Visual Disparity Research Articles

The effects of stereo disparity on the behavioural and electrophysiological correlates of perception of audio–visual motion in depth

Motion is represented by low-level signals, such as size-expansion in vision or loudness changes in the auditory modality. The visual and auditory signals from the same object or event may be integrated and facilitate detection. We explored behavioural and electrophysiological correlates of congruent and incongruent audio–visual depth motion in conditions where auditory level changes, visual expansion, and visual disparity cues were manipulated. In Experiment 1 participants discriminated auditory motion direction whilst viewing looming or receding, 2D or 3D, visual stimuli. Responses were faster and more accurate for congruent than for incongruent audio–visual cues, and the congruency effect (i.e., difference between incongruent and congruent conditions) was larger for visual 3D cues compared to 2D cues. In Experiment 2, event-related potentials (ERPs) were collected during presentation of the 2D and 3D, looming and receding, audio–visual stimuli, while participants detected an infrequent deviant sound. Our main finding was that audio–visual congruity was affected by retinal disparity at an early processing stage (135–160ms) over occipito-parietal scalp. Topographic analyses suggested that similar brain networks were activated for the 2D and 3D congruity effects, but that cortical responses were stronger in the 3D condition. Differences between congruent and incongruent conditions were observed between 140–200ms, 220–280ms, and 350–500ms after stimulus onset.

Does Changing Vertical Disparity Induce Horizontal Head Movement?

Theoretically, one can estimate the direction of an object that is relative to the head using vertical disparity if the distance from the head to the object is known. However, several reports describe vertical disparity as having little or no effect on the perception of visual direction. It has been suggested, however, that the visual processes involved in action are different from those involved in perception, and the effect of visual disparity on action has not been investigated in previous studies. This study investigated the influence of vertical disparity on the stability of head direction as a motor response to visual information. We presented a stimulus consisting of horizontal lines with vertical size-disparity oscillation, and examined whether the stimulus affected the subject’s head movement. The results showed that the head movement in the condition of vertical size-disparity oscillation was not significantly different from that in the condition of no disparity oscillation. Our results suggest that, despite theoretical validity, vertical disparity is not used for controlling head movement.

The role of stereopsis (three-dimensional vision) in dentistry: review of the current literature.

Clinical dental work is placing increasing demands on a clinician's vision as new techniques that require fine detail become more common. High hand-eye coordination requires good visual acuity as well as other psychological and neurological qualities such as stereopsis. Stereopsis (three-dimensional vision) is the highest form of depth perception obtained by visual disparity of images formed in the retinas of two eyes. It is believed to confer functional benefits on everyday tasks such as hand-eye coordination. Although its role in depth perception has long been established, little is known regarding the importance of stereopsis in dentistry. This article reviews the role of stereopsis in everyday life and the available literature on the importance of stereopsis in dentistry.

Influence of Water Quality on Exchange Phase-Solution Phase Behavior of Texturally Different Salt-affected Soils

