Inna Tsirlin

The Effect of Crosstalk on the Perceived Depth From Disparity and Monocular Occlusions

Crosstalk in stereoscopic displays is defined as the leakage of one eyes image into the image of the other eye. All popular commercial stereoscopic systems suffer from crosstalk to some extent. Studies show that crosstalk causes distortions, reduces image quality and visual comfort, and increases perceived workload. Moreover, there is evidence that crosstalk effects depth perception from disparity. In the present paper we present two experiments. The first addresses the effect of crosstalk on the perceived magnitude of depth from disparity. The second examines the effect of crosstalk on the magnitude of depth perceived from monocular occlusions. Our data show that crosstalk has a detrimental effect on depth perceived from both cues, but it has a stronger effect on depth from monocular occlusions. Our findings taken together with previous results suggest that crosstalk, even in modest amounts, noticeably degrades the quality of stereoscopic images.

Stereoscopic transparency: constraints on the perception of multiple surfaces.

Stereo-transparency is an intriguing, but not well-understood, phenomenon. In the present experiment, we simultaneously manipulated the number of overlaid planes, density of elements, and depth separation between the planes in random dot stereograms to evaluate the constraints on stereoscopic transparency. We used a novel task involving identification of patterned planes among the planes constituting the stimulus. Our data show that observers are capable of segregating up to six simultaneous overlaid surfaces. Increases in element density or number of planes have a detrimental effect on the transparency percept. The effect of increasing the inter-plane disparity is strongly influenced by other stimulus parameters. This latter result can explain a difference in the literature concerning the role of inter-plane disparity in perception of stereo-transparency. We argue that the effects of stimuli parameters on the transparency percept can be accounted for not only by inhibitory interactions, as has been suggested, but also by the inherent properties of disparity detectors.

Behavioral Training as New Treatment for Adult Amblyopia: A Meta-Analysis and Systematic Review.

PURPOSE New behavioral treatment methods, including dichoptic training, perceptual learning, and video gaming, have been proposed to improve visual function in adult amblyopia. Here, we conducted a meta-analysis of these methods to investigate the factors involved in amblyopia recovery and their clinical significance. METHODS Mean and individual participant data meta-analyses were performed on 24 studies using the new behavioral methods in adults. Studies were identified using PubMed, Google Scholar, and published reviews. RESULTS The new methods yielded a mean improvement in visual acuity of 0.17 logMAR with 32% participants achieving gains ≥ 0.2 logMAR, and a mean improvement in stereo sensitivity of 0.01 arcsec-1 with 42% of participants improving ≥2 octaves. The most significant predictor of treatment outcome was visual acuity at the onset of treatment. Participants with more severe amblyopia improved more on visual acuity and less on stereo sensitivity than those with milder amblyopia. Better initial stereo sensitivity was a predictor of greater gains in stereo sensitivity following treatment. Treatment type, amblyopia type, age, and training duration did not have any significant influence on visual and stereo acuity outcomes. CONCLUSIONS Our analyses showed that some participants may benefit from the new treatments; however, clinical trials are required to confirm these findings. Despite the diverse nature of the new behavioral methods, the lack of significant differences in visual and stereo sensitivity outcomes among them suggests that visual attention-a common element among the varied treatment methods-may play an important role in amblyopia recovery.

Monocular occlusions determine the perceived shape and depth of occluding surfaces

Recent experiments have established that monocular areas arising due to occlusion of one object by another contribute to stereoscopic depth perception. It has been suggested that the primary role of monocular occlusions is to define depth discontinuities and object boundaries in depth. Here we use a carefully designed stimulus to demonstrate empirically that monocular occlusions play an important role in localizing depth edges and defining the shape of the occluding surfaces in depth. We show that the depth perceived via occlusion in our stimuli is not due to the presence of binocular disparity at the boundary and discuss the quantitative nature of depth perception in our stimuli. Our data suggest that the visual system can use monocular information to estimate not only the sign of the depth of the occluding surface but also its magnitude. We also provide preliminary evidence that perceived depth of illusory occluders derived from monocular information can be biased by binocular features.

Perceptual asymmetry reveals neural substrates underlying stereoscopic transparency

We describe a perceptual asymmetry found in stereoscopic perception of overlaid random-dot surfaces. Specifically, the minimum separation in depth needed to perceptually segregate two overlaid surfaces depended on the distribution of dots across the surfaces. With the total dot density fixed, significantly larger inter-plane disparities were required for perceptual segregation of the surfaces when the front surface had fewer dots than the back surface compared to when the back surface was the one with fewer dots. We propose that our results reflect an asymmetry in the signal strength of the front and back surfaces due to the assignment of the spaces between the dots to the back surface by disparity interpolation. This hypothesis was supported by the results of two experiments designed to reduce the imbalance in the neuronal response to the two surfaces. We modeled the psychophysical data with a network of inter-neural connections: excitatory within-disparity and inhibitory across disparity, where the spread of disparity was modulated according to figure-ground assignment. These psychophysical and computational findings suggest that stereoscopic transparency depends on both inter-neural interactions of disparity-tuned cells and higher-level processes governing figure ground segregation.

