Sign Of Disparity Research Articles

Sociolinguistics Stance of Language as the Pedestal for Gender Inequality in the Kurya of Tanzania

This study was about sociolinguistics stance of language as the pedestal for gender inequality in the Kurya of Tanzania. The study employed the case study design using the Kurya speech community from Kitenga Village of Bumera Ward in Tarime District as a case. The study used the qualitative approach in which words and sentences are being applied in determining inequality between men and women apart from their natural biological sexes. Purposive sampling was applied in selecting the Kurya speech community because it is one of communities in Tanzania whereby gender inequality seems to be normal life styles. The study employed random sampling in which only 10 children of 10 to 20 years and 10 adults of 40 to 60 years were sampled. The study applied two instruments of data collection namely unstructured observation and focus group discussion. The study found that the Kurya speech community provided evidences on how language is a benchmark sign of gender disparity among men and women. Based on the findings, the study recommended that gender inequality and inequity should be demystified out in the globalized world so that such practices should be mitigated. Women and men should be considered equal as human beings.

Contrast-reversed binocular dot-pairs in random-dot stereograms for depth perception in central visual field: Probing the dynamics of feedforward-feedback processes in visual inference

In a random-dot stereogram (RDS), the spatial disparities between the interocularly corresponding black and white random dots determine the depths of object surfaces. If a black dot in one monocular image corresponds to a white dot in the other, disparity-tuned neurons in primary visual cortex (V1) respond as if their preferred disparities become non-preferred and vice versa, reversing the disparity sign reported to higher visual areas. Reversed depth is perceptible in the peripheral but not the central visual field. This study demonstrates that, in central vision, adding contrast-reversed dots to a noisy RDS (containing the normal contrast-matched dots) can augment or degrade depth perception. Augmentation occurs when the reversed depth signals are congruent with the normal depth signals to report the same disparity sign, and occurs regardless of the viewing duration. Degradation occurs when the reversed and normal depth signals are incongruent with each other and when the RDS is viewed briefly. These phenomena reflect the Feedforward-Feedback-Verify-and-reWeight (FFVW) process for visual inference in central vision, and are consistent with the central-peripheral dichotomy that central vision has a stronger top-down feedback from higher to lower brain areas to disambiguate noisy and ambiguous inputs from V1. When a RDS is viewed too briefly for feedback, augmentation and degradation work by adding the reversed depth signals from contrast-reversed dots to the feedforward, normal, depth signals. With a sufficiently long viewing duration, the feedback vetoes incongruent reversed depth signals and amends or completes the imperfect, but congruent, reversed depth signals by analysis-by-synthesis computation.

AB002. The role of equivalent internal noise and processing efficiency in individual differences in stereoacuity

Background: The human visual system can use binocular disparity to make depth judgements. Previous studies looking at the normal population have found a wide range in ability to perform depth-polarity tasks. We explored if these large individual differences are also present when using a depth increment paradigm, and if they depend on the sign of disparity.

A New Method to Detect Moving Targets

In the moving target detection, there are a lot of methods. But the effects of those algorithms are limited, especially in complex environment. This paper putts forward a new method to detect moving targets, which uses virtual binocular disparity. It is called virtual because the environment uses one camera but the theory is about two cameras. Virtual binocular disparity algorithm regards moving targets as static targets under two cameras. It uses two neighboring images, the current frame image and the next frame image. The algorithm looks the two images as two static images under two cameras, then uses stereo match theory to calculate the disparity of the neighboring images. Because the background of the two images is the same, the disparity of their background is about zero. And the disparity of moving targets is positive or negative. The sign of disparity means the direction of targets moving. So we can use the sign of disparity to distinguish the targets moving in different directions. The direction detected out will be helpful for subsequent work, for example, targets tracking and counting etc. This algorithm fully uses the continuity property of moving targets, so it can have good effect. In the end of the paper, experiments are used to prove the algorithm.

