BINOCULAR AND MONOCULAR STIMULI FOR MOTION IN DEPTH - CHANGING-DISPARITY AND CHANGING-SIZE FEED THE SAME MOTION-IN-DEPTH STAGE

Although changing-size stimulation and changing-disparity stimulation can both produce a sensation of motion in depth, they act largely independently. The motion-in-depth sensation produced by changing-size can be cancelled by antagonistic changing-disparity stimulation. Again, a motion-in-depth aftereffect built up by inspecting a changing-size stimulus can be nulled either by changing-size stimulation or by changing-disparity stimulation. The relative effectiveness of changing-disparity and changing-size as stimuli for motion-in-depth sensation varies as follows: (a) changing disparity grows relatively more effective as velocity increases (according to a power law): (b) changing disparity grows relatively more effective as inspection time increases; (c) changing disparity grows relatively more effective as the linear horizontal width of the target decreases; (d) the relative effectiveness of changing disparity and changing size shows marked intersubject variability (at least 80:1). But relative effectiveness does not depend on viewing distance except at very short ranges. The existence of channels for changing-disparity (θD) and changing-size (θS) provide the visual system with a possible means of computing the absolute linear width of a stimulus independently of its distance, since we calculate that linear width equals interpupillary separation multiplied by θS θD. © 1979.