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Rigorous Science

See more colors?

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Normally, the human retina contains four types of light-sensitive receptors: three types of cones and one type of rods. The receptor proteins contain the chromo "” iodopsin in the sticks, the rhodopsin in the cones. The role of the latter in bright lighting is insignificant, so for a person there are three "basic" colors: blue, red, green "” all the shades we perceive are formed by their combinations.

Since each of the yodopsins allows you to differentiate about a hundred shades, a person with normal vision is potentially able to distinguish about a million color combinations. Adding another type of receptor increases this number to one hundred million. Concetta Antico is a carrier of a mutation in the "red" iodopsin gene, whose sensitivity has shifted to the short-wave region. Special features are best displayed when distinguishing reddish-yellowish and purple shades: the color scheme of her paintings focuses on these colors. The additional color pigment also increased color sensitivity in low light, allowing you to distinguish between shades at dusk and in the shade. 

The eyes of the mantis shrimp (Oratosquilla oratoria) have 16 light-sensitive receptors.

My question is: What needs to be changed in the structure of the human eye to be able to see ultraviolet and infrared radiation, as well as to be able to see better in the dark ( That is, to have a good enough night vision). And at the same time distinguish significantly more colors in the visible range ( if you consider that the appearance of the 4 receptor allows you to distinguish 100 times more colors than ordinary people. Then when the same 16 light-sensitive receptors appear, we can distinguish hundreds of millions of colors, or even several billion! )?

Also keep in mind that you need to turn the chromatins in the retina so that the nerve comes out from behind, not in front. This will remove the blind spot to reduce the overall length of the nerve and provide a greater amount of chromatin for each surface area. With appropriate adaptation of the primary processing layer on the back of the eye ball (duplication and offset integration), which can be used to increase the speed of perception by a factor of 2x to 4x, or the details of perception. 

( Human eyes absorb 90% of all photons before they reach the photon receptors. And we need at least 9 photons hitting an individual receptor before it registers a light source, (before it "sees something). This means that by gluing the receptors further forward, we could (optimally) increase the light sensitivity by a factor of ten. )

When making decisions, it is advisable to familiarize yourself with similar questions, where there are several interesting solutions that it is desirable to combine:

Colors of Things Outside the Spectrum

How to modify the human eye to see into the ultraviolet and infrared bands?

Supplement: Please offer solutions related only to biology, so no implants or artificial eyes. Also do not ask questions regarding too much information and the difficulty of processing ( if you know the ways of how you can reduce the difficulty of processing, I will be glad to hear ).

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The first step is to give a look (pun intended) at the retina of most birds eyes, which have a 4th cone type to see UV. Differently than mammals, their cones have an oil drop to better constrain the wavelengths detected and reduce the overlap with other cone types. Also, birds' cone are much more thin than mammalian ones.

However, birds also have some downsides. Mammals perceive contrast better than birds and birds have a pecten inside their eye blocking part of their view creating large blindspots. Their retina have no blood vessels, so this is the reason why they need the pecten.

Also, humans, like all vertebrates have an inverted retina, which means that blood vessels and nerves are in front of the rods and cones instead of behind them. Cephalopods have non-inverted retinas.

Cats have a tapetum lucidum behind the retina to allow them see better in the darkness, but at the expense of decreasing their visual acuity.

As elemtilas said, people who get a surgey of cataract can see some UV. See here for more about that.

Further, even on mammals, reindeers do sees UV light.

For IR vision, that is more complicated. The reason is that since mammals are warm-blooded, they simply glow in the near IR-range, so any receptive cone would be always saturated and blinded. Animals which are able to see some IR are all cold-blooded, mostly are insects, but some cephalopods, crustaceans, molluscs, fishes, amphibians and some snakes do see IR. But no way birds or mammal can do that. Note that altough snakes see IR, they don't use their eyes for that, instead they use their pit organs, as if those are a distinct set of eyes for detecting IR, but with a very poor visual acuity, resolution and contrast. So, to add IR vision, you would need to somehow shield the eye from the body own glow.