The influence of total electrolyte concentration (TEC) and sodium adsorption ratio (SAR) of water on ESR-SAR relationships of normal clay loam, saline silty loam and calcareous sodic loam soils was studied in a laboratory experiment. Twelve solutions, encompassing three TEC levels viz., 25, 50, and 100 me L−1 and four SAR levels viz., 5, 10, 20 and 30 mmol1/2 L−1/2 were prepared to equilibrate the soil samples using pure chloride salts of calcium, magnesium and sodium at Ca: Mg = 2: 1. The SAR of equilibrium solution decreased as compared to the equilibrating solution and more so in waters of low salt concentration and low SAR. At all electrolyte concentration, SAR values were not attained to the equilibrium solution because of addition of Ca and Mg from mineral dissolution or supply of Ca and Mg from exchange sites. At higher TEC levels, considerable increase in exchangeable sodium percentage (ESP) was observed when it was correlated for anion exclusion and more so in calcareous sodic loam followed by saline silty loam and normal clay loam soils. Irrespective of TEC, the exchangeable sodium in all the soils increased by 2.1 to 3.8-fold and irrespective of SAR, it increased by about 1.1 to 2.1-fold, respectively. So, there is a positive interaction of TEC and SAR in sodification of soils. A positive interaction of TEC and SAR influenced the ESP build-up and CEC and silt + clay content played a major role in the visual disparity in sodification of these soils. Gapon's selectivity coefficient values were perceptible in the order of calcareous sodic loam > saline silt loam > normal clay loam. This indicates the preference of normal clay loam soils for Ca2+ + Mg2+ than that of Na+ on the exchange complex, whereas loam soil exhibited high affinity for sodium. Regression coefficient of ESR-SAR relationships was maximum for sodic loam followed by saline silty loam and normal clay loam soil. The exchange equilibrium was strongly affected by TEC of the solution phase. Variation in soil pH was gradual with respect to TEC and SAR of equilibrating solution and a sharp change was observed. At a fixed TEC, critical ESP values were observed calcareous sodic loam followed by saline silt loam and normal clay loam. On the other hand, SAReq needed for critical ESP built-up was in the order of calcareous sodic loam > saline silt loam > normal clay loam. This may be because of dissolution of calcium bearing minerals in calcareous sodic loam; and wash out of calcium and magnesium from the exchange sites for saline silt loam soil.

Examination of binocular disparity information of normal vision children

To explore the binocular disparity information for children with a normal vision based on computer-assisted evaluation system. We examined the random dot zero-order disparity, line zero-order disparity, 2nd-order disparity and random dot motion parallax for 97 children with normal vision. And 94 children reached 100＂vision disparity both in random dot zero-order disparity and line zero-order disparity (pass rate of 96.9%); all 94 cases passed the 2nd-order disparity and random dot motion parallax. Thus children with a normal vision develop their stereopsis. Key words: Vision disparity; Vision, binocular

Perceiving gloss in surfaces and images

Color Appearance Models are successfully used to model the color perception differences seen when the same stimuli are presented on different media, e.g. hard copy or a self-luminous display. It is currently unknown if the similar effects are present in gloss perception and if there is need for Gloss Appearance Models. Gloss communication, and the higher level material appearance communication is becoming more important everyday with the increase in customized manufacturing and the need for the costumer to preview a final product while short-runs, time and cost constraints prohibit the use of hard-copy proofs. Three experiments are proposed in order to analyze this phenomenon. The Gloss matching performance of observers on real objects is first going to be studied. Then, the same experiment will be repeated with synthetic images. Finally, a cross-media matching experiment will be performed, where the observers will have to match a real material with synthetic representations. The same trend was observed in the experiment using only real objects and in the cross-media situation, where a high matching accuracy was obtained for low gloss samples, and the gloss of mid and high gloss samples was underestimated. The same accuracy for low gloss samples was obtained for the experiment with only synthetic images, but mid and high gloss samples were overestimated. The sensitivity of the observers was higher when only real samples were used, it decreased when the display was used due the lack of visual disparity and multiple viewing conditions, and it was lowest on the last experiment, influenced by the multiple media and the above limitations.

Audio-Visual Perception of 3D Cinematography: An fMRI Study Using Condition-Based and Computation-Based Analyses

The use of naturalistic stimuli to probe sensory functions in the human brain is gaining increasing interest. Previous imaging studies examined brain activity associated with the processing of cinematographic material using both standard “condition-based” designs, as well as “computational” methods based on the extraction of time-varying features of the stimuli (e.g. motion). Here, we exploited both approaches to investigate the neural correlates of complex visual and auditory spatial signals in cinematography. In the first experiment, the participants watched a piece of a commercial movie presented in four blocked conditions: 3D vision with surround sounds (3D-Surround), 3D with monaural sound (3D-Mono), 2D-Surround, and 2D-Mono. In the second experiment, they watched two different segments of the movie both presented continuously in 3D-Surround. The blocked presentation served for standard condition-based analyses, while all datasets were submitted to computation-based analyses. The latter assessed where activity co-varied with visual disparity signals and the complexity of auditory multi-sources signals. The blocked analyses associated 3D viewing with the activation of the dorsal and lateral occipital cortex and superior parietal lobule, while the surround sounds activated the superior and middle temporal gyri (S/MTG). The computation-based analyses revealed the effects of absolute disparity in dorsal occipital and posterior parietal cortices and of disparity gradients in the posterior middle temporal gyrus plus the inferior frontal gyrus. The complexity of the surround sounds was associated with activity in specific sub-regions of S/MTG, even after accounting for changes of sound intensity. These results demonstrate that the processing of naturalistic audio-visual signals entails an extensive set of visual and auditory areas, and that computation-based analyses can track the contribution of complex spatial aspects characterizing such life-like stimuli.

