Tetrachromatic Vision

Mutant females walk the planet, possessing a rare capability: they have four types of cones in their retinas (tetrachromacy) instead of the normal three (trichromacy), which may create the ability to perceive a broader range of hues than normal.

The fourth pigment results from a mutation in one of the longer-wavelength X-linked pigment genes and shifts the spectral sensitivity of the retina.

Women with this mutation would not necessarily be aware of their enhanced visual power, as it is the norm to them.

The first known human tetrachromat, an English social worker identified in 1993, sees 10 distinct colors looking at a rainbow, whereas the rest of us see only five.

University of Washington color vision researcher Jay Neitz estimates that 2 to 3 percent of the world's women may have the fourth type of cone.

Wrote Mark Roth in a Pittsburgh Post-Gazette story, "Each of the three standard color-detecting cones in the retina — blue, green, and red — can pick up about 100 different gradations of color, Dr. Neitz estimated. But the brain can combine those variations exponentially, he said, so that the average person can distinguish about 1 million different hues."

"A true tetrachromat has another type of cone in between the red and green — somewhere in the orange range — and its 100 shades theoretically would allow her to see 100 million different colors."

Ryan Sutherland's 2001 paper entitled "Aliens Among Us: Preliminary Evidence of Superhuman Tetrachromats," concluded with a section entitled "What would it be like to be a tetrachromat?"

Excerpts follow.

Unfortunately, in this day and age it would likely be very frustrating, especially since most tetrachromats are likely unaware of their unique abilities.

In time, though, this may change as we learn about what it is and how to recognize it.

Besides the genetic, cognitive, and philosophical interest in learning something new about perception, the brain, and the evolution of our species, tetrachromacy suggests many practical possibilities, but also psychological concerns.

What advantages would a tetrachromat have?

It's hard to say, though Gabriele Jordan suggests superior skin tone distinction, such that a tetrachromat mother may be able to more easily spot if her child is flushed or pale.

No doubt, tetrachromats would be capable of far superior colour-matching.

Unfortunately, the modern world is geared up exclusively for trichromat perception.

To a tetrachromat, television and photography would fail to reproduce colours correctly.

Computer monitors, paper inks, clothing dyes, and even artwork would not be perceived as intended.

But this could be a good thing, making tetrachromats invaluable for jobs involving colour comparison, such as authenticating artwork and pattern matching, or for recognizing subtle distinctions in skin tones for patient diagnosis, mood reading, lie detection, and make-up artistry.

In addition to seeing more colours, a tetrachromat might possess a red photopigment shifted slightly further into infrared wavelengths, enabling them to see beyond the natural limit of human perception, allowing for cat-like night-vision, and perhaps even directly perceiving hints of body heat.

More on the subject here.