Uncrossed Disparity Research Articles

Manual target tracking reveals a perceptual asymmetry between crossed and uncrossed disparities

Manual target tracking reveals a perceptual asymmetry between crossed and uncrossed disparities

Sensitivity and bias in the discrimination of two-dimensional and three-dimensional motion direction.

Sensory systems are faced with an essentially infinite number of possible environmental events but have limited processing resources. Posed with this challenge, it makes sense to allocate these resources to prioritize the discrimination of events with the most behavioral relevance. Here, we asked if such relevance is reflected in the processing and perception of motion. We compared human performance on a rapid motion direction discrimination task, including monocular and binocular viewing. In particular, we determined sensitivity and bias for a binocular motion-in-depth (three-dimensional; 3D) stimulus and for its constituent monocular (two-dimensional; 2D) signals over a broad range of speeds. Consistent with prior work, we found that binocular 3D sensitivity was lower than monocular sensitivity for all speeds. Although overall sensitivity was worse for 3D discrimination, we found that the transformation from 2D to 3D motion processing also incorporated a pattern of potentially advantageous biases. One such bias is reflected by a criterion shift that occurs at the level of 3D motion processing and results in an increased hit rate for motion toward the head. We also observed an increase in sensitivity for 3D motion trajectories presented on crossed rather than uncrossed disparity pedestals, privileging motion trajectories closer to the observer. We used these measurements to determine the range of real-world trajectories for which rapid 3D motion discrimination is most useful. These results suggest that the neural mechanisms that underlie motion perception privilege behaviorally relevant motion and provide insights into the nature of human motion sensitivity in the real world.

Evaluating stereoacuity with 3D shutter glasses technology.

BackgroundTo determine the stereoacuity threshold with a 3D laptop equipped with 3D shutter glasses, and to evaluate the effect of different shape and size of test symbols and different type of disparities to stereoacuity.MethodsThirty subjects with a visual acuity in each eye of at least 0 logMAR and a stereoacuity of at least 32 arcsec (as assessed in Fly Stereo Acuity Test) were recruited. Three target symbols—tumbling "E", tumbling "C", and "□"—were displayed, each with six different sizes representing a visual acuity ranging from 0.5 to 0 logMAR when tested at 4.1 m, and with both crossed and uncrossed disparities. Two test systems were designed - fixed distance of 4.1 m and one for variable distance. The former has disparities ranging from 10 to 1000 arcsec. Each subject completed 36 trials to investigate the effect of different symbol sizes and shapes, and disparity types on stereoacuity. In the variable distance system, each subject was tested 12 times for the same purposes, both proximally and distally (the point where the 3D effect just appears and where it just disappears respectively), and the mean value was calculated from the mean proximal and distal distances.ResultsNo significant difference was found among the groups in the fixed distance test system (Kruskal-Wallis test; Chi-square = 29.844, P = 0.715). Similarly, no significant difference was found in the variable distance system (Kruskal-Wallis test; proximal: Chi-square = 5.687, P = 0.338; distal: Chi-square = 5.898, P = 0.316; mean: Chi-square = 6.152, P = 0.292).ConclusionsEvaluating stereoacuity using this measurement system was convenient and effective. Changes in target shape and size and disparity types had no significant effect on stereoacuity. It would be helpful to choose optimal targets according to different purposes using computer-assisted 3D measurements.Electronic supplementary materialThe online version of this article (doi:10.1186/s12886-016-0223-3) contains supplementary material, which is available to authorized users.

Effect of Ocular Dominance on Touch Position

In this paper, we analyzed the effect of ocular dominance on touch positions when users touched a three-dimensional (3D) object on a two-dimensional (2D) touch panel while watching a 3D display. We performed a psychophysical experiment where eight subjects (four right-eye-dominant and four left-eye-dominant) participated. When touching 3D objects with uncrossed disparities, touch positions were mainly influenced by ocular dominance and depth of the 3D image $(P . For crossed disparities, touch positions were mainly influenced by ocular dominance $(P . However, the depth of the 3D image had no significant effect on touch positions $(P = 0.783)$ . Our findings can help to design more accurate and comfortable interfaces for 3D systems with touch feedback.

The Role of Parieto-Occipital Junction in the Interaction between Dorsal and Ventral Streams in Disparity-Defined Near and Far Space Processing.

