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At least 1,603 records · Page 89Linked to original sources
PubMed1996

Perceiving self-motion in depth: the role of stereoscopic motion and changing-size cues.

During self-motions, different patterns of optic flow are presented to the left and right eyes. Previous research has, however, focused mainly on the self-motion information contained in a single pattern of optic flow. The present experiments investigated the role that binocular disparity plays in the visual perception of self-motion, showing that the addition of stereoscopic cues to optic flow significantly improves forward linear vection in central vision. Improvements were also achieved by adding changing-size cues to sparse (but not dense) flow patterns. These findings showed that assumptions in the heading literature that stereoscopic cues facilitate self-motion only when the optic flow has ambiguous depth ordering do not apply to vection. Rather, it was concluded that both stereoscopic and changing-size cues provide additional motion-in-depth information that is used in perceiving self-motion.

Adolescent↗
PubMed1986

Quantitative assessment of disparity vergence components.

Earlier evidence suggests qualitatively that at least two control modes may mediate a single vergence response. Thus, in a vergence response to step disparity, the transient component drives the initial fast dynamic portion of the response, while the sustained component maintains the latter slower portion of the response. The authors extended this hypothesis by quantitatively defining the stimulus pattern and dynamics that elicit this dichotomous behavior. The disparity target consisted of vertical lines 2 deg in height presented to each eye. Ramp disparity velocities ranged from 0.7 deg/sec to 36 deg/sec with amplitude of up to 4 deg. Photoelectric recordings of eye movements from both eyes were subtracted to give the vergence response. Fast and slow ramp stimulus velocities were found to elicit transient and sustained component responses respectively. In addition, the finding of staircase-like responses to fast ramp stimuli has strong implications on control mechanisms, indicating a sampling process in the transient component of the disparity vergence system.

Eye Movements↗
PubMed1977

Fixation disparity and stereopsis.

The magnitude of fixation disparity has been proposed to be uncorrelated with stereoscopic sensitivity. Studies on this relationship have been confined to the effects of vergence-induced fixation disparity on stereoacuity: some subjects exhibited decreased stereoacuity with induced fixation disparity. The present study was designed to determine whether prismatic correction of naturally occurring horizontal fixation disparity would result in increased stereoacuity. Five subjects with eso and 5 with exo fixation disparity had their fixation disparity curves and stereothresholds evaluated before and after wearing corrective lenses and prisms that neutralized the fixation disparity. Five subjects with no fixation disparity served as controls. After 1 month most subjects showed no change in their fixation disparity curves and stereothresholds.

Depth Perception↗
PubMed1981

Adaptation to prism-induced heterophoria in subjects with abnormal binocular vision or asthenopia.

In a previous study we investigated how normal subjects adapted to prism-induced heterophoria. In this study we have continued this work by investigating this phenomena in 15 patients with abnormal binocular vision and/or asthenopia. It was found that the majority of subjects lacked or had a deficient adaptation system to base-in and/or base-out prisms, but all except two subjects examined adapted normally to vertical prism. These results suggest that it may be possible to treat the horizontal adaptation system independently from the vertical one. Prism vergences, heterophoria measurements, and the presence of fixation disparity gave little indication of the adaptation ability of the subjects. Symptoms correlated well with adaptation ability.

Accommodation, Ocular↗
PubMed1988

Comparison of associated heterophoria measurements using the Mallett test for near vision and the Sheedy Disparometer.

The Mallett test for near vision and the Sheedy Disparometer are compared in terms of their ability to measure associated heterophoria. Twenty-two asymptomatic subjects were used. With the Disparometer, ten of these subjects, familiar with making prism vergence measurements, exhibited stable forced vergence fixation disparity curves, and the associated heterophoria values using both instruments were not significantly different. However, the twelve subjects not familiar with making such measurements generated fluctuating, unstable fixation disparity curves, and the associated heterophoria values were significantly different. Repeated trials with the randomly selected naïve subjects led to flatter, more stable fixation disparity curves and lower values for the x- and y-intercepts when using the Disparometer. The Mallett test, however, produced identical values for associated heterophoria in each successive trial. Therefore, the validity of measurements using the Disparometer in a clinical setting is questioned.

