Binocular depth perception from unpaired image points need not depend on scene organization

The Stereoscopic Sliver: A Comparison of Duration Thresholds for Fully Stereoscopic and Unmatched Versions

Just as positional disparities of image features seen with both eyes provide depth information, the presence of an area visible to one eye but not the other within a binocularly viewed scene can indicate an occlusion at a depth discontinuity,. The close geometrical association between these two kinds of cues suggests they may both be exploited by stereopsis. To investigate this, we developed a novel binocular stimulus entirely lacking in classical disparity that contains an unmatched vertical sliver which elicits a warping of the surrounding surface to accommodate a depth discontinuity. We measured depth-discrimination performance at a range of stimulus durations, correcting for variations in stimulus visibility, to characterise the decline of the efficacy of the depth signal with limited integration time. Results show a close correspondence of performance for similar stimuli with unmatched features and classical binocular disparity across a sixtyfold range of viewing durations, supporting the notion of a close association between the two types of cues in human stereopsis. Control experiments excluded simple eye-of-origin cues and long-range false matches as explanatory factors.

The role of monocularly visible regions in depth and surface perception

The mainstream of binocular vision research has long been focused on understanding how binocular disparity is used for depth perception. In recent years, researchers have begun to explore how monocular regions in binocularly viewed scenes contribute to our perception of the three-dimensional world. Here we review the field as it currently stands, with a focus on understanding the extent to which the role of monocular regions in depth perception can be understood using extant theories of binocular vision.

Solving da Vinci stereopsis with depth-edge-selective V2 cells

We propose a new model for da Vinci stereopsis based on a coarse-to-fine disparity energy computation in V1 and disparity-boundary-selective units in V2. Unlike previous work, our model contains only binocular cells, relies on distributed representations of disparity, and has a simple V1-to-V2 feedforward structure. We demonstrate with random-dot stereograms that the V2 stage of our model is able to determine the location and the eye-of-origin of monocularly occluded regions, and improve disparity map computation. We also examine a few related issues. First, we argue that since monocular regions are binocularly defined, they cannot generally be detected by monocular cells. Second, we show that our coarse-to-fine V1 model for conventional stereopsis explains double matching in Panum's limiting case. This provides computational support to the notion that the perceived depth of a monocular bar next to a binocular rectangle may not be da Vinci stereopsis per se [Gillam, B., Cook, M., & Blackburn, S. (2003). Monocular discs in the occlusion zones of binocular surfaces do not have quantitative depth--a comparison with Panum's limiting case. Perception 32, 1009-1019.]. Third, we demonstrate that some stimuli previously deemed invalid have simple, valid geometric interpretations. Our work suggests that studies of da Vinci stereopsis should focus on stimuli more general than the bar-and-rectangle type and that disparity-boundary-selective V2 cells may provide a simple physiological mechanism for da Vinci stereopsis.

The role of binocular stereopsis in monoptic depth perception

In his study of depth from monocular elements, Kaye (1978) [Kaye, M. (1978). Stereopsis without binocular correlation. Vision Research, 18(8), 1013-1022] reported that monocular stimuli, briefly presented to one eye in a stereoscopic display, generated reliable depth percepts. Here we replicate and extend Kaye's findings in an effort to identify the mechanism underlying the phenomenon. Our experiments show that the perception of depth is not a simple result of monocular local sign, for the percept of depth disappears when one eye is patched. In subsequent experiments we assess the possibility that the percept results from a very coarse stereoscopic match to either the centroid of the luminance distribution in the unstimulated eye or a simple match to the line of sight in the unstimulated eye. Our results consistently support the match-to-fovea account, and lead us to conclude that monoptic depth is a stereoscopic phenomenon.

A long-distance stereoscopic detector for partially occluding surfaces

An external noise technique was used to investigate the stereoscopic process that generates an illusory phantom occluder from binocularly unmatched elements. Observers were required to identify the quadrant in which a binocularly defined target was presented. We had three targets: (a) two vertical binocular bars with the unmatched portions arranged to induce a stable phantom occluder (valid), (b) the same stimuli except the image for the left eye was switched with that for the right eye therefore not inducing a stable occluder (invalid), and (c) a single binocular bar with the same unmatched portion (single-bar). For each target, the luminance contrast of the signal required for 75% correct responses was measured at four levels of external interocular noise. Contrast thresholds were found to be lower for the valid target than for both the invalid and the single-bar targets. The results suggest that the visual system has a stereoscopic detector that responds to stimuli that meet a long-distance requirement for the perception of partially occluding surfaces.