Stereo Thresholds Research Articles

Measurement of paracentral stereopsis using a new method with the binocular open perimeter imovifa® in normal adults.

No method to quantitatively evaluate stereopsis within the 15º visual field has been clinically established. We developed a program to measure paracentral stereopsis and evaluated its feasibility in visually normal participants. Experimental investigation METHODS: Ten visually normal volunteers with stereopsis of 60 arcseconds or better were included. The Stereo Eccentricity Analysis (SEA) program for stereopsis measurement across the visual field was integrated into the binocular visual field analyzer imovifa®. Subjects with established binocular stereopsis detected a stereoscopic circular target presented with crossed disparity on random dots at the fovea, 3°, 5°, 10°, and 15° on the 45°, 135°, 225°, and 315° meridians. The subjects performed two tasks for measurement in the periphery: a detection task by pressing the response button when the circular target was perceived and a localization task by tilting a joystick to indicate in which quadrant the circular target was perceived. The duration of the target presentation was 500 ms. The stereo thresholds at 0º and 3° did not significantly differ. The thresholds at 10º and 15º were significantly higher than at 0° (P < 0.01). While no inter-individual threshold difference was observed at the fovea, the difference was large at 15°. The stereo thresholds for the detection and localization tasks also did not differ significantly. With the SEA program, paracentral stereopsis can be measured and the stereo threshold increases with eccentricity. The SEA program appears to be a feasible clinical method to evaluate paracentral stereopsis.

Integration and suppression interact in binocular vision.

Contingent on stereo compatibility, two images presented dichoptically can lead to either binocular integration, thus generating stable stereopsis, or interocular suppression that induces binocular rivalry with bistable perception that alternates between the two images. The relationship between binocular integration and interocular suppression concerns how our brain processes binocular inputs to form unified visual awareness but remains unclear. Here, a series of psychophysical experiments were conducted to address this question, revealing that these collaborative and competitive binocular interactions are interconnected and would mediate one another according to their strength. Specifically, Experiments 1a and 1b showed that the presence of binocular rivalry inhibited peripheral stereopsis, significantly elevating the stereo threshold, with higher elevation resulting from increasing rivalry contrast. Experiments 2a and 2b showed that existing stereopsis with increasing binocular disparity balanced the dynamics of peripheral binocular rivalry, rendering more equivalent eye dominance. Based on these interactions, we suggest that binocular integration and interocular suppression may mediate one another through an overlapping mechanism for regulating eye dominance, with strong stereo percepts tending to reduce eye dominance and strong rivalry tending to increase eye dominance.

Impact of monocular vs. binocular contrast and blur on the range of functional stereopsis

Stereopsis depends on the smallest stereo threshold (lower limit) and the upper fusion limit. While studies have shown that the lower limit worsens with reduced contrast and blur, more strongly in monocular than in binocular conditions, the effect on the upper limit remains uncertain. Here, we assess the impact of contrast and blur on the range of the disparity sensitivity function (DSF) in a stereo letter recognition task. Subjects had to identify the stereo letters embedded in a random dot stereogram, and adaptive staircases were used to estimate the two limits. Five subjects performed the experiment at baseline contrast (100%), with different contrast (32% and 10%) and blur (+0.75DS and +1.25DS) in monocular and binocular degradation. We proposed three possible outcomes: 1) the range collapses in both directions 2) the lower limit threshold reduces, but the upper limit is not affected 3) the threshold for both limits increases and the range remains the same. We found that the curve for both limits was lowpass in shape, resulting in a smaller range at higher SFs. The results were similar to the first prediction, where the threshold for the lower limit increased while the upper limit was reduced at lower contrast and higher blur. The shrinkage of DSF is significant in monocular conditions. However, with blur, there was inter-subject variability. A simple cross-correlation stereo-matching algorithm was used to quantify the effect of contrast and blur. The results were consistent with the behavioral result that the range of DSF decreases with image degradation.

