I learned the importance of trichromacy when a friend and I came across a patch of wild strawberries. I'm partially red-green colorblind and for every strawberry I found, my friend found ten. They were almost invisible to me. It's neat to see that the fourth cone's response curve peaks right between the red and green cones' curves in tetrachromats. I bet they are amazing at finding berries.
This probably has nothing to do with chromacy, but is related to finding berries and other odd things. My sister is gifted with finding four leaf clovers. She walks in a field and seems to just see them. Every time she picks one, it's a four leaf. Her record find is a 7 leaf clover.
It's conceivable that a mutation in the gene for the red or green light-sensing protein gets a mutation that just shifts its sensitive wavelength closer to the other. So "partial" r/g colorblindness could occur if there was still some separation between those wavelengths, but not as much as is typical.
I don't know how it works, but I have it - I can see red and green and pink in big blobs, but when there's lots of small red and green (or pink) details mixed - they seem the same to me (if their darkness is similar).
Also I have problems with big uniform colour areas it there's small amount of green mixed with pink or red and vice-versa. I was making a sunset skybox for a game, and friends were wondering why the sky is slightly green - for me it was pinkish-red-yellow, but I put there some green by mistake.
> Deuteranomaly ... The medium-wavelength pigment is shifted towards the red end of the spectrum resulting in a reduction in sensitivity to the green area of the spectrum. [0]
The closer the spectrum perceived by the M (green) cone is to L (red) cone, the harder is is to differentiate red from green.
Very inaccurate summary, since I skimmed: Up to 12% of women have an X chromosome mutation that creates a fourth cone. This cone generally overlaps the spectral region covered by the cones sensitive to red and green. The exact area of overlap determines whether or not each woman sees "more": If the fourth cone completely overlaps the region covered by an existing cone, no new information is presented to the visual system and the input is effectively discarded (she sees "just as much" red or green, not more, not less). If, however, the fourth cone has peak sensitivity in the gap between the cones covering red and green, she will she up to 100% more colour than women with normal vision.
That's not quite correct. Where one cone type has a peak response, another may respond with a signal that is only one percent or less of its peak response, but the frequency regions in which hey have _any_ response basically overlap. Given the sensitivity curves, that difference is academic for blue versus red and green sensitive cones, but not quite for red versus green sensitive cones.
What differs is the amount in which having a fourth type of come allows one to get rid of metameries (https://en.m.wikipedia.org/wiki/Metamerism_(color), a term that the article surprisingly doesn't mention)
If your fourth come type has a response curve that is very similar to one of te 'normal' three, there should still be _some_ effect, but it will be hard to devise an experiment that shows the ability to discriminate additional colors.
But given the impact that not having red or green cones with their fairly similar sensitivity curves has, I suspect having a fourth curve, even if it falls between the two, will have a measurable (in the lab) effect on one's ability to discriminate colors.
Scientists are looking at direct delivery of gene therapy to retinal cells to cure serious eye diseases like macular degeneration, pigmentosa blindness, etc. Should this work well, then the next step would be lesser conditions like male color blindness. I read of some successful attempts to give dicromatic animals, genrally carnovoires, the trichromatic gene directly to the retina. These subjects can be tested by giving rewards hidden in standard color blindess test images.
The next step, more controversial, would be super-vision of tetrachromacity, perhaps infra-red and ultra-violet sensitivity. Night vision glasses no longer needed for enhanced soldiers.
> The next step, more controversial, would be super-vision of tetrachromacity, perhaps infra-red and ultra-violet sensitivity. Night vision glasses no longer needed for enhanced soldiers.
Utter poppycock.
The cornea and lens in humans are UV opaque, which is a very good thing because UV light is damaging. People without a lens (aphakia) are reported to perceive UV light, but this is otherwise an undesirable condition. As to infrared, some people can already see up to around 750nm or so (NIR) with awful quantum efficiency. Pit vipers and some fish have limited perception of IR, but I'm not aware of any animals that can see IR in the conventional sense… being warm blooded presents a real problem, for one.