Changes in Binocular Color Fusion Limit Caused by Different Disparities

When the color asymmetry between the left and right eyes exceeds a threshold value, named binocular color fusion limit, the color rivalry is said to occur. For stereoscopic displays, the horizontal disparity is the most important information to produce depth perception. When the stereo pair stimuli are presented separately to both eyes with disparities and those two stimuli also differ in color but share an iso-luminance polarity, it is possible for stereopsis and color rivalry to coexist. In this paper, we conducted a psychophysical experiment to quantitatively measure the color fusion limit at different disparity levels. In particular, it examined how disparities affect the binocular color fusion limit. A binocular color fusion limit was measured at five relative disparity levels: 0, ±60, and ±120 arc minutes for five sample color points, which were selected from the 1976 CIE u'v' chromaticity diagram. The experimental results show that the color fusion limit for each sample point varies with the disparity magnitude, disparity sign, and color direction. It is new research finding that the color fusion limit increases as the disparity increases from -120 to +120 arc minutes. The average color fusion limit ranges from 0.036 to 0.064 in terms of Euclidean distance in the u'v' chromaticity diagram (ΔE u'v' ). The new finding shows that the human eye has different information processing mechanisms for crossed disparity (sign -) and uncrossed disparity (sign +), and uncrossed disparity can contribute to color fusion. We suggest that the color fusion limit varies with the color direction, but it has nothing to do with the distribution of cone cells. The color fusion limit was quantified by using ellipses in the chromaticity diagram, and the axis of the ellipses ranges from 0.017 to 0.145 ΔE u'v' . The experiments and data analysis in this paper indicate that the binocular disparity fusion affects binocular color fusion. This research result can strongly support 3D system design and 3D content creation.

Stereoscopic processing of crossed and uncrossed disparities in the human visual cortex

BackgroundBinocular disparity provides a powerful cue for depth perception in a stereoscopic environment. Despite increasing knowledge of the cortical areas that process disparity from neuroimaging studies, the neural mechanism underlying disparity sign processing [crossed disparity (CD)/uncrossed disparity (UD)] is still poorly understood. In the present study, functional magnetic resonance imaging (fMRI) was used to explore different neural features that are relevant to disparity-sign processing.MethodsWe performed an fMRI experiment on 27 right-handed healthy human volunteers by using both general linear model (GLM) and multi-voxel pattern analysis (MVPA) methods. First, GLM was used to determine the cortical areas that displayed different responses to different disparity signs. Second, MVPA was used to determine how the cortical areas discriminate different disparity signs.ResultsThe GLM analysis results indicated that shapes with UD induced significantly stronger activity in the sub-region (LO) of the lateral occipital cortex (LOC) than those with CD. The results of MVPA based on region of interest indicated that areas V3d and V3A displayed higher accuracy in the discrimination of crossed and uncrossed disparities than LOC. The results of searchlight-based MVPA indicated that the dorsal visual cortex showed significantly higher prediction accuracy than the ventral visual cortex and the sub-region LO of LOC showed high accuracy in the discrimination of crossed and uncrossed disparities.ConclusionsThe results may suggest the dorsal visual areas are more discriminative to the disparity signs than the ventral visual areas although they are not sensitive to the disparity sign processing. Moreover, the LO in the ventral visual cortex is relevant to the recognition of shapes with different disparity signs and discriminative to the disparity sign.

Stereoscopic Segmentation Cues Improve Visual Timing Performance in Spatiotemporally Cluttered Environments.

