A limitation of position constancy

Abstract

Examined position constancy in human vision with 86 college students. When the eyes track a moving object, the image of a stationary target shifts on the retina colinearly with the eye movement. A compensation process called position constancy prevents this image shift from causing perceived target motion commensurate with the image shift. Four experiments were conducted to investigate whether position constancy operates when the image shift and the eye movement are not colinear. Exp I investigated the induced motion of a target that, while subject to induction, moved perpendicularly to its induced motion. In Exp II, the perceived target motion differed significantly from the objective target motion. In Exps III and IV, the perceived target motions were also in close agreement with the presumed image paths. Overall results indicate that position constancy can occur when, during the eye movement, the target undergoes a motion of its own. Results indicate that position constancy failed to operate when the direction of the target motion formed an angle with the direction of the eye movement. (12 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1984 American Psychological Association.