Wednesday, September 21, 2005

How is colorblindness tested?

My first color vision test ever, I think, was an article in Popular Science that my dad thrust in front of me. I was 7 or 8, and I had just commented about the orange-ness of the grass. By that point I had already made skies purple in coloring books, but this magazine confirmed it for my dad.

My next test, administered by my opthalmologist a few years later, consisted of his pointing to the woven pattern on his office wallpaper and asking me to identify a strand or two of color. "Red-green colorblind," he said.

I've since failed a number color plate tests in books, on Web sites, in science museums, but I haven't really been tested as an adult, and I've felt like I've been missing some important self-knowledge--especially now that I'm in art school.

So a month ago I asked my opthalmologist, who handed me a booklet of Ishihara plates (circles made up of colored dots, some of which form letters, numbers or curved lines from one edge to the other). Some numbers and lines were obvious, others nearly invisible. I stared at some plates, certain I could figure out the path of dots if I could just have a moment alone with them. But my doctor grew impatient; she started turning the pages for me. Her professional opinion: "You're colorblind."

"Can you be more specific?" I asked.

"You'll have to come in again for a more in-depth evaluation."

That in-depth evaluation, the Farnsworth Dichotomous something-or-other, took place today. Here's how it works: in a long narrow box lies a row of 15 pastel-colored pegs (like little plastic game pieces). The first peg is immobile; your task is to choose the peg among the others that most closely matches it and place that one second. Then you choose the peg that most closely resembles the second, and place it third.

A lab technician administered the test--rather unscientifically. First of all, she casually allowed me to see the pegs before she mixed them up. What I saw was a spectrum of colors from bluish-purplish something on one end to yellowish-orangish-greenish something in the middle to bluish-purplish something on the other end. I averted my eyes and tried to ignore what I'd seen. She put a patch over my right eye, scrambled the pegs and handed the box back to me.

Peg #1 looked blue to me. Or purple. Several others looked similar, in value if not in hue, so I placed those next. After I had ordered 4 or 5 pegs, the test administrator said, "You understand what you're supposed to do, right? You choose the one that looks most like the first one and place it second."

Clearly I was bombing. My arrangement looked different from what I had seen minutes earlier, but I thought I should ignore that and just try to follow the directions. At some point I reached what I would call the "from here on out, one guess is as good as another" moment, and I handed the box back to her.

She flipped the pegs over and started copying numbers down on a form. "You've got some real color problems," she said with a laugh. I asked her how often she administers the test.

"Oh, it goes in waves," she said. "We always get the guys from the police academy. That's awful. They go through the whole training, and then they have to take this test. If they fail it, they can't graduate. I've seen men in tears."

She moved my patch to the other eye and rescrambled the pegs. "Actually," she said, "you've pretty well scrambled them up yourself!"

This time I decided to use my head. The yellowish ones go in the middle, I thought, and the darker ones look either blue or reddish. They must go from cool to warm. It must go from blues to greens to yellows to oranges to reds, like a counter-clockwise trip around the color wheel. I took my time, comparing pegs, looking for hints of warmth and coolness.

"You did much better this time," she said. "If you want, you can do the first eye over again."

So I did, following the same strategy.

"Wow," she said. "I've never seen so much improvement." My score was nearly perfect with the left eye the second time around.

She asked me which results I wanted her to submit to her director for the formal report. "Do you want the results to be better or worse?" she asked, thinking I might need the poor results to get some accommodations at school. "Whichever is more accurate," I answered.

But I'm not really sure which would be more accurate. Obviously her feedback helped me, but it didn't change my color vision--it just changed my understanding of what I was supposed to do. We decided to submit the first try, since the resulting report would probably be more interesting.

In any case, the results suggest that I have this problem, to lesser or greater degree:

PROTAN (red, blue green)

"What does that mean?" I asked.

"It means you confuse red, blue and green. Or red and blue-green." So she didn't know.

"I think I might be an anomolous trichomat," I said. She gave me a blank look. "This form says dichotomous, but isn't that also a type of color blindness?" I asked. "Anomolous trichomat?"

"Could be," she said.

OK, so was that a waste of time? In the hands of a less clueless technician, would my results have been different? Will the report tell me something I don't already know, something that can help me negotiate expectations with my art teachers?

We'll see--it should arrive in the mail in a week.

2 Comments:

At 6:04 AM, Blogger Stuart said...

Haha wow, great story! That really emphasises how important colour theory is to a colourblind person. I really should make a priority of studying the colour-wheel. Since I've known I'm colourblind since I can remember, I never even considered trying. A couple of weeks ago I got frustrated in photoshop so I asked a friend to come and show me once and for all where green ends and yellow begins in the colour pallette, and tell me the names of the colours that exists in areas of the pallette I have always classified as "undefined".
You said you thought that by spending some time looking at the colour test that you might be able to eventually see the shapes. Well lately I have been making a concioius effort to actually look for colour where previously I wouldn't have. I'm noticing amazing things. On a clear sunny day I noticed the footpath was very blue when it was in shadow (or what I guessed was blue). Grass occasionally has a definate (what I would define as a) blueish tinge, and the underside of the leaves on my mint in my little herb garden was a vibrant blue. And it's not all about blue! The other day I was sitting in the cinema and the red velvet curtains were closed with lights shining on them. I decided to concentrate and look to see if there were any colours in the curtain I was missing. After concentrating for a while I noticed that the curtain had large areas of different colours all over it caused by the lighting. There were yellows, blues, different reds, and once I noticed it I couldn't stop noticing, it was quite amazing. I think I've just learned to ignore "undefined" colours and it felt almost like an awakening. Not saying I knew what the colours were, but I could see that it wasn't just one hue, red, which I would have dismissed it as previously.

 
At 8:53 AM, Anonymous Paul said...

Stuart, you've just defined the difference between "looking" and "seeing", which is a very important skill for artists to develop, whether they're colorblind or not. Your initial "red" reaction to the curtain is what 99% of the population does, and your closer inspection is what artists do. Excellent example!

The peg test sounds interesting - I've never done that one. The technician should be summarily fired though. Interfering with a test in progress, telling you your progress halfway through, allowing you the opportunity to pick and choose the results submitted. I'm sure glad this person is only administering vision tests instead of doing something important like quality control on prescription drugs... :0)

 

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