Apparent Movement,Eye Movements and Phoria When Two Eyes Alternate in Viewing a Stimulus

Three experiments were conducted to test the hypothesis that the apparent movement of a stimulus when the two eyes, are alternately occluded can be explained by phoria and Hering's principles of visual direction. In experiments 1 and 2, the direction of apparent movement, eye position, and eye movements were measured when eye movements did and did not occur. In experiment 3, the magnitude of apparent movement and the extent of phoria were compared. Results from experiments 1 and 2 indicated that the direction of apparent movement could be predicted from the direction of phoria, in conjunction with Hering's principles, and was not contingent on eye movements. In experiment 3, a high positive correlation (r = 0.95) between the magnitude of apparent movement and the extent of phoria was obtained.