Effect of crosstalk on depth magnitude in thin structures

Stereoscopic displays must present separate images to the viewer’s left and right eyes. Crosstalk is the unwanted contamination of one eye’s image from the image of the other eye. It has been shown to cause distortions, reduce image quality and visual comfort and increase perceived workload when performing visual tasks. Crosstalk also affects one’s ability to perceive stereoscopic depth although little consideration has been given to the perception of depth magnitude in the presence of crosstalk. In this paper we extend a previous study (Tsirlin, Allison & Wilcox, 2010, submitted) on the perception of depth magnitude in stereoscopic occluding and non-occluding surfaces to the special case of crosstalk in thin structures. Crosstalk in thin structures differs qualitatively from that in larger objects due to the separation of the ghost and real images and thus theoretically could have distinct perceptual consequences. To address this question we used a psychophysical paradigm, where observers estimated the perceived depth difference between two thin vertical bars using a measurement scale. Our data show that crosstalk degrades perceived depth. As crosstalk levels increased the magnitude of perceived depth decreased, especially for stimuli with larger relative disparities. In contrast to the effect of crosstalk on depth magnitude in larger objects, in thin structures, a significant detrimental effect was found at all disparities. Our findings, when considered with the other perceptual consequences of crosstalk, suggest that its presence in S3D media even in modest amounts will reduce observers’ satisfaction.

A computational theory of da Vinci stereopsis

In binocular vision, occlusion of one object by another gives rise to monocular occlusions—regions visible only in one eye. Although binocular disparities cannot be computed for these regions, monocular occlusions can be precisely localized in depth and can induce the perception of illusory occluding surfaces. The phenomenon of depth perception from monocular occlusions, known as da Vinci stereopsis, is intriguing, but its mechanisms are not well understood. We first propose a theory of the mechanisms underlying da Vinci stereopsis that is based on the psychophysical and computational literature on monocular occlusions. It postulates, among other principles, that monocular areas are detected explicitly, and depth from occlusions is calculated based on constraints imposed by occlusion geometry. Next, we describe a biologically inspired computational model based on this theory that successfully reconstructs depth in a large range of stimuli and produces results similar to those described in the psychophysical literature. These results demonstrate that the proposed neural architecture could underpin da Vinci stereopsis and other stereoscopic percepts.

Disparity biasing in depth from monocular occlusions.

Monocular occlusions have been shown to play an important role in stereopsis. Among other contributions to binocular depth perception, monocular occlusions can create percepts of illusory occluding surfaces. It has been argued that the precise location in depth of these illusory occluders is based on the constraints imposed by occlusion geometry. Tsirlin et al. (2010) proposed that when these constraints are weak, the depth of the illusory occluder can be biased by a neighboring disparity-defined feature. In the present work we test this hypothesis using a variety of stimuli. We show that when monocular occlusions provide only partial constraints on the magnitude of depth of the illusory occluders, the perceived depth of the occluders can be biased by disparity-defined features in the direction unrestricted by the occlusion geometry. Using this disparity bias phenomenon we also show that in illusory occluder stimuli where disparity information is present, but weak, most observers rely on disparity while some use occlusion information instead to specify the depth of the illusory occluder. Taken together our experiments demonstrate that in binocular depth perception disparity and monocular occlusion cues interact in complex ways to resolve perceptual ambiguity.

Perceptual Artifacts in Random-Dot Stereograms

Unrestricted positioning of elements in random-dot stereograms with steep disparity gradients, such as stereo-transparent stereograms depicting overlaid surfaces, can produce perceptual artifacts similar to disparity noise. It is shown that these artifacts hinder the segregation of overlaid surfaces in transparent random-dot stereograms and thus disrupt the perception of stereo-transparency. This effect is intensified with increases in the overall element density of the stimuli. We outline the origin of this phenomenon and discuss techniques to prevent such artifacts.

Crosstalk reduces the amount of depth seen in 3D images of natural scenes

Crosstalk remains an important determinant of stereoscopic 3D (S3D) image quality. Defined as the leakage of one eyes image into the image of the other eye it affects all commercially available stereoscopic viewing systems. Previously we have shown that crosstalk affects perceived depth magnitude in S3D displays. We found that perceived depth between two lines separated in depth decreased as crosstalk increased. The experiments described here extend our previous work to complex images of natural scenes. We controlled crosstalk levels by simulating them in images presented on a zero-crosstalk mirror stereoscope display. The observers were asked to estimate the amount of stereoscopic depth between pairs of objects in stereo-photographs of cluttered rooms. Data show that as crosstalk increased perceived depth decreased; an effect found at all disparities. Similarly to our previous experiments a significant decrease in perceived depth was observed with as little as 2-4% crosstalk. Taken together these results demonstrate that our previous findings generalize to natural scenes and show that crosstalk reduces perceived depth magnitude even in natural scenes with pictorial depth cues.