Apparent motion in depth resulting from changing size and changing vergence

Two experiments are reported in which the effect of combining stimuli of changing size and changing vergence on the perception of motion in depth was examined. Changing size and changing vergence corresponded to in-phase or anti-phase sinusoidal motions of an outline circle, with different amplitudes. In-phase stimuli had approximately additive effects on the estimated peak-to-peak amplitude of apparent motion in depth. Anti-phase stimuli did not cancel each other; apparent motion was in-phase with one or the other stimulus. When apparent motion was in-phase with one stimulus, there was only a limited influence of the other stimulus. The results are discussed with regard to a model proposed by Regan and Beverley for the combination of changing size and changing disparity.