, which cannot be done if the cone is completely missing. So anomalous people may only rarely notice a difference or defect in extremely limited conditions.

Strictly speaking, we never "notice" the difference - what we notice is that we get into arguments with other people over the exact color/shade something is The brain isn't "compensating" at all, what is seen is what is seen, and there's never been normal color vision in that person to compare with what they see. There's no "compensating", it's that the difference is so small that it really is that meaningless outside those specific conditions you mentioned.

And, given how little being an anomalous trichromat actually affects one's ability to function, and that most of the disability is due to societal rules (those "extremely limited conditions" you mentioned), I'm sure if "defect" is really the best word to describe it. I mean, being left-handed is statistically rare and sometimes awkward, but for the most part we've dropped calling it an outright defect.

[thelurkinghorror]

Originally Posted by Broomstick

Strictly speaking, we never "notice" the difference - what we notice is that we get into arguments with other people over the exact color/shade something is The brain isn't "compensating" at all, what is seen is what is seen, and there's never been normal color vision in that person to compare with what they see. There's no "compensating", it's that the difference is so small that it really is that meaningless outside those specific conditions you mentioned.

And, given how little being an anomalous trichromat actually affects one's ability to function, and that most of the disability is due to societal rules (those "extremely limited conditions" you mentioned), I'm sure if "defect" is really the best word to describe it. I mean, being left-handed is statistically rare and sometimes awkward, but for the most part we've dropped calling it an outright defect.

If you determine what a anomalous trichromat's actual peak sensitivities are, and use them to determine what a picture would look like to this individual solely based upon the cones, then you would see an extremely impoverished color experience. However, the brain can adapt by adjusting color weightings, or ratios, etc. post-receptorally, thus these individuals see almost normal. So no it's not really a defect, although the one or two anomalous trichromats I have spoken to say they "believe" they don't have normal color vision, but can't say how. I doubt the difference is large enough to say, pose a evolutionary disadvantage, and mainly shows up in things like pigments and computer displays.

[EdwardLost]

After looking at a number of color-shifted pictures I've reached the conclusion that my particular brand of "red-green" colorblindness is a decreased sensitivity to red. I still see red but it's obviously more vibrant to chromo-typicals. As others have mentioned my difficulties are all from color disagreements with CTs or with color schemes that were designed or chosen by CTs.

However I remember reading some speculation that color blind men fared poorly during the Irish potato famine -- I suppose because they couldn't distinguish good from infected plants. Thus Irish immigrants to America were disproportionately colorblind. I don't know if there is any substance to either of those claims.

[Broomstick]

Originally Posted by thelurkinghorror

If you determine what a anomalous trichromat's actual peak sensitivities are, and use them to determine what a picture would look like to this individual solely based upon the cones, then you would see an extremely impoverished color experience.

Well, no, actually I wouldn't, as I'm an anomalous trichomat myself and thus that IS my normal. I suspect that if someone bothered to color-adjust something so that my eyes would see it as a normal trichromat would I'd think the result to be garrish, over-saturated, perhaps cartoonish or something.

But if you're going that route, you might as well say that all photographs should be viewed upside-down as that is how the images are actually projected onto the retina. Vision isn't just what's going on in the eyes, it involves lots of neural processing.

For that matter, people with normal color vision perceive colors as constant even under wildly different levels of light. If you were to project a picture of, say, a backyard on an overcast day based solely on what the cells of the eyes perceive and set it next to that of a bright, sunny day at noon the overcast day would also be extremely impoverished color-wise, yet for the most part people just don't notice it. Their brains "color-correct" to a very large degree, so really what you're talking about is something both normal trichromats and anomalous trichromats share.

So no it's not really a defect, although the one or two anomalous trichromats I have spoken to say they "believe" they don't have normal color vision, but can't say how.

I was well into my 30's before I was informed I was an anomalous trichromat, despite pursuing a career in the arts which included as some points color illustrations. It is entirely possible for an anomalous trichromat to live his or her entire life without ever realizing he or she has the condition. That's a damn small difference.

About the only place it shows up in my life is that I have a coat which, in most light, I perceive as a greenish brown and normal trichromats perceive as a brownish green.

