Normal Stereo Research Articles

General and Specific Effects of Stereo Learning.

Technological advancements in virtual reality challenge the human vision, especially stereopsis, a function, which characterizes how two eyes coordinate to form a unified three-dimensional (3D) representation of the external world and is found to be deficient in 30% of the normal population. Although a few previous studies have consistently found that the perceptual learning of stereopsis significantly improved stereoacuity, an underlying mechanism of stereo learning remains heavily debated. Here, we trained subjects with normal stereo vision (assessed with the FLY Stereo Acuity Test) to judge stereopsis containing three types of binocular disparity orders (i.e., zero-, first-, and second-order), aiming to systematically examine the characteristics and plasticity of stereo learning. Thirty subjects were randomly assigned to the three training groups (each for the zero-, first-, or second-order disparity separately). The disparity thresholds were measured before and after training. The disparity threshold was measured in 10 additional control subjects only at the pre- and post-training phase. Stereoscopic images were displayed through a shutter goggle, which is synchronized to a monitor. We found that the training significantly improved the zero-, first-, and second-order disparity threshold by 52.42, 36.28, and 14.9% in the zero-order training condition; 30.44, 63.74, and 21.07% in the first-order training condition; and 30.77, 25.19, and 75.12% in the second-order training condition, respectively. There was no significant improvement in the control group. Interestingly, the greatest improvements in the first- and second-order disparity threshold were found in the corresponding disparity training group; on the contrary, the improvements in the zero-order disparity threshold were comparable across all the three disparity training groups. Our findings demonstrated both general (related to the zero-order disparity) and specific improvements (related to the first- and second-order disparity) in stereo learning, suggesting that stereo training occurs at different visual processing stages and its effects might depend on the specific training sites.

Rectification Using Different Types of Cameras Attached to a Vehicle.

The rectification process is a compulsory step in stereo matching computation. To obtain depth information, stereo camera systems are often installed in vehicles for outdoor and street-related applications, including vehicle and pedestrian detection, lane detection, and traffic sign recognition. In this paper, we propose a rectification method that uses currently available front- and rear-view vehicle cameras to produce rectified stereo images. The proposed method can be employed with different types of cameras that have varying focal lengths. In addition, this method tolerates the problem of camera alignment variation from normal stereo camera systems. To achieve this, a compensation method for different focal lengths and the estimation of image relationships are introduced. The experimental results demonstrate that the proposed method can operate robustly and accurately with different kinds of stereo images and significantly outperforms a state-of-the-art rectification method.

Age is highly associated with stereo blindness among surgeons: a cross-sectional study.

The prevalence of stereo blindness in the general population varies greatly within a range of 1-30%. Stereo vision adds an extra dimension to aid depth perception and gives a binocular advantage in task completion. Lack of depth perception may lower surgical performance, potentially affecting surgical outcome. 3D laparoscopy offers stereoscopic vision of the operative field to improve depth perception and is being introduced to several surgical specialties; however, a normal stereo vision is a prerequisite. The aim of this study was to establish the prevalence of stereo blindness among surgeons in the field of general surgery, gynecology, and urology as these are potential users of 3D laparoscopy. The study was conducted according to the STROBE guidelines for cross-sectional studies. Medical doctors from the department of general surgery, gynecology, and urology were recruited and stereo tested by the use of the Random Dot E stereo test. Upon stereo testing, a demographic questionnaire was completed. Multivariate logistic regression analysis was employed to assess the association between stereo blindness and the variables resulting from the univariate analysis. Three hundred medical doctors completed the study. Of these 9.7% were stereo blind. There were 47% women and 53% men, aged 25-71years. General surgery was represented with 64% of the participants, gynecology with 26%, and urology with 10%. Age (OR 5.6; CI 1.7-18.9; P=0.005) and not being aware of having any vision anomaly in need for correction (OR 4; CI 1.4-11.4; P=0.010) were significantly associated with stereo blindness. Approximately one in ten medical doctors in general surgery, gynecology, and urology were stereo blind with an increasing prevalence with age. This is relevant since stereo blind surgeons will not benefit from the implementation of 3D laparoscopy.