Neuropsychological and functional MRI data suggest that two functionally and anatomically dissociable streams of visual processing exist: a ventral perception-related stream and a dorsal action-related stream. However, relatively little is known about how the two streams interact in the intact brain during the production of adaptive behavior. Using functional MRI and a virtual three-dimensional paradigm, we aimed at examining whether the parieto-occipital junction (POJ) acts as an interface for the integration and processing of information between the dorsal and ventral streams in the near and far space processing. Virtual reality three-dimensional near and far space was defined by manipulating binocular disparity, with -68.76 arcmin crossed disparity for near space and +68.76 arcmin uncrossed disparity for near space. Our results showed that the POJ and bilateral superior occipital gyrus (SOG) showed relative increased activity when responded to targets presented in the near space than in the far space, which was independent of the retinotopic and perceived sizes of target. Furthermore, the POJ showed the enhanced functional connectivity with both the dorsal and ventral streams during the far space processing irrespective of target sizes, supporting that the POJ acts as an interface between the dorsal and ventral streams in disparity-defined near and far space processing. In contrast, the bilateral SOG showed the enhanced functional connectivity only with the ventral stream if retinotopic sizes of targets in the near and far spaces were matched, which suggested there was a functional dissociation between the POJ and bilateral SOG.

Visual discomfort relaxation for stereoscopic 3D images by adjusting zero-disparity plane for projection

It is a challenging task to improve the visual comfort of a stereoscopic 3D (S3D) image with satisfactory viewing experience. In this paper, we propose a visual comfort improvement scheme by adjusting zero-disparity plane (ZDP) for projection. The degree of visual discomfort is predicted by considering three factors: spatial frequency, disparity response, and visual attention. Then, the selection of an optimal ZDP is guided by the predicted visual discomfort map. Finally, the disparity ranges of the crossed and uncrossed disparities are automatically adjusted according to the ZDP as requirements. Experiment results show that the proposed scheme is effective in improving visual comfort while preserving the unchanged depth sensation.

Accommodation and pupil responses to random-dot stereograms

We investigated the dynamics of accommodative and pupillary responses to random-dot stereograms presented in crossed and uncrossed disparity in six visually normal young adult subjects (mean age=25.8±3.1 years). Accommodation and pupil measures were monitored monocularly with a custom built photorefraction system while subjects fixated at the center of a random-dot stereogram. On each trial, the stereogram initially depicted a flat plane and then changed to depict a sinusoidal corrugation in depth while fixation remained constant. Increase in disparity specified depth resulted in pupil constriction during both crossed and uncrossed disparity presentations. The change in pupil size between crossed and uncrossed disparity conditions was not significantly different (p>0.05). The change in pupil size was also accompanied by a small concomitant increase in accommodation. In addition, the dynamic properties of pupil responses varied as a function of their initial (starting) diameter. The finding that accommodation and pupil responses increased with disparity regardless of the sign of retinal disparity suggests that these responses were driven by apparent depth rather than shifts in mean simulated distance of the stimulus. Presumably the need for the increased depth of focus when viewing stimuli extended in depth results in pupil constriction which also results in a concomitant change in accommodation. Starting position effects in pupil response confirm the non-linearity in the operating range of the pupil.

Characterizing the role of disparity information in alleviating visual crowding.

The ability to identify a target is reduced by the presence of nearby objects, a phenomenon known as visual crowding. The extent to which crowding impairs our perception is generally governed by the degree of similarity between a target stimulus and its surrounding flankers. Here we investigated the influence of disparity differences between target and flankers on crowding. Orientation discrimination thresholds for a parafoveal target were first measured when the target and flankers were presented at the same depth to establish a flanker separation that induced a significant elevation in threshold for each individual. Flankers were subsequently fixed at this spatial separation while the disparity of the flankers relative to the target was altered. For all participants, thresholds showed a systematic decrease as flanker-target disparity increased. The resulting tuning function was asymmetric: Crowding was lower when the target was perceived to be in front of the flankers rather than behind. A series of control experiments confirmed that these effects were driven by disparity, as opposed to other factors such as flanker-target separation in three-dimensional (3-D) space or monocular positional offsets used to create disparity. When flankers were distributed over a range of crossed and uncrossed disparities, such that the mean was in the plane of the target, there was an equivalent or greater release of crowding compared to when all flankers were presented at the maximum disparity of that range. Overall, our results suggest that depth cues can reduce the effects of visual crowding, and that this reduction is unlikely to be caused by grouping of flankers or positional shifts in the monocular image.

