Tetrachromacy in Humans: You May Have Super Color Vision

"Nah-na-na-na-nah-na! I can see more colors than you!" I can just hear all those scrunchy-clad-pony-tailed girls taunting me on the school playground, if only they had known about the possibility of tetrachromacy in females back then...

It has been long accepted that human color vision is based on having 3 cone receptors (trichromat) red, green and blue, but since the early 90's researches have been searching for people who have four (tetrachromat). These people would have a heightened color sense and the ability to see "rare subtleties of color." Unfortunately, for half the population, it seems in order to lay claim to such super color vision you need to have two X chromosomes. So, if you've ever been in a hopeless debate with a man who easily pairs two colors as exactly the same, and to you they're clearly not the same at all, he may not be colorblind–as you may infer during this type of situation, but rather you actually see the colors differently.

Image by Lucee. | Color 'tertrachomat' by ryandemall

Maybe We're All Tertrachromats After All

Men, don't fear, we may still be able to call ourselves tetrachromats even if we can't say we have super color vision. As it turns out humans are better described as 'blocked tertrachromats' rather than trichromats, according to one paper. A distinction is made between "retinal tetrachromacy (having four pigments in cone cells in the retina, compared to three in trichromats) and functional tetrachromacy (having the ability to make enhanced color discriminations based on that retinal difference)" (wiki) but even this widely differs from from current perceptions:

The architecture of the human visual system, along with that of most animals, is tetrachromatic. The performance of the human system at very short wavelengths is blocked by the absorption of its own optics. Therefore it can be more properly described as a blocked tetrachromat instead of a trichromat.

This paper also expands known human chromatic visual performance from past literature:

The presence of four spectrally sensitive channels in the architecture of the human visual system (even though one is partly blocked on a wavelength selective basis) is very important in research. Besides expanding the number of photoreceptor (cone) types in the Young-Helmholtz Theory, it expands the number of chromatic axes in the Hering Theory to three. Because of this expansion, a three dimensional color space is required to describe human color vision completely (without introducing the black-white axes). Such a color space is presented below.

Spectral colors with a wavelength between 300 and 437 nm are represented along the third axes drawn in the upper right. True purple occurs along this axis between 410 and 420 nm. There is a chromatic null along the third axis near 395 nm. The color at this point is defined as lilac. It plays a role similar to azure at 494 nm and "spectral yellow" at 572 nm. Within this color space, white is defined by the intersection of lilac, azure and spectral yellow. Thus white is described by three coordinates instead of the conventional two. The precise sensation of color perceived by the human visual system in the region from 300 nm to 395 nm has not been quantified. -The Human is a Blocked Tetrachromat.

The rotation of the third axis into the vertical alignment results in a two-dimensional presentation that is quite useful except when trying to illustrate mixtures of purple and green. The resulting New Chromaticity Diagram for Research is available on this site.

The Genetics

"In an odd twist of fate, the same genetic glitch that creates color-blind males may create females with better-than-usual color vision." - 'A Life More Colorful' By Cynthia Wood

"In humans, two cone cell pigment genes are located on the sex X chromosome, the classical type 2 opsin genes OPN1MW and OPN1MW2. It has been suggested that as women have two different X chromosomes in their cells, some of them could be carrying some variant cone cell pigments, thereby possibly being born as full tetrachromats and having four different simultaneously functioning kinds of cone cells, each type with a specific pattern of responsiveness to different wave lengths of light in the range of the visible spectrum. One study suggested that 2–3% of the world's women might have the kind of fourth cone that lies between the standard red and green cones, giving, theoretically, a significant increase in color differentiation. Another study suggests that as many as 50% of women and 8% of men may have four photopigments." - Tetrachromacy

Common Colorblindness Test

"Dr. Gabriele Jordan of Cambridge University tested the color perception of fourteen women who each had at least one son with the right kind of color-blindness. She set up a test where the subjects had to manipulate and blend two wavelengths of colored light to produce any hue they liked. They then had to match their own results a second time. With normal color vision, several different combinations would match any given hue, with a tetrachromat the possible combinations to produce a visible match would be much reduced. Dr. Jordan reported that two of the fourteen women showed exactly the results she would have expected from a tetrachromat. At least one of the two women reports having a different sense of color from the people around her, with both better color matching and better color memory. While not completely conclusive, this initial study has so far provided our best candidates for natural human tetrachromats." - 'A Life More Colorful' By Cynthia Wood

How Many Colors Can You See?

The accepted number of hues an average human can differentiate between is one million.  Based on the same math, a functioning tetrachromats with 'super color vision' could see 100 million colors. - post-gazette.com

Mrs M - an English social worker, and the first known human "tetrachromat" - sees rare subtleties of colour. Looking at a rainbow, she can see 10 distinct colours. Most of us only see five. She was the first to be discovered as having this ability, in 1993, and a study in 2004 found that two out of 80 subjects were tetrachromats. - The Independent

Below, Simulated tetrachromatic vision (i.e. bird vision: UV=blue, Blue, Green, Red) © Dr. Klaus Schmitt

But even if we find our tetrachromats, they may not all be created equal. If the modified color receptor is sensitive to wavelengths very close to a normal receptor, then the tetrachromat would merely have slightly better color-vision. The further apart the wavelength sensitivities of the receptors, the more the tetrachromat’s vision would differ from the norm. So in all probability, even among tetrachromats few have a dramatically better color sense, but for that rare exception the world may truly be a more colorful place." - 'A Life More Colorful' By Cynthia Wood

Sources

THE HUMAN IS A BLOCKED TETRACHROMAT, Fulton, James T., Processes in Biological Vision {online} {Corona Del Mar, CA. USA} Vision Concepts, {published 2000-08-01}, {revised 2000-08-01},{cited 2000-08-01}. Available on the Internet: URL: http://neuronresearch.net/vision/

'A Life More Colorful' By Cynthia Wood

Wikipedia: Tetrachromacy

'Some Women May See 100 Million Colors, Thanks to their Genes' - post-gazette.com

'You won't believe your eyes: The mysteries of sight revealed' - The Independent

Flower images © Dr. Klaus Schmitt, Weinheim Photography of the Invisible

More reads:

Half of the Women See More Colors than the Rest of the People

Tetrachromat Females

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