Test retest variability in stereoacuity measurements

ABSTRACT Background: A clinician’s choice of stereotest is influenced by the robustness of the measurement, in terms of sensitivity, specificity and test–retest variability. In relation to the latter aspect, there are limited data on the test–retest variability of these new tests and how they compare to the more commonly used stereotests. Therefore, the aim of the study was to determine the test–retest variability of four different measures of stereoacuity (TNO, Frisby, Lang Stereopad and Asteroid (Accurate STEReotest On a mobIle Device)) and to compare the stereoacuity measurements between the tests in an adult population. Methods: Stereoacuity was measured twice using TNO, Frisby, Lang Stereopad and Asteroid. Inclusion criteria included adult participants (18 years and older), no known ophthalmic condition and VA (Visual Acuity) equal to or better than 0.3 logMAR (Logarithm of the Minimum Angle of Resolution) with interocular difference of less than 0.2 logMAR. Bland–Altman analysis was used to assess agreement within and between stereotests. Differences in stereo thresholds were compared using signed Wilcoxon tests. Results: Fifty-four adults (male: 23 and female: 31) with VA equal to or better than 0.3 logMAR in either eye and interocular difference less than 0.2 logMAR were assessed (mean age: 38 years, SD: 12.7, range: 18–72). The test–retest variability of all the clinical stereotests, with the exception of the Lang Stereopad (p = .03, Wilcoxon signed-rank test), was clinically insignificant as the mean bias was equal or less than 0.06 log seconds of arc (equivalent to 1.15 seconds of arc). While the Asteroid test had the smallest variation between repeated measures (mean bias: −0.01 log seconds of arc), the Frisby and Lang Stereopad tests had the narrowest and widest limits of agreement respectively. When comparing results between tests, the biggest mean bias was between Frisby and Lang Stereopad (−0.62 log seconds of arc), and 64.8% and 31.5% of differences were in the medium (21–100” of arc) and larger (>100” of arc) ranges respectively. Conclusion: The TNO and Frisby tests have good reliability but measure stereoacuity over a narrower range compared to the Asteroid which shows less variation on repeated testing but has a larger testing range. The data reported here show varying degrees of agreement in a cohort of visually normal participants, and further investigation is required to determine if there is further variability when stereoacuity is reduced.

The Stereoscopic Anisotropy Is Smaller in Elderly Population.

The stereoscopic anisotropy is one of the most intriguing phenomena of stereoscopic vision. It shows that the disparity thresholds to detect three-dimensional sinusoidal horizontal corrugations are much lower than for vertical corrugations for spatial frequencies lower than 1 cycles/deg. A recent study has shown that the anisotropy increases during childhood and that visual experience probably plays an important role in its development (Serrano-Pedraza et al., 2016). Here we want to determine the impact that the visual experience has throughout life in the stereoscopic anisotropy. We performed two experiments testing two age groups of 35 participants each: the young group aged 18 to 45 years and the old group aged 62 to 90 years. We measured disparity thresholds for three-dimensional sinusoidal corrugations of 0.1 cyc/deg, with either vertical or horizontal orientation. Detection thresholds were obtained using Bayesian adaptive staircases. For each participant we computed the anisotropy index by subtracting the thresholds in logarithmic units of the vertical minus the horizontal corrugation. The analyses show that stereo thresholds for vertical corrugations are similar for both groups, however, for horizontal corrugations the thresholds are much lower for the young group. Therefore, the anisotropy was much stronger in the young group (mean, 0.67 ± 0.46) than for the old group (mean, 0.24 ± 0.3). Pearson correlation between the anisotropy index and age shows a negative and significant correlation (r = -0.49; P = 1.83 × 10-5; N = 70), that is, as age advances, the anisotropy decreases. Thus, visual experience plays an important role in the development of stereo vision. Although disparity thresholds for horizontal corrugations in the older group are higher, surprisingly, disparity thresholds for vertical corrugations remain stable and do not change. Therefore, the stereoscopic anisotropy decreases with aging.

Assessment of depth perception with a comprehensive disparity defined letter test: A pilot study.