Stereoscopic Visual Acuity in Types of Ametropic Amblyopia in Children

To evaluate the presence of stereopsis in children with ametropic amblyopia, including hyperopia, myopia, and astigmatism. A total of 205 children with the average age of 5.2 years were selected, including 65 cases of astigmatic amblyopia, 30 of myopic amblyopia, and 110 of hyperopic amblyopia. The near stereoacuity test (zero disparity stereoacuity, crossed disparity, and uncrossed disparity) and distance stereoacuity test by synoptophore with Yan's random-dot test in The Examination Chart of Stereoscopic Acuity were performed. Visual acuity was examined with the standard Snellen chart. Distance fusion was determined with the synoptophore. Correlations between amblyopia and stereopsis were performed with logistic procedure. Differences between zero disparity stereoacuity of hyperopia, myopia, and astigmatism were statistically significant in children with mild and moderate amblyopia determined by the near stereoacuity test (P < .05). Individuals with hyperopia have better central stereopsis and macular stereopsis, whereas children with astigmatism have significantly decreased stereoacuity. No difference was identified between the three types in children with severe amblyopia (P > .05). Results of different degrees of amblyopia at distance and near were approximate. In amblyopic eyes, difference between hyperopia, myopia, and astigmatism, determined with synoptophore, was not significant (P > .05). The types and degrees of amblyopia were closely related with stereopsis (P < .001). In mild and moderate amblyopic eyes, children with astigmatism had the worst stereoacuity. This group should pay more attention to visual stimulation training and stereopsis training.

A Study on the Cognitive Process of Stereopsis in Small Uncrossed Disparity

Static random-dot stereograms (RDS) were used as stimuli to investigate the uncrossed disparity in 15 normal subjects. The response of every subject was recorded with different disparities of 3.27 arc min, 6.54 arc min, 8.18 arc min, 11.45 arc min, 14.72 arc min, 17.99 arc min, 21.26 arc min and 24.53 arc min. The results showed that the human visual system was the most sensitive to stereo images at disparity of 8.18 arc min. Disparity of 21.26 arc min had significant differences with other small disparities in reaction times, as supported the viewpoint that it was reasonable to limit the fine disparity in 20 arc min.

Technology Study on the Different Cognitive Process of Stereopsis between Crossed and Uncrossed Fine Disparity

Considerable improvements in display technology were made in stereoscopic imaging and image quality rose with technical progress. But there was not enough effort on reducing visual fatigue. The study was to investigate one of the ways to reduce visual fatigue caused by three-dimensional images. Static random-dot stereograms (RDS) were used as stimuli. The performance of every subject was recorded with disparate disparities of 3.27', 6.54', 8.18', 11.45', 14.72', 17.99', 21.26', and 24.53'. Results showed that reaction times were always longer in the uncrossed disparities relative to the crossed disparities. For crossed disparities, human visual system was the most sensitive to the images with disparity of 6.54'. As to uncrossed disparities, human visual system was the most sensitive to the images with disparity of 8.18'.

Stereoacuity norms for school-age children using the Frisby stereotest

The Frisby stereotest and the TNO test for stereoscopic vision are popular clinical tests forassessing stereoacuity: however, reference data for school-age children for the Frisby stereotest are limited. This study compared stereoacuity results of both tests in a large sample of typically developing school-age children. Primary (elementary school grades 1-6) and post-primary (high school grades 7-11) students aged 6-16 years were recruited and assessed in schools. Stereoacuity thresholds were measured using the Frisby and TNO stereotests. Children with ocular pathology, anisometropia of ≥1.00 D, interocular difference of visual acuity ≥0.2 logMAR, or strabismus were excluded. A total of 212 children were recruited; data for 186 subjects were analyzed. Median Frisby stereoacuity scores were, for crossed disparity, 20 arcsec for primary and 10 arcsec for post-primary children and, for uncrossed disparity, 25 arcsec (primary) and 10 arcsec (post-primary). TNO stereoacuity was 60 arcsec for both age groups. For Frisby stereoacuity, scores of 85 arcsec (crossed) and 170 arcsec (uncrossed) or better were achieved by 95% of primary school children; scores of 85 arcsec (crossed and uncrossed) or better were achieved by 95% of post-primary subjects. A statistically significant difference in median stereoacuity scores was noted across age groups for the Frisby stereotest (crossed: z = 4.67, P < 0.0001; uncrossed: z = 4.67, P< 0.0001). No statistically significant difference in stereoacuity scores was noted with the TNO stereotest (z = 1.35, P=0.18). A significant weak correlation was found between the Frisby and TNO stereotests (Frisby [crossed], r = 0.21 P < 0.005). These data describe normative values for the Frisby stereotest for children aged 6-16 years. Participants recorded significantly better stereoacuity scores with the Frisby stereotest than the TNO stereotest. The Frisby stereotest values are weakly correlated with the TNO stereoacuity test.

