Found it on Dosenation with the following post.
Stare at the center of any of the circles in this graphic and you will see the circles on either side rotating either clockwise or counter-clockwise depending on their orientation within your peripheral field. This is not an animation, this is caused by a recursive line-resolution bug in your visual processing system.
If you look at the rungs of any of the wheels in this illusion, you will see that each blue-black-green dot cluster is made up of tiny oval lines, not straight lines. Because the pattern-recognition wetware in the eye's peripheral field expects to see a straight-line "spoke" radiating out from the center of each wheel, the elliptical lines and alternating colors in each rung causes an un-resolvable ambiguity in line-differentiation wetware.
In other words, visual comprehension in the periphery is constructed by "fill-in" algorithms that "paint" in patterns and fills as they radiate out from the center of perception where information is densest. While focal perception in the center remains still and constant, the peripheral wetware struggles to resolve a solid line that it can cling to, and thus keeps passing the line-resolution task back and forth between successive lateral analyses resulting in the illusion of creeping motion.
What is nice about this illusion is that it clearly demonstrates what happens when the inhibitory processes that "lock" line resolution in the periphery malfunction: you get fluid creeping lines that wiggle around at the edge of your field of vision and refuse to resolve themselves. I would call this a clear stage one or even stage two visual hallucination on the standard rating scale, and it is the optic equivalent of the creeping carpets and melting walls you get on a mild-dose LSD trip.
And the awesome thing is that you can almost clock how fast each one of these lateral iterations occurs; I estimate my refresh rate is roughly 18-35 Hz (cycles-per-second) with very fluid frame advance and some frame stuttering as peripheral lines "set" and then become fluid again. This one simple illusion demonstrates so much about the processes and limitations of our visual processing system it is insane. It also elegantly explains why so many things appear curiously animated when glimpsed "out of the corner of your eye" as opposed to being stared at directly. This image is so awesome it actually hurts my brain. I love it!
