Tetrachromacy is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cells in the eye. Most people have three cones (making them trichromats), which enables them to see about one million colors. But tertachromats have four cones, so their eyes are capable of picking up dimensions and nuances of color-an estimated 100 million of them—that the average person cannot.
Humans are usually trichromats, but recent studies suggested that 2–3% of the world's women might have the type of fourth cone whose sensitivity peak is 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 and corresponding increased chromatic discrimination compared to trichromats.
Concetta Antico is a tetrachromat and so is able to see 100 times more colors than the average person:
When Concetta Antico looks at a leaf, she sees much more than just green. “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,” she said. “It’s like a mosaic of color. It’s shocking to me how little color people are seeing,” she said.
Same Neurology as Trichromats
Interestingly, although tetrachromats have more receptors in their eyes, their brains are wired the same way as a person with normal vision. So how can a brain like Antico’s change to see more colors? Like anything else, practice makes perfect, even when it comes to neural pathways.
Researchers Jameson and Winkler are on the hunt for more tetrachromats in order to better understand how their brains work. Jameson became fascinated with how people are able to form and communicate concepts, especially when the way they perceive the world can vary so widely. “If you have an extra cone class in the retina, that greatly complicates how that signal might be taking shape as it leaves the retina. We want to understand how that’s happening,” she said. This likely has to do with how the brain wires itself when it receives certain signals frequently over time—a concept called neuroplasticity. Lots of studies about neuroplasticity in animals and some in humans have shown that two individuals with the same capacity for visual perception can have drastically different vision later in life just based on what they were exposed to early on. Researchers still aren’t totally sure why this is the case. “One possibility is that the system learns how to use these signals—the wiring creates the proper code so they can be used in the cortex,” Jameson said.
So even though many more tetrachromats may exist in the world, they may not have exceptional color perception, because they haven’t trained their brains to pay attention. Antico, in this case, presents a rare exception. “I was different than a regular 5-year-old — I was painting at age 7, I was so fascinated with color,” she said. For years, she was exposed to exceptional color, so her brain became wired to take advantage of her tetrachromacy.