Motion-induced position shift in stereoscopic and dichoptic viewing.

The static envelope of a Gabor patch with a moving sinusoidal carrier appears shifted in the direction of the carrier motion (De Valois & De Valois, 1991). This phenomenon is called motion-induced position shift. Although several motion-processing stages, ranging from low- to high-level processes, may contribute to position estimation, it is unknown whether a binocular matching stage or an even earlier stage exerts an influence. To elucidate this matter, we investigated the disparity tuning of this illusion by manipulating the binocular disparities of the carrier and the envelope. If the mechanisms underlying the illusion have disparity selectivity, the illusory shift should disappear when the carrier and envelope have sufficiently different disparities. We conducted an experiment in which a sinusoidal grating inside a Gaussian envelope had a crossed or uncrossed disparity and the background was filled with static random noise; each subject correctly judged whether the grating was in front of or behind the fixation plane. Position shift occurred even when the moving carrier had a vastly different disparity from that of the envelope, suggesting that one of the mechanisms responsible for the phenomenon exists at a monocular visual stage. To confirm this, in the next experiment we examined whether depth perception can be produced by an illusory disparity due to illusory position shifts in opposite directions between eyes. Two Gabor-like patches moving in opposite directions were presented at the same retinal position dichoptically. We found that when each monocular patch had a soft edge in its contrast envelope, the depth perception of such a patch was biased toward the depth consistent with the illusory crossed or uncrossed disparity, whereas depth perception of a stimulus with a hard edge was less biased. We suggest that the underlying mechanisms of motion-induced position shift are present at an early stage of monocular visual processing, and that the altered positions are represented in the left-eye and right-eye monocular pathways in a way that allows them to function as tokens of binocular matching.

Stereoanomaly for crossed disparity in the upper visual field and uncrossed disparity in the lower visual field

Stereoanomaly for crossed disparity in the upper visual field and uncrossed disparity in the lower visual field

Perceived Suprathreshold Depth Under Conditions that Elevate the Stereothreshold

Previous studies considered the possibility that individuals with impaired stereoacuity can be identified by estimating the perceived depth of a target with a suprathreshold retinal image disparity. These studies showed that perceived suprathreshold depth is reduced when the image presented to one eye is blurred, but they did not address whether a similar reduction of perceived depth occurs when the stereothreshold is elevated using other manipulations. Stereothresholds were measured in six adult observers for a pair of bright 1-degree vertical lines during normal viewing and under five conditions that elevated the stereothreshold: monocular dioptric blur, monocular glare, binocular luminance reduction, monocular luminance reduction, and imposed disjunctive image motion. The observers subsequently matched the perceived depth of degraded targets presented with crossed or uncrossed disparities corresponding to two, four, and six times the elevated stereothreshold for each stimulus condition. The image manipulations used elevated the stereothreshold by a factor of 3.7 to 5.5 times. For targets with suprathreshold disparities, monocular blur, monocular luminance reduction, and disjunctive image motion resulted in a significant decrease in perceived depth. However, the magnitude of perceived suprathreshold depth was unaffected when monocular glare was introduced or the binocular luminance of the stereotargets was reduced. Not all conditions that increase the stereothreshold reduce the perceived depth of targets with suprathreshold disparities. Observers who have poor stereopsis therefore may or may not exhibit an associated reduction of perceived suprathreshold depth.

P1-21: A Study on Stereoanomalies: Comparison of Upper and Lower Visual Field

Stereoanomalies suggest that some people lack disparity detectors or have a disorder of the subsystem associated with stereopsis and consequently fail to perceive correct depth. Crossed and uncrossed disparity detectors are well-established mechanisms. The current study searches other stereoanomalies. In the experiment, a fixation and a test target were presented for 500 msec in a darkroom. The fixation was right in front of the subject, and the test was on the median plane. The test appeared at a upper or lower visual field with crossed or uncrossed disparity. The eccentricity of the position of the test target was 2, 4, or 6 deg. The given disparity was between the average threshold of depth percept and the average fusion limit; so observers with normal vision must percept them correctly. The task of the subject was to report the apparent depth of the test target: far, near, or zero. Some 14 subjects participated: 9 of these subjects gave no anomalous signs; 1 indicated defection of uncrossed disparity ...

