Nonveridical visual direction produced by monocular viewing

In Exp I, 19 undergraduates pointed to a small light and moved a small light to their subjective median plane. The extent of constant error under monocular and binocular viewing conditions differed in both tasks. The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm. Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of E. Hering's (1942) principle of visual direction can account for these results. In Exp II, the same Ss adapted to phoria-induced error by placing a finger over a monocularly viewed target. The difference in their pointing responses before and after the task were reliable, and the correlations between phoria and the pre- to posttest differences were .45 or .77, depending on the number of adaptation trials. It is argued that all monocular experiments dealing with visual direction should control for these effects. (19 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).