Current clinical tests mostly assess stereopsis with crossed disparity at near. These tests are designed with fine targets (high spatial frequency) and may fail to capture the “functional stereopsis” in real-world scenes, which consist of a range of spatial frequencies (SFs). We developed a stereo letter test that can assess crossed and uncrossed stereoacuity at near and far, at different SFs defined by the letter size. The test consists of disparity-defined letters embedded in random-dot stereograms. At each letter size, the letters are arranged in sets of trigrams like in the Pelli-Robson chart. The letter sizes correspond to SFs ranging from 0.3 to 2cpd. Within each triplet, all letters have the same disparity and the amount of disparity decreases after each set. Subjects report the letters verbally to determine the smallest disparity at each letter size. Twenty-four subjects were tested with eight different charts: crossed vs. uncrossed disparity at far and near, with two versions (different letter sequences). The disparity sensitivity function (DSF) had an inverted U-shape, with decreasing sensitivity for smaller stereo letters. The subjects had better stereopsis at far than near. All the subjects had lower stereo thresholds with crossed disparity than uncrossed, consistently at both distances. We found no effect of age or heterophoria on the DSF. The charts have good test-retest reliability (Pearson’s r = 0.89, p<0.001) and are easy to perform. Our results with stereo letters as stimuli are comparable to results from studies using depth corrugations. This stereo acuity letter test permits assessment of stereopsis at different testing distances, directionality of disparity, and across a range of SFs, which can help diagnose selective stereo losses in binocular vision anomalies and monovision. Assessment of stereopsis at different SFs may provide additional information for understanding daily stereovision demands than the conventional tests.

ViMoT - Development of Visual-Motor Tests Methodology Including the Adoption of Uniform Rules and Digital Test Development

The authors have previously researched and analyzed, both manually and with the help of a computer program, preschool and primary school children's performance in the eye-hand coordination test and their depth perception. The study used the standardized DTVP-2 test - a psychophysiological test, and it will report as a golden standard for evaluation of visual - motor and visual perception integration. Computer-aided test processing significantly accelerates the collection and acquisition of test results - as we know, time is now a very high resource that everyone needs to spare. We evaluated the stereo vision of 56 participants by using the TNO test and eye-hand coordination. The participants were children of preschool and primary school age. Twenty of them were from a school for children with cognitive disabilities. The TNO test results showed that 54% of children between the ages of 5.5 and 9.0 years old had 60 arcsec, 18% - 120 arcsec, and 29% - 240 arcsec. The DTVP -2 test execution rate shows a very strong correlation with the stereoacuity (r = 0, 90; p < 0, 05). A computerized DTVP -2 test performance coefficient shows a higher correlation with stereo (r =0, 99; p < 0, 05). The DTVP -2 performance coefficient related to stereovision value - the higher the eye-hand coordination performance coefficient, the lower are the stereo threshold value. The conclusions of master thesis research became hypotheses of PhD research and started developing a ViMoT methodology. The development of a new methodology (ViMoT) for assessing visual-motor coordination and visual perception in electronic format and the subsequent development of a computer program will facilitate many specialists' work. It will make it possible to devote more time to processing, but correction or help of an individual (patient), depending on his problem. By working in an interdisciplinary manner, there is an in-depth knowledge of the topic, researched, and new solutions relevant to e-learning. Ensures the quality of the research and increases competitiveness. The following primary research methods will be applied to achieve the aim of the study: theoretical data research as descriptive analysis, content analysis, and comparative method; mixed type of methods as both qualitative research methods and quantitative research methods – document use, case studies, surveys, focus groups discussions and interviews with target groups, experimental and practical testing of recommendations; analysis methods as descriptive analysis, statistical analysis, and others. Today's users and learners require a user-oriented and personalized approach, not only in applications but also in education. The primary study aims to develop components for improving e-learning and learning process Visual-Motor Test (ViMoT) methodologies based and a new computerized tool on visual science basic principles, psychophysiological, and learners' needs.

Evaluating the Mechanism by Which the TNO Stereo Test Overestimates Stereo Thresholds.