Recently, Cass and Van der Burg demonstrated that temporal order judgment (TOJ) precision could be profoundly impaired by the mere presence of dynamic visual clutter elsewhere in the visual field. This study examines whether presenting target and distractor objects in different depth planes might ameliorate this remote temporal camouflage (RTC) effect. TOJ thresholds were measured under static and dynamic (flickering) distractor conditions. In Experiment 1, targets were presented at zero, crossed, or uncrossed disparity, with distractors fixed at zero disparity. Thresholds were significantly elevated under dynamic compared with static contextual conditions, replicating the RTC effect. Crossed but not uncrossed disparity targets improved performance in dynamic distractor contexts, which otherwise produce substantial RTC. In Experiment 2, the assignment of disparity was reversed: targets fixed at zero disparity; distractors crossed, uncrossed, or zero. Under these conditions, thresholds improved significantly in the nonzero distractor disparity conditions. These results indicate that presenting target and distractor objects in different planes can significantly improve TOJ performance in dynamic conditions. In Experiment 3, targets were each presented with a different sign of disparity (e.g., one crossed and the other uncrossed), with no resulting performance benefits. Results suggest that disparity can be used to alleviate the performance-diminishing effects of RTC, but only if both targets constitute a single and unique disparity-defined surface.

Separation of foreground and background from light field using gradient information.

Studies of computer vision or machine vision applications using a light field camera have been increasing in recent years. However, the abilities that the light field camera has are not fully used in these applications. In this paper, we propose a method for direct separation of foreground and background that uses the gradient information and can be used in various applications such as pre-processing. From an optical phenomenon whereby the bundles of rays from the background are flipped, we derive that the disparity sign of the background in the captured three-dimensional scene has the opposite disparity sign of the foreground. Using the majority-weighted voting algorithm based on the gradient information with the Lambertian assumption and the gradient constraint, the foreground and background can be separated at each pixel. In regard to pre-processing, the proposed method can be used for various applications such as occlusion and saliency detection, disparity estimation, and so on. Experimental results with the EPFL light field dataset and Stanford Lytro light field dataset show that the proposed method achieves better performance in terms of the occlusion detection, and thus can be effectively used in pre-processing for saliency detection and disparity estimation.

Accommodation and pupil responses to random-dot stereograms

We investigated the dynamics of accommodative and pupillary responses to random-dot stereograms presented in crossed and uncrossed disparity in six visually normal young adult subjects (mean age=25.8±3.1 years). Accommodation and pupil measures were monitored monocularly with a custom built photorefraction system while subjects fixated at the center of a random-dot stereogram. On each trial, the stereogram initially depicted a flat plane and then changed to depict a sinusoidal corrugation in depth while fixation remained constant. Increase in disparity specified depth resulted in pupil constriction during both crossed and uncrossed disparity presentations. The change in pupil size between crossed and uncrossed disparity conditions was not significantly different (p>0.05). The change in pupil size was also accompanied by a small concomitant increase in accommodation. In addition, the dynamic properties of pupil responses varied as a function of their initial (starting) diameter. The finding that accommodation and pupil responses increased with disparity regardless of the sign of retinal disparity suggests that these responses were driven by apparent depth rather than shifts in mean simulated distance of the stimulus. Presumably the need for the increased depth of focus when viewing stimuli extended in depth results in pupil constriction which also results in a concomitant change in accommodation. Starting position effects in pupil response confirm the non-linearity in the operating range of the pupil.

Binocular Disparity Magnitude Affects Perceived Depth Magnitude despite Inversion of Depth Order

The hollow-face illusion involves a misperception of depth order: our perception follows our top-down knowledge that faces are convex, even though bottom-up depth information reflects the actual concave surface structure. While pictorial cues can be ambiguous, stereopsis should unambiguously indicate the actual depth order. We used computer-generated stereo images to investigate how, if at all, the sign and magnitude of binocular disparities affect the perceived depth of the illusory convex face. In experiment 1 participants adjusted the disparity of a convex comparison face until it matched a reference face. The reference face was either convex or hollow and had binocular disparities consistent with an average face or had disparities exaggerated, consistent with a face stretched in depth. We observed that apparent depth increased with disparity magnitude, even when the hollow faces were seen as convex (ie when perceived depth order was inconsistent with disparity sign). As expected, concave faces appeared flatter than convex faces, suggesting that disparity sign also affects perceived depth. In experiment 2, participants were presented with pairs of real and illusory convex faces. In each case, their task was to judge which of the two stimuli appeared to have the greater depth. Hollow faces with exaggerated disparities were again perceived as deeper.

