Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Vision Disparity”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,387 records · Page 77Linked to original sources
PubMed1997

Influence of the luminance and opponent chromatic channels on stereopsis with random-dot stereograms.

The present work examines the relationship between random-dot stereograms (via the disparity range parameter) and color-vision mechanisms (via the luminance channel and red-green and tritan directions at isoluminance). The results clearly indicate that the variations in the stereograms along red-green confusion lines contribute to stereopsis. Stereoscopic perception depends on spatial information for stereograms generated with variations along tritan confusion lines. For observers who perceive stereopsis via tritan directions, the results show a gradation in the disparity range, with the disparity range for stereograms generated by luminance variations being greater than for stereograms generated in red-green directions; the latter range is, in turn, greater than for stereograms generated along tritan directions.

Color Perception↗
PubMed1999

Stereoscopic occlusion and the aperture problem for motion: a new solution.

Recent work has shown that the ability of moving contour terminators to determine the perceived motion of untextured contours is strongly constrained by whether contour terminators are classified as intrinsic (belonging to a moving contour) or extrinsic (belonging to a surface occluding a moving contour). It has also been demonstrated that stereopsis can play a decisive role in this classification. Specifically, Shimojo, Silverman and Nakayama (1989, Vision Research 29, 619-626) argued that the efficacy of stereopsis in classifying moving contour terminators as intrinsic or extrinsic stemmed from the relative depth relationships specified by binocular disparity. Here, evidence is presented which demonstrates that the visual system relies on the presence of unpaired contour terminators to classify stereoscopic contour terminators as extrinsic. The author shows that the tendency to perceive untextured contours translating in a single rectangular aperture in a direction parallel to the longer axis of the aperture (the barberpole illusion) was not abolished by stereoscopic depth differences when the contour terminators were interocularly paired. However, the illusion was abolished when the contours terminators along the longer axis of the aperture were interocularly unpaired. Moreover, contours translated within a square aperture revealed a systematic shift towards the direction of motion signaled by the binocularly paired contour terminators along the horizontal edges of the aperture. These results demonstrate that the classification of stereoscopic contour terminators along an extrinsic-intrinsic dimension results from the presence of local, unpaired contour terminators rather than the relative depth or disparity differences per se, or via the global integration of contour terminators across multiple apertures when multiple apertures are present.

Depth Perception↗
PubMedDate not supplied

Encoding of both vertical and horizontal disparity in random-dot stereograms by Wulst neurons of awake barn owls.

In binocular vision, the lateral displacement of the eyes gives rise to both horizontal and vertical disparities between the images projected onto the left and right retinae. While it is well known that horizontal disparity is exploited by the binocular visual system of birds and mammals to enable depth perception, the role of vertical disparity is still largely unclear. In this study, neuronal activity in the visual forebrain (visual Wulst) of behaving barn owls to vertical disparity was investigated. Single-unit responses to global random-dot stereograms (RDS) were recorded with chronically implanted electrodes and transmitted via radiotelemetry. Nearly half of the cells investigated (44%, 16/36) varied the discharge as a function of vertical disparity. Like horizontal-disparity tuning profiles, vertical-disparity tuning curves typically exhibited periodic modulation with side peaks flanking a prominent main peak, and thus, could be fitted well with a Gabor function. This indicates that tuning to vertical disparity was not caused by disrupting horizontal-disparity tuning via vertical stimulus offset, but by classical disparity detectors whose orientation tuning was tilted. When tested with horizontal in addition to vertical disparity, almost all cells investigated (92%, 12/13) were tuned to both kinds of disparity. The emergence of disparity detectors sensitive in two dimensions (horizontal and vertical) is discussed within the framework of the disparity energy model.

Animals↗
PubMed1994

Stereo vision by self-organization.

We propose a new algorithm for stereoscopic depth perception, where the depth map is the momentary state of a dynamic process. To each image point we assign a set of possible disparity values. In a dynamic process with competition and cooperation, the correct disparity value is selected for each image point. Therefore, we solve the correspondence problem by a dynamic, self-organizing process, the structure of which shows analogies to the human visual system. The algorithm can be implemented in a massive parallel manner and yields good results for either artificial or natural images.

Algorithms↗
PubMed1998

Large scale stereopsis and optic flow: depth enhanced by speed and opponent-motion.

