Stereoscopic Performance Research Articles

Context-based modulations of 3D vision are expertise dependent.

An object's identity can influence depth-position judgments. The mechanistic underpinnings underlying this phenomenon are largely unknown. Here, we asked whether context-dependent modulations of stereoscopic depth perception are expertise dependent. In 2 experiments, we tested whether training that attaches meaning (i.e. classification labels) to otherwise novel, stereoscopically presented objects changes observers' sensitivity for judging their depth position. In Experiment 1, observers were randomly assigned to 3 groups: a Greeble-classification training group, an orientation-discrimination training group, or a no-training group, and were tested on their stereoscopic depth sensitivity before and after training. In Experiment 2, participants were tested before and after training while fMRI responses were concurrently imaged. Behaviorally, stereoscopic performance was significantly better following Greeble-classification (but not orientation-discrimination, or no-) training. Using the fMRI data, we trained support vector machines to predict whether the data were from the pre- or post-training sessions. Results indicated that classification accuracies in V4 were higher for the Greeble-classification group as compared with the orientation-discrimination group for which accuracies were at chance level. Furthermore, classification accuracies in V4 were negatively correlated with response times for Greeble identification. We speculate that V4 is implicated in an expertise-dependent, object-tuning manner that allows it to better guide stereoscopic depth retrieval.

Binocular vision training for professional athletes

Optimal visual abilities including stereo acuity seem to be an important issue in sports. There is increasing evidence that stereo acuity can be sustainably improved by digital vision training even for people with good stereo acuity. In this study 31male and female tennis players (professionals, young professionals, coaches and former professionals) completed at least 6training units each with 192 dynamic stereoscopic tasks (N = 1152) within 6 weeks including a4-option testwith different levels of difficulty on a3D screen at a distance of 5 m. The parameter reaction time and correctness at 15-300 arcseconds was determined. For amore precise representation of the reaction time improvement as afunction of the difficulty level, the parameter reaction time increase per stereo disparity reduction (ReST) was defined. Reaction time to 15 arcsecond stimuli significantly decreased from 3.9 s to 1.6 s (59%) as aresult of digital vision training. The correctness at 30 arcsecond stimuli significantly increased by 23%. The observed improvement in reaction time during vision training did not result in decreasing correctness when answering the visual questions. This represents an overall improvement in stereo vision. Dynamic visual training over 6 weeks improves stereoscopic performance including stereo acuity, response time and correctness.

A Joint Lateral Motion-Stereo Constraint.

PurposeWe developed a stereo task that is based on a motion direction discrimination to examine the role that depth can play in disambiguating motion direction.MethodsIn this study, we quantified normal adults’ static and dynamic (i.e., laterally moving) stereoscopic performance using a psychophysical task, where we dichoptically presented randomly arranged, limited lifetime Gabor elements at two depth planes (one plane was at the fixation plane and the other at an uncrossed disparity relative to the fixation plane). Each plane contained half of the elements. For the dynamic condition, all elements were vertically oriented and moved to the left in one plane and to the right in another plane; for the static condition, the elements were horizontally oriented in one plane and vertically oriented in another plane.ResultsFor the range of motion speed that we measured (from 0.17°/s to 5.33°/s), we observed clear speed tuning of the stereo sensitivity (P = 3.0 × 10−5). The shape of this tuning did not significantly change with different spatial frequencies. We also found a significant difference in stereo sensitivity between stereopsis with static and laterally moving stimuli (speed = 0.67°/s; P = 0.004). Such difference was not evident when we matched the task between the static and moving stimuli.ConclusionsWe report that lateral motion modulates human global depth perception. This motion/stereo constraint is related to motion velocity not stimulus temporal frequency. We speculate that the processing of motion-based stereopsis of the kind reported here occurs in dorsal extrastriate cortex.