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

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

Development of an Image Fringe Zero Selection System for Structuring Elements with Stereo Vision Disparity Measurements

When performing image operations involving Structuring Element (SE) and many transforms it is required that the outside of the image be padded with zeros or ones depending on the operation. This paper details how this can be achieved with simulated hardware using DSP Builder in Matlab with the intention of migrating the design to HDL (Hardware Description Language) and implemented on an FPGA (Field Programmable Gate Array). The design takes few resources and does not require extra memory to account for the change in size of the output image.

Age Related Macular Degeneration and Visual Disability

Age-related macular degeneration (AMD) is the leading cause of central blindness or low vision among the elderly in industrialized countries. AMD is caused by a combination of genetic and environmental factors. Among modifiable environmental risk factors, cigarette smoking has been associated with both the dry and wet forms of AMD and may increase the likelihood of worsening pre-existing AMD. Despite advances, the treatment of AMD has limitations and affected patients are often referred for low vision rehabilitation to help them cope with their remaining eyesight. The characteristic visual impairment for both forms of AMD is loss of central vision (central scotoma). This loss results in severe difficulties with reading that may be only partly compensated by magnifying glasses or screen-projection devices. The loss of central vision associated with the disease has a profound impact on patient quality of life. With progressive central visual loss, patients lose their ability to perform the more complex activities of daily living. Common vision aids include low vision filters, magnifiers, telescopes and electronic aids. Low vision rehabilitation (LVR) is a new subspecialty emerging from the traditional fields of ophthalmology, optometry, occupational therapy, and sociology, with an ever-increasing impact on the usual concepts of research, education, and services for visually impaired patients. Relatively few ophthalmologists practise LVR and fewer still routinely use prismatic image relocation (IR) in AMD patients. IR is a method of stabilizing oculomotor functions with the purpose of promoting better function of preferred retinal loci (PRLs). The aim of vision rehabilitation therapy consists in the achievement of techniques designed to improve PRL usage. The use of PRLs to compensate for diseased foveae has offered hope to these patients in regaining some function. However, in a recently published meta-analysis, prism spectacles were found to be unlikely to be of substantial benefit in people with age-related macular degeneration. Prescription filters are one of the most beneficial visual aids that people with macular degeneration. In principle, one aims both at reducing short-wavelength light to reduce glare and at identifying light with specific wavelengths (colours) preferred by the patient for viewing. In both instances, such interventions result in apparent improved contrast sensitivity and better visual acuity. Although specific tests are performed to determine the best colour, tint, lens material, and type of frame for the patient's need, no scientific protocol has been developed so far to assist in prescribing tinted or selective transmission lenses . Magnifying optical lenses are available in a wide range of dioptric powers and are made from materials that correct for weight (plastic), thickness (high index), spherical aberrations (aspherical), and variable light intensities (photochromatic). These lenses can be used as loose lenses, mounted on optical frames, or used with a wide variety of attachments. As the dioptric power of plus lenses increases, the viewing distance of the target decreases, hence their usefulness mainly for tasks requiring near resolution acuity, like reading. Magnification can also be achieved with the use of telescopic devices that are built of two or more plus and (or) minus (minifying) optical lenses. Normal resolution acuity levels can be achieved with these devices for all viewing distances. Therefore, all telescopic devices are useful only for stationary patient tasks that do not require mobility and orientation. Electronic magnification has the great advantage over plus lenses of producing an acuity reserve enabling reading skills for almost all levels of visual acuity. The additional benefit provided is preservation of binocularity, even at high levels of visual disparity between the two eyes. Vision rehabilitation can help patients to maximize their remaining vision and adapt to activities of daily living. The support of the patient's social network is critical to patient's well-being as patients adjust to being partially sighted.

