Science: The Fourth Dimension of Color

RadioLab, the always intriguing show on public radio, aired a story Saturday about ordinary people with seemingly superhuman abilities to see minuscule differences in color. Put five shades of yellow in front of most of us, and we see five identical shades. Put the same cards before these special folks, and they can detect real differences between all of them.

The people blessed with this amazing ability are called tetrachromats — tetra meaning four, chroma meaning color. The reason four is important is that most of us are trichromats. We have three varieties of the usual photoreceptor cells in the retinas of our eyes for detecting colors. These color-grabbing cells are called cones (the other major kind of retina cell for light detection are called rods). Most of us trichromats have cones that detect the three primary colors: magenta (essentially red, although it looks purplish), yellow, and cyan (blue). Most of the colors we see, be it in nature, on TV, or in various other forms of media, are combinations of these three.

tetrachromatTetrachromats have a fourth kind of cone, and it sends their color perception ability off the charts. People who you used to think were being extra-precious, or perhaps just imagining differences that weren’t there, may be the Supermen of color detection.

Except that tetrachromats are almost always women, at least theoretically. Ironically, tetrachromats are often the mothers or daughters of color-blind men. Color blindness runs in families, but almost always affects men and not women. Scientists found that while color blind men have two normal cones and one mutant one that doesn’t detect red or green properly, their mothers (and sometimes their daughters) have three normal cones plus a mutant fourth. Among this four-coned group, an English neuroscientist successfully tested for a tetrachromat woman in 2007 — the first scientific proof that tetrachromats actually exist. (This concise article on the Discover website explains the history and investigation of the theory.)

A compounded irony, and a frustrating one, is that despite all science is able to prove, there is still no way for we trichromats to imagine the lush palette of colors a tetrachromat is able to enjoy. Color is a personal perception and difficult to reduce to language; a tetrachromat could be forgiven for being unable to make us understand what she sees. And there may well be tetrachromats whose ability remains unfed: in a world colored by trichromats for trichromats, there may be very little for a tetra’s fourth cone to perceive.

But the mere existence of such super-sensory people is as exciting as the compelling argument for extraterrestrial life: in a universe so large, how could we be the only ones? Whether you believe that or not, the existence of tetrachromacy makes one wonder about the possibilities of people with enhanced touch, hearing, taste and smell (I knew someone once who had the last two; she was a professional flavor expert, happily). And tetrachromats seem to be unremarkable in other ways — which leads to visions of walking down the street, looking into the eyes of thousands, and wondering what color you are to them, and how much world there is that we simply don’t see.♦

© 2013 Adam Barr

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