Definition: The Ponzo illusion is an optical illusion that was first described in 1913 by an Italian psychologist named Mario Ponzo. He suggested that people judge the size of an object based on the background. In the Ponzo illusion, two identically-sized lines appear to be different sizes when placed over parallel lines that seem to converge as they recede into the distance. Learn more about the Ponzo illusion.
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Image from Wikimedia Commons

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you guys are awesome
Thanks for defining this fascinating phenomenon!