Ponzo illusion

Common card · No. 449681

The Ponzo illusion is a geometrical-optical illusion that takes its name from the Italian psychologist Mario Ponzo (1882–1960). Two identical horizontal lines placed on vertical converging lines will appear to be of different lengths. Ponzo never claimed to have discovered it, and it is indeed present in earlier work. Much confusion is present about this including many references to a paper that Ponzo published in 1910 on the Aristotle illusion. This is a tactile effect and it has nothing at all to do with what we now call the Ponzo illusion. The illusion can be demonstrated by drawing two identical lines across a pair of converging lines, similar to railway tracks, but the effect works also at different orientations. One of the explanations for the Ponzo illusion is the "perspective hypothesis", which says that the perspective feature in the figure is produced by the converging lines ordinarily associated with distance; the two oblique lines appear to converge toward the horizon or a...

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