This is the entry page for the Ponzo Illusion. The Ponzo illusion, named after Italian artist and psychologist Mario Ponzo (1882-1960), is one of a set of geometrical illusions that produce misjudgment of relative line length. This misjudgment reflects our tendency to perceive two-dimensional geometric illustrations in certain contexts as if they were three-dimensional objects in our environment. Participants adjust the length of one of the horizontal lines until they perceive the two lines as being of equal length.