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PubMed1995

Binocular correspondence and visual direction.

Two classic theories of direction vision, one by Hering, the other by Wells, are expressed in mathematical form and compared. The Hering disparity field differs considerably from the Wells disparity field, but if both are scaled for the change of acuity with eccentricity their differences are much more subtle. This explains why it is hard to determine which theory predicts direction perception best, although the tests favour Hering's theory. It is proved that Wells's construction (his rule 3) follows directly from his first two rules and Aguillonius's assumption that the horopter in the fixation plane is a frontoparallel line. Wells's theory is clearly outdated and does not mesh well with modern three-dimensional geometry of binocular vision, which Hering's theory does. Moreover, Wells inextricably mixes distance and direction vision right from the start, whereas Hering properly treats the two-dimensional manifold of directions and the depth-gauging principles separately. The use of terms such as 'Wells-Hering' rules should be discouraged and both Wells and Hering should be remembered separately for their clearly distinct and independent contributions. The work of Hering is still relevant to modern theory and praxis of binocular vision. The extension of Hering's approach to vertical disparities is treated for stimuli in frontoparallel planes. It is shown that acuity-scaled vertical-disparity information sampled at a single glance is below resolution beyond about arm's length. It can only be used if eye movements are allowed. Throughout, the simplest derivations of the geometrical relations that it was possible to find are given, so that the review of binocular geometry might also be of some didactical use. Finally it is indicated in which direction it might be necessary to modernise the concept of binocular correspondence.

History, 18th Century↗
PubMed1978

The relationship between fixation disparity and heterophoria.

Twenty-five asymptomatic subjects with normal binocular vision underwent determination of the magnitude and direction of their heterophoria and their fixation disparity. Fixation disparity was measured at a 2-m fixation distance with the phase-difference haploscope under conditions simulating those of casual seeing. When combined with careful attention to symmetrical control of accommodation, this method eliminates several known technical artifacts. Examples of the normal fluctuation of the magnitude and direction of fixation disparity for individual subjects were demonstrated. Whereas only a slight preponderance of subjects were esophoric, many subjects had convergent fixation disparity (esodisparity). Linear regression analysis of the data revealed a coefficient of correlation between fixation disparity and heterophoria at 6 m of 0.61, and at 33 cm of 0.50. The results suggest that normal, small magnitude heterophoria does not necessarily produce fixation disparity and that fixation disparity does not necessarily sustain heterophoria.

Adult↗
PubMed1993

Disparity-sensitive cells in the owl have a characteristic disparity.

We experience the visual world as being three-dimensional. A major source of depth information derives from the slightly different views of each eye, leading to small variations in the retinal images ('disparities'). Neurons sensitive to visual disparities are thought to form the neural basis of stereo vision. Barn owls as well as several mammalian species have neurons that are sensitive to visual disparities. But how visual disparities are represented in the brain has been a matter of discussion ever since the first disparity-sensitive neurons were found some 25 years ago. Here we adopt a new approach to this problem and study the neural computation of visual disparities with a paradigm borrowed from auditory research. The measurement of interaural time difference (ITD) has many similarities with the measurement of visual disparity on the formal, algorithmic level. We speculate that the similarities might extend to the level of neural computation. The neural representation of ITD is well understood, and we have studied the representation of disparities with visual stimuli analogous to those successfully used in acoustic experiments. For example, ITD is converted in the brain to a pathlength on an axon that, owing to the finite conduction velocity in neurons, exactly matches the external ITD. This pathlength is called 'characteristic delay'. Our results suggest that there is an analogue of the characteristic delay in stereo vision which we propose to call 'characteristic disparity'.

Animals↗
PubMed2002

Neural correlates for perception of 3D surface orientation from texture gradient.

A goal in visual neuroscience is to reveal how the visual system reconstructs the three-dimensional (3D) representation of the world from two-dimensional retinal images. Although the importance of texture gradient cues in the process of 3D vision has been pointed out, most studies concentrate on the neural process based on binocular disparity. We report the neural correlates of depth perception from texture gradient in the cortex. In the caudal part of the lateral bank of intraparietal sulcus, many neurons were selective to 3D surface orientation defined by texture gradient, and their response was invariant over different types of texture pattern. Most of these neurons were also sensitive to a disparity gradient, suggesting that they integrate texture and disparity gradient signals to construct a generalized representation of 3D surface orientation.