I actually have a very good idea at this point how and when there is a difference between my color perception and the norm, but then, I do have a degree in art and for a layperson I'm literate in science in medicine.

I doubt the difference is large enough to say, pose a evolutionary disadvantage, and mainly shows up in things like pigments and computer displays.

More computer displays than pigments, in my experience. For awhile, when green and greenish colors seemed to become trendy for a bit I encountered a few problematic websites.

When it comes to painting and illustration, which I have done both in the sense of painting buildings and in making images, there are practices that virtually eliminate problems. For example, when painting a house for a customer I let the customer choose anyway (though I might offer some very tentative advice or opinion if asked) and then get all the paint mixed at one time, for a completely consistent color. In many instances when doing illustrative or dye work you're using either very specific colors such as the Pantone group or precise formulas to give consistent results.

Where my anomalous trichromacy was discovered was when I went for my first FAA physical to get my pilot's license. At the time they were using the Ishihara test, which is way more sensitive than piloting really requires (I've applied for other jobs that involved testing color perception with different testing methods where I tested out completely normal thus demonstrating once again that anomalous trichromacy is often an irrelevant difference. A lot of color-testing won't catch it.) I easily passed the light-gun demonstration of ability test. Even though there was a detectable difference I still have no difficulty in the real world distinguishing colors in aviation sufficiently to avoid safety hazards, which is the real concern there. That is probably why the FAA is no longer requiring a SODA but using wavier letters for those of us with slightly off the norm color perception.

[thelabdude]

Originally Posted by clairobscur

That should be quite easy to determine. For instance train the animal to find food in, say, a red container, then present it with two containers of different colors and see if it can pick the right one.

Not really. They are supposed to see red as a shade of yellow. That would only prove that they see the colors as different, not what they see them as.

Do different cones look different under a microscope? How do we sort out the dichromats, tri chromats, tetrachromats?

[Broomstick]

With humans, we can do non-invasive testing and based on their answers make a determination.

But with individual cells I suppose there's some very fancy way of determining what makes it react. Maybe analyzing light-sensitive pigments, or seeing when a nerve fires in response to a stimulus.

[Lemur866]

The only reason I would ever imagine I have some sort of color deficiency is that when they give those "what number do you see in the dots" tests, I sometimes see different numbers than I'm supposed to. But I see red, I see green, I see every color I'm supposed to see. If I look closely at the dots on the Ishihara tests I can see that there are some dots that are green rather than the background reds and pinks, but the clusters of dots don't resolve into numbers. My wife has called some shirts of mine green when I would call them brown with a touch of green. I'm semi-convinced that color-blindness is a big practical joke on gullible kids.

[engineer_comp_geek]

Originally Posted by clairobscur

That should be quite easy to determine. For instance train the animal to find food in, say, a red container, then present it with two containers of different colors and see if it can pick the right one.

This has proven to be problematic with some animals. If you look at the cells of their eyes, cats and dogs should both be partially colorblind. With dogs, this is actually fairly easy to prove using food and colored bowls or containers, exactly as you suggested. You can tell pretty accurately what colors a dog can and can't see.

Cats, however, despite having some color receptors in their eyes, won't choose food based on container color. For a very long time, researchers thought that cats were somehow deficient elsewhere, perhaps lacking something in their brain to process the color information from their eyes. It wasn't until the 60s or 70s that someone was able to prove that cats are not in fact colorblind, and can be trained to select food based on container color. For some reason, though, training cats to do this is extremely difficult. And by extremely difficult we're talking well over a thousand tries before they finally start to get it right. No wonder researchers used to believe they were colorblind. After trying it a few hundred times with complete failure you'd be tempted to write cats off as colorblind as well.

And after googling to make sure I had the order of magnitude of the cat trials right, it turns out I learned this originally from Uncle Cecil. Here's his article on it:
http://www.straightdope.com/columns/...w-do-they-know

[dorsk188]

If I can wildly speculate on the topic question a bit...