Several studies have revealed that results of the TNO stereo test may overestimate the stereoacuity value (the less the better) compared with other testing measurements. The manner in which vision is divided among two eyes of a person wearing anaglyph glasses may play an important role. This study aimed to examine the effect of anaglyph glasses on stereopsis measurements. A stereopsis measurement system using a phoropter and two Sony smartphones was established. Four types of test patterns, including the original TNO stereo test pictures, isoluminant red-green pictures, grayscale pictures, and black and white dots pictures, were designed. A total of 32 participants were recruited for this study. A significant difference was found among the four groups (Friedman test, chi-square = 50.985, P < 0.001). The Wilcoxon signed-rank test was used to detect differences between the groups. The stereoacuity of the original TNO group was significantly worse than those of the isoluminant, grayscale, and black-white groups. However, no significant difference was found between the isoluminant and grayscale groups. The correlation coefficient between the original TNO and isoluminant groups was 0.952 (Spearman's rho, P < 0.001; 95% confidence interval (CI), 0.901–0.988), while that between the original and grayscale groups was 0.771 (Spearman's rho, P < 0.001; 95% CI, 0.550–0.916). Anaglyph glasses played an important role in determining the stereoacuity values with the TNO stereo test, and the results were overestimated when compared with that of the other testing methods. The imbalance of chroma and luminance between the two eyes caused by the anaglyph glasses was indicated as one of the reasons for the overestimation of stereo thresholds.

ASTEROID stereotest v1.0: lower stereo thresholds using smaller, denser and faster dots.

In 2019, we described ASTEROID, a new stereotest run on a 3D tablet computer which involves a four-alternative disparity detection task on a dynamic random-dot stereogram. Stereo thresholds measured with ASTEROID were well correlated with, but systematically higher than (by a factor of around 1.5), thresholds measured with previous laboratory stereotests or the Randot Preschool clinical stereotest. We speculated that this might be due to the relatively large, sparse dots used in ASTEROID v0.9. Here, we introduce and test the stereo thresholds and test-repeatability of the new ASTEROID v1.0, which uses precomputed images to allow stereograms made up of much smaller, denser dots. Stereo thresholds and test/retest repeatability were tested and compared between the old and new versions of ASTEROID (n=75) and the Randot Circles (n=31) stereotest, in healthy young adults. Thresholds on ASTEROID v1.0 are lower (better) than on ASTEROID v0.9 by a factor of 1.4, and do not differ significantly from thresholds on the Randot Circles. Thresholds were roughly log-normally distributed with a mean of 1.54 log10 arcsec (35 arcsec) on ASTEROID v1.0 compared to 1.70 log10 arcsec (50 arcsec) on ASTEROID v0.9. The standard deviation between observers was the same for both versions, 0.32 log10 arcsec, corresponding to a factor of 2 above and below the mean. There was no difference between the versions in their test/retest repeatability, with 95% coefficient of repeatability=0.46 log10 arcsec (a factor of 2.9 or 1.5 octaves) and a Pearson correlation of 0.8 (comparable to other clinical stereotests). The poorer stereo thresholds previously reported with ASTEROID v0.9 appear to have been due to the relatively large, coarse dots and low density used, rather than to some other aspect of the technology. Employing the small dots and high density used in ASTEROID v1.0, thresholds and test/retest repeatability are similar to other clinical stereotests.

Stereotest Comparison: Efficacy, Reliability, and Variability of a New Glasses-Free Stereotest.