Animals↗
PubMed2000

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.

Depth Perception↗
PubMed1995

Effects of heterophoria on stereopsis.

The effects of horizontal heterophoria on Howard-Dolman stereopsis scores were investigated in a population of 1765 stereophotogrammetrists with no obvious impediment to binocular vision as determined in a vision screening. Exophoria over the 1 to 7 delta range showed no systematic and statistically valid effect on stereopsis but esophoria did show an effect. In a related population of 1339 stereophotogrammetrists, subjects with as little as 1 delta (+/- 0.5 delta) of vertical heterophoria exhibited a small but statistically significant decrease in stereopsis test scores compared to those with vertical orthophoria. Therefore, a heterophoria had different effects on stereoacuity depending on whether it was in the exo, eso, or vertical direction. An explanation for the difference is proposed using the known dependence of heterophoria and stereoacuity on fixation disparity.

Depth Perception↗
PubMed1998

Spatial vision in the course of an insect's life.

Praying mantises are considered to be phylogenetically ancient insects with their roots in the palaeozoic Protoblattoidea. They have evolved two mechanisms for spatial vision: (a) estimating the distance to moving prey objects with the use of binocular disparity [Rossel, 1983] and (b) estimating the distance to stationary target objects with motion parallax produced by head movements [Poteser and Kral, 1995]. There is no doubt that the ability to use both visual cues is congenital, but the degree to which either mechanism is developed and its significance to the individual depends to some extent upon the animal's age and exposure to prey species and environmental cues. Experience and learning play an important role. It appears that young mantises can perform both binocular and monocular calculations of distance but they grow to depend more on the binocular mechanism. Motion parallax plays an important role in movement strategy throughout the course of a mantis's life, but this mechanism appears to be particularly in early life.

Animals↗
PubMed1999

Listing's plane rotation with convergence: role of disparity, accommodation, and depth perception.

Earlier studies have reported temporal rotation of Listing's plane with convergence of the eyes causing torsion, which is dependent on eye elevation. The amount by which the planes rotate differs from study to study. To gain insight into the functional significance of the temporal tilt of Listing's plane for vision, we examined whether the rotation of the plane depends on the visual conditions, namely on the stimuli driving vergence. In different conditions, accommodative vergence, disparity-vergence, combinations of disparity with accommodation or depth perception were used and the resulting rotation of Listing's plane was measured. Our findings show, for the first time, that the relationship between convergence and Listing's-plane temporal rotation depends on the stimuli driving vergence. When the stimulus contains only disparity cues, vergence and Listing's plane rotate immediately and consistently among subjects. Accommodative vergence, the mutual couplings between vergence and accommodation, can influence the orientation of Listing's plane, but they do so in a idiosyncratic way. The largest rotation was elicited by stereograms combining disparity-vergence with depth perception. These findings support the idea of a functional role of Listing's plane rotation for binocular vision, perhaps for depth perception.

Accommodation, Ocular↗
PubMed1993

The neural representation of stereoscopic depth contrast.

Stereoscopic vision provides examples of contrast phenomena broadly analogous to those seen with brightness. Several authors have suggested that lateral inhibition between disparity-tuned neurons might underlie these phenomena. This type of lateral inhibition would differ from the more familiar kind which occurs with retinal ganglion cells, where an inhibitory surround has essentially a linear subtractive effect. Lateral inhibition by disparity-tuned units would introduce the nonlinearity of the tuning curve. I argue here that the evidence nonetheless suggests that a linear subtractive mechanism operates in the stereo realm--in fact, that there is a stereo equivalent of the classical centre-surround. This seems at first sight implausible, partly because of the occurrence of the nonlinearity mentioned above, but also because disparity is only provided at certain locations in the retinal field, namely those where appropriate features are matched. I show that both objections can be easily overcome, the first because Laplacian-like centre-surrounds can be constructed from disparity-tuned cells, the second because interpolation can fill in between features, and can provide precisely the quantitative dependence upon disparities of neighbouring features which matches the experimental data.