Treatment with individual orbital wall implants in humans – 1-Year ophthalmologic evaluation

Background In 2009 a method of creating individual, patient specific orbital wall implants using rapid prototyping (RP) was shown in a preliminary human study. That study showed that it is financially viable to produce anatomical models and that this technology could be used in the repair of orbital floor fractures. Materials and methods In this study, 24 consecutive subjects who had sustained orbital fractures (14 males, 6 females) without any coexisting central nervous system or globe injury were assessed post-operatively. The first series of 12 patients, recruited during the period 2005–2006, were treated with classical method (CM) of forming titanium mesh by manual manipulation, based on individual subjective assessment of the extent and shape of damaged orbital walls. The following 12 cases, recruited between 2007 and 2008, were treated with patient specific titanium mesh implants designed with an RP method. Early (2 weeks) and late (12 months) follow-up was performed. Patients were evaluated by binocular single vision (BSV) test and an assessment of eye globe motility. Results The superiority of the RP treatment method over CM was shown on the basis of early results when BSV loss area and reduction of vertical visual disparity (VVD) in upgaze were considered. Better outcomes for the RP group were confirmed in the late follow-up results which showed a reduction of BSV loss area, correction of primary globe position and a very significant improvement in upgaze. Conclusions One-year post-operatively, functional assessment of pre-bent individual implants of the orbital wall has shown the technique to be a predictable reconstruction method. Nevertheless longer follow-up and an increase in the number of cases treated are required for the full evaluation of the technique.

Reducing Visual Health Disparities in At-Risk Community Health Center Populations

Community health centers (CHCs) have an impressive record of addressing health disparities through consistently delivering high-quality and affordable care in a culturally competent manner, while also producing cost savings to the nation's healthcare system. Thus CHCs are optimally positioned to reduce visual health disparities and improve visual health outcomes by being included in the primary care services that they deliver. An estimated three million health center patients have risk factors for vision disorders and eye disease, yet a recent policy briefing survey conducted by The George Washington University reported that about 20 percent of centers provide on-site eye and vision care.

What technical barriers exist for real‐time fluoroscopic and video image overlay in robotic surgery?

A hypothetical advantage of the da Vinci console is its ability to integrate multiple visual data sources. Current platforms for augmented reality surgery fuse pre-operative radiographic studies but are limited with their ability to update with intra-operative imaging. The aim of our study was to evaluate the feasibility of real-time radiographic image overlay with current technology. S-video composite output from a fluoroscopic C-arm was superimposed onto the video output of the da Vinci device. Image superimposition disparity measurements were evaluated in a bench model. The feasibility of robotic dissection assisted by real-time cholangiogram and intravenous pyelogram was evaluated. Image alignment resulted in a radiographic blind spot and image disparity with severely limited application in an in vivo model. External collisions of the robotic device and visual disparity in multiple planes negate the current implementation of fluoroscopic overlay and will require more elegant methods of computer-assisted registration.