Evidence for relative disparity matching in the perception of an ambiguous stereogram

To compute depth from binocular disparity, the visual system must correctly link corresponding points between two images, given multiple possible correspondences. Typically, model solutions to this problem use some form of local spatial smoothing, with many physiologically inspired models doing so implicitly, through the use of local cross-correlation-like procedures. In this paper we show that implicit smoothing, without the explicit consideration of relative disparity, cannot account for biases in the perception of a novel ambiguous stereo stimulus. Observers viewed a stereogram consisting of multiple strips of periodic random-dot patterns, perceived as either a slanted surface, or a triangular wedge in depth, and reported their perception in a 4AFC task. Biases in the perception of this stimulus are shown to depend upon the stimulus configuration in its entirety, and cannot be accounted for by low-level preferences for disparity sign. Such results are not consistent with local smoothing effects arising solely at the level of cross-correlation-like absolute disparity detectors. Instead, our results suggest the presence of smoothing constraints that consider the differences in disparity between neighboring image regions. These results further suggest that such smoothing generally biases matching toward solutions that minimize relative disparity, regardless of the presence of changes in disparity sign.

Projected disparity, not horizontal disparity, predicts stereo depth of 1-D patterns

Binocular disparities have a straightforward geometric relation to object depth, but the computation that humans use to turn disparity signals into depth percepts is neither straightforward nor well understood. One seemingly solid result, which came out of Wheatstone’s work in the 1830s, is that the sign and magnitude of horizontal disparity predict the perceived depth of an object: ‘positive’ horizontal disparities yield the perception of ‘far’ depth, ‘negative’ horizontal disparities yield the perception of ‘near’ depth, and variations in the magnitude of horizontal disparity monotonically increase or decrease the perceived extent of depth. Here we show that this classic link between horizontal disparity and the perception of ‘near’ versus ‘far’ breaks down when the stimuli are one-dimensional. For these stimuli, horizontal is not a privileged disparity direction. Instead of relying on horizontal disparities to determine their depth relative to that of two-dimensional stimuli, the visual system uses a disparity calculation that is non-veridical yet well suited to deal with the joint coding of disparity and orientation.

Asymmetric interaction between motion and stereopsis revealed by concurrent adaptation

Although contingent aftereffects between motion and stereopsis have been referred to as behavioral evidence for the joint processing of the two features, the reciprocal nature of encoding the two features has not been systematically studied. Using a novel form of concurrent adaptation, we probed the perception of direction- and disparity-defined coherent surfaces in parallel before and after adaptation to a stimulus that moved in a single direction at a particular binocular disparity. Contrary to earlier findings, we found a strong asymmetry between motion and stereopsis: the detection of disparity signal after adaptation was more impaired when the test stimulus was moving in the adapted direction than in the non-adapted direction, whereas the test disparity hardly affected the detection of coherent motion. However, motion adaptation became dependent on disparity when we added another surface that was moving in the opposite direction at the opposite sign of disparity to those of the original adaptor, as in previous studies of contingent aftereffects. The observed asymmetric contingency between motion and disparity adaptation urges the reinterpretation of previously reported contingent aftereffects and suggests a corresponding asymmetry between neural mechanisms devoted to processing of motion and stereopsis in human visual cortex.

Multivoxel Pattern Selectivity for Perceptually Relevant Binocular Disparities in the Human Brain