Plainly, there are limits to what can be achieved in hyperspectral imaging due to materials, and that's without the constraints of biology thrown in the mix.
That seems... strong, especially if referring to the "Night vision glasses no longer needed for enhanced soldiers" bit.
They eventually formulate a chlorin e6 solution for human use. A few drops are dripped into Licina’s eyes, and they had him look for people hidden among trees as well as symbols on objects in dim light. Licina seemed to perform a lot better than the four other people who did not get eyedrops.
My frustration was more directed towards the UV-Vis-NIR part (and I read night vision as thermal IR, but who knows), but I wouldn't say that your linked article is something of substance. To quote the article, quoting the experimenter/ee, "In Licina’s own words: 'Let’s be fair here. It’s kind of crap science.'"
I wouldn't even know where to begin in criticizing their study as disseminated on their website except to say it is completely unscientific. There are no proper controls, for one. I think it's wholly irresponsible of the press to report on this work in this fashion at such a premature stage. I respect the enthusiasm of the citizen science crowd and think it's a neat idea, but stuff like this is going to quickly earn it a very bad reputation.
Honestly, if this were reddit I would have deleted the entire post when scott_s pointed out it was harsh; it was hastily written in a moment of supreme frustration. Sorry!
The reason I commented is that the rest of your comment was excellent, and very informative. (I did not know our cornea and lens are UV opaque. And then the subsequent follow-ups to your point, explaining that it's more subtle than that by nl and blincoln, were also very interesting.) Your knowledge of the subject and willingness to explain it indicates to me that you're valuable to the HN community. So I felt it was worthwhile to point out the one bit of your comment which doesn't work well on HN, since your account is new.
> Your knowledge of the subject and willingness to explain it indicates to me that you're valuable to the HN community.
You're too charitable. The truth is I'm unemployed at what feels to be a particularly bad time of the year to be unemployed (think of all the family and friends get-togethers… "so, what do you do?"), and I'm bludgeoning people on the internet with domain knowledge in some lame effort to stroke ego rather than facing a bleak job market for someone of my background. It's a harsh toke, but admitting it (even pseudononymously) is the only way I'm going to do anything about it.
You don't have to say "I'm unemployed to that answer". You can still say you're a programmer, if you're a programmer! Even better, you can start a little project and call it a "startup". Tell 'em you're a hip little entrepreneur - that's even cooler than being employed in some circles. :)
By the way, being charitable in iterperting what others write here is one of HN's tenets. You've demonstrated self reflection and contrition. That puts you ahead of most.
The natural human cornea is opaque to shorter-wavelength UV, but there's no reason it couldn't be replaced with something transparent to UV-A at least. This is supposedly an unintended side-effect of some cornea replacement surgery[1].
UV may have the potential to be damaging, but plenty of animals see UV-A safely - for example, bees[2] and mantis shrimp[3] can perceive UV to 300nm. Some birds (whose eyes are much more like ours, of course) can also perceive UV[4][5].
If we wanted some ready-made genes, I vote for borrowing from the European starling, which has receptors that sit in our enormous gap between blue/violet and green as well as UV-A [6].
Near infrared could be very useful, because (in combination with red, green, etc.) it can be used to easily distinguish vegetation, and it scatters less in the atmosphere, so it could allow clear vision at much farther distances. Most materials that are transparent to red/green/blue are also transparent to NIR, so as far as I know, the rest of the eye shouldn't need to be modified.
Most people can apparently see a little bit into the NIR if they wear NIR-bandpass goggles, but it's extremely dim and doesn't have a perceived colour that's distinct from the rest of the visible spectrum, so that's not really what the GP is suggesting. They're suggesting wiring up a true NIR-specific receptor in the eye which would provide a fourth, fifth, or sixth primary colour (in addition to red, green, blue, and optionally the in-between-red-and-green that tetrachromats see as well as a hypothetical UV-A receptor).
