Optical illusion
Old but still great…
Stare at the four black dots in the center of the image for 30 – 60 seconds. Then quickly close your eyes and look at something bright (like a lamp or a window with sunlight coming through it). You should see a white circle with an image inside it.
Click on image to enlarge
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Just for curiosity: pick the image, invert its color (you can do it using IrfanView) and repeat the experience. I’ll refrain from commenting my own experience until you have your own unbiased opinion.
Probably the latter, but I have no idea how this works, it freaked me out the first time I ever did it.
Amazing. Interesting that the small doodles don’t appear in the the illusion: pos-processing in the brain or the detail is too small to register?