Processing of binocular disparity is thought to be widespread throughout cortex, highlighting its importance for perception and action. Yet the computations and functional roles underlying this activity across areas remain largely unknown. Here, we trace the neural representations mediating depth perception across human brain areas using multivariate analysis methods and high-resolution imaging. Presenting disparity-defined planes, we determine functional magnetic resonance imaging (fMRI) selectivity to near versus far depth positions. First, we test the perceptual relevance of this selectivity, comparing the pattern-based decoding of fMRI responses evoked by random dot stereograms that support depth perception (correlated RDS) with the decoding of stimuli containing disparities to which the perceptual system is blind (anticorrelated RDS). Preferential disparity selectivity for correlated stimuli in dorsal (visual and parietal) areas and higher ventral area LO (lateral occipital area) suggests encoding of perceptually relevant information, in contrast to early (V1, V2) and intermediate ventral (V3v, V4) visual cortical areas that show similar selectivity for both correlated and anticorrelated stimuli. Second, manipulating disparity parametrically, we show that dorsal areas encode the metric disparity structure of the viewed stimuli (i.e., disparity magnitude), whereas ventral area LO appears to represent depth position in a categorical manner (i.e., disparity sign). Our findings suggest that activity in both visual streams is commensurate with the use of disparity for depth perception but the neural computations may differ. Intriguingly, perceptually relevant responses in the dorsal stream are tuned to disparity content and emerge at a comparatively earlier stage than categorical representations for depth position in the ventral stream.

The Effects of Interocular Correlation and Contrast on Stereoscopic Depth Magnitude Estimation

Decreasing the interocular correlation in random dot stereograms elevates disparity detection thresholds. Whether decorrelation also affects perceived depth from suprathreshold disparity magnitudes is unknown. The present study investigated the effects of interocular correlation and contrast on the magnitude of perceived depth in suprathreshold random dot stereograms. Stereoscopic depth magnitude estimation as a function of percent interocular correlation of dynamic random dot stimuli was measured for five human subjects with clinically normal binocular vision. Each trial's stimulus was randomly assigned one of two magnitudes of either crossed or uncrossed relative disparity. Subjects verbally reported the direction and magnitude of perceived relative depth for each trial using a modulus-free scale. Normalized depth magnitude estimations as a function of the percent interocular correlation demonstrated the relationship between perceived depth, interocular correlation and contrast within subjects. Inter-subject variability was examined with comparisons of data across subjects. The depth magnitude perceived for a given magnitude of disparity declined as the percent of correlation of elements between the eyes decreased for both crossed and uncrossed directions. The effect generally was greater for uncrossed disparities and lower contrast. Some subjects demonstrated asymmetries in perceived depth for crossed vs. uncrossed disparities of the same magnitude. Magnitude estimation of suprathreshold stimuli provided a method of studying performance characteristics of stereoscopic depth perception across the range of functional disparities. Differences found in depth magnitude estimation as a function of the sign of disparity suggest that the neural mechanisms underlying depth perception from uncrossed disparity are more sensitive to image decorrelation, particularly at low contrast, than the mechanisms underlying depth estimation from crossed disparity. These results could occur from differences in near and far disparity-sensitive neurons, from the geometrical relationship between disparity and physical distance in normal viewing, or from the response measure independent of perception.

Reglamentos de bibliotecas públicas: ideas para elaborarlos

Public libraries are managed by inside standards, sometimes called rules, codes of behaviour or user guidelines. The variety of terms to mention them is only the first sign of disparity. What is the good of them?, what does characterize good rules?, what steps must fulfil rules to be legal?, which sides of the library usage are usally included?, what do they forget? To answer to these questions we have taken 40 different rules, from two extreme backgrounds, Catalonia and the United States, and we analyse them. The result is a synthesis thought to help public library managers to write rules.

Illusory depth perception of oblique lines produced by overlaid vertical disparity

Our visual system matches images from both eyes to establish a single view and stereo depth even when they contain a certain amount of vertical disparity. This paper demonstrates a new stereo effect showing an aspect of vertical disparity processing. When oblique lines without disparity are overlaid with sparse random dots with vertical disparity, the lines look closer or farther in depth. The characteristics of this stereo illusion were experimentally investigated. The results showed that the sign of the perceived depth of the oblique lines depended on the combination of the line orientation and the vertical disparity sign, and that the amount of perceived depth became larger as the line orientation became more horizontal. The depth illusion robustly existed even under conditions that ruled out eye movements (i.e., vertical vergence and cyclovergence) by local-parallel or brief presentations of the stereo figures. This phenomenon suggests that the visual system locally measures vertical disparity and is not simply tolerating a small amount of vertical disparity. Stereo capture of vertical disparity and horizontal matching after vertical image shifts were proposed as possible explanations for the depth illusion.

