Friday, October 13, 2006

An Island of Colorblindness

I don't spend much time thinking about what life would be like if I couldn't see the difference between cyan, turquoise, indigo, cerulean, and azure or even between red and green, but after watching Oliver Sacks documentary "An Island of Colorblindness" I have a whole new appreciation for being a trichromat. The documentary chronicles the rare condition of achromatopsia that affects many of the residents of Pingelap, an atoll in the South Pacific. People with the condition see entirely in shades of gray.

Achromatopsia is caused by a genetic mutation that results in the complete or partial absence of cones, the retinal cells that translate photons of light into color with a bit of help from the brain. Light doesn't have any color to it all; color is a construction of our visual system. For the people with achromatopsia on Pingelap, vision that is dominated by rods instead of cones presents its own set of challenges. They have poor visual acuity and sunlight is very painful. They look down virtually all of the time during the day, squint, and blink a lot.

Now that sort of photophobia was actually something I could empathize with; I've experienced that fairly often and acutely so after a brush with something called microcystic edema. I had extreme sensitivity to light, couldn't see to read unless I held the pages about 5 inches from my face, and saw huge rainbow halo around lights. It was awful - there was no treatment, no correction for my vision available - but fortunately it cleared up on its own and hasn't appeared since. Phew. I also stopped wearing contact lenses.

That's probably the last time I thought seriously about vision until I took a graduate level class on vision. I've thought about it a lot since then too. As a psychology professor it's an occupational requirement. And as a primatologist I've read a paper or two about the evolution of color vision among primates. Some species of monkeys are dichromats - they have only two kinds of cones and see much like what most people think of when the term colorblind comes up. Scientists believe the ability to distinguish red from green helped newly evolving diurnal monkeys spot edible leaves and fruit better in the daytime. Previously, monkeys had been nocturnal and ate insects and tree sap. Monkeys who could distinguish colors in the daytime could exploit new niches. They thrived. As a dabbler in art, I appreciate matching and mixing colors for the most pleasing aesthetic effect. But, I take for granted the ability to actually see in color.

Los colores son mi vida is the motto of my impressively talented and successful mother-in-law who weaves multi-colored palettes of yarn into beautiful fabrics. My husband weaves too. They have an entire vocabulary of color terms that never fails to impress me when I eavesdrop on their plans for "warping the loom." I might look at a selection of threads and call them purple while they toss around terms like plum, violet, lavender, eggplant and more. While watching the story of the Pingelapese I was struck by how totally unnecessary such an advanced linguistic library would be for them.


Anonymous said...

Amazing! I couldn't live with black and white, nor could I live without my spectrum of indigo and violet and plum and mauve and all the rest. It surprised me, at first, that there should be people that lack the ability to process colour (is that the right description?) but on reflection, perhaps it is not so astonishing.

Field Notes said...

Evidently the island population was nearly wiped out by a typhoon years ago. There were only twenty survivors. At least one carried the recessive gene that is responsible for this condition. Years of isolation and inbreeding created the current situation. Sacks brought them a suitcase full of wrap around sunglasses. Some eye docs have made contacts with a red center that provide some relief. The people with the condition fish at night and are considered normal, valuable members of the community. The video also features a Norwegian man who has achromatopia. According to the video, there's a small group of Scandinavian people (mostly in Finland) who have it to.

Anonymous said...

Why is that the red centers for the contacts provides relief?

I feel for them: I am not a big fan of bright light, and when I worked a swing shift, I felt even more that way. I think I could get used to living at night, if I had to...