I experienced this at an exhibition of James Turrell's art, specifically a piece called "Spread". It consisted of a room filled with blue light. At a far wall, recessed lighting sources gave the distinct impression of a boundary that seemed to evaporate upon approach. That was curious enough, but then the squiggly things appeared. I guess I know why now. Thanks for pointing this out and solving that mystery. Being the wiser about this aspect of vision makes it even more wondrous.

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