DEVELOPMENTAL CHANGES IN FIVE ILLUSIONS MEASURED BY THE UP-AND-DOWN METHOD

Abstract

College students and children from nursery school through grade 5 judged five visual geometric illusions according to the Up-and-Down Method which, by limiting each subject to one response per illusion, eliminates errors associated with repeated judgments. Results for the Miiller-Lyer, HorizontalVertical, and Inverted-T illusions contradict earlier studies in varying degrees. Data for the Ponzo illusion confirm earlier results, but their interpretation is complicated by findings for a modification of this illusion. The method shows several advantages over conventional psychophysical methods for studying perceptual development in children.