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Hey Matt:

My husband thinks I'm wacko for this. We recently had a ceiling fan installed in our bedroom. I've noticed that, as I lie in bed, staring at the blades spinning round and round and round, my eyes start to glaze over, salivary glands get to work on drool, and suddenly it looks as if the blades start turning the other way for a few seconds. I also remember this same optical phenomenon happening with airplane propellers at an air show I attended as a kid. My husband says this can only happen on film, since whatever is spinning is doing it faster than the 24 frames a second the film captures. Is this like those crappy 3-D hidden picture things where some people see it and some don�t, or should I contact an optometrist?

--Kate in Kensington

No, no Kate, you should contact Matthew Alice. We'll usher you right into the doctor's office. No bad magazines, no waiting. This situation requires an emergency fact transplant. Just lie back, stay calm, stare at the big ceiling fan, and don't listen to your husband. The so-called wagon-wheel illusion is visible under normal light conditions and without the aid of a movie camera. We're assuming here that you and Mr. Kate haven't installed strobes in the bedroom, or fluorescent lights for that matter. If so, it's the flicker from those sources that's causing the illusion. But if you have ordinary dull-normal incandescents, we have some science here to back you up.

About 10 years ago, neurobiologist at Duke took reports of wagon-wheel illusion under "normal" light seriously enough to actually do some research. He rigged up official-looking spinning experiment-type stuff, had 12 average, unsuspecting folk stare at it, and 11 of them (and the experimenters) reported seeing exactly what you see when you zone out under the bedroom fan. The illusion appeared suddenly, lasted a few seconds, then went away. Most people continued to see the alternating spin for quite a while. And the apparent backward movement looked faster than the forward movement. The Duke research was another bit of data to support the idea that we do not process visual information in a continuous stream but in "snapshsots," like a strip of movie film. So the next time Mr. Kate calls you wacko, get him to stare at the fan�stare at the fan�stare at the fan..

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