To understand better the range of conditions supporting stereoscopic vision, we explored the effects of speed, as well as specific optic flow patterns, on judgments of the depth, near or far of fixation, of large targets briefly presented in the upper periphery. They had large disparities (1-6 deg) and moved at high speeds (20-100 deg/sec). Motion was either vertical or horizontal, as well as either unidirectional or layered in bands of alternating directions (opponent-motion). High stimulus speeds can extend dmax. The effects are explained by models having linear filters that signal both faster speeds and larger disparities. Stereo depth localization can also be enhanced by opponent-motion even when kinetic depth itself is not apparent. Improvements are greatest with wide-field, horizontal opponent-motion. The results imply functions such as vection, posture-control, and vergence may benefit from disparity information enhanced by optic flow patterns that are commonly available to a moving, binocular observer.

Depth Perception↗
PubMed1999

Abnormal depth perception from motion parallax in amblyopic observers.

Many similarities exist between the perception of depth from binocular stereopsis and that from motion parallax. Moreover, Rogers (1984, cited in, Howard, I. P., & Rogers, B. J. (1995). Binocular vision and stereopsis. Oxford Claridon, New York.) suggests a relationship between an observer's ability to use disparity information and motion parallax information in a depth perception task. To more closely investigate this relationship, depth perception was studied in normal observers and amblyopic observers with poor stereo vision. As expected, amblyopic observers performed much worse than normal observers on depth discriminations requiring use of binocular disparity. However, amblyopic observers also performed much worse than normal observers on depth discriminations based on motion parallax. This result provides supporting evidence for a psychoanatomical link between the perception of depth from motion and the perception of depth from binocular disparity.

Amblyopia↗
PubMed2002

Recent trends in disability and functioning among older adults in the United States: a systematic review.

CONTEXT: Several well-publicized recent studies have suggested that disability among older Americans has declined in the last decade. OBJECTIVES: To assess the quality, quantity, and consistency of recent evidence on US trends in the prevalence of self-rated old age disability and physical, cognitive, and sensory limitations during the late 1980s and 1990s and to evaluate the evidence on trends in disparities by major demographic groups. DATA SOURCES: We searched MEDLINE and AGELINE for relevant articles published from January 1990 through May 2002 and reviewed reference lists in published articles. STUDY SELECTION: From more than 800 titles reviewed, we selected 16 articles based on 8 unique repeat cross-sectional and cohort surveys of US prevalence trends in disability or functioning among persons generally aged 65 or 70 years or older. DATA EXTRACTION: We evaluated survey quality according to 10 criteria, ranked the surveys as good, fair, or poor, and calculated for each outcome the average annual percent change. DATA SYNTHESIS: Among the 8 surveys, 2 were rated as good, 4 as fair, 1 as poor, and 1 as mixed (fair or poor, depending on the outcome) for assessing trends. Analyses of surveys rated fair or good showed consistency of declines in any disability (-1.55% to -0.92% per year), instrumental activities of daily living disability (-2.74% to -0.40% per year), and functional limitations. Surveys provided limited evidence on cognition and conflicting evidence on self-reported ADL (changes ranged from -1.38% to 1.53% per year) and vision trends. Evidence on trends in disparities by age, sex, race, and education was limited and mixed, with no consensus yet emerging. CONCLUSIONS: Several measures of old age disability and limitations have shown improvements in the last decade. Research into the causes of these improvements is needed to understand the implications for the future demand for medical care.

Activities of Daily Living↗
PubMed2001

Envelope size-tuning for transient disparity vergence.

Our prior studies have demonstrated that the transient-vergence system responds preferably to dichoptic stimulus pairs that contain the highest combined energy, regardless of dichoptic differences in spatial frequency, contrast, orientation, or luminance polarity (Edwards, M., Pope, D. R., & Schor, C. M. (1998), Vision Research 38, 705; Pope, D. R., Edwards, M., & Schor, C. M. (1999) Vision Research 39, 575). This broadband tuning for spatial frequency, orientation and contrast is indicative of a second order (non-linear) extraction system. The current study examined the potential size-tuning of binocular channels to the contrast envelope that is extracted by a non-linear process. Stimuli were size-scaled Gabor patches with parallel and orthogonal carrier orientations that subtended a large (3.8 degrees ) disparity. Results indicate that the transient-vergence system exhibits broad band-pass tuning to overall size of dichoptic targets, independent of interocular differences in carrier orientation, spatial frequency or contrast. Equal sizes elicited a higher proportion of vergence responses than unequal sizes, however responses to unequal size still occurred over a 2-octave range, illustrating broad band-pass tuning. Size tuning was found to be broader for small than large envelope sizes. The broad tuning for envelope size is likely to result from the overlapping extracted low-pass frequency spectra of the contrast envelopes. However, the transient-vergence system also responds to monocular, hemi-retinal stimuli over a larger (3-octave) range. Thus some of the observed "binocular tuning" may be due to these monocular responses.

