Tactual Poggendorff Illusion in Blind and Blindfolded Subjects

Abstract

Tactual Poggendorff illusions were presented to 11 blind and 19 blindfolded normal Ss according to the method of constant stimuli. The reports of both groups showed small illusions which did not differ significantly in magnitude. These results indicate that sensory experience per se is probably not an important determinant of the illusion's magnitude since the greater experience of the blind Ss should produce a smaller illusion. The equivalence of the illusions obtained for the two groups argues against receptor sensitivity as an important factor, although the direction of the difference favors Pollack's (1969) explanation. Theoretical explanation of illusions should rely on central mechanisms and not the visual system.