Attention↗
PubMed2006

Depth scaling in phantom and monocular gap stereograms using absolute distance information.

The present study aimed to investigate whether the visual system scales apparent depth from binocularly unmatched features by using absolute distance information. In Experiment 1 we examined the effect of convergence on perceived depth in phantom stereograms [Gillam, B., & Nakayama, K. (1999). Quantitative depth for a phantom surface can be based on cyclopean occlusion cues alone. Vision Research, 39, 109-112.], monocular gap stereograms [Pianta, M. J., & Gillam, B. J. (2003a). Monocular gap stereopsis: manipulation of the outer edge disparity and the shape of the gap. Vision Research, 43, 1937-1950.] and random dot stereograms. In Experiments 2 and 3 we examined the effective range of viewing distances for scaling the apparent depths in these stereograms. The results showed that: (a) the magnitudes of perceived depths increased in all stereograms as the estimate of the viewing distance increased while keeping proximal and/or distal sizes of the stimuli constant, and (b) the effective range of viewing distances was significantly shorter in monocular gap stereograms. The first result indicates that the visual system scales apparent depth from unmatched features as well as that from horizontal disparity, while the second suggests that, at far distances, the strength of the depth signal from an unmatched feature in monocular gap stereograms is relatively weaker than that from horizontal disparity.

Convergence, Ocular↗
PubMed1989

Panum's fusional area estimated with a criterion-free technique.

It has been reported that criterion-free estimates of the upper disparity limits for fusion of line targets are small enough to be accounted for by monocular vernier sensitivity. However, targets such as lines, which contain high spatial frequencies, may ensure small fusion limits, since fusion limits obtained with criterion-dependent methods for narrow-band targets, such as sinusoids or difference-of-Gaussian luminance profiles, are proportional to target spatial periods. Experiment 1 therefore explored whether criterion-free methods give fusion limits for narrow-band targets that can be accounted for by vernier sensitivity. Vertical fusion limits were estimated by a method that forced observers to discriminate a disparate sinusoidal grating from an immediately adjacent zero-disparity grating. Fusion limits were too large to be explained by monocular vernier thresholds obtained for the same targets. In addition, fusion limits were not affected by large changes in target contrast, whereas vernier thresholds increased as contrast was decreased. The results of Experiment 1 also argued against interocular suppression as the cause of single vision, since vernier offsets that were visible when viewed monocularly were invisible under binocular viewing conditions. In Experiment 2, manual adjustment of disparities yielded fusion limits little different from those obtained with the forced-choice method of Experiment 1, demonstrating that it is possible to design adjustment methods for assessing fusion limits that are as sensitive as forced-choice methods. In Experiment 3, large reductions in target contrast, which have the effect of decreasing disparity sensitivity, did not alter fusion limits, disconfirming the idea that fusion limits estimated with discriminative procedures represent disparity-detection thresholds. In Experiment 4, disparities were adjusted until a just noticeable difference in grating contrast appeared. These disparities were larger than fusion limits, indicating that fusion limits did not represent a change in apparent contrast arising from disparity limitations of binocular summation. Together, the four experiments support the existence of binocular fusion as a unique category of sensory performance, disconfirm several nonfusional explanations of single vision, and support the use of criterion-free as well as adjustment methods in measuring fusion limits.

Attention↗
PubMed1998

Cues to viewing distance for stereoscopic depth constancy.