Adult↗
PubMed1989

Clinical suppression and binocular rivalry suppression: the effects of stimulus strength on the depth of suppression.

In observers with abnormal binocular vision (such as strabismics or anisometropes) one eye's view is often suppressed. This clinical suppression serves to eliminate binocular diplopia and confusion. Suppression may also occur in observers with normal binocular vision, when the two eyes view disparate retinal images, a phenomenon known as binocular rivalry. When the image in an eye is suppressed, it is possible to determine the amount by which that suppressed stimulus is below the visibility threshold, or the depth of suppression. In the experiments presented here, the depth of suppression in an eye was measured as the strength of the stimulus in the contralateral eye (the stimulus inducing suppression) was varied. This was done for both clinical suppressors and normal observers undergoing binocular rivalry suppression. Independent changes were made to the contrast, the luminance, and the spatial frequency of the inducing stimulus. For both clinical suppression and binocular rivalry suppression, the depth of suppression was constant, regardless of the changes to the inducing stimulus.

Adult↗
PubMed1998

Cortical area MT and the perception of stereoscopic depth.

Stereopsis is the perception of depth based on small positional differences between images formed on the two retinae (known as binocular disparity). Neurons that respond selectively to binocular disparity were first described three decades ago, and have since been observed in many visual areas of the primate brain, including V1, V2, V3, MT and MST. Although disparity-selective neurons are thought to form the neural substrate for stereopsis, the mere existence of disparity-selective neurons does not guarantee that they contribute to stereoscopic depth perception. Some disparity-selective neurons may play other roles, such as guiding vergence eye movements. Thus, the roles of different visual areas in stereopsis remain poorly defined. Here we show that visual area MT is important in stereoscopic vision: electrical stimulation of clusters of disparity-selective MT neurons can bias perceptual judgements of depth, and the bias is predictable from the disparity preference of neurons at the stimulation site. These results show that behaviourally relevant signals concerning stereoscopic depth are present in MT.

Animals↗
PubMed1981

[New stereoprojector with polarized tests, for exploration of aniseikonia and the perception of relief].

We describe a stereoprojector in polarized light built at the Laboratory of Physics, Museum (Paris) with a battery of stereograms specially designed for the two following aspects of binocular vision examination. a) Determination of Aniseikonia from 0 to 15% with both the direct comparison target and the spatial cikonic target. b) Studies on stereopsis in focal and peripheral vision, using tests for local stereopsis with disparities going from 0 to 350" by steps of 15", or some kinds of Random Dot stereograms of Julesz.

Aniseikonia↗
PubMed1991

Neural models of stereoscopic vision.

Human stereopsis remains an enigma: how does the brain match features between the left and right eye images and compute disparity between these matched features? Developments in computational neuroscience and machine vision have led to several models of human stereopsis that provide insight into possible mechanisms underlying this phenomenon. These models, reviewed in this paper, adopt one of three general strategies. One class of models employs cooperative interactions, whereby a unique solution to the matching problem emerges from excitatory and inhibitory interactions among binocular neural elements. A second class of models implements matching and disparity computation serially over multiple spatial scales. A third class relies on local, non-interacting computations performed in parallel to overcome speed limitations inherent in the other models. Considered together, these theoretical developments offer fresh insights concerning the actual neural concomitants of binocular stereopsis.

Animals↗
PubMed2004

Bone marrow-derived stem cells preserve cone vision in retinitis pigmentosa.

Retinitis pigmentosa is a heritable group of blinding diseases resulting from loss of photoreceptors, primarily rods and secondarily cones, that mediate central vision. Loss of retinal vasculature is a presumed metabolic consequence of photoreceptor degeneration. A new study shows that autologous bone marrow-derived lineage-negative hematopoietic stem cells, which incorporate into the degenerating blood vessels in two murine models of retinitis pigmentosa, rd1 and rd10, prevent cone loss. The use of autologous bone marrow might avoid problems with rejection while preserving central cone vision in a wide variety of genetically disparate retinal degenerative diseases.

