The average human being can see and differentiate a million different colors. Although none of us could give names to all of these colors, the number is mathematically derived from the physiology of how we perceive color.
All humans have specialized cells in the retinas of their eyes called cones. Most of us have three types of cones, each of which is triggered by certain wavelengths of light. When we “see” colors, what we’re really seeing is how the brain interprets the signals coming from these three types of cones and converts it into the sensation that we call “color.” Each cone can distinguish roughly 100 different shades of color, so the mathematical total number of possible colors comes to 1003, or one million.
The condition we call “color blindness” occurs in men when they have two normal types of cones, but the third type is mutated in such a way that it is less sensitive to the wavelengths of light we call “green” and “red.” As a result, these men can see only a fraction of the colors that we can – approximately 10,000 colors instead of 1,000,000. These men are literally blind to hundreds of thousands of shades of color that we can see.
Many women may be able to see colors that the rest of us cannot
Just as traditional color blindness occurs only in men, there is a condition found (so far) only in women that may make the rest of us with vision that we consider normal “color blind” in a different way when compared to them. These women effectively have four types of cones. So doing the math, this means that theoretically these women can perceive and distinguish up to 1004 colors, or 100 million different shades.
Traditional color blindness runs in families, usually affecting only the males, who wind up with two normal cones and one mutant cone. But the women in these families sometimes end up with three normal cones and one extra mutant cone. Scientists have theorized for years that some of these women might be able to see literally 100 times the number of colors that the rest of us can.
The search for cDa29 – the woman with “super vision”
To test this theory, neuroscientist John Mollon of Cambridge University and his associate Gabriele Jordan of Newcastle University created a test in which women with four cones (mothers of color-blind sons) were asked to compare shades of color that were technically different, but so close to one another that people with normal sight could not see any difference between them. Jordan gave this test to 24 subjects, and disappointingly none of them could detect the subtle color difference any better than people with normal vision.
Twenty years after the study began, the 25th woman tested by Jordan – a physician living in the north of England who is unidentified except by her code name in the study, cDa29 – got every question right. Compared to the rest of us, she literally has “super vision.”
What is it like to see all these extra colors?
Naturally, that is one of the first questions the researchers asked of cDa29. Her answer was unsurprising, when you think of it – she has no way of knowing how we perceive color, so she has no way to tell us how it differs from the way that she perceives color. She was born with this ability and has never known anything else.
And if you think about it, what else could she say? Can you give exact names to two similar but (to you) different shades of red, or describe what the color red itself looks like to you when talking to someone who can’t see it?
So we don’t know exactly what having “super vision” is like, only that it exists. But knowing that it exists may allow scientists to figure out more about how normal vision works, and enable us all to eventually see better.