Stereoacuity thresholds in the presence of a reference surface

With isolated binocular targets, the best depth discrimination is found in the fixation plane (Blakemore, C., Journal of Physiology 211 (1970) 599). More recent studies have suggested that stereoscopic thresholds are not always a simple function of absolute disparity, but depend on the relative disparities in the stimulus. Here, we explored the effects of relative disparity in more detail, taking particular care to control for the possibility that subjects might change their binocular eye position or exploit monocular information provided by additional reference cues. Subjects judged the depth of a vertical target line presented above a comparison line in a blank window within a fronto-parallel reference surface composed of randomly positioned dots. On individual trials, the reference surface was presented at one of three disparities (−10, 0 and +10 arc min). To control for changes in binocular eye position, exposure duration was 150 ms, and experimental conditions with different disparities of the reference surface and comparison line were randomly interleaved. To control for monocular cues, changes in threshold were determined with respect to a disparity noise condition that was in all ways identical to the reference plane condition, except that the disparities of the dots were randomly assigned between 10 and +10 arc min. Stereo-thresholds were lowered by a factor of about 2 when the surface was at the same depth as the comparison line. Thresholds were also lowered when the comparison disparity was close to the same depth as the reference surface, but were often raised when the comparison disparity had the opposite disparity sign. These results provide unequivocal evidence that the fundamental sensitivity of the disparity detecting system can be influenced by relative disparity cues that are not related to the task.

Weighted directional energy model of human stereo correspondence

Previous work [Prince, S. J. D, & Eagle, R. A. (1999). Size-disparity correlation in human binocular depth perception. Proceedings of the Royal Society: Biological Sciences, 266, 1361–1365] has demonstrated that disparity sign discrimination performance in isolated bandpass patterns is supported at disparities much larger than a phase disparity model might predict. One possibility is that this extended performance relies on a separate second-order system [Hess, R. F., & Wilcox, L. M. (1994). Linear and non-linear filtering in stereopsis. Vision Research, 34, 2431–2438]. Here, a ‘weighted directional energy’ model is developed which explains a large body of crossed versus uncrossed disparity discrimination data with a single mechanism. This model assumes a population of binocular complex cells at every image point with a range of position disparity shifts. These cells sample a local energy function which is weighted so that energy at large disparities is relatively attenuated. Disparity sign is determined by summing and comparing energy at crossed and uncrossed disparities in the presence of noise. The model qualitatively predicts matching data for one-dimensional Gabor stimuli. This scheme also predicts DMax in Gabor stimuli and filtered noise. Moreover, a range of ‘non-linear’ phenomena, in which disparity is perceived from contrast envelope information alone, can be explained. The weighted directional energy model presents a biologically plausible, parsimonious explanation of matching behaviour in bandpass stimuli for both ‘first-order’ and ‘second-order’ stimuli which obviates the need for multiple mechanisms in stereo correspondence.

The scintillating grid illusion in stereo-depth

The dark scintillating dots occurring on a gray-on-black, modified Hermann grid [Schrauf, M., Lingelbach, B., & Wist, E. R. (1997). The scintillating grid illusion. Vision Research, 37, 1033–1038] were studied in stereo-depth by assigning various degrees of disparity to the white inducing disks. Dependent on the sign of disparity, the disks and the dark illusory spots within them appeared to lie either in the same plane, in front of, or behind the grid. At zero disparity, illusory strength was maximum and was the same for stereo, binocular and monocular viewing. With increasing disparity, the illusion became progressively weaker; however, the decrease for stereo-patterns was significantly less than for control patterns presented binocularly or monocularly. These results suggest a central contribution to the scintillation effect.