Adolescent↗
PubMed2005

Complementary medicine and genetic medicine: polar disciplines or dynamic partners?

For more than a decade, a powerful movement promoting the integration of complementary and alternative medicine (CAM) and conventional medicine has evolved. Throughout the same period, there has been a monumental shift in the biologic sciences, and in perspectives on disease, resulting from advances in genetics. It is noteworthy, and perhaps not coincidental, that these "movements" have been occurring in parallel. The simultaneous growth of complementary medicine and genetic medicine may be fueled by a deep interest in the development of "personalized" medicine. There is a prevailing view that the metaphysical visions of these two fields are in conflict. To advance discussion of this question, we describe what we believe are the common philosophies and goals of these apparently disparate fields, and why it would be advantageous for them to work together in the service of the public's health.

Complementary Therapies↗
PubMed1988

Integration of depth modules: stereo and shading.

We studied the integration of image disparities, edge information, and shading in the three-dimensional perception of complex yet well-controlled images generated with a computer-graphics system. The images showed end-on views of flat- and smooth-shaded ellipsoids, i.e., images with and without intensity discontinuities (edges). A map of perceived depth was measured by adjusting a small stereo depth probe interactively to the perceived surface. Our data show that disparate shading (even in the absence of disparate edges) yields a vivid stereoscopic depth perception. The perceived depth is significantly reduced if the disparities are completely removed (shape-from-shading). If edge information is available, it overrides both shape-from-shading and disparate shading. Degradations of depth perception corresponded to a reduced depth rather than to an increased scatter in the depth measurement. The results are compared with computer-vision algorithms for both single cues and their integration for three-dimensional vision.

Computer Graphics↗
PubMed1988

[Random dot stereograms and the limits of their detectability].

The influence of contrast reduction combined with aniseikonia on disparities in the TNO test was investigated with monocular induced refractive errors by spherical convex and concave lenses. Single contrast reduction was produced by Bangerter foils. Unilateral near vision of 0.1-0.2 is compatible with a positive TNO test. The average tolerance limit of the TNO test was 6% when produced by monocular induced refractive error. Otherwise, pure aniseikonia values of 5% to 9% produced by overall-size lenses are compatible with the TNO test.

Adult↗
PubMed1991

Depth is encoded in the visual cortex by a specialized receptive field structure.

Binocular neurons in the visual cortex are thought to perform the first stage of processing for the fine stereoscopic depth discrimination exhibited by animals with frontally located eyes. Because lateral separation of the eyes gives a slightly different view to each eye, there are small variations in position (disparities), mainly along the horizontal dimension, between corresponding features in the two retinal images. The visual system uses these disparities to gauge depth. We studied neurons in the cat's visual cortex to determine whether the visual system uses the anisotropy in the range of horizontal and vertical disparities. We report here that there is a corresponding anisotropy in the cortical representation of binocular information: receptive-field profiles for left and right eyes are matched for cells that are tuned to horizontal orientations of image contours. For neurons tuned to vertical orientations, left and right receptive fields are predominantly dissimilar. Therefore, a major modification is required of the conventional notion of disparity processing. The modified scheme allows a unified encoding of monocular form and binocular disparity information.

Action Potentials↗
PubMed1978

Population study of fixation disparity, heterophoria, and vergence.

Data on phorias, vergences, and fixation disparities were gathered for distant and near viewing conditions from a nonclinical, young adult population. Normative values were computed from the data for analysis and comparison. Our study revealed slightly less exophoria at far and near than Morgan's study, together with large base-out vergence readings. We found proportionately more esophores with exo fixation disparity who require base-in prism to neutralize the fixation disparity than Ogle's studies found.

Adult↗
PubMed1981

Effect of vision training on patients who fail Sheard's criterion.

One hundred convergence insufficiency patients who did not meet Sheard's criterion at near were given a program of in-office and at-home training. The objective was to see if they would meet Sheard's criterion after training. Results were analyzed in terms of the numbers successfully meeting this criterion as well as other criteria, i.e. Percival's, elimination of symptoms, improvement of stereopsis, and elimination of fixation disparity. Of the 100 patients, 84 successfully met Sheard's criterion after therapy. Failure to meet Sheard's criterion correlated well with having subjective symptoms.