PurposeTo test the validity of the ASTEROID stereotest as a clinical test of depth perception by comparing it to clinical and research standard tests.MethodsThirty-nine subjects completed four stereotests twice: the ASTEROID test on an autostereo 3D tablet, a research standard on a VPixx PROPixx 3D projector, Randot Circles, and Randot Preschool. Within 14 days, subjects completed each test for a third time.ResultsASTEROID stereo thresholds correlated well with research standard thresholds (r = 0.87, P < 0.001), although ASTEROID underestimated standard threshold (mean difference = 11 arcsec). ASTEROID results correlated less strongly with Randot Circles (r = 0.54, P < 0.001) and Randot Preschool (r = 0.64, P < 0.001), due to the greater measurement range of ASTEROID (1–1000 arcsec) compared to Randot Circles or Randot Preschool. Stereo threshold variability was low for all three clinical stereotests (Bland–Altman 95% limits of agreement between test and retest: ASTEROID, ±0.37; Randot Circles, ±0.24; Randot Preschool, ±0.23). ASTEROID captured the largest range of stereo in a normal population with test–retest reliability comparable to research standards (immediate r = 0.86 for ASTEROID vs. 0.90 for PROPixx; follow-up r = 0.68 for ASTEROID vs. 0.88 for PROPixx).ConclusionsCompared to clinical and research standards for assessing depth perception, ASTEROID is highly accurate, has good test–retest reliability, and measures a wider range of stereo threshold.Translational RelevanceThe ASTEROID stereotest is a better clinical tool for determining baseline stereopsis and tracking changes during treatment for amblyopia and strabismus compared to current clinical tests.

Efficient estimation of stereo thresholds: What slope should be assumed for the psychometric function?

Bayesian staircases are widely used in psychophysics to estimate detection thresholds. Simulations have revealed the importance of the parameters selected for the assumed subject’s psychometric function in enabling thresholds to be estimated with small bias and high precision. One important parameter is the slope of the psychometric function, or equivalently its spread. This is often held fixed, rather than estimated for individual subjects, because much larger numbers of trials are required to estimate the spread as well as the threshold. However, if this fixed value is wrong, the threshold estimate can be biased. Here we determine the optimal slope to minimize bias and maximize precision when measuring stereoacuity with Bayesian staircases. We performed 2- and 4AFC disparity detection stereo experiments in order to measure the spread of the disparity psychometric function in human observers assuming a Logistic function. We found a wide range, between 0.03 and 3.5 log10 arcsec, with little change with age. We then ran simulations to examine the optimal spread using the empirical data. From our simulations and for three different experiments, we recommend selecting assumed spread values between the percentiles 60–80% of the population distribution of spreads (these percentiles can be extended to other type of thresholds). For stereo thresholds, we recommend a spread around the value σ = 1.7 log10 arcsec for 2AFC (slope β = 4.3 /log10 arcsec), and around σ = 1.5 log10 arcsec for 4AFC (β = 4.9 /log10 arcsec). Finally, we compared a Bayesian procedure (ZEST using the optimal σ) with five Bayesian procedures that are versions of ZEST-2D, Psi, and Psi-marginal. In general, for the conditions tested, ZEST optimal σ showed the lowest threshold bias and highest precision.

Characterizing the Randot Preschool stereotest: Testability, norms, reliability, specificity and sensitivity in children aged 2-11 years.

To comprehensively assess the Randot Preschool stereo test in young children, including testability, normative values, test/retest reliability and sensitivity and specificity for detecting binocular vision disorders. We tested 1005 children aged 2-11 years with the Randot Preschool stereo test, plus a cover/uncover test to detect heterotropia. Monocular visual acuity was assessed in both eyes using Keeler Crowded LogMAR visual acuity test for children aged 4 and over. Testability was very high: 65% in two-year-olds, 92% in three-year-olds and ~100% in older children. Normative values: In 389 children aged 2-5 with apparently normal vision, 6% of children scored nil (stereoblind). In those who obtained a threshold, the mean log threshold was 2.06 log10 arcsec, corresponding to 114 arcsec, and the median threshold was 100 arcsec. Most older children score 40 arcsec, the best available score. We found a small sex difference, with girls scoring slightly but significantly better. Test/retest reliability: ~99% for obtaining any score vs nil. Agreement between stereo thresholds is poor in children aged 2-5; 95% limit of agreement = 0.7 log10 arcsec: five-fold change in stereo threshold may occur without any change in vision. In children over 5, the test essentially acts only as a binary classifier since almost all non-stereoblind children score 40 arcsec. Specificity (true negative rate): >95%. Sensitivity (true positive rate): poor, <50%, i.e. around half of children with a demonstrable binocular vision abnormality score well on the Randot Preschool. The Randot Preschool is extremely accessible for even very young children, and is very reliable at classifying children into those who have any stereo vision vs those who are stereoblind. However, its ability to quantify stereo vision is limited by poor repeatability in children aged 5 and under, and a very limited range of scores relevant to children aged over 5.

