This animation is part of the demos for:
Bai, D., & Strickland, B. The "double ring illusion": The physical constraint of solidity shapes visual processing.
Explanation
Here, observers saw the rings move in stable 180° co-rotations,
as if they are "avoiding" to pass through each other.
In reality, the rings are the same as before, except that now they overlap.
This suggests that our visual system uses the physical constraint of "solidity"
(i.e., objects cannot pass through each other) to interpret ambiguous object motions: When the stimuli are compatible
with multiple interpretations, the interpretations respecting solidity (180° rotations) are favored over those that violate it (360° rotations).
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