Pulfrich Phenomenon
Simple trick, astonishing effect.
An object is swinging. Observed with a dark filter in front of one eye: the swinging object now moves along a circular path!
The dimming slows down the transmission of stimuli from the eye to the brain. The two eyes thus see the object at different positions, which the brain interprets as spatial depth. A phenomenon named after Carl Pulfrich, who himself could never see the shadows.
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