Aside from the already great answers given about how colorblind people see camouflage differently, I would venture that full-colored brains are "wasting" energy on color that colorblind brains may devote to edge and motion recognition. When analyzing pictures, a common thing to do is use filters that effectively reduce the amount of information your brain is receiving at one time. Being colorblind could reduce the overall complexity of the scene, making it easier to spot an anomaly like movement.

The brain is a plastic thing and developing with color-compromised vision would most likely result in a focus on things the eyes can see. It wouldn't be "super-vision" or anything like that, but it might give you an edge.

Of course, colorblindness also leaves you vulnerable to all the troubles listed above and more, which is why you would not want to rely exclusively on people with it.

[RaftPeople]

Originally Posted by thelurkinghorror

...The upper theoretical limit of your acuity is limited by the width of one cone (rods are wider), but they are already packed in there, I don't know if the amount of new cones you can add would be enough to make a difference?

I just read something related to this, research showing that the retina detects more detail than is transmitted downstream for conscious processing.

http://mentalhealth.about.com/librar...lcortex501.htm

[barbitu8]

Originally Posted by thelurkinghorror

Have a link? Sometimes LASIK leaves people with 20/10, but it doesn't affect the retina. The upper theoretical limit of your acuity is limited by the width of one cone (rods are wider), but they are already packed in there, I don't know if the amount of new cones you can add would be enough to make a difference?

Some are born with better than 20/20. I knew someone who had 20/10. Many pilots have better than 20/20. I was told by an optometrist that the difference is in the number of cones. If this is not so, how do you explain vision better than 20/20?

[jovan]

Originally Posted by engineer_comp_geek

Rods see black and white (they give you your detail vision) and see in low light conditions.

Nitpick: in the daytime, rods do not contribute significantly to vision, as the rods are completely inhibited by the brightness. (Somewhat un-intuitively, retinal receptors are inhibited by light, they fire less and less, the brighter the light.) Furthermore, more receptors does not necessarily translate to greater visual acuity. In the case of rods, the greater number of cells allows larger "sensor sizes", with the output of several rods being summed before leaving the retina. Overall, rods have much lower spatial acuity than cones. Even with cones, the signal that goes out of the eye goes through spatial filters that involve several neighbouring cells.

Originally Posted by Colibri

As mentioned above, some primates, including Old World Monkeys, apes, and humans, and a few New World Monkeys, re-evolved a third color receptor. This is probably an adaptation for locating fruit, which was already brightly colored so birds could find it.

That's the common view, but there is also a hypothesis, championed by Mark Changizi, that the purpose of the third cone is to allow primates to better read each others' skin. The argument goes that dichromats that depend on fruit don't have that much problem finding them so the evolutionary pressure isn't huge there. Trichromat primates all have naked skin visible on their faces, whereas dichromats do not. The peak spectral sensitivity of the L (red) and M (green) cone perfectly match a spectral peak and trough of skin spectral reflectance that are due to oxygenated hemoglobin. In other words, primates who have L and M cones are able to tell the level of oxygenation of others' capillaries. With a naked face, we're able to tell when others blush, are angry, or sick. For social animals that need to intensively care for their newborns, this is a great advantage. That it also allows you to better judge the ripeness of fruit is a secondary advantage. Or so goes the argument. (Changizi has a bad tendency to overstate his case in his popular writing.)

[clairobscur]

Originally Posted by Colibri

It's really impossible to understand how colors we can't perceive might look to an animal which can see them. How would you describe the sensation of "red" to a color-blind person?
.

That wasn't was I wanted to ask. Rather, I wanted to know if they could see two kinds of "red", or rather two kinds of "blue", or whether it depended on the specie, or maybe if it was something weirder than that.

But Broomstick's mantis shrimp is weird enough. Not only is it dodecachromat (while I was making up this word fully expecting that no creature would be like that), not only have they eyes mounted on stalks that can move in any possible direction, not only do they see in the infrared and the ultraviolet, but they also see stuff I didn't even know existed like "circular polarized light".

[clairobscur]

Originally Posted by thelurkinghorror

Colibri covered it, but for example see spectral sensitivity curves. A new cone would work best if it is in a area of "low coverage," e.g. ultraviolet to the left, between S/M in middle, or infrared to the right. Most suspected human tetrachromats would have a fourth cone close to the L, M, so no mindblowing changes.