COMPARISON AND ANALYSIS OF ACCURACY OF ELEVATION EXTRACTION BASED ON THE ZY-3 01 AND 02 SATELLITES STEREOSCOPIC IMAGES

Abstract. The ZY-3 is the civil high-resolution optical stereoscopic mapping satellite independently developed by China. The ZY-3 constellation of the twin satellites operates in a sun-synchronous, near-polar, circular 505 km orbit, with a descending location time of 10:30 AM and a 29-day revisiting period. The panchromatic triplet sensors, pointing forward, nadir, and backward with an angle of 22°, have excellent base-to-height ratio, which is beneficial to the extraction of DEM. In order to extract more detailed and highprecision DEM, the ZY-3 (02) satellite has been upgraded based on the ZY-3 (01), and the GSD of the stereo camera has been optimized from 3.5 to 2.5 meters. In the paper case studies using the ZY-3 01 and the 02 satellite data for block adjustment and DEM extraction have been carried out in Liaoning Province of China. The results show that the planimetric and altimetric accuracy can reach 3 meters, which meet the mapping requirements of 1 : 50,000 national topographic map and the design performance of the satellites. The normalized elevation accuracy index (NEAI) is adopted to evaluate the twin satellite stereoscopic performance, and the NEAIs of the twin ZY-3 satellites are good and the index of the ZY-3(02) is slightly better. The comparison of the overlapping DEMs from the twin ZY-3 satellites and SRTM is analysed. The bias and the standard deviation of all the DEMs are better than 5 meters. In addition, in the process of accuracy comparison, some gross errors of the DEM can be identified, and some elevation changes of the DEM can also be found. The differential DEM becomes a new tool and application.

The Nature of Collaboration

Andrew Bluff and Andrew Johnston, both at the University of Technology Sydney (UTS) in Australia, collaborated with Stalker Theatre on numerous multi-disciplinary interactive stereoscopic performance environments.

Random-dot stereopsis in microstrabismic children: stimulus size matters.

Although children with microstrabismus demonstrate stereoscopic abilities when assessed with clinical tests containing visible contours (local stereopsis), severe stereoscopic impairments are reported when using random-dot stereogram (RDS). This differential performance may be associated with the decreasing interocular correlation resulting from the central suppression present in the deviated eye, affecting global stereopsis to a greater extent. To test this hypothesis, stereoscopic performance on tasks using contour/local (experiment 1), RDS depth (experiment 2), and RDS shape discrimination (experiment 3) was obtained in nine microstrabismic children and compared with that of control participants. For each task, stereoscopic stimuli of 4 and 12 degrees diameter were used to differentially solicit the contribution of the central suppression area. Results demonstrated that performance on the local stereopsis task was very similar for both target sizes, measurable for all microstrabismic participants, and comparable to that of control subjects. On the other hand, global stereoacuity using RDS was not measurable for one-third of the microstrabismic participants when small stimuli were used, but stereoperception became possible for large stimuli condition in which the interocular correlation disruption was presumably negligible. Along these lines, global shape stereopsis was found to increase by nearly 50% in the microstrabismic group when large targets were used. In all experiments, only coarse stereopsis could be measured in microstrabismic children, regardless of the stimulus size. Although our findings suggest that interocular correlation may play a role in deficits of stereopsis in microstrabismus, other altered processes such as abnormal experience, retinal correspondence, and high-level coding are likely to also be involved.

Intérêt d’une bascule d’asphéricité pour une plus grande multifocalité dans la chirurgie de la cataracte

One of the remaining challenges in cataract surgery is to compensate for lost accommodative function. The purpose of our study is to evaluate reading ability with a combination of two different aspheric intraocular lenses. This retrospective study included 40 eyes (20 patients). The control group (28 eyes, 14 patients) received two negative aspheric intraocular lenses (Acrismart 36A(®), Carl Zeiss Meditec), while the aspheric-optimized group (12 eyes, six patients) received an AcriSmart 36A(®) in the dominant eye and a zero-aspheric intraocular lens (Acrismart 46 LC(®), Carl Zeiss Meditec) in the fellow eye. Patients with corneal asphericity between 0.15 and 0.30 μm and a bilateral monocular postoperative visual acuity of at least 20/20 were eligible for inclusion. Uncorrected and best corrected visual acuity was measured for near, intermediate and distance vision. Corneal and total higher-order aberrations, monocular and binocular defocus curve, and stereoscopic performance were assessed. Postoperative spherical equivalent and best corrected distance visual acuity were not significantly different between the two groups (P=0.11 and P=0.82 respectively). However, the aspheric-optimized group (36A(®)/46 LC(®)) exhibited better near and intermediate visual acuity (P<0.05), and better stereoscopic vision (P=0.027). The depth of field results in pseudophakes implanted with "mix-and-match" aspheric lenses demonstrates that the binocular combination of two different aspheric profiles seems to improve near vision without affecting stereoscopic vision.

