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.
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.
> 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
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.
Do they?