Visual Functioning of Individuals and Communities: A Conceptual Framework

Abstract: The prevalence of visual impairment and blindness increases dramatically with advancing age. The major diseases that cause visual impairment and blindness, speci fi cally cataract, macular degeneration, and glaucoma, are age-related. The number of visually impaired Americans older than 40 years is projected to double by 2030. Half of all cases of blindness may be preventable. Research in the area of vision has developed into ophthalmologically de fi ned silos that follow speci fi c diseases or study subparts of the eye. To overcome the limitations of current subspecialty conceptualization of vision prob-lems, it is necessary to develop new models that can expand the current research paradigms in new directions. This review paper details literature within a conceptual model to explain the increases in visual impairment, the age and other demo-graphic disparities in prevalence, and the lack of vision screening, treatment, and rehabilitation. At the core of the conceptu al framework are the twin phenomena of vision health as perceived by the individual and vision health as clinically-measured. Other domains of the framework include adaptation, vision demands, quality of life, and cues to using vision services such as access to care and social support. The framework incorporates multiple demographic, behavioral, and social factors that infl uence the vision health of individuals and communities. Areas of future research include population-based study of the knowledge, attitudes, and practices regarding vision health among both individuals and providers and multi-pronged interventions aimed at the individual, provider, organizational, and community levels to improve visual function.

A Map for Horizontal Disparity in Monkey V2

The perception of visual depth is determined by integration of spatial disparities of inputs from the two eyes. Single cells in visual cortex of monkeys are known to respond to specific binocular disparities; however, little is known about their functional organization. We now show, using intrinsic signal optical imaging and single-unit physiology, that, in the thick stripe compartments of the second visual area (V2), there is a clustered organization of Near cells and Far cells, and moreover, there are topographic maps for Near to Far disparities within V2. Our findings suggest that maps for visual disparity are calculated in V2, and demonstrate parallels in functional organization between the thin, pale, and thick stripes of V2.

Reshaping the motor car

In previous work on aesthetics and the urban road environment, the authors drew attention to the growing visual disparity between the modern automobile and its urban setting, and suggested a new design approach which would provide some measure of visual integration of cars into the urban landscape, and make them less alien to pedestrians. Here, the authors broaden their critique, exploring the cultural implications of car design, and how cars might be used more effectively to promote mobility while reducing their impact on the urban environment. They argue that conventional fantasies of freedom, speed and power on which the outward form of the modern automobile is presently based, are inappropriate during a period of growing congestion, urban traffic blight, climate change and diminishing fuel resources. The role and function of the automobile must change, and this in turn implies a change in ‘car culture’. Certain processes are already at work, which will assist change in the proposed direction independently of what people actually want. The authors propose additionally a reshaping of the external form of the private car to reflect a new and more environmentally appropriate role, helping, we suggest, to decouple its image from outworn fantasies, and bringing it into the public realm as a more sociable apparatus for modern living.

Effects of an eyeglass-free 3-D display on the human visual system.

To investigate the effect on the human visual system of viewing 3-dimensional (3-D) computer graphics (CG) images with an eyeglass-free rear-cross-lenticular-type 3-D display. Positive accommodation velocity (GRAD) during the accommodative step response was measured in ten healthy young adults before and after they viewed CG images. Although the distance between the viewer and the 3-D display was 600 mm, the apparent distance between the viewer and the virtual object was varied (515, 600, and 722 mm) by changing the visual disparity. A significant slowdown of average GRAD was observed by 60 min after a 30-min 3-D viewing of 3-D CG images [P<0.05, analysis of variance (ANOVA)] but not after a 30-min viewing of the CG images on a 2-D display or after a 15-min 3-D viewing. When the virtual object was at 722 mm, a significant slowdown of average GRAD was observed only at 30 min after the 30-min 3-D viewing (P<0.05, ANOVA). When the virtual object was at 515 mm, a significant slowdown of average GRAD was observed at 30 and 60 min after the 3-D viewing (P<0.05, ANOVA). The effect on the human visual system of 3-D viewing of 3-D CG images depends on both the duration of the viewing and the apparent distance between the viewer and the virtual objects.

Nonlinear blind source separation using kernels

We derive a new method for solving nonlinear blind source separation (BSS) problems by exploiting second-order statistics in a kernel induced feature space. This paper extends a new and efficient closed-form linear algorithm to the nonlinear domain using the kernel trick originally applied in support vector machines (SVMs). This technique could likewise be applied to other linear covariance-based source separation algorithms. Experiments on realistic nonlinear mixtures of speech signals, gas multisensor data, and visual disparity data illustrate the applicability of our approach.