Postoperative Shifts in Adult Strabismus Patients with Visual Deficits

ABSTRACTObjective: To evaluate the effects of corrective surgery in adult strabismic patients with visual deficits and the stability of postoperative alignments. Methods: Retrospective study. Alignment and binocular visual function were evaluated in adult patients with visual deficits (best corrective visual acuity (BCVA) <0.3 in one or both eyes) with at least 6 months postoperative follow-up. The results in these patients were compared to those in patients with normal or nearly normal vision (BCVA ≥ 0.6 in the worse eye) matched by the type of strabismus, magnitude of deviation, age at the time of corrective surgery, and length of time before final follow-up.Results: Sixty-four patients aged 28.3 ± 12.0 (17~65) years were included in the visual deficit group, and 64 subjects aged 26.8 ± 9.4 (17~58) years were included in the matched control group. No significant difference was found in the age or deviation angle between the two groups. The surgery was considered a success in 42 patients (65.6%) in the visual deficit group and 55 patients (86%) in the control group at the last visit (Χ2 = 7.19, p = 0.008). Normal or partially normal stereo acuity was achieved by three patients in the visual deficit group and 29 patients in the control group. An average shift toward exotropia of 7.3 prism diopter (PD) in the visual deficit group and 4.9 PD in the control group was observed between postoperative day 1 and the final visit (t = 2.08, p = 0.04). Of the 22 patients in the visual deficit group that were defined as “not a success,” 20 were under-corrected, and two were over-corrected.Conclusion: Adults with poor vision experienced positive results from corrective surgery via a postoperative shift toward exotropia. Full correction of deviation and postoperative shift should be considered before surgery.

3D 환경에서 가보 영상을 이용한 입체 시력 검사도구의 개발: 탐색적 연구

최근 3D 디스플레이 환경들이 확대되면서 컴퓨터와 3D 디스플레이 장치들을 통해 개인의 입체 시력을 검사하려는 다양한 시도들이 제안되었다. 기존의 입체검사도구들에 비해 3D 디스플레이를 이용한 입체 시력 검사는 여러 장점들을 갖고 있지만, 3D TV나 모니터에서는 최소로 조작할 수 있는 양안시차의 한계가 1픽셀이다. 관찰거리가 짧은 pc 환경에서는 1 픽셀의 양안 시차 값은 정상 입체 시력을 구분해 낼 수 있는 기준보다 너무 크다. 본 연구에서는 이러한 문제를 극복하고자 가보 자극을 사용하여 1픽셀보다 작은 단위의 양안 시차를 제공할 수 있는 입체 검사 자극을 생성한 후 이 자극이 입체 시력 검사자극으로 적용가능한 지를 탐색적으로 살펴보았다. 넓은 범위의 시차를 1회만 측정하는 기존의 입체 시력 검사 대신에 좁은 범위의 시차 값에 대해 조건 당 10번의 반복 측정을 실시하여 각 개인별 정답률을 구하였다. 가보 영상을 사용한 검사결과의 신뢰도와 타당도를 살펴보기 위해 기존 입체 시력 검사에 사용되는 무선점 입체 자극을 이용한 검사 결과와 가보 영상을 이용한 검사결과를 비교하였고 그 결과 온건한 정도의 상관관계를 보여주었다. 또한 검사 결과가 얼마나 신뢰도운지를 평가하기 위해 약 1개월 후에 동일한 환경에서 가보 영상을 이용하여 입체 시력을 측정한 후, 두 검사 결과를 비교한 결과 높은 검사-재검사 신뢰도를 보였다. 이러한 결과는 가보 자극을 사용하여 입체 검사 도구를 개발하는 경우 충분히 신뢰로운 결과를 산출할 수 있음을 시사하는 것으로, 가보 자극은 충분한 관찰거리가 제공되지 않거나 혹은 매우 정밀한 단위로 입체 시력을 평가할 필요가 있는 상황에서 개인의 입체 시력을 평가하기에 적절한 자극임을 보여준다. Many studies tried to develop a 3D display based stereo test as a substitute for the conventional stereo test. Although many 3D monitor based stereo tests have various advantages over the conventional stereo tests with printed stimuli, they have a crucial limitation in manipulating disparity. The least value for disparity manipulation is one pixel, which is too big to screen the normal stereo acuity in pc environment with a short viewing distance. In this explorative study, a Gabor image was employed as a test stimulus, because its position can be manipulated by changing its phase information, which allows sub-pixel manipulation for disparity. Instead of employing the methods of the conventional stereo tests where measurement was made only once for each of a wide range of disparity values, 10 replications were administrated for each of 6 disparity levels. The results from the test using Gabor images were compared with those using random dot stimulus because the latter stimulus was exactly the same as that of the conventional stereo test. The correlation coefficient between two tests was found to be moderate. After one month later, the whole test was repeated in the same settings. The correlation coefficient between test and retest results from Gabor images was found to be as high as that from a random dot stimulus, implying high test-retest reliability. These results suggest that a Gabor stimulus could be used as a test stimulus for the valid and reliable stereo test, even in the limited condition, such as 3D environment with a short viewing distance and a condition for evaluating the stereo acuity very precisely.