Three-Dimensional Display-Induced Transient Myopia and the Difference in Myopic Shift between Crossed and Uncrossed Disparities

To investigate whether three-dimensional (3D) images cause nearwork-induced transient myopia (NITM) more than 2D images and whether there is any difference between 3D images with crossed and uncrossed disparities in the development of NITM. Twenty-five volunteers, enrolled in this study, watched 2D and 3D movies and read 3D texts with crossed and uncrossed disparities for 2 to 3 hours with spectacle correction. The viewing distance was 50 to 70 cm. The refractive error was measured before and after each visual task. If there was a myopic shift after a task, the refractive error was measured at 3-minute intervals until it was resolved. The changes in the refractive error and the amount of NITM were evaluated and compared. The mean age of volunteers was 27.8 ± 2.87 years, and the mean refractive error before the visual tasks was -4.19 ± 2.87 diopters (D). Thirteen subjects (52%) showed NITM after watching a 2D movie, whereas 20 subjects (80%) had NITM after a 3D movie (P = 0.037). The mean extent of NITM was 0.36 ± 0.27 D after watching a 3D movie and 0.10 ± 0.28 D after a 2D movie (P = 0.002). The 3D text with crossed disparity significantly induced NITM (P < 0.001), but that with uncrossed disparity did not. There was a tendency for the NITM to persist longer after subjects watched a 3D movie than after a 2D movie. Viewing 3D images with crossed disparity induced a greater degree of NITM than 2D images. These results suggest that the greater NITM induced by 3D images may have a greater effect on the development and progression of permanent myopia.

Decoding conjunctions of direction-of-motion and binocular disparity from human visual cortex

Motion and binocular disparity are two features in our environment that share a common correspondence problem. Decades of psychophysical research dedicated to understanding stereopsis suggest that these features interact early in human visual processing to disambiguate depth. Single-unit recordings in the monkey also provide evidence for the joint encoding of motion and disparity across much of the dorsal visual stream. Here, we used functional MRI and multivariate pattern analysis to examine where in the human brain conjunctions of motion and disparity are encoded. Subjects sequentially viewed two stimuli that could be distinguished only by their conjunctions of motion and disparity. Specifically, each stimulus contained the same feature information (leftward and rightward motion and crossed and uncrossed disparity) but differed exclusively in the way these features were paired. Our results revealed that a linear classifier could accurately decode which stimulus a subject was viewing based on voxel activation patterns throughout the dorsal visual areas and as early as V2. This decoding success was conditional on some voxels being individually sensitive to the unique conjunctions comprising each stimulus, thus a classifier could not rely on independent information about motion and binocular disparity to distinguish these conjunctions. This study expands on evidence that disparity and motion interact at many levels of human visual processing, particularly within the dorsal stream. It also lends support to the idea that stereopsis is subserved by early mechanisms also tuned to direction of motion.

Evidence that convergence rather than accommodation controls intermittent distance exotropia

This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Nineteen distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2 m and 33 cm. Stimulus and response AC/A and CA/C ratios were calculated. Accommodation responses for near targets (p = 0.017) and response gains (p = 0.026) were greater in the exotropes than in the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p = 0.02), but significantly higher CA/C ratios (p = 0.02). All the exotropes, whether the angle changed most with lenses ('controlled by accommodation') or on occlusion ('controlled by fusion'), used binocular disparity not blur as their main cue to target distance. Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting overaccommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios.

A comparison of self-reported and measured autostereogram skills with clinical indicators of vergence ability in esophores

Perception of the disparity-defined form in autostereograms requires achieving and maintaining the precise vergence angle necessary to place the intended left and right images on corresponding areas of the two retinas. Most commercially available autostereograms are designed to be viewed only with one vergence posture, usually the parallel or “wall-eyed” technique1, meaning that the visual axes need to converge by one or more periods of the pattern to a point farther from the viewer than the plane of the stereogram. Converging the eyes (“cross-eyed” technique) in front of these autostereograms by one or more periods of the pattern will reverse the depth direction of the stereoscopic image, perhaps making the form more difficult to perceive. Our previous work2 compared common clinical indicators of vergence ability with subjects' self-reported and measured autostereogram skills and found significant differences between those with poor versus good self-reported and measured autostereogram skill for vergence facility, near phoria, and TNO stereoacuity for subjects who were exophoric at near. The present study was undertaken to compare clinical indicators of vergence ability to perceived and measured autostereogram skills in esophores. Our results show that esophores whose self-rated and measured autosterogram skills were “poor” demonstrated significantly poorer performance on clinical tests of vergence facility and were more likely to demonstrate differences in threshold performance for crossed vs. uncrossed disparities on the TNO stereoacuity test than were subjects with “excellent” autostereogram skills. Attempts to fuse using “wall-eyed” vs. “cross-eyed” viewing did not differ between the two groups for those subjects able to perceive the autostereogram form.