Accommodation, Ocular↗
PubMed2004

Evidence for patchwork approximation of shape primitives.

Investigators have proposed that qualitative shapes are the primitive information of spatial vision: They preserve an approximately one-to-one mapping between surfaces, images, and perception. Given their importance, we examined how the visual system recovers these primitives from sparse disparity fields that do not provide sufficient information for their recovery. We hypothesized that the visual system interpolates sparse disparities with planes, resulting in a patchwork approximation of the implicitly defined shapes. We presented observers with stereo displays simulating planar or smooth curved surfaces having different curvatures. The observers' task was to detect whether dots deviated from these surfaces or to discriminate planar from curved or planar from scrambled surfaces. Consistent with our hypothesis, increasing curvature had detrimental effects on observers' performance (Experiments 1-3). Importantly, this patchwork approximation leads to the recovery of the proposed shape primitives, since observers were more accurate at discriminating planar-from-curved than planar-from-scrambled surfaces with matched disparity range (Experiment 4).

Computer Graphics↗
PubMed1992

Development of binocular vision in the kitten's striate cortex.

Studies of the development and plasticity of the visual pathway are well documented, but a basic question remains open: what is the physiological status of the system prior to extensive visual experience? Somewhat conflicting answers have been put forward, and in a major area, binocular vision, reports have ranged from severe immaturity to well-developed maturity. This is an important question to resolve since binocular cells in the visual cortex are thought to be the neural substrate for stereoscopic depth perception. We have addressed this question by recording from single cells in the striate cortex of kittens at postnatal ages 2, 3, and 4 weeks and from adults for comparison. Gratings with sinusoidal luminance distribution are presented to left, right, or both eyes. For each cell, we determine optimal values for orientation and spatial frequency. Relative phase (retinal disparity) is then varied in a dichoptic sequence so that binocular interaction may be studied. Results are as follows. In the normal adult, we have shown in previous work that most binocular interaction in the visual cortex can be accounted for on the basis of linear summation. Results from 3 and 4 week postnatal kittens are closely similar to those from adults. All types of binocular interaction found in adults are present in kittens. This includes phase-specific and non-phase-specific suppression or facilitation. Furthermore, monocular and binocular tuning characteristics are comparable in kittens and adults. The clear changes that occur with age are optimal spatial frequencies and peak responses. In addition, at 2 weeks, there is a substantially higher proportion of monocular cells compared to other ages and correspondingly, lower relative numbers of cells that exhibit phase-specific or suppressive binocular interactions. From increases in optimal spatial frequency and interpupillary distance with age, we calculated predicted changes in binocular disparity thresholds (stereo acuity) with age. Although there are methodological limits with respect to the behavioral testing of young kittens, the predicted results are comparable to some of the values obtained. Considered together, our results show that the physiological apparatus for binocular vision is functional at an early stage in postnatal development. It is possible that the connections that underlie this function are developed rapidly during early postnatal experience. An alternative possibility is that there is an elaborate genetic organization of binocular vision, but our study does not address this issue directly. A combination of these factors may be applicable.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1995

Vergence eye movement control and multivalent perception of autostereograms.

We introduce a dynamical model for automatic vergence eye movement control. In connection with our dynamical system of binocular model neurons that solves the correspondence problem of stereo-vision, we present a complete model for stereo-vision. Our automatic vergence eye movement control adjusts an image segment, which is of momentary interest to the observer. The adjustment is done in such a way that we only need to define a disparity search range of minimal extension. Recently, a new method of encoding (3D) three-dimensional information in 2D pictures was designed in the form of computer-generated patterns of colored dots. At first glimpse, these so-called autostereograms appear as structured but meaningless patterns. After a certain period of observation, a 3D pattern emerges suddenly in an impressive way. Applying our algorithm to autostereograms, we find a fully satisfactory agreement with the multivalent perception experienced by humans. As in nature, in our model the phase transition between the initial state and the 3D perception state takes place in a very short time. Our algorithm is very robust against noise, and there is no need to interpolate a sparse depth map.

Algorithms↗