As you look at this black and white figure, move your head back and forth.
You may notice that the circle seems to shift independently from the background.
|Ouchi-Spillman Illusion, Lothar Spillman|
The apparent drifting or jumping in the design mirrors your eye movements and head movements as you peruse it. Scientists propose that: "Slow sliding movements may represent involuntary ocular drifts, while occasional jerks suggest a contribution by microsaccades."
|"Ouchi-Spillmann-Vasarely illusion"©Akiyoshi Kitaoka 2014 Via Op Art 11|
|Rotating tilted lines illusion via CR Society|
In this variation, the central circle and the ring around seem to shift and shimmer in relation to the background.
Researchers have noticed that these effects diminishes with age. There's some debate about whether that fall-off is due to weaker eye movements or less robust perceptual abilities within the brain itself.