.

Interesting. It seems that our "coverage" isn't optimal at all, with two close peaks.

As for tetrachromat people I envisioned asking if there were any, then deleted the question thinking it would be too important a mutation to exist, or that if it had existed it would have been so incredibly rare in the history of mankind that it would have gone unoticed. Things are much weirder than I thought, both for animals and humans.

[RaftPeople]

Originally Posted by barbitu8

Some are born with better than 20/20. I knew someone who had 20/10. Many pilots have better than 20/20. I was told by an optometrist that the difference is in the number of cones. If this is not so, how do you explain vision better than 20/20?

Based on the link I posted above, it would seem (possibly) it relates more to the structure of the visual cortex.

[thelurkinghorror]

Broomstick: I don't know where you got that I suggested color normals do not adapt to their environment. The point is: if you run tests on a person's physiology and then make an assumption on what they see, you would be making an error. Anomalous trichromats have much better color vision then their physiology suggests, due to post-receptor factors. Their difficulties only show up in very specific situations. Thus, the only way to "prove" what someone sees is to test their behavior, not what pigments they have or neural connections.

and re: flight, I think there are different rules/criteria for exclusion between the FAA, military, European groups etc. Some people are in the odd position of being excluded from flying in one and allowed in another. The lease stringent test accepted by many has you discriminating between red, green, and white lights at various brightnesses. I am glad that it worked out for you, 99% of people with color deficiencies are likely at little risk while flying. It would be better if non-opposing colors were used on planes however.

Originally Posted by engineer_comp_geek

Cats, however, despite having some color receptors in their eyes, won't choose food based on container color. For a very long time, researchers thought that cats were somehow deficient elsewhere, perhaps lacking something in their brain to process the color information from their eyes. It wasn't until the 60s or 70s that someone was able to prove that cats are not in fact colorblind, and can be trained to select food based on container color. For some reason, though, training cats to do this is extremely difficult. And by extremely difficult we're talking well over a thousand tries before they finally start to get it right. No wonder researchers used to believe they were colorblind. After trying it a few hundred times with complete failure you'd be tempted to write cats off as colorblind as well.

Terminology: in the scientific context, colorblind means "less color perception than humans." In other words, dogs and cats are colorblind, as are all mammals besides apes, some monkeys and cetaceans and pinnipeds (those last two can't normally see color at all). Despite being colorblind, cats and dogs can see many colors. Confusing yet?

Originally Posted by barbitu8

Some are born with better than 20/20. I knew someone who had 20/10. Many pilots have better than 20/20. I was told by an optometrist that the difference is in the number of cones. If this is not so, how do you explain vision better than 20/20?

A number of ways. But I wouldn't jump to cone count as my first conclusion. See here, the cone matrix (coloration is artificial, they look identical under a microscope). There's not much room to squeeze new cones in.

Originally Posted by clairobscur

Interesting. It seems that our "coverage" isn't optimal at all, with two close peaks.

As for tetrachromat people I envisioned asking if there were any, then deleted the question thinking it would be too important a mutation to exist, or that if it had existed it would have been so incredibly rare in the history of mankind that it would have gone unoticed. Things are much weirder than I thought, both for animals and humans.

There are people (females) with 4 cone types, it is still being tested whether there are any actual behavioral differences. I'm not up to speed on the research here. And actually, the peaks I showed in that link are "ideal" numbers, there are tons of different expressions across humans, the main constant is that color normal people have three types, and the types (especially L & M) are sufficiently far apart.

By the way: really cool website. You can simulate the three types of colorblindness on an image from the internet or uploaded.

[Broomstick]

Originally Posted by clairobscur

As for tetrachromat people I envisioned asking if there were any, then deleted the question thinking it would be too important a mutation to exist, or that if it had existed it would have been so incredibly rare in the history of mankind that it would have gone unoticed. Things are much weirder than I thought, both for animals and humans.