A veridical estimate of viewing distance is required in order to determine the metric structure of objects from binocular stereopsis. One example of a judgment of metric structure, which we used in our experiment, is the apparently circular cylinder task (E B Johnston, 1991 Vision Research 31 1351-1360). Most studies report underconstancy in this task when the stimulus is defined purely by binocular disparities. We examined the effect of two factors on performance: (i) the richness of the cues to viewing distance (using either a naturalistic setting with many cues to viewing distance or a condition in which the room and the monitors were obscured from view), and (ii) the range of stimulus disparities (cylinder depths) presented during an experimental run. We tested both experienced subjects (who had performed the task many times before under full-cue conditions) and naïve subjects. Depth constancy was reduced for the naïve subjects (from 62% to 46%) when the position of the monitors was obscured. Under similar conditions, the experienced subjects showed no reduction in constancy. In a second experiment, using a forced-choice method of constant stimuli, we found that depth constancy was reduced from 64% to 23% in naïve subjects and from 77% to 55% in experienced subjects when the same set of images was presented at all viewing distances rather than using a set of stimulus disparities proportional to the correct setting. One possible explanation of these results is that, under reduced-cue conditions, the range of disparities presented is used by the visual system as a cue to viewing distance.

Cues↗
PubMed2000

Horizontal-disparity tuning of neurons in the visual forebrain of the behaving barn owl.

Stereovision plays a major role in depth perception of animals having frontally-oriented eyes, most notably primates, cats, and owls. Neuronal mechanisms of disparity sensitivity have only been investigated in anesthetized owls so far. In the current study, responses of 160 visual Wulst neurons to static random-dot stereograms (RDS) were recorded via radiotelemetry in awake, fixating barn owls. The majority of neurons (76%) discharged significantly as a function of horizontal disparity in RDS. The distribution of preferred disparities mirrored the behaviorally relevant range of horizontal disparities that owls can exploit for depth vision. Most tuning profiles displayed periodic modulation and could well be fitted with a Gabor function as expected if disparity detectors were implemented according to the disparity energy model. Corresponding to this observation, a continuum of tuning profiles was observed rather than discrete categories. To assess a possible clustering of neurons with similar disparity-tuning properties, single units, and multi-unit activity recorded at individual recording sites were compared. Only a minority of neurons were clustered according to their disparity-tuning properties, suggesting that neurons in the visual Wulst are not organized into columns by preferred disparity. To assess whether variable vergence eye movements influenced tuning data, we correlated tuning peak positions on a trial-by-trial basis for units that were recorded simultaneously. The general lack of significant correlation between single-trial peak positions of simultaneously recorded units indicated that vergence, if at all, had only a minor influence on the data. Our study emphasizes the significance of visual Wulst neurons in analyzing stereoscopic depth information and introduces the barn owl as a second model system to study stereopsis in awake, behaving animals.

Action Potentials↗
PubMed1997

Deficiency of adaptive control of the binocular coordination of saccades in strabismus.

Disconjugate (different in the two eyes) oculomotor adaptation is driven by the need to maintain binocular vision. Since binocular vision is deficient in strabismus, we wondered whether oculomotor disconjugate adaptive capabilities are deficient in such subjects. We studied eight adult subjects with constant, long-standing convergent strabismus of variable angles (4-30 prism D). No subject had severe amblyopia. Binocular vision was evaluated with stereoacuity tests. Two subjects had peripheral binocular vision and gross stereopsis; two other subjects had abnormal retinal correspondence and abnormal or pseudo gross stereopsis. In the other subjects binocular vision and stereopsis were absent. To stimulate disconjugate changes of saccades, subjects viewed for 20 min an image that was magnified in one eye (aniseikonia). Subjects with residual peripheral binocular vision and even subjects with pseudo or abnormal binocular vision showed disconjugate changes of the binocular coordination of their saccades; these changes reduced the disparity resulting from the aniseikonia. In contrast, for subjects without binocular vision the changes were not correlated with the disparity induced by the aniseikonia. Rather, these changes served to improve fixation of one or the other eye individually.

Adaptation, Physiological↗
PubMed1985

Responses of neurons in visual cortex (V1 and V2) of the alert macaque to dynamic random-dot stereograms.

A substantial proportion of both simple and complex neurons in the cortex subserving central vision are differentially sensitive to binocular disparity of isolated line patterns (local stereopsis), a sensitivity based on a positional disparity between the neuron's receptive fields in the two eyes. In addition, a subset of cortical neurons, nearly all complex neurons, responds to dynamic random-dot stereograms containing no depth cues other than disparity. These neurons are capable of signaling the correct binocular matches among a multitude of false matches in the stereograms (global stereopsis). The discovery of cyclopean neurons in striate cortex, at early stages of the processing neural network for stereoscopic vision provides a new insight of the basic neural mechanisms underlying binocular depth perception.

