Apparent displacement with a monocular prism differs from optical displacement.

This experiment showed that phoria-induced displacement adds to or subtracts from prism-induced displacement. A near stimulus (25 cm) was apparently displaced more than the optical displacement when the base of a prism was out and less when the base was in. In contrast, a far stimulus (200 cm) was displaced less when the base was out and more when the base was in. Moreover, the between-subjects variability of the apparent displacement was greater with monocular than with binocular viewing. Some implications for studies on monocular prism adaptation are discussed.