Sensory eye balance in surgically corrected intermittent exotropes with normal stereopsis.

Surgery to align a deviated or strabismic eye is often done for both functional as well as cosmetic reasons. Although amblyopia is often an impediment to regaining full binocularity in strabismics in general, intermittent exotropes, because their deviation is intermittent, have no amblyopia and some degree of stereopsis. Binocular function, including a balanced ocular dominance, could be expected to be normal after surgical correction if normal levels of stereopsis and visual acuity are postsurgically achieved. Here we used a binocular phase combination paradigm to quantitatively assess the ocular dominance in a group of surgically corrected intermittent exotropes who have normal stereo and visual acuity as defined clinically. Interestingly, we found significant interocular imbalance (balance point < 0.9) in most of the surgically treated patients (8 out 10) but in none of the controls. We conclude that the two eyes may still have a residual sensory imbalance in surgically corrected strabismus even if stereopsis is within normal limits. Our study opens the possibility that a further treatment aimed at re-balancing the ocular dominance might be necessary in surgically treated intermittent exotropia to provide more efficient binocular processing in the long term.

Can Human Amblyopia be Treated in Adulthood?

Amblyopia is a common visual disorder that results in a spatial acuity deficit in the affected eye. Orthodox treatment is to occlude the unaffected eye for lengthy periods, largely determined by the severity of the visual deficit at diagnosis. Although this treatment is not without its problems (poor compliance, potential to reduce binocular function, etc) it is effective in many children with moderate to severe amblyopia. Diagnosis and initiation of treatment early in life are thought to be critical to the success of this form of therapy. Occlusion is rarely undertaken in older children (more than 10 years old) as the visual benefits are considered to be marginal. Therefore, in subjects where occlusion is not effective or those missed by mass screening programs, there is no alternative therapy available later in life. More recently, burgeoning evidence has begun to reveal previously unrecognized levels of residual neural plasticity in the adult brain and scientists have developed new genetic, pharmacological, and behavioral interventions to activate these latent mechanisms in order to harness their potential for visual recovery. Prominent amongst these is the concept of perceptual learning—the fact that repeatedly practicing a challenging visual task leads to substantial and enduring improvements in visual performance over time. In the normal visual system the improvements are highly specific to the attributes of the trained stimulus. However, in the amblyopic visual system, learned improvements have been shown to generalize to novel tasks. In this paper we ask whether amblyopic deficits can be reduced in adulthood and explore the pattern of transfer of learned improvements. We also show that developing training protocols that target the deficit in stereo acuity allows the recovery of normal stereo function even in adulthood. This information will help guide further development of learning-based interventions in this clinical group.

