[rekabis]

> The magic number to remember is the "Just Noticeable Difference" (JND). For dE00, JND is around 2.0. Below that, people struggle to tell two colours apart. Below 1.0, basically no one can.

Except for a tetrachromat. Specifically, a strong tetrachromat that has both four colour channels in the brain and a different frequency on the fourth cone.

Who are, admittedly, hella rare. Apparently there are less than a few dozen confirmed world-wide.

But they do exist.

[lucideer]

> admittedly, hella rare. Apparently there are less than a few dozen confirmed world-wide

What's actually hella rare is tests for tetrachromacy. Given the total number of people who have ever taken such a test, I think it's reasonable to assume there are significantly more than a few dozen actual tetrachromats out there.

[mark-r]

It's theoretically related to color blindness, so you'd expect it to be as common. But the problem is even if your eye has the extra primary, your brain may not have developed the ability to "see" it. They had to test quite a few people with the proper genetic background before they finally found one.

[lucideer]

That's fair but even colour blindness is mostly undiagnosed in practice - even with the comparatively high prevalence & awareness, actual figures for colour blindness are still grounded in speculative extrapolation.

I think it fundamentally comes down to whether your sense anomaly represents a significant disability. Colour blindness is a disability, but not one that's significant for the vast majority of people who suffer from it - I've worked with multiple colour blind graphic designers & they were good at their job. There's very little impetus to even seek diagnosis - if they weren't working in a colour-focused industry I suspect they may not have ever realised they had a disability at all.

Tetrachromacy then is an even harder case because it's not a disability at all. The impetus to seek "diagnosis" is zero. Also, even though as you mention there's technically multiple ways of detecting the various factors that need to coexist in tetrachromacy (i.e. (1) sensory testing, (2) physical presence of extra primaries, (3) neurological processing pathways), the latter two are either not directly detectable or never directly tested for - even in speculative cases of people having a 4th primary, the number of primaries present is generally hypothesised via some other avenue like testing for anomalous trichromacy. Ultimately we're heavily relying on direct sensory testing which is almost nonexistent in the general population. There's no way to accurately speculate on how prevalent it might be.

[snarkconjecture]

Computer screens have three-dimensional color spaces. Tetrachromacy doesn't change that.

[Zardoz84]

And the eye cones not are sharp filter, they overlap ranges with mid-low sensibility. That must be nought to someone with Tetrachromacy to percibe something different on a RGB screen.

> More precisely, she had an additional cone type L′, intermediate between M and L in its responsivity, and showed 3 dimensional (M, L′, and L components) color discrimination for wavelengths 546–670 nm (to which the fourth type, S, is insensitive). Source: Wikipedia

[tgv]

Is that so? Our color perception is weird. It's one dimension split in three overlapping sectors. Adding a fourth sector may add information that makes it easier to distinguish colors.

[giraffe_lady]

Something I think about often is an oliver sacks book about an ethnic group that has a particularly high rate of true monochromacy. And the people with no color perception at all are particularly adept at spotting certain plants based on some characteristic of their leaves that is obscured by color. So even removing information can change perception in surprising ways.

OTOH sacks seems to have fabricated a lot of shit over the years so who knows if this is even real. Another thing I think about a lot now.

[Jensson]

We do have four sectors, 3 color perception and then the brightness perception that is used in the dark. In mid darkness you get a mix of all of those, although the fourth is not really perceived as a color so it can be a bit hard to use.

[tgv]

Brightness is another dimension, not a "sector" (as I dubbed it) on the color spectrum. But it would be equal for all subjects in a test, so it can't add information.

[altairprime]

Thanks to a genetic variation I have a variation that may be similarly useful. I aced the JND test without contacts and with adaptive white balance enabled, and I already know from playing I Love Hue that my fidelity and velocity improves when I have stereo vision.

It turns out that my left and right eyes are skewed apart along a magenta/cyan axis. Left is more cyan, right is more magenta. It’s not as strong an effect as 3d glasses, maybe no more than a 1-2% light gel, and under normal circumstances I mostly don’t notice it unless I’m doing color matching work.

If I try to do color matching with one eye, it’s boringly fine - 0.0022 JND, same as everyone else above. I’ll get some things slightly wrong as usual, in patterns that make sense for the hue shift.

But when I use both eyes, the binocular process that leads to 3d vision also locks on to color differentials as well as spatial, and synthesizes imaginary color gradients out of flat surfaces diagonally from contrasting corner edges. It’s not a problem for writing on paper or anything, but if you give me a grid of flat paint chips I can order them by hue because their gradient depths are wrong — like, the whole sort by hue in 2d grid thing is just “equalize the difference vector intensity across the vector field” and that’s a nice relaxing thing to do, right? In essence, it’s sort of like MIMO 3x2 vs. normal vision’s 3x1 or tetrachromacy’s 4x1.

I know this isn’t true 4x1 tetrachromacy because I discovered, through the video game Intake (in which I reached 10th place on the world leaderboard), that my ability to snap-differentiate color is considerably more error prone when the two colors are the exact hues of magenta-cyan that my eyes differ by. Which makes sense: those would be my lowest fidelity colors, because they have the least distance from the differential centerline, so trying to figure out which eye to use causes little stutters in my color parsing and more frequent errors in outcome. If it was “the same tetrachromatic in both eyes” I wouldn’t have trouble telling magenta and cyan apart, because I’d have a fourth receptor with which to detect R/B vs G/B shifts easily by their B/T difference.

I’m not sure if this is a normal circumstance or not, but since my vision is extremely bizarre (-5 left, +2 right) and I can function and drive without eye correction due to forming partial stereo depth out of blurry hue fields from the left eye and telescopic light fields from the right, I think that growing up without eye correction forced my brain to use hue matching to stabilize my visual field in the absence of the usual higher-fidelity “both eyes have the same focal plane” convenience that most people have. And my depth perception remains to this day extremely flawed; it works, enough that I can drive with absolute precision, but I can’t catch a thrown object for crap and I occasionally parse 2d shapes with contrast interplay as 3d shapes and then realize a moment later that there is no 3d shape there — painted lines on a particularly damaged bit of road might at first blink read as a curb — b/c my depth perception was formed by prioritizing hue and contrast at a reflexive level.

There’s probably a formula somewhere that I could use to calculate the theoretical boost in hue SNR by modeling two towers, each with tri-frequency radio receivers with slightly offset frequencies, and then calculating the net boost effect of frequency trilateration across a spectrum for radio signals of different frequencies. Someday I hope learn enough about radio to document that and prove where my nodes of worsened acuity are! Not that it much matters, but what a fun test it would be.

[NetMageSCW]

I have somewhat similar left/right near/far difference but because I am older, my focusable range is limited and I use contacts with what’s called monovision - one eye is for close vision and one eye is for far vision. Because my eyes are naturally almost the same (one contact is 0 and the other +0.25) I don’t need contacts for driving - I have natural monovision. But the gap in clear vision is at my computer monitor distance, so I have computer glasses that reverse the monovision.

[xyzsparetimexyz]

> But they do exist

Do they?

[IAmBroom]

Do you doubt genetic and microbiological science?

[rerdavies]

Sometimes.