The blind have "optical illusions."

Abstract

In this study 28 totally blind and 28 seeing individuals tactually explored well-known illusion patterns mounted in relief on veneer-ply boards. The only observable difference in the behavior of the seeing and the blind, under similar conditions, was in the number of the illusions. Consistent, repeated responses showed that the Muller-Lyer illusion was experienced by 24 blind and 2 visuals; the Poggendorff by 22 blind and 4 visuals; the vertical-horizontal by 22 blind and 3 visuals; the two equal circles within an acute angle by 12 blind and no visuals; the Zöllner by 10 blind and no visuals; and the two segments of a ring by 7 blind and 2 visuals. The great majority of the visuals when finally permitted to use sight experienced illusions with every standard pattern. This shows that their inferiority to the blind in active touch perception was due to lack of practice in perceiving. The older the person, whether blind or a visual, the more illusions he experienced, and the better his school work the more were his illusions. These facts indicate that those who are equipped to perceive best are also most likely to have these misperceptions. (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1938 American Psychological Association.