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A Different Kind of "Trick of the Eye"

Jaume's discussion elsewhere reminded me of something I stumbled onto some time back. If this isn't a for-real "trick of the eye," I'm not certain what is!

No, that's NOT an animated GIF; it is indeed a JPEG ... and I'm sure someone somewhere has an explanation for what and how it does what it does.

Meantime, stare and go crazy or not, as you prefer!

Tags: Optical Illusion

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Permalink Reply by Sandra Stott on May 8, 2010 at 10:37am

It's because of the way they are shaped, (and the colours, I suspect) makes the eyes think that it's in motion if you're not looking directly at it. When you look directly at one, then it stops the trick.

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Permalink Reply by Howard S. Dunn on May 8, 2010 at 12:18pm

Close - it has to do with the way motion is 'reported.' This pattern gives a number of 'clues' that motion is occurring that can only be dispelled by direct focus. Ever look at a fan blade - first clue of circular motion is lack of focus - which occurs here in all circles except the one you focus on.

BTW - there is a secondary illusion in each 'wheel' - though the patterns are concentric circles - they appear to be continuous spirals.

Second, fan blades can often look like they're going the wrong way or change direction. This effect relates to how animation works - your eye reports only about 16 images a second to your brain - so the 'direction' of the blade is based on what makes most sense in that regard. Since your lights (in US) blink 60 times a second (50 in Europe) there are 60 frames of which your eye will pick out approximately 16 - and this often results in incorrect or even variable interpretation of rotation.

Another clue is logical - notice the wheels are aligned to agree with the way gears would turn - given yet another clue; the little bumps in the pattern.

So - all wheels that are out of focus trigger the other indicators of motion and, rather than simply 'decide' the circles are stationary but out of focus, your brain 'decides' they are in motion.

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Permalink Reply by Howard S. Dunn on May 8, 2010 at 12:25pm

Secondary illusion in every wheel - the black, white and dark green 'objects' are arranged in a pattern of concentric circles. However, they appear to form continuous spirals.

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Permalink Reply by JayBarti on May 8, 2010 at 12:25pm

I used to have that as my wall paper on my desktop and a few people asked me to remove it because it made them dizzy to look at it when they walked past.

It is a lovely optical illusion.

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Permalink Reply by sacha on May 8, 2010 at 12:40pm

Neave Strobe

also, if you are interested in optical illusions, you must find out about Dr. Richard Wiseman

He finds things like this on a regular basis and posts them on his blog. He's quite interesting.