Definition of Ponzo illusion in US English:

Ponzo illusion


  • An optical illusion in which two transversely placed parallel bars of equal length, or any two figures of equal size, appear unequal when situated between converging straight lines, the bar or figure nearer the point of convergence appearing longer or larger. Also more widely: an illusion in which the observer misjudges the size of an object when it appears close to a line, especially the horizon.


1940s; earliest use found in Journal of Experimental Psychology. From the name of Mario Ponzo, Italian psychologist, who first identified the phenomenon in 1913 + illusion.


Ponzo illusion

/ˈpɒnzəʊ ɪˌl(j)uːʒn/