Effect of Interocular Contrast Difference on Stereopsis in Observers With Sensory Eye Dominance.

PurposeWe investigated how sensory eye dominance (SED) affects stereopsis when the half-images of random-dot-stereo stimuli had different interocular contrast.MethodsWe measured crossed and uncrossed stereo disparity thresholds and reaction time to seeing random-dot-stereograms with variable interocular contrast differences (ICD), where ICD = (log10 [CLE] − log10 [CRE]) = −0.4, −0.2, 0, 0.2, or 0.4 log unit. The mean contrast of the stimuli, (log10 [CLE] + log10 [CRE])/2, remained constant at 1.2 log unit to ensure that the measured effect was solely due to ICD. We also measured SED using, respectively, dichoptic horizontal sine wave gratings with different phases (revealing SEDcombo) and dichoptic vertical and horizontal gratings (revealing SEDinhibition).ResultsBoth measures of SEDinhibition and SEDcombo revealed the observers had the same eye as dominant although the magnitudes differed. The observers had lower stereo thresholds and shorter stereo reaction time on stimuli with unequal interocular contrast when the non–sensory-dominant eye viewed the higher contrast half-image, suggesting a stimulus-compensating effect. We then estimated the ICD of random-dot-stereo half-images (compensating stimuli) that would lead to minimum stereo threshold (SEDstereo-threshold) and reaction time (SEDstereo-RT) based on the stereo performance and ICD relationship, and found that they were significantly smaller than SEDinhibition and SEDcombo.ConclusionsBy linking SEDinhibition and SEDcombo with the effect of ICD on stereopsis, we provided further support for the notion that the stimulus-compensating effect is mediated by the interocular inhibitory and interocular gain control mechanisms. Furthermore, the interocular contrast for SEDstereo-threshold and SEDstereo-RT can be potentially applied for improving stereopsis in individuals with SED.

ASTEROID: A New Clinical Stereotest on an Autostereo 3D Tablet.

PurposeTo describe a new stereotest in the form of a game on an autostereoscopic tablet computer designed to be suitable for use in the eye clinic and present data on its reliability and the distribution of stereo thresholds in adults.MethodsTest stimuli were four dynamic random-dot stereograms, one of which contained a disparate target. Feedback was given after each trial presentation. A Bayesian adaptive staircase adjusted target disparity. Threshold was estimated from the mean of the posterior distribution after 20 responses. Viewing distance was monitored via a forehead sticker viewed by the tablet's front camera, and screen parallax was adjusted dynamically so as to achieve the desired retinal disparity.ResultsThe tablet must be viewed at a distance of greater than ∼35 cm to produce a good depth percept. Log thresholds were roughly normally distributed with a mean of 1.75 log10 arcsec = 56 arcsec and SD of 0.34 log10 arcsec = a factor of 2.2. The standard deviation agrees with previous studies, but ASTEROID thresholds are approximately 1.5 times higher than a similar stereotest on stereoscopic 3D TV or on Randot Preschool stereotests. Pearson correlation between successive tests in same observer was 0.80. Bland-Altman 95% limits of reliability were ±0.64 log10 arcsec = a factor of 4.3, corresponding to an SD of 0.32 log10 arcsec on individual threshold estimates. This is similar to other stereotests and close to the statistical limit for 20 responses.ConclusionsASTEROID is reliable, easy, and portable and thus well-suited for clinical stereoacuity measurements.Translational RelevanceNew 3D digital technology means that research-quality psychophysical measurement of stereoacuity is now feasible in the clinic.

On Sensory Eye Dominance Revealed by Binocular Integrative and Binocular Competitive Stimuli.

