So you’re a tetrachromat? But are you the “strong” type?

Tetrachromacy is the possession of four cone cells. This allows organisms to have a four-dimensional color experience—something that fish, reptiles, and diural birds all have. Humans normally detect color through three cone cells in the eyes, making us trichromats. Ultimately, this difference means that humans see far less colors than these other organisms. 

In the 1940s, however, scientists began to theorize that some humans may be tetrachromats. Females in particular are more likely to inherit this trait. Specifically, they are more likely to have Long Wavelength Sensitive (LWS) and Middle Wavelength Sensitive (MWS) retinal photopigments compared to males, due to having only one X-chromosome.

But while 12% of the female population is estimated to be tetrachromatic, it doesn’t necessarily count: Having four types of cone cells alone does not give you the legendary “supervision” tetrachromats supposedly enjoy. Without the ability to communicate the right amount of signals to your brain, you’re just a “weak tetrachromat,” which is nothing really special. It means you still see colors as a normal trichromatic person would.

“Weak tetrachromacy occurs if an observer has four different cone classes but lacks the postreceptoral capacity to transmit four truly independent color signals,” according to a paper published by Nagy, MacLeod, Heyneman & Eisner in 1981.

A strong tetrachromat, however, has the four cone classes and the ability to actually interpret them.

“Strong tetrachromacy arises from four different cone types plus the capacity to transmit four independent cone signals. Such observers would reject large-field trichromat color matches and require four variables to match all colors,” Kimberly Jameson and colleagues published for "The Oxford Companion to Consciousness."

Where are they?

While you would probably find millions of selfrachromats in online forums, we can’t really take everyone’s word for it.

Finding these strong tetrachromats, who theoretically see around 99 million additional colors that the rest of us can’t see, has been a search that was, hereto, in vain.

However, in 2010, neuroscientist Gabriele Jordan from Newcastle University and her colleagues found a doctor in northern England, only referred to as cDa29, who was consistently able to detect subtle differences in color that weak tetrachromats could not distinguish. The search involved putting these women in a dark room (not in a horror movie kind of way), and flashing three colored circles of light before their eyes.

Studies suggest that there are several more like cDa29 amongst us, so why aren’t we finding more people with this ability?

For one thing, these studies are limited to areas where there are researchers conducting these tests. Another thing could be that the world we live in does not give strong tetrachromats the visual work out they need to even realize they have the ability.

"Most of the things that we see as coloured are manufactured by people who are trying to make colours that work for trichromats," says Jay Neitz, a vision researcher at the University of Washington. "It could be that our whole world is tuned to the world of the trichromat."

Jordan’s study is still in progress and has not been published and peer-reviewed yet. So we’re going to have to wait until it is verified.

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