Control of vergence: gating among disparity inputs by voluntary target selection

Summary. The ability of human beings to shift their vergence between multiple disparity stimuli was investi-gated. The stimulus was a stereogram consisting of a single bar (1 • 0.3 ~ projected in the center of a larger circular pattern (28 ~ dia) of dots (0.3 ~ dia). In the initial condition, the subjects perceived a single bar in the center of a cluster of dots, all lying in a single depth plane. The subjects were instructed to fixate either the bar or one of the dots close to the bar. Stepwise changes of target-vergence of either the bar, or of all dots, or of both configurations in opposite directions, were imposed in a random sequence. Under these conditions, ocular vergence was controlled by the target-vergence of the selected target at all times, even if this implied a loss of binocular fusion for the non-selected target. The effect of target selection per se, without con