A novel way to make transient-VEPs a better predictor of human binocular integration

To establish an electrophysiological marker of binocular vision, visual evoked potentials were recorded in normal observers for whom interocular refraction differences were induced with converging lenses under five dioptre conditions. Patterns of binocular interaction were categorized (facilitation, averaging or suppression) by comparing monocular and binocular responses. Quantitative and continuous indexes of binocular integration were also calculated (binocular response minus the sum of monocular responses). Results indicated that patterns of interaction were not optimal to account for stereoscopic performance. The latter was, however, best explained by binocular integration indexes. This study shows evidence of predicting binocular vision based on a novel index that allows continuous quantification of binocular transient-visual evoked potential responses.

Accommodation to multiple-focal-plane displays: Implications for improving stereoscopic displays and for accommodation control

Most stereoscopic displays present images at a single focal plane, resulting in "conflicts" between the stimuli to vergence and accommodation. Minimizing these conflicts is beneficial because they can cause distorted depth percepts, visual fatigue, and reduced stereoscopic performance. One proposed solution is to present a sum of images at multiple focal planes and to vary focal depth continuously by distributing image intensity across planes-a technique referred to as depth filtering. We evaluated this digital approximation to real-world variations in focal depth by measuring accommodation responses to depth-filtered stimuli at various simulated distances. Specifically, we determined the maximum image-plane separation that supported accurate and reliable accommodation. We used an analysis of retinal-image formation to predict when responses might be inaccurate. Accommodation to depth-filtered images was accurate and precise for image-plane separations up to ∼1 diopter, suggesting that depth filtering can be used to precisely match accommodation and vergence demands in a practical display. At larger plane separations, responses broke down in a manner consistent with our analysis. We develop this approach to consider how different spatial frequencies contribute to accommodation control. The results suggest that higher spatial frequencies contribute less to the accommodation response than has previously been thought.

Surgical outcomes of primary foldable intraocular lens implantation in children: Understanding posterior opacification and the absence of glaucoma

To evaluate visual and stereoscopic performance after pediatric cataract extraction with intraocular lens (IOL) implantation performed by the same surgeon over 24 years and to review the complications. The Alberta Children's Hospital, Calgary, Alberta, Canada. This retrospective review comprised children aged 1 month to 18 years who had small-incision cataract extraction with foldable posterior chamber IOL implantation from 1995 to 2008. The postoperative follow-up was 6 months to 12 years. Posterior capsule opacification (PCO) requiring secondary surgical membranectomy developed in 22.7% of the children. Younger children developed PCO more often than older children. The PCO rate was 70.8% in children younger than 1 year and decreased steadily to 6.1% in children older than 7 years. The mean onset of PCO was 6.1 months postoperatively. Other complications were vitreous tags (12.0%), IOL dislocation (4.7%), and loose corneal sclera sutures (2.7%). Of the eyes in which vision could be recorded, 89.5% had improved corrected visual acuity, with no eye losing acuity. Stereopsis was present in 35% of testable children preoperatively and 91% postoperatively. Cataract surgery in children younger than 2 years should be considered a 2-stage procedure in view of the higher incidence of PCO. Secondary glaucoma decreased significantly when surgery was performed after 30 days of age and the eye was left pseudophakic after surgery. Further improvements in IOL design, surgical instrumentation, and implantation techniques will continue to improve the ability to visually rehabilitate children.

The third dimension in the primary visual cortex

Anatomical superposition of the cortical projections from the overlapping visual fields of the two eyes does not make it obvious how the disposition of objects in the third dimension is encoded. Hubel and Wiesel's demonstration that units in the primary visual cortex of the mammal respond preferentially to elongated contours of specific orientation encouraged the inquiry into whether binocular disparity might not similarly be represented as an attribute interdigitated within the orderly progression of position. When this was found to indeed be the case, this entrained a brisk research activity into the disparity of receptive fields of single units in the primary visual cortex and the influence on their response of the three-dimensional locations of outside world stimuli. That cells' preferred orientations covered the whole gamut whereas space perception required only horizontal disparity was an apparent paradox that needed resolution. A connection with an observer's stereoscopic performance was made by the discovery that cells in the primate primary visual cortex display good tuning to the disparity in random-dot stereograms. But a wide gap still remains between the properties of these cortical units and human stereo thresholds in simple target configurations, let alone depth judgments in which perceptual and cognitive factors enter. When the neural circuits in the primary visual cortex that are involved in processing depth are eventually traced in detail they will also need to have properties that allow for the plasticity in learning and experience.