Full Leg Control of a Quadruped Robot Using Linear Visual Servoing with a Stereo Omnidirectional Camera

The authors have previously proposed foot tip control for quadruped robots using linear visual servoing (LVS) with a normal stereo camera. However, a normal stereo camera has a narrow field of view and is incapable of seeing all four legs simultaneously. Consequently, it has been a problem that the control of all the legs have required that the rotatation of the camera be controlled. This article proposes a method by which a stereo omnidirectional camera is provided at a position low on the body to control all four legs through LVS. In this article, we at first present a transformation equation from an omnidirectional image to a binocular visual space, and we develop a servo equation of LVS in which an omnidirectional image is used. Then, through simulation, we confirm trajectories with the LVS applied to foot tip control. We also conduct an experiment using TITAN-VIII to demonstrate the efficacy of the proposed method.

Grasping Deficits and Adaptations in Adults with Stereo Vision Losses

To examine the effects of permanent versus brief reductions in binocular stereo vision on reaching and grasping (prehension) skills. The first experiment compared prehension proficiency in 20 normal and 20 adults with long-term stereo-deficiency (10 with coarse and 10 with undetectable disparity sensitivities) when using binocular vision or just the dominant or nondominant eye. The second experiment examined effects of temporarily mimicking similar stereoacuity losses in normal adults, by placing defocusing low- or high-plus lenses over one eye, compared with their control (neutral lens) binocular performance. Kinematic and error measures of prehension planning and execution were quantified from movements of the subjects' preferred hand recorded while they reached, precision-grasped, and lifted cylindrical objects (two sizes, four locations) on 40 to 48 trials under each viewing condition. Performance was faster and more accurate with normal compared with reduced binocular vision and least accomplished under monocular conditions. Movement durations were extended (up to approximately 100 ms) whenever normal stereo vision was permanently (ANOVA P < 0.05) or briefly (ANOVA P < 0.001) reduced, with a doubling of error rates in executing the grasp (ANOVA P < 0.001). Binocular deficits in reaching occurred during its end phase (prolonged final approach, more velocity corrections, poorer coordination with object contact) and generally increased with the existing loss of disparity sensitivity. Binocular grasping was more uniformly impaired by stereoacuity loss and influenced by its duration. Adults with long-term stereo-deficiency showed increased variability in digit placement at initial object contact, and they adapted by prolonging (by approximately 25%) the time spent subsequently applying their grasp (ANOVA P < 0.001). Brief stereoreductions caused systematic shifts in initial digit placement and two to three times more postcontact adjustments in grip position (ANOVA P < 0.01). High-grade binocular stereo vision is essential for skilled precision grasping. Reduced disparity sensitivity results in inaccurate grasp-point selection and greater reliance on nonvisual (somesthetic) information from object contact to control grip stability.

Binocularity in Refractive Accommodative Esotropia

To investigate whether restoration of normal stereo acuity is possible in refractive accommodative esotropia. Twenty patients with refractive accommodative esotropia were included in the study. The cycloplegic refraction and the best corrected visual acuity of each patient were recorded. The patients were evaluated by the 4-prism-diopter test, Bagolini striated glasses, the Worth 4-dot test, the TNO stereo test, and the stereo fly plate of the Titmus test. Eight patients had orthotropia with normal retinal correspondence and 12 patients had a small deviation with abnormal retinal correspondence. Nine patients (8 patients with orthotropia and 1 patient with microtropia) demonstrated a gross level of stereo acuity, whereas the others demonstrated no stereopsis. In patients with refractive accommodative esotropia, the prognosis is not favorable for restoration of normal stereopsis, even if orthotropia is achieved.

Varieties of Binocular Interaction in Human Vision

Binocular processing was investigated using a quantitative, process-oriented metatheory of response times. The analyses are not confined to particular distributional assumptions or specific models. Upper and lower performance boundaries for probability summation in parallel processing are defined and compared with observed distributions of reaction times using a variety of dichoptic stimuli. Performance that exceeds the upper bound strongly suggests facilitatory convergence between the two eyes (binocular channel summation). Performance below the lower bound suggests that inputs to the two eyes are processed serially. The results indicate that binocular channel summation in subjects with normal stereo vision requires targets of the same luminance polarity (paired increments or decrements) in corresponding retinal locations. When corresponding retinal locations are stimulated with opposing luminance polarities (increment to one eye, decrement to the other), performance is consistent with probability summation, indicating that parallel ON and OFF pathways remain segregated at least to the level of binocular fusion. Further analyses of data from a stereo-blind observer suggest serial processing of binocular inputs.