I can't find a cite at the moment, but some birds have NIR patterning on their feathers (I have photographed this myself at a zoo), and the last time I looked into it, there was some speculation that tropical birds in particular had some NIR sensitivity (in addition to UV-A) and had evolved spectrally-complex colouration as a result.
Thermal infrared is a much longer wavelength, and I'm not aware of a good material for lenses/eyes that is transparent to both. It's possible to have an uncooled sensor that detects it, but I agree that it's a much larger leap than UV-A or NIR.
If it's okay, I think we should set the non-vertabrates aside for the discussion since their optical systems are so different.
As to the safety of UV-A, I don't think you're correct. A common element of all the comparative species selected is that their life span in the wild is far shorter than our own, and there isn't going to be selection pressure happening before they would accumulate UV damage. UV damage to the eye is kind of like yellowing of plastics, it accumulates over time. As is pointed out in your first linked article, aphakia patients are advised to wear blue-blocking glasses to protect their vision. My first thought as to how bad could it be was retinoblastoma—I am not aware of any studies looking at the incidence rate of Rb in aphakia patients and PubMed doesn't show anything either, but I don't think it's an unreasonable thought.
Aside from the ionization problem, UV light also has a much higher propensity towards scatter. Floaters are bad enough for some in visible light! Of course, we're talking futuristic gene augmentation, so it's not unreasonable to suggest we'd vacuum the eyes out every now and then, so maybe floaters will not be a problem :) We still have a problem with the much higher dispersion of UV light relative to visible, given the materials we have to work with in the eye; that, plus scatter, means we're probably going to have very fuzzy UV vision. Replace the whole lens system and maybe you get better UV-vis vision, but we still haven't overcome the safety problem. Maybe instead of vacuuming out the eyes, we just swap them out for a new autologous gene-tweaked set every couple years.
NIR would seem to be more realistic than UV (certainly considering safety), but here, the quantum efficiency of the pigments would seem to be a limiting factor. As you point out, we can already actually see a little into NIR (IIRC, in scotopic with something like 10-6 QE at 750nm relative to 555nm). At first glance, the chemical structure of human receptor pigments doesn't look to be super favorable for modification to getting something that would have a good absorption cross-section in NIR. Compare the structure of vitamin A or retinal with a strongly NIR-active chromophore, there's a lot of steps bridging the two and the structure as a whole is hostile towards selective modifications, not to speak of the rings where the modifications need to happen.
As to thermal IR, I think we'd need a metamaterial for something that would work in vis and in LWIR, and that's a handwavey statement on my part. It would definitely be of interest to the military!
Overall, I think it's more plausible to augment our vision by wiring a camera directly into our visual cortex. Biology is too hard.
Creatures with infra-red vision are usually cold blooded. We shine too brightly in infrared from within to be able to see something outside.
But tetrachromacy should rightfully belong to us. It was lost by our pre-mammal ancestors, while reptiles still have base tetrachromacy, and some fish perceive even more colors.
Most animals only perceive two colors and grow two pigments. Makes animal coloring (and animal world) kind of boring for us. Birds use bright colors because they can distinguish them.
I just visited my retina guy and he told me about the latest developments. These days they're modifying the genome of stem cells and printing small clusters of retinal cells onto a substrate for implantation.
There have been some successes curing serious blindness issues but they will be hesitant for a good long while to "cure" things like colorblindness. If things go wrong a blind person is still blind, but a colorblind person has quite a bit to lose.
The usual pattern is that only one X chromosome gets transcribed in any given cell.[1] This keeps the dosage of all those proteins correct. Otherwise there would need to be a separate set of dosage controls for XX and XY people.
The inactivation occurs pretty early in life, and when cells replicate they keep the inactivation. This results in macroscopic regions of the body with consistent inactivation. Usually this isn't noticeable, but in cats coat pigment is on the X chromosome, and heterozygous cats often show "tortoiseshell" or "calico" coloring. The patches of contiguous color there are larger than a retina.
So it seems entirely likely that all the cells in a human woman's retina would use the same X chromosome.