Stereoscopic depth discrimination with contrast windowed stimuli

Depth discrimination with a shifted contrast window was compared to that with a fixed contrast window. Stereoscopic performance with the fixed window was limited to small disparities and varied with spatial frequency. Performance with the shifted window extended to larger disparities and was more similar for low and high spatial frequencies. The results depended upon window shape, indicating that edge blur is an important factor. Stereoscopic performance with shifted patterns was supported at disparities larger than a phase disparity model might predict, suggesting that a combination of position and phase disparity computations are used for the perception of stereoscopic depth.

8.1: Invited Paper: Achieving Near-Correct Focus Cues in a 3D Display using Multiple Image Planes

Focus cues specify inappropriate 3d scene parameters in conventional displays because the light comes from a single surface, independent of the depth relations in the portrayed scene. We examine the efficacy of a stereo-display prototype designed to minimize these problems by using multiple image planes to present near-correct focus cues. Each eye's view is the sum of several images presented at different focal distances. Variation in focal distance is provided by either multiple beam splitters or by use of a switchable lens. The stimulus to accommodation is more consistent with the portrayed depth than with conventional displays. Compared to a normal, fixed-distance display, observers show improved stereoscopic performance in different psychophysical tasks including speed of fusing stereoscopic images. The multiple image-planes approach provides a practical solution for some shortcomings of conventional displays.

Neuronal Computation of Disparity in V1 Limits Temporal Resolution for Detecting Disparity Modulation

The human ability to detect modulation of binocular disparity over time is poor compared with detection of luminance modulation. We examined the physiological origin of this limitation by analyzing neuronal responses to temporal modulation of binocular disparity in striate cortex of awake monkeys. When neurons were presented with random-dot stereograms in which disparity varied sinusoidally over time, their responses modulated at the stimulus temporal frequency, with little change in mean firing rate. We calculated modulation amplitude as a function of temporal frequency and compared this with the psychophysical performance of four human observers. Neuronal and psychophysical functions showed similar peak frequencies (2 Hz) and comparable high-cut frequencies (10 and 5.5 Hz, respectively). Thus, V1 (primary visual cortex) neurons appear to limit psychophysical performance. The temporal resolution of the same neurons for contrast modulation was approximately 2.5 times greater, which parallels the superior psychophysical performance for contrast. There is a simple mathematical explanation for this difference: it results from calculating cross-correlation between temporally broadband monocular images that are bandpass filtered before measuring correlation. The limit on temporal resolution is a direct consequence of the binocular energy model that adds to the list of properties of human stereoscopic performance that are explained by this simple model of disparity encoding in V1: the same neurons can account for the performance of psychophysical tasks that result in either high (contrast) or low (disparity) temporal resolution. Because this principle holds whenever a broadband input is bandpass filtered before computing correlation, it may limit the resolution of other neuronal systems.

Stereopsis From a Performance Perspective

A patient can demonstrate a poor stereoscopic test or task performance for reasons inherent within the test/task itself for reasons dependent on normal physiology common to all human subjects, and also for reasons that are outside of normal physiology and are unique or idiosyncratic to a particular person's visual system. This article reviews the literature for the first two reasons, but emphasizes the pathophysiology involved in the idiosyncratic and abnormal reasons. Using control systems analysis, it is shown that deficits in stereoscopic performance can be explained by reference to the quantitative aspect of stereoscopic threshold and qualitative aspects such as speed of response, reliability-robustness, and strength of percept. The relationship between fixation disparity and stereopsis is seen to be central to this explanation. Proceeding from diagnosis to treatment, control systems analysis offers physiologically based explanations for the corrective procedures necessary to ameliorate abnormal conditions. Several topics for applied research in stereopsis are suggested.