Is amblyopia an impediment to binocular function?

While there is good agreement that the strabismic and/or anisometropic deficit in early life plays a key role in disrupting developing binocular connections, it is still not clear what impediment amblyopia is to binocular function in the adult. The answer to this depends upon our combined understanding of the normal stereo mechanism and the amblyopic deficit.

Stereoimages--a practical approach.

In the absence of any aids most people find it easier to cross their eyes than to maintain parallel alignment and thus view the left hand figure with the right eye, since the eyes naturally converge when viewing nearby objects. By accentuating this natural tendency good stereo images can be obtained, except that front and back are reversed and right-handed helices become left handed [8xAmbiguities in stereopsis. Tucker, V. Nature. 1989; 337: 605CrossrefSee all References[8]. This is acceptable for simple line drawings, but if depth cues such as shading or discontinuity in the peptide chain are present then the pseudoscopic image can be confusing. By taking a photocopy and exchanging the left and right diagrams a normal stereo image can be obtained. A useful practical approach to acquiring the technique [9xVisualising molecules without really trying your eyes. Speakman, J.C. New Scientist. 1978; 78: 827See all References[9] is summarized in Box 2Box 2. A further aid, which also provides useful magnification, is an 8 cm diameter (or better 8 ×10 cm) reading lens [10xStereo viewing simplified. Green, N.M. Nature. 1983; 301: 279Crossref | PubMed | Scopus (1)See all References[10]. If the pair of exchanged diagrams is viewed by both eyes through this single lens the amount of convergence required to superimpose the images is decreased by about 30th %. The diagrams should be viewed from about 30 cm and the lens should be moved slowly from the plane of the paper until it is about 10 cm from the eyes. A double image will be seen and, if the eyes are crossed, it will move over and superimpose on its complement as the lens approaches the eye. Often, one image seems almost stationary and the other appears to move, depending on which of the eyes is dominant. Once the images fuse to give the stereo effect the distances can be readjusted to optimize focus and magnification. The use of the lens facilitates crossing of the eyes and, after repeated use, it becomes much easier to obtain the stereoimage without any aid.Table 2Box 2Cross-eyed stereopsis [9xVisualising molecules without really trying your eyes. Speakman, J.C. New Scientist. 1978; 78: 827See all References[9]View the right hand pair of molecules (Figure1Figure1) from about 30 cm and interpose the tip of a pencil 20 cm from the nose. Focus on the tip and move the pencil slowly towards the eyes. The out of focus diagrams will be seen to move together and when superimposed they will fuse to a single stereo image. The eyes may then be refocussed while maintaining the convergence. Repeat the experiment on the left hand pair and note the reversed image and the contradictory depth cues.

Fusion and Rivalry of Illusory Contours

The general question is raised: “Are visual contours given directly from striate-cortex feature-detector activity?‘’ Phenomena of ‘subjective’ or ‘cognitive’ contours are examined to challenge this view, on the ground that contours can be extrapolations across low-probability gaps. The contours may be curved and may have poor ‘gestalt’ qualities—so ‘gestalt closure’ is not appropriate, but may be a sub-class of these phenomena. It is suggested that these illusory contours (and brightness differences) are generated by perceptually postulated masking objects—these being part of perceptual ‘scene analysis strategy’, since strong evidence for nearer objects is provided by improbable gaps. Experiments are reported, in which each eye is given a different ‘cognitive’ contour figure such that there are disparate but illusory contours. It is found that these are fused to give three-dimensional illusory. surfaces bowing in front of the display. Masking objects must be in front of gaps; what happens here with reversal of stereo depth? Switching the eyes often gives rivalry of the illusory contours when masking is incompatible with the stereo depth. Implications for normal stereo vision are discussed.

Listener ratings of stereophonic systems

Subjective listening tests have been completed which indicate that stereo in any of the forms compared is preferred over monaural, but normal stereo from two full range speakers well physically separated is, in all probability, the most preferred.