Explanation
Most observers reported experiencing an unstable percept:
The rings alternate between 360° co-rotations and 180° co-rotations ("flipping" back and forth).
This animation is part of the demos for:
Bai, D., & Strickland, B. The "double ring illusion": The physical constraint of solidity shapes visual processing. Journal of Experimental Psychology: General. Advance online publication. https://doi.org/10.1037/xge0001839
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Separated
Overlapping
Gapped
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