So, I think that you could:

  • Start with a human eye.

  • Replace the mammal cones and rods by avian ones, including adding the avian UV cone. If you are unable to do this, try to at least introduce the reindeer UV cone.

  • Make the nerves and blood vessels connect them from behind the cones and rods, instead of in the front of them. This would also allow those cells to collect more light and be better vascularized. Then they could also be cramped more tighter, yielding a sharpen image. Since the much better vascularization also gives those cells more nutrients and oxygen, I think (not sure though) that they would then be able to yield a better contrast and get rid of the need of having either pectens or blindspots.

  • Make a special tapetum lucidum in the eye that can progressively change from reflective in darkness to opaque black under direct sunlight to make better adaptation for different light conditions beyond what the iris is capable.

  • Change the IOL in the eye for something that is also transparent in UV, maybe you can get an inspiration from reindeers to keep it compatible with being mammal.

  • You end up with three layers at the retina. The internal one features rods and cones. The other two are (a) the blood vesses, nerve endings and retinal ganglion cells and (b) the tapetum lucidum. Not sure which one would work best as being the middle layer.

Adding a UV cone might have a few downsides. Notably, if you add a new type of cone in the retina, you will need to spread the existing ones a bit to make room for the new ones, which might reduce visual acuity. Also, human eyes focus images with the red and green cones while the blue ones suffer from chromatic aberration and due to them being far less numerous, poor visual acuity in the blue. However, it shouldn't be very hard to balance this, specially if you use avian cones which are much thiner than mammalian ones. Also, the human brain already does a pretty good job "photoshopping" the image from retina to compensate for a lot of the vision shortcomings.

Then when the same 16 light-sensitive receptors appear, we can distinguish hundreds of millions of colors, or even several billion!

Unlikely to work as you think. It is probable that seeing so many colors would require the correspondent neuron wiring in the brain. So, altough some animals have a large number of photo-receptors, this could be at the expense of being unable to properly blend all those color or having trouble to discern different similar shades of the same color or something else. Also, user MJ713 points out in a comment that research on mantis shrimps shows that they are actually fairly bad at distinguishing between similar colors.

About tetrachromacy, I will cite this:

However, the most stringent test of our hypothesis was between the female trichromatic subjects and the female four-photopigment heterozygote subjects. As shown in rows 1 and 2 of Table 2, the mean numbers of bands delineated by the two groups of females (7.6 vs. 10) were significantly different ( p < .01). This comparison eliminated differences in performance attributable to gender and thus was a stronger test of our hypothesis that having four pigments yields a perceptual difference.

At present, four-photopigment female individuals are reported to be rather common, by some estimates occurring in up to 50% of the female population (M. Neitz, Kraft, & J. Neitz, 1998). It is also the case that an estimated 8% of males presumed to be color "normal" likely represent a four-photopigment retinal phenotype (expressing multiple L-pigment opsin gene variants that could significantly contribute to color vision; Sjoberg, M. Neitz, Balding, & J. Neitz, 1998).

I.E. There could be more tetrachromats around us that we might be aware. Even most of the tetrachromats themselves must be unaware.

Also, excelent to read:

Also, some years ago, I seen a paper where someone made an experiment with many women and found out some tetrachromats and even identified two different types of tetrachromats with functional tetrachromacity. If my memory don't betray me, one of those groups had an orange as the 4th primary colour and the other had a greenish-yellow as the 4th primary color. However, it was some years ago and googleing for it I was unable to find it again. This basically happens because the red and the green cones are encoded by two genes called OPN1LW and OPN1MW (ha, could find their names with Google at least), which are neighbours in the X chromosome (but absent in the Y chromosome), so during crossover (for women only), a gene that is a mix of half-OPN1LW and half-OPN1MW might end being produced, and there is more than one way to mix them.

Also, in the same occasion some years ago, I also seen a very good webpage which described in profound details, but still in a clean and easily understandable language, all the nuances of how the color vision evolved and how it worked out in the retina, in the retinal ganglion cells and in the brain. However, once again, Google betrayed me.

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