Animals↗
PubMed1997

Shading and stereo in early perception of shape and reflectance.

Recent experiments involving shaded 2-D stimuli have shown that early-vision mechanisms are capable of interpreting 3-D shape from shading. In particular, target discrimination tasks suggest that a target 'pops out' when background distractors, but not the target, can be interpreted as convex and lit from above or top-left. Since the problem of extracting 3-D shape from shading is intrinsically ill-defined, early vision may need to make these twin assumptions of convexity and top-left lighting in order to constrain the problem. Would these assumptions be recognized as unnecessary and consequently discarded when 3-D shape could be unambiguously defined by some other cue, like stereo disparity? A 2AFC stimulus onset asynchrony paradigm with masking was used in target discrimination experiments. The performance of five naive subjects on tasks where only shading cues were present was compared with that on tasks involving shading as well as stereo cues that define shape unambiguously. The results show that although stereo disparity information is incorporated by early-vision 3-D mechanisms, it is not used to overturn the default assumptions of lighting and shape. Stereo information is interpreted within the framework of top-left lighting, and a consistent preference for convexity is seen over concavity.

Contrast Sensitivity↗
PubMed2003

Monocular gap stereopsis: manipulation of the outer edge disparity and the shape of the gap.

A binocular stimulus that arises when two black frontal plane surfaces located at different depths have a gap between them for one eye but not for the other eye is interesting since the gap is monocular--it has no matching contours in the other eye--and yet binocular processes resolve a depth step effortlessly (Vision Research, 39, 493). In two experiments we investigate the processes and constraints underlying this depth resolution by varying the width of the solid image (the one without the gap) and the shape of the gap. The results show that the processes underlying monocular gap stereopsis can handle a situation in which the images of two surfaces in depth are effectively overlapping for one eye's view with the other eye seeing between them and that binocular depth is seen even when there is no disparity present. We also show that under ecologically appropriate conditions, depth curvature and warping can result when the monocular gap has a curved or warped edge. Both these experiments imply that the visual system responds to the ambiguity of the stimulus by adopting a minimum slant constraint.

Depth Perception↗
PubMed1982

Configurational differences in stereovision.

Retinal disparities which produce perceived depth in stereoscopic vision result from configurational differences in the retinal images in the two eyes of objective three-dimensional arrangements. Experiments reported earlier demonstrated special effectiveness of differences in the alignment in the vertical dimensions of the images of points that are at different depth. Here a stereoscopic experiment is reported where alignment differences were increased without altering disparity. An increase in perceived depth resulted and was measured by estimation and by matching. The reason for the special effectiveness of binocular alignment differences is discussed.

Depth Perception↗
PubMed1980

Fixation of disparity: a steady state error of disparity-induced vergence.

Fusional vergence eye movements are controlled by a fast-acting mechanism that aligns the eyes in response to retinal image disparity and a slow-acting mechanism that sustains binocular alignment. These two control mechanisms are distinguished by their decay time constants and stimuli. Fast fusional vergence responds to retinal image disparity, and slow fusional vergence responds to the effort or output of the fast control mechanism. Fixation disparity is modeled as a steady-state error of fast fusional vergence. Fixation disparity is shown to be inversely related to prism adaptation, a manifestation of slow fusional vergence, in normal but not abnormal binocular vision. Sensory factors such as interocular suppression influence the magnitude of fixation disparity in strabismus. Clinical implications concerning the relation between fixation disparity and heterophoria in normal and abnormal binocular vision are discussed.

Adaptation, Ocular↗
PubMed1995

An augmented computer vision approach for enhanced image understanding.

This paper addresses the design concept of a spatially and spectrally augmented computer vision approach toward enhanced image analysis and understanding. The concept of spatially augmented computer vision refers to the inclusion of the stereo disparity measure (1/2-D) along with the two-dimensional (2-D) spatial coordinates of the images, together yielding the augmented (2 1/2-D) representation. The concept of spectrally augmented computer vision refers to the implementation of the multiresolution concept of the wavelet theory to analyze and assess in detail the local properties of the 2-D images. The principal objective in applying this augmented, and more revealing, computer vision approach is to provide the added dimension in spatial and spectral resolutions for the enhanced understanding of images. To this end, imaging techniques are developed to exploit, in an optimal fashion, the information acquired by the camera system to yield useful descriptions of the viewed scenes. Experimental results are provided in support of this research direction.

Image Processing, Computer-Assisted↗