Animals↗
PubMed2003

[Asthenopic complaints and ocular convergence at the computer workstation: new test procedures for practice and research].

BACKGROUND: The present paper summarizes a series of ergonomic studies on the relation between asthenopic complaints and binocular vision at the computer workstation. In particular, the paper reports on measurements of the accuracy of ocular convergence during fixation of central fusion stimuli (i. e. fixation disparity) as a function of viewing distance. METHODS: Different versions of subjective tests for fixation disparity (using dichoptic nonius lines) are presented, including a computer-controlled procedure (the eye-test PC). RESULTS: These new tests suggest that non-presbyopic subjects with normal binocular vision may suffer from asthenopic complaints if they have - in near vision - an exo fixation disparity larger than average. CONCLUSION: In these cases, the stress exercised on the convergence system can be reduced by using a longer viewing distance at the workplace.

Accommodation, Ocular↗
PubMed2006

Prevalence and correlates of children's diagnosed eye and vision conditions.

PURPOSE: Little is known about the distribution of eye and vision conditions among children and about possible disparities in the distribution of these conditions. The purpose of this report is to describe the prevalence of diagnosed eye and vision conditions among children younger than 18 years in the United States. DESIGN: Repeated population-based cross-sectional study. PARTICIPANTS: Forty-eight thousand three hundred four members of randomly selected households in the U.S. who were younger than 18 years in the years 1996 through 2001 were analyzed. METHODS: The prevalence of children with diagnosed eye and vision conditions was estimated using self-reported information from the nationally representative Medical Expenditure Panel Surveys (MEPS) for 1996 through 2001. Descriptive statistics are presented, and the associations between the likelihood of diagnosed eye and vision conditions and child and family characteristics were assessed using logistic regression analyses adjusted for the complex survey design of MEPS. MAIN OUTCOME MEASURES: Prevalence of diagnosed eye and vision conditions and measures of the association between diagnosed eye and vision conditions and child and family characteristics. RESULTS: On average, approximately 6.8% (95% confidence interval [CI], 6.4%-7.2%) of children < 18 years in the U.S. have a diagnosed eye and vision condition, ranging from 8.6% (95% CI, 7.8%-9.5%) in 1996 to 5.8% (95% CI, 5.2%-6.4%) in 2001. Excluding conjunctivitis, the 4 most common conditions were refractive disorders, potentially blinding disorders, trauma or injury, and other disorders not elsewhere classified. White children, children with more educated mothers, and children living in higher income families were more likely to have a diagnosed eye and vision condition. Hispanic children, children in very good or excellent health, and uninsured children were less likely to have any self-reported diagnosed eye and vision condition. CONCLUSIONS: This article presents a method for using MEPS to identify children younger than 18 years with eye and vision conditions. Although this method does not identify all children with eye and vision conditions, it does identify children with diagnosed eye and vision conditions. Results provide some evidence that underprivileged children may be underdiagnosed, undertreated, or both, placing them at risk for future problems.

Adolescent↗
PubMed2004

Vision impairment and hearing loss among community-dwelling older Americans: implications for health and functioning.

OBJECTIVES: We investigated the health, activity, and social participation of people aged 70 years or older with vision impairment, hearing loss, or both. METHODS: We examined the 1994 Second Supplement on Aging to determine the health and activities of these 3 groups compared with those without sensory loss. We calculated odds ratios and classified variables according to the International Classification of Functioning, Disability and Health framework. RESULTS: Older people with only hearing loss reported disparities in health, activities, and social roles; those with only vision impairment reported greater disparities; and those with both reported the greatest disparities. CONCLUSIONS: A hierarchical pattern emerged as impairments predicted consistent disparities in activities and social participation. This population's patterns of health and activities have public health implications.

Activities of Daily Living↗