PurposeTwo core processes underlie 3-D binocular vision. The first, a binocular combination/summation process, integrates similar feature signals from the two eye channels to form a binocular representation. The second, a binocular inhibitory process, suppresses interocular conflicting signals or falsely matched binocular representations to establish single vision. Having an intrinsic interocular imbalance within one or both processes can cause sensory eye dominance (SED), related to imbalances of combination (SEDcombo) and/or inhibition (SEDinhibition). While much has recently been revealed about SEDcombo and SEDinhibition, the relationship between them is still unknown.MethodsWe measured observers' foveal SEDcombo and SEDinhibition, respectively, with a pair of dichoptic horizontal sine wave gratings with different phases and binocular rivalry stimulus with vertical and horizontal gratings. We then measured horizontal and vertical monocular contrast thresholds using sinusoidal grating stimuli, and stereo thresholds using random-dot stereograms.ResultsThere exists a strong correlation between SEDcombo and SEDinhibition. An observer's interocular difference in contrast threshold was not always consistent with his/her SEDcombo and SEDinhihition, suggesting a partial binocular origin for the underlying imbalances. We also found stereo thresholds significantly increased with the magnitudes of SEDcombo, as well as with the magnitude of SEDinhibition.ConclusionsOur findings suggest a common origin for interocular imbalance in the two different binocular processes and that both types of sensory eye dominance are significant factors in impeding stereopsis.

Impact of intraocular scatter on stereopsis

To investigate the effect of intraocular scatter on stereopsis, we measured stereoacuity with scatter either remaining at the natural eye-induced level or further enhanced by a set of three different scatter filters. Stereo thresholds at different viewing durations were obtained using a psychophysical method of constant stimuli. The results indicate that stereoacuity was degraded with a binocular increase in scatter levels for all the subjects. Measurements were also performed in the presence of interocular differences in scatter levels. In this case, stereoacuity was found to be even a little worse than that obtained with both eyes at a higher scatter level. This suggests that stereoacuity in the presence of interocular differences in scatter levels is mainly dependent on the higher scatter level.

Impaired Binocular Depth Perception in First-Episode Drug-Naive Patients With Schizophrenia.

Binocular depth perception (BDP) is one of the most demanding visual function that involves both dorsal and ventral visual information streams. Substantial research has been conducted on the disruption of BDP in patients with schizophrenia. However, research on first-episode and drug-naive patients with schizophrenia (FEDN) is limited. To assess the BDP of schizophrenia patients while controlling for the effects of antipsychotics and the duration of illness. We investigated BDP in patients with schizophrenia via the Titmus Stereopsis Test in this study, by matching the patients into three groups: FEDN (n = 17), long duration of illness and medicine treatment (LDMT) (n = 31) and the healthy control group (n = 40). Results showed that both the FEDN (mean = 1.71, 95% confidence interval [CI]: [1.57, 1.84]) and LDMT (1.73, 95% CI: [1.66, 1.81]) patients displayed a significant decline (p = 0.01, Cohen’s d = 0.67, p = 0.001, Cohen’s d = 0.92, respectively) in depth perception compared to the healthy control (1.55, 95% CI: [1.48, 1.61]) group. Additionally, there were no significant differences (p = 0.68, Cohen’s d = 0.11) between the FEDN and LDMT groups, and no correlation (Pearson r = -0.16, p = 0.38, R2 = 0.03) was observed between the duration of illness and impaired BDP in the LDMT group. The proportion of individuals with stereopsis detection in either FEDN (12/17) or LDMT (26/31) groups under stereo threshold 63 arc seconds (″), were significantly lower (Pearson χ2 = 6.29, p = 0.043, φc = 0.27) compared to the healthy control group (38/40). Significant difference in stereopsis detection also occurred at 50″ (Pearson χ2 = 12.31, p = 0.001, φc = 0.37), 40″ (Pearson χ2 = 12.38, p = 0.002, φc = 0.38), 32″ (Pearson χ2 = 6.69, p = 0.035, φc = 0.28), 25″ (Pearson χ2 = 14.82, p = 0.001, φc = 0.41) and 20″ (Pearson χ2 = 6.73, p = 0.034, φc = 0.28) between the three groups. These findings showed a moderately strong association between schizophrenia and defective stereopsis.