Interactions between chromatic- and luminance-contrast-sensitive stereopsis mechanisms

It is well known that chromatic information can assist in solving the stereo correspondence problem. It has also been suggested that there are two independent first-order stereopsis mechanisms, one sensitive to chromatic contrast and the other sensitive to luminance contrast ( Vision Research 37 (1997) 1271). Could the effect of chromatic information on stereo correspondence be subserved by interactions between these mechanisms? To address this question, disparity thresholds (1/stereoacuity) were measured using 0.5 cpd Gabor patches. The stimuli possessed different relative amounts of chromatic and luminance contrast which could be correlated or anti-correlated between the eyes. Stereoscopic performance with these compound stimuli was compared to that with purely isoluminant and isochromatic stimuli at different contrasts. It was found that anti-correlated chromatic contrast severely disrupted stereopsis with achromatic stimuli and that anti-correlated luminance contrast severely disrupted stereopsis with chromatic stimuli. Less dramatic, but still significant, was the improvement in stereoacuity obtained using correlated colour and luminance contrast. These data are consistent with there being positive and negative interactions between chromatic and achromatic stereopsis mechanisms that take place after the initial encoding of disparity information, but before the extraction of stereoscopic depth. These interactions can be modelled satisfactorily assuming probability summation of depth sign information between independent mechanisms.

Perceptual latency and complex random-dot stereograms.

Naive observers of random-dot stereograms depicting complex surfaces often find that they require several tens of seconds before the impression of depth emerges. With practice, however, perception times often decrease markedly: perceptual learning occurs. Current explanations of these effects were assessed in two experiments. In the first experiment the perception times of naive observers for random-dot stereograms which depicted the same complex shape but contained different ranges of disparity were measured. In the second experiment the minimum times required by experienced observers to perceive a given complex shape in stereograms that contained different ranges of disparity were determined. Perception times for the naive observers were all very fast (<3 s) and showed no evidence of perceptual learning. There was no effect of disparity range on perception times in either experiment. It was found that very large-disparity (80 min arc) complex stereograms could be perceived quickly, even by naive observers. It is concluded that the long initial latencies previously reported are not due to surface complexity nor to the range of disparities present. Other factors. such as dot size, dot density, and the correlation of the stereo images, appear to be important determinants of efficient stereoscopic performance when viewing complex random-dot stereograms.

Some effects of chromostereopsis on stereoscopic performance: implications for microscopes.

Stereoscopic performance was found to be superior for achromatic as compared to chromatic stimulus materials when observing through small pupillary apertures. When interpupillary settings were individually predetermined to eliminate chromostereopsis, chromatic stereo performance improved. A theoretical analysis of the results is presented based on the discrepancy between the optic and visual axes and the centration of the pupil. Microscope design guidance data are provided and suggestions made for improved performance in microscope viewing of chromatic materials.

Binocular utilization of monocular cues that are undetectable monocularly.

The latency time of tracking dynamic random-dot stereograms can be shortened by as much as 100 ms when monocular cues are added by introducing a difference in dot density between target and surround. It has been tacitly assumed that perception time will be reduced only if the added monocular cues are above the detection threshold for each eye. However, the experiments reported here clearly show that stereoscopic performance as measured by an eye tracking task can be greatly enhanced by added monocular cues that cannot be detected. Observers were instructed to track a suddenly displaced vertical bar (portrayed as a dynamic random-dot stereogram) while their eye movements were recorded by EOG. The bar had either a given binocular disparity or zero binocular disparity with respect to its surround. For the target with a disparity (in a wide range), the latency time of tracking decreased by more than 30 ms (10%) as density difference increased from 0 to 4%, whereas in the control conditions with no stereoscopic cues (zero disparity) subjects were unable to track the bar at all within that range of density difference. Thus stereopsis is greatly aided by minimal monocular cues that by themselves elude monocular detection.

Monocular occlusion impairs stereoscopic acuity, but total visual deprivation does not

Wallach and Karsh (1963) reported that 24 h of monocular occlusion leads to a significant deterioration of stereoscopic depth estimates and attributed this phenomenon to “disuse.” We designed an apparatus for testing stereoscopic accuracy which eliminated all cues to depth save binocular disparity. With it, we tested the relative effect of 8 h of monocular—;as opposed to binocular—;occlusion on subsequent stereoscopic performance. Monocular patching led to significant increases in mean standard deviation and in mean absolute error as compared to baseline testing. Binocular patching led to no such impairment. Thus, truedisuse (such as occurs during binocular deprivation) did not impair stereopsis, whereas monocular occlusion, which may involve temporarymisuse of the stereoscopic system, did.