Currently on my mind both figuratively and literally: the McCollough effect. The horizontal bars below shimmer green to me and the vertical shimmer red:
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We've probably all done that thing where you look at something for so long that looking away at a neutral color causes you to see an afterimage. That would be an example of retinal adaptation, and it usually goes away shortly.
The McCollough effect differs in that it is interocular, meaning you can look at the induction stimuli with one eye and then see the effect with the other. So it isn't retinal; it occurs in higher regions of the brain.
It also differs in that it can last up to
three months if induced correctly.
I won't bother posting the induction stimuli, but it's fascinating to read about.