The effect of display size on disparity scaling from differential perspective and vergence cues

Abstract

The present study compared the relative effectiveness of differential perspective and vergence angle manipulations in scaling depth from horizontal disparities. When differential perspective and vergence angle were manipulated together (to simulate a range of different viewing distances from 28 cm to infinity), approximately 35% of the scaling required for complete depth constancy was obtained. When manipulated separately the relative influence of each cue depended crucially on the size of the visual display. Differential perspective was only effective when the display size was sufficiently large (i.e., greater than 20 deg) whereas the influence of vergence angle, although evident at each display size, was greatest in the smaller displays. For each display size the independent effects of the two cues were approximately additive. Perceived size (and two-dimensional spacing of elements) was also affected by manipulations of differential perspective and vergence. These results confirm that both differential perspective and vergence are effective in scaling the perceived two-dimensional size of elements and the perceived depth from horizontal disparities. They also show that the effect of the two cues in combination is approximately equal to the sum of their individual effects.

Reaching for virtual objects: binocular disparity, retinal motion and the control of prehension

“…It has long been established that both cues can evoke independently a strong impression of depth structure (1,2) and determine relative depth with immense precision (3) . The degree to which either cue supports veridical judgments of an object's size and depth, however, has been questioned in a recent, well-focused sequence of experiments on depth constancy and shape perception (3)(4)(5)(6)(7)(8)(9)(10)(11) . The general conclusion of these experiments is that depth constancy is considerably less than perfect, perceived shape is distorted and absolute distance is typically misestimated.…”

“…To recover veridical depth structure, initial measurements of horizontal binocular disparity and retinal image motion must be scaled using additional (e.g. extra-retinal) information or, if both cues are available simultaneously, this scaling problem can be avoided as there is sufficient information in the retinal image to determine structure and viewing distance uniquely through the combination of the information that each cue provides (3,10,12,13) . Whether perceptual performance improves when both cues are available simultaneously remains uncertain (3,(14)(15)(16)(17) see also Landy & Brenner (18) for a recent review).…”

<title>The camera convergence problem revisited</title>

“…It has been shown that vertical disparity patterns can have a strong influence on frontal plane judgements, particularly for large field of view displays 18 . If a viewer fixates a point on a fronto-parallel screen then, at all distances nearer than infinity, the images of other points on the screen have horizontal disparity.…”

“…Vertical disparities have been shown to be effective in the scaling of depth, shape and size from disparity 12,18 . When the cameras are toed-in the vertical disparities indicate a nearer surface.…”

“…The relationship between the retinal image size of an object and its linear size in the world is also a function of distance. From psychophysical experiments, it appears that humans in fact do use vertical disparity gradients as an indicator of distance and vertical disparity gradients strongly affect perception of stereoscopic shape, size and depth 9,12,18 .…”