Repetitive dynamic stereo test improved processing time in young athletes.

Current studies revealed the importance of perceptual training for the treatment of amblyopia. To improve stereo vision on a higher level, visual tasks have to be completed within a limited time window like in repetitive visual function tests. "Processing time" as the reaction time in which the absence or presence of depth was identified correctly, is of better predictive value for perceiving the depth than the stereo threshold only. To examine the long-term effects of repetitive dynamic testing of stereopsis on processing time. 15 male soccer athletes (13.3±3.2 years) underwent twelve sessions of a 15 minutes repetitive dynamic stereovision training over a period of six weeks, presented on a polarized 3D-TV in a four-alternative forced choice setup. We measured the response time of correct identified visual tasks of 11, 22, 44, 55, 66, 77 and 88arcsecs disparity before, after six sessions, after twelve sessions and after six month without testing. As response time is the sum of stereo processing time plus the motor reaction time, we defined the difference between the response times at 11 and 88arcsecs as "stereo processing time at 11arcsecs". A Wilcoxon Signed Rank Test was conducted between the testing sessions to evaluate significant changes in response time and stereo processing time. After six sessions the mean stereo processing time at 11arcsecs decreased significantly from 804.4 ms to 403.7 ms (Z = -2.499, p = 0.012). Six months after the last training the stereo processing time at 11arcsecs remained at the level of the last session. Our results suggest that repetitive testing of stereovision is effective in improving processing time of stereoscopic tasks in young male athletes significantly long-term.

Overestimation of stereo thresholds by the TNO stereotest is not due to global stereopsis.

PurposeIt has been repeatedly shown that the TNO stereotest overestimates stereo threshold compared to other clinical stereotests. In the current study, we test whether this overestimation can be attributed to a distinction between ‘global’ (or ‘cyclopean’) and ‘local’ (feature or contour‐based) stereopsis.MethodsWe compared stereo thresholds of a global (TNO) and a local clinical stereotest (Randot Circles). In addition, a global and a local psychophysical stereotest were added to the design. One hundred and forty‐nine children between 4 and 16 years old were included in the study.ResultsStereo threshold estimates with TNO were a factor of two higher than with any of the other stereotests. No significant differences were found between the other tests. Bland‐Altman analyses also indicated low agreement between TNO and the other stereotests, especially for higher stereo threshold estimates. Simulations indicated that the TNO test protocol and test disparities can account for part of this effect.DiscussionThe results indicate that the global – local distinction is an unlikely explanation for the overestimated thresholds of TNO. Test protocol and disparities are one contributing factor. Potential additional factors include the nature of the task (TNO requires depth discrimination rather than detection) and the use of anaglyph red/green 3D glasses rather than polarizing filters, which may reduce binocular fusion.

The absolute disparity anomaly and the mechanism of relative disparities.

There has been a long-standing debate about the mechanisms underlying the perception of stereoscopic depth and the computation of the relative disparities that it relies on. Relative disparities between visual objects could be computed in two ways: (a) using the difference in the object's absolute disparities (Hypothesis 1) or (b) using relative disparities based on the differences in the monocular separations between objects (Hypothesis 2). To differentiate between these hypotheses, we measured stereoscopic discrimination thresholds for lines with different absolute and relative disparities. Participants were asked to judge the depth of two lines presented at the same distance from the fixation plane (absolute disparity) or the depth between two lines presented at different distances (relative disparity). We used a single stimulus method involving a unique memory component for both conditions, and no extraneous references were available. We also measured vergence noise using Nonius lines. Stereo thresholds were substantially worse for absolute disparities than for relative disparities, and the difference could not be explained by vergence noise. We attribute this difference to an absence of conscious readout of absolute disparities, termed the absolute disparity anomaly. We further show that the pattern of correlations between vergence noise and absolute and relative disparity acuities can be explained jointly by the existence of the absolute disparity anomaly and by the assumption that relative disparity information is computed from absolute disparities (Hypothesis 1).