Designed 3 experiments to determine the basis of the horizontal-vertical (HV) illusion using an L figure. Exp. I, using 14 undergraduates, showed that there were no differences in the size of the effect in darkness, semidarkness, and in the light, a result contrary to the visual field explanation. In Exp. II the figure was viewed in the dark with 28 Ss upright and recumbent, and in Exp. III (N = 98) the L figure was oriented between 0- (vertical) and 90- (horizontal) in 15- steps. Data from Exp. II and III show that apparent length is a function of the retinal meridians with which the lines correspond irrespective of their physical or apparent orientation to an external reference. (15 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved).
- horizontal-vertical illusion with L figure & apparent length