Human tetrachromats probably do, in fact, exist (two cases are mentioned here). So far as I know, they're invariably female. What happens is that a woman who is a carrier for certain forms of colorblindness, the "anamalous" trichromats, winds up with, say, two types of cone cells that respond to green (or red, or whatever the mutation is for). This should give them four different cone cells with different peak sensitivities. It does seem to improve their color discrimination, but there hasn't been a lot of research done the topic. It might be 2-3% of women worldwide, but no one really knows for sure.

[Snnipe 70E]

Originally Posted by barbitu8

Some are born with better than 20/20. I knew someone who had 20/10. Many pilots have better than 20/20. I was told by an optometrist that the difference is in the number of cones. If this is not so, how do you explain vision better than 20/20?

I doubt that there are many color blind pilots. I would think that being color blind would disqualify them.

I had a few classmates at the Maritime Academy who applied for the deck division. During the physical their being colorblind was discovered. They were told they could not qualify as a Mate so they could not apply to the deck department, but if they changed major to engineering they would be admitted to the Academy.

[Broomstick]

Originally Posted by thelurkinghorror

and re: flight, I think there are different rules/criteria for exclusion between the FAA, military, European groups etc. Some people are in the odd position of being excluded from flying in one and allowed in another. The lease stringent test accepted by many has you discriminating between red, green, and white lights at various brightnesses. I am glad that it worked out for you, 99% of people with color deficiencies are likely at little risk while flying. It would be better if non-opposing colors were used on planes however.

The problem is that finding non-opposing colors that truly work for everyone is nearly impossible. Red/green are problematic, but there are people with other forms of non-normal color vision with different problem pairing, like blue/yellow.

The US's FAA take the position that what really matters is can you tell the various signal lights apart in a reliable manner. If you can, it doesn't matter if you can see the correct colors or not because you'll still respond properly to the signal. Other nations just flat-out say unless your color vision is perfectly normal you can't legally fly, regardless. This can also play out in driving laws - the US pretty much ignores whether someone is colorblind or not while driving, but some other nations (I think Hungry is one of them) just flat out forbid anyone with any form of colorblindness from driving a car.

In one case, the governing authority is saying "we only want normal people to do this" and in the other the authority is saying "if you can understand lights/colored signals and consistently respond in an appropriate manner you can drive regardless of what colors you actually see." This can happen with one-eyed people as well - the US makes prospective one-eyed pilots take a specific test to demonstrate they can adequately compensate for the lack of stereoscopic vision and if so, they can fly without restrictions. Other countries just flat out say you need two functional eyes to be allowed to fly. While there is no disputing that the one-eyed lack stereoscopic depth perception, that's not the only way the brain determines depth in what is seen and in fact out past about 50 feet binocular vision is not terribly useful for depth perception, your brain uses other cues. Again, most of the problem is that the mainstream overestimates the impact of the visual anomaly in regards to actual function. Sure, one-eyed vision does have drawbacks in very specific conditions, but those conditions seldom apply in the real world.

By the way: really cool website. You can simulate the three types of colorblindness on an image from the internet or uploaded.

I really wish someone would try to come up with an alogarithim to "color correct" for us anomalous trichomats - so much emphasis seems to be on the "opes" who completly lack a particular color perception, the anomalous seem to get lost.

[thelurkinghorror]

Thanks for the info. By non-opposing, I meant say putting signal lights in red and blue, then it is unlike that the colorblind pilot would confuse then.

Seems kinda annoying: games like Bioshock make an essential discrimination task rely on red vs. green, so truly colorblind gamers are screwed.

Opes are looked at because they are more extreme and "sexy." Still, the anomalous should get more interest than they do. For example, deuteranomaly is IIRC ~8% of males. It's pretty common, and it would be nice if there was more interest/recognition in both simulations and aviation and driving.

[RaftPeople]

Originally Posted by Snnipe 70E

I doubt that there are many color blind pilots. I would think that being color blind would disqualify them.

I know a former air force pilot that knew the color blindness would be tested for and he ordered all of the different color blindness tests (different mfg's) and practiced by looking for any identifying characteristics, serial numbers, other patterns, etc. which allowed him to pass the tests.