Tetrachromats see the world with more colors, sort of like an impressionist painting. (Photo: AdrianHillman/iStock)
Human color vision is based on the structure of our eyes. We have three cones, one each for red, green, and blue — which is why human beings are designated as trichromats. We see more colors than most other mammals (which only have two color receptors), but birds see better than we do. "Pigeons have five color receptors (and five types of cell receptors) and can process visual information up to 10 times faster than human beings," according to Softpedia. And certain types of spiders can see more than we do too, with four receptors. They're called tetrachromats. Some people might be tetrachromats, too. That is, some women.
"In an odd twist of fate, the same genetic glitch that creates color-blind males may create females with better-than-usual color vision," writes Cynthia Wood in A Life More Colorful.
What does it mean to have this extra ability to see color? Well, most normal-seeing humans see around 1 million different colors. Tetrachromats might be able to discern 100 million. Translated into a real-world situation, that means that while a non-tetrachromat can see seven colors in a rainbow, someone with extra ability can see hundreds.
Beginning in the 1990s, researchers have been looking into this phenomenon (the first tetrachromat woman was documented at Oxford University in 1993). Studies since then have found that as few as 1 percent and as great as 50 percent of women might be tetrachromats. The greater number takes into account women who have at least more ability to see colors than is typical. That's because there can be some variation in how the fourth cone works within the eye's physical structure (which varies from person to person). The tests for determining which people might be tetrachromats are imperfect and the body of knowledge is evolving, but it's an idea that's no longer disputed.
According to a definitive 2001 paper by a group of three female doctors then at UC San Diego, "Women with four-photopigment genotypes are found to perceive significantly more chromatic appearances in comparison with either male or female trichromat controls." The doctors Jameson, Highnote and Wasserman also note that "...gender-based differences in color perception might be a greatly understudied aspect of color and cognition research."
In other words, this phenomenon may have only recently been uncovered because previously, male subjects have been considered the basis for most science about human beings (and in fact this is an ongoing problem in health care research).
But back to the fascinating world of tetrachromats. What is it like to be one?
Concetta Antico, who is — no surprise — a talented impressionist painter, told Popular Science that when she looks at a leaf, “Around the edge I’ll see orange or red or purple in the shadow; you might see dark green but I’ll see violet, turquoise, blue. It’s like a mosaic of color.”
Antico, who calls herself "the world's first tetrachromat painter," has been attuned to colors since she was a young girl. (The tiger painting at right is one of her works.) She first started painting at age 7. So her particular ability is tied to both her biology, and her neurology. Because she has been "fascinated" with color since she was a kid, Antico has developed strong neural pathways to see those extra colors, a great example of how neuroplasticity works. Other women, who may have the physical component of tetrachromacy, but have never recognized it, may not be as able to see as many colors, since they have not "practiced" seeing them. It's like when you happen to have been born with any other genetic advantage, but never utilize it. Being tall, for example, doesn't mean you are good at basketball. It just means you might be if you practiced it.
Researcher Jameson, along with colleagues at the Institute for Mathematical Behavioral Sciences at the University of California in Irvine, has been working with Antico. And she's looking for more tetrachromats to test. Jameson says, “If we understand genetic potential for tetrachromacy and how their perception differs, we can understand quite a lot about visual processing of color that we currently don’t understand."
You can check out the Human Tetrachromacy Research Collaborative to learn more about the genetic details, impacts on vision and myths of tetrachomancy.
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- Vision evolved 700 million years ago, researchers find
Inset photo of what water may look like to a tetrachromat: Alexander/flickr