A controlled study of vitrectomy for diabetic macular edema

PURPOSE: To compare eyes that underwent surgery with untreated fellow eyes to assess the efficacy of vitrectomy for diabetic macular edema. METHODS: In a nonrandomized clinical trial, seven adult patients with mean age of 53 years (range 42 to 64) and the same degree and duration of diabetic macular edema in both eyes were followed up for more than 5 months after unilateral vitrectomy. The treated eye was selected at random, but if visual disparity between the both eyes was more than 3 lines, we operated on the worse side. We compared the preoperative and postoperative foveal thicknesses (the distance between the inner retinal surface and retinal pigment epithelium) and the best-corrected visual acuity by a certified examiner with those of the untreated fellow eye. RESULTS: In the seven eyes that underwent surgery, the foveal thickness decreased by an average of 622 to 269 μm ( P = .027, Wilcoxon signed-rank test). In the fellow eyes, the average decrease in foveal thickness was from 617 to 546 μm ( P = .176, Wilcoxon signed-rank test). The best-corrected postoperative visual acuity in the eyes that underwent surgery improved more than 2 lines in four eyes (57%) and remained the same in three eyes (43%). In the fellow eyes, it improved more than 2 lines in one eye (14%), remained the same in three eyes (43%), and decreased more than 2 lines in three eyes (43%). CONCLUSION: In eyes with diabetic macular edema that underwent surgery, the foveal thickness significantly decreased after vitrectomy. Vitrectomy may be effective for treating diabetic macular edema.

Effect of water quality on exchange phase — solution phase behavior of three soils

The effect of total electrolyte concentration (TEC) and sodium adsorption ratio (SAR) of water on ESR-SAR relationships of clay (Typic Haplustert), clay loam (Vertic Haplustept) and silt loam (Lithic Haplorthent) soils was studied in a laboratory experiment. Twenty four solutions, encompassing four TEC levels viz., 5, 10, 20, and 50 mmolc l—1 and six SAR levels viz., 2.5, 5, 10, 15, 20, and 30 mmol1/2l—1/2 were synthesized to equilibrate the soil samples using pure chloride salts of calcium, magnesium, and sodium at Mg:Ca = 1:2. SAR of equilibrium solution decreased as compared to the equilibrating solution and more so in waters of low salt concentration and high SAR. At low electrolyte concentration, high SAR values were not attained in the equilibrium solution because of addition of calcium and magnesium from the mineral dissolution and from the exchange phase. Irrespective of TEC, exchangeable sodium in all the soils increased by about 4.5 to 5-fold and irrespective of SAR, it increased by about 1.4- to 1.8-fold. A positive interaction of TEC and SAR influenced the ESP build-up and CEC played a major role in the visual disparity in sodication of these soils. At higher TEC levels, considerable increase in ESP was observed when it was corrected for anion exclusion and more so in silt loam followed by clay loam and clay soils. The values for Gapons' constant were in the range 0.0110—0.0176, 0.0142—0.0246, and 0.0189—0.0344 mmol—1/2l1/2 in clay, clay loam, and silt loam soils, respectively. Increase in TEC from 5 to 50 mmolc l—1 resulted in 5.84, 8.33, and 9.77 % decrease in Gapons' constant of clay, clay loam, and silt loam soils, respectively. The soils exhibited differential affinity for Ca2+, Mg2+ or Na+ under different quality waters. Regression coefficients of ESR-SAR relationship were lower for low TEC as compared with high TEC waters. The exchange equilibrium was strongly affected by TEC of the solution phase. Variation in soil pH was gradual with respect to TEC and SAR of equilibrating solution and no sharp change was observed. Soluble salt concentration was doubled upon equilibration with low salt waters at all SAR levels in all the soils. However, the salt concentration remained unchanged upon equilibration with high salt waters. Considering pH 8.5 a boundary between soil salinity and sodicity, ESP values attained at TEC 5 mmolc l—1 were 7.34, 8.02, and 14.32 for clay, clay loam, and silt loam soils, respectively.