May 17, 2013

Science facts: Human tetracromacy

Do you perceive infestiminal nuances of color invisible to most humans?

One of my current areas of interest is human tetrachromacy. In a nutshell, most humans have three cone cells (or cones) in their eyes, which allow them to perceive approximately 100^3 shades of color (each cone perceives about 100 shades). Most mammals are dicromates (i.e. with two cones), and can thus perceive 100^2 shades. However, some women (genetically, it's apparently a XX trait) appear have four cones - and can thus perceive 100^4 shades of color.

As per a comprehensive article in Discover magazine, Dr. Gabriele Jordan at Newcastle University is to be the current leading authority on human tetrachromacy. I wonder how many emails a day she gets from people saying "I'm a tetrachromat! Study me!" - but who then turn out to have supremely ordinary vision. Since it appears that Jordan has only found one true tetrachromat thus far...

There aren't any conclusive online tests I could find which can fully diagnose tetracromacy. X-rite, the company behind Pantone, has an online exercise where you sort shades of color into their correct order. I found it incredibly tedious but passed with...flying colors and just missed the perfect score of 0. According to this article on Apartment Therapy, this might make me a tetrachrome...but then on Tumblr there is this image which apparently contains shapes visible only to tetrachromes, and I just see spots. So it's likely the same thing that happened to me when I diagnosed myself with synesthesia as a youngster, while in reality I'm probably just overly sensitive to light, colors, sounds, textures, smells, and sounds.

The information on tetrachromacy is relatively sparse - I did find a handful of articles through Google Scholar (some have restricted access):

G. Jordan, J.D. Mollon
A study of women heterozygous for colour deficiencies
Vision Research, Volume 33, Issue 11, July 1993, Pages 1495–1508
http://dx.doi.org/10.1016/0042-6989(93)90143-K

S.M. Hood, J.D. Mollon, L. Purves, G. Jordan
Color discrimination in carriers of color deficiency
Vision Research, Volume 46, Issue 18, September 2006, Pages 2894–2900
http://dx.doi.org/10.1016/j.visres.2006.02.028

Vitali V. Gavrik
Tetrachromacy of human vision: spectral channels and primary colors
Proc. SPIE 4421, 9th Congress of the International Colour Association, 315 (June 6, 2002)
http://dx.doi.org/10.1117/12.464730

Sutherland, R.
Aliens among us: Preliminary evidence of superhuman tetrachromats
http://nexthumanproject.com/references/Tetrachromats.pdf

Oh, and this artist has a website which also discusses how her certified tetracromacy has influenced her work.

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