On the other hand, that predicts half of het women would be colorblind, which isn't observed. So maybe not so simple...
I have a second thought about downstream neural hookups and the mechanisms for those, but it'll have to wait for later.
The article explains X-inactivation, and it doesn't play the role you think here: both copies are broadly equally expressed among retinal cells. Also even if all cells in a retina used the same X-chromosome copy it doesn't predict color-blindness, since we would still have a trichromatic system.
The answer to the question posed by the title is simply that all mutant fourth cone types are not created equal. Most have a spectral response curve similar enough to an existing type not to make a real difference; a few have peak responses more squarely in-between those of the usual trichromat photopigments, allowing more finely graded color perception. (The article takes its time getting round to explaining this, but it's all there.)
I wonder how those poor women deal with RGB displays. It must feel weird to see a difference between red+green and actual yellow.
Although, on second thought, color vision doesn't seem to work perfectly anyway. I never understood how red+blue can be perceived the same as far violet, it just doesn't make sense if you look at those frequency response curves.
I doubt it will be that bad. It will probably seem a little more dull, like some of the colorblind simulators you can find around the net. It's probably not just screens; pigments have the color they have because they reflect certain wavelengths, tuned to the proportion that a trichromat would consider identical. A tetrachromat is almost certain to notice that pigments of pictures on paper might be drastically different in color to the color of the objects the pictures are supposed to represent.
The brain doesn't perceive color just by addition of the stimulation of the cones. Your red and green cones are still (slightly) stimulated when you see blue, and your brain tells you that blue is the color; with violet, the stimulation among the cones have a different proportion, hence violet. Incidentally, this is also why the sky appears blue; the sky is too polluted by other wavelengths to appear violet.
Actual violet (like UV LED or mercury lamp) should stimulate almost exclusively S cones. But it turns out that if you take blue, which stimulates M and L more than violet, and then add even more L stimulation, you end up with something that "feels" more violet than blue (at least to me). This is what bothers me. It looks like two distinct inputs producing the same output, even though there exists an intermediate input which produces different output.
You aren't paying attention, by "inputs" I meant "inputs from retina to the nervous system", not "inputs to the eye".
Most metamerism can be trivially explained by different combinations of light stimulating cones in the same way. But it looks like red+blue and violet are different and there is just no reason for them to be perceived the same, except that apparently there is also no reason to distinguish between them.
None of the red cone sensitivity plots I've seen previously showed secondary peak, but that's because they were always cut somewhere in the blue region.
It opens with an Australian painter who displays her extraordinary vidual experiences in her art. But if she was born this way, why would she find it extraordinary?
Hi! I wrote the Neurosphere article you're discussing, and noticed this lively comments section. I agree with the question you're asking - if she was born this way, why did she question it? From the research I did on her life, it appears that she always assumed people could see these colours, and apparently when teaching her students in art school she would try to say things like "Try to depict all the colours you see in this leaf, like the turquoise and orange on the sides..." and her students often just found it too embarassing to tell her they didn't see any of these colours. She slowly started realising that her colour perception may be different, until one day a neurology student taking her class suggested she took a genetic test. That's it. Since then I suppose she has really harnessed the results of the test to market her vibrant art as reflecting her 'tetrachromatic reality'. Some people have commented on Twitter questioning this, and it's something I think I will write about in the near future because it's a completely fair point.
I thought in females half of X chromosomes are deactivated as to not producing conflicting similar proteins. If the extra cone gene is on the deactivated half, then it is not produced.
It is suggested that imperfect deactivation leads to female increased occurrence of autoimmune syndromes over males.
The key is that which X chromosome is deactivated is not the same in all cells.
It does occurs fairly early in the development process (a stage called gastrulation), and the deactivation does persist for all cells that descend from a given cell present. But critically, it's late enough that a retina could conceivably possess cells descending from two different "lineages".
You can actually visibly see the "resolution" of the deactivation by looking at tortoiseshell cats. Each blotch of orange/black represents one cell present at the deactivation stage.
