Abstract
It is known that modulations of absolute binocular disparity of a textured surface do not create a sensation of motion in depth (MID) when the image does not change size (loom). We reported previously that modulations of disparity do create some MID in a surface containing a radial pattern that lacks a looming signal when it moves in depth. We have built an instrument that allows us to independently control looming, changing absolute disparity (vergence), and changing relative disparity of surfaces actually moving in depth. A textured surface and a surface with a radial pattern moved back and forth in depth between 40 cm and 70 cm. With monocular viewing, looming created MID of the textured display but not of the radial display. Modulation of absolute disparity (vergence) produced no MID of the textured display but some MID of the radial display. When modulation of absolute disparity was increased relative to looming, MID was increased for both displays. When disparity modulation and looming were in conflict, MID decreased for both stimuli. These results indicate cue summation. Superimposition of a stationary reference stimulus that provided changing relative disparity, generally increased MID for both stimuli. Addition of the reference stimulus to the radial display with reversed vergence produced MID in accordance with the vergence signal. Addition of the reference stimulus to the patterned display with vergence reversed relative to looming, produced a paradoxical effect. The textured display appeared to move simultaneously in opposite directions. When it appeared to move forward relative to the observer, it appeared to move backward relative to the stationary reference stimulus. This indicates strong cue dissociation. We will demonstrate this unique paradoxical effect.
Supported by a grant from the Natural Sciences and Engineering Research Council of Canada.