Normal Stereo Vision 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.

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.

Early Onset of Acquired Comitant Non-Accommodative Esotropia in Childhood

The aim of this study was to describe the clinical characteristics and surgical outcome of acquired comitant non-accommodative esotropia without obvious cause in children with an early onset ≤ three years of age. 24 consecutive patients (13 females) with acquired comitant non-accommodative esotropia underwent strabismus surgery. Outcome measures included amount of deviation and level of binocularity at last follow-up. An acute onset of strabismus was observed in 83 % of patients. Accompanying features such as diplopia, covering one eye or stumbling were observed in 40 % of the children. Cycloplegic retinoscopy revealed a mild to moderate hypermetropia in all children (mean hypermetropia + 2.2 diopters). 90.5 % of children were aligned within 8 PD of orthotropia. 81 % regained normal stereovision (Lang I/II). All children exhibited the typical features of acute acquired comitant esotropia (AACE) type II (Burian-Franceschetti). Collective characteristics of this form of strabismus are a comitant and relatively large deviation, mild hypermetropia, a potential of normal binocular cooperation and absence of an accommodative component and neurological pathology. Time and suddenness of strabismus onset may be less helpful in defining this entity.

Long-term follow-up of children with acute acquired concomitant esotropia

To study the clinical features and surgical outcome of type 2 (Burian-Franceschetti) acute acquired concomitant esotropia (AACE). Retrospective analysis of children with AACE type 2. All patients underwent strabismus surgery to restore ocular alignment. All children underwent a complete assessment including medical history and pre- and postoperative ophthalmological and orthoptic examinations. Postoperative follow-up was at least 12 months in all cases. A total of 25 consecutive patients were included. All but 2 patients (92%) were aligned within 8(∆) or less of orthotropia. Of the 25, 15 (60%) regained normal stereovision. In 6 additional cases (24%) some level of binocular vision (Titmus test, 200'' to 3000'') was demonstrated. All of the patients who finally achieved normal stereopsis had lower levels of binocularity on the first postoperative day. The mean interval between surgery and first occurrence of full stereovision was 18 months (range, 2 to 58 months). General features of AACE type 2 are concomitance of strabismus, absence of an accommodative component even in the presence of hyperopic refractive errors, and no neurological pathology. The potential for normal binocular vision plays a key role in defining this entity. The reemergence of full stereopsis may take several years.

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.

Virtual stereovision system: new understanding on single-lens stereovision using a biprism

Some new understanding of a single-lens binocular stereovision system using a biprism (2F filter) is presented. One image captured by this system is divided into two halves and assumed to be one stereo image pair captured by two virtual cameras generated by the biprism. Hence, this system can also be called a virtual stereovision system. Two different approaches to understanding this system are introduced. One approach is based on a camera calibration technique and another is based on a geometrical analysis of ray sketching. Both approaches enable this system to perform depth recovery in a close range like a typical stereovision system. As the approach based on geometrical analysis requires no complex calibration, great implementation and calibration effort can be saved, in contrast with a normal stereovision system. This approach provides a way to build a binocular stereovision system with a simpler implementation but sufficient accuracy. A complete analysis of this system and the related calibration, depth recovery, and experimentation techniques are presented. Experimentation results are presented to prove the effectiveness of both approaches used to understand this system.

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.

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.