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PubMed1978

Improvement of visual acuity in partially and fully sighted subjects as a function of practice, feedback, and instructional techniques.

Three experiments were conducted to examine improvement of partially (20/200 or 6/60) and normally (20/20 or 6/6) sighted adults. Measures of resolution and vernier acuity were examined in the first two experiments to determine whether practice, feedback, and instructions would have differential effects on the degree of visual improvement achieved in a 20-min. testing session. The results indicated extensive visual work to be the important factor in the improvement of impaired vision. The third experiment compared monocular and binocular depth perception of individuals with unilateral optic atrophy. The results yielded an unexpected finding where binocular depth perception was, in most cases, inferior to that of the strong eye alone. The first two experiments demonstrated the possibility of improving impaired visual functions and the third experiment suggests important implications for a theoretical model of depth perception with limited vision.

Depth Perception↗
PubMed1997

Differences in perceived shape from shading correlate with activity in early visual areas.

The perception of shape from shading depends on the orientation of the shading gradient [1] [2] [3] [4]. Displays composed of elements with vertically oriented shading gradients of opposite polarity produce a strong and stable percept of 'concave' and 'convex' elements. If the shading gradients are rotated 90 degrees , the depth percept is reduced and appears much more ambiguous. Results from psychophysical [1] [2] [3] [4] [5] [6], neuropsychological [7] and computational studies [8] [9] suggest that the perception of shape from shading engages specific mechanisms in early cortical visual areas. In a three-dimensional functional magnetic resonance imaging (fMRI) study at 1.5 Tesla using a three-dimensional, interleaved-echoplanar imaging technique and a surface radio frequency (RF) coil placed under the visual cortex, we investigated the activity in these early visual areas associated with viewing shape from shading displays at two different orientations. We found significantly greater activation in area V1 and neighbouring low-level visual areas of cortex when subjects viewed displays that led to weak and unstable depth percepts than when they viewed displays that led to strong and stable depth percepts.

Adult↗
PubMed1988

[Binocular functional exploration: fundamental aspects and analysis by the Fusio-Test].

After reviewing psychophysical and neurophysiological data concerning disparity processing and stereoscopic depth perception, as well as the limits of variation in perceived depth and fusion in function of binocular disparity, a new computer controlled apparatus named Fusio-Test is presented for functional binocular exploration. A battery of stereograms available in the test library made it possible to study in particular depth perception or stereoacuity, aniseikonia and fixation disparity, using the most suitable preprogrammed psychophysical procedure such as the limit method, constant stimuli, Cornsweet's psychophysical staircase, and one alternative forced choice method or multiple choice method. The test selected for each phase of the binocular examination was presented in polarized light on two Video Units. The required measurements were displayed on a small terminal and occasionally the data variations were recorded in real time. For the control of depth perception and the evaluation of stereoscopic acuity, two types of tests were programmed: line stereograms made of series of vertical lines varying in number and relative spacing or stylized shapes, random dot stereograms with different cyclopean shapes (circle, square, triangle or scaled pyramid), some of them with reduced binocular correlation according to Julesz. The originality of this apparatus for aniseikonia lies in its use of a battery of Ogle's spatial test stereograms, having incorporated vertical and horizontal magnifications ranging from 0 to 15% by 1% increments. The measurements were obtained by trying to find the pair of stereograms that must be presented to the right and the left eyes in order to eliminate the perceived distorsions (geometric or induced effect) and to recover the normal classical configuration of the spatial test. The test for fixation disparity was comprised of the Ogle arrangement with two polarized vertical lines forming a binocular nonius in the middle of a field surrounded with letters to stimulate fusion. Data for a sample of observers wearing glasses, contact lenses or implants, are presented and analyzed, bringing to light certain anomalies in binocular disparity processing. Differences in stereoacuity are noted: partial or total stereoblindness depending on the test selected (line stereograms or random dot stereograms, crossed or uncrossed disparities), on the spacing of the test elements; variations of threshold in time.(ABSTRACT TRUNCATED AT 400 WORDS)

Aniseikonia↗
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↗
PubMed2001

[The Goldmann Memorial Lecture--historical and current aspects of stereopsis].

According to Goldmann stereopsis is the highest performance of binocular recognition. A historical review shows that binocular stereopsis was explained only in 1838 by Wheatstone, whereas the monocular clues for stereopsis e.g. size, position and covering of the objects, light and shadow, perspective of the air, parallax and linear perspective were known long ago. The denomination depth perception is ambiguous: "depth" is the opposite of "height". Stereopsis means natural recognition of distance and objects in space, stereoscopy means recognition by the aide of an instrument. Natural and dichoptic stereopsis and the influences of vertical structures, of pupillary distance and of astigmatism are discussed. Examination of stereopsis is discussed, among others the two pencil test, the stereo-modification Bagolini-glasses, the combination of the plano-cylinders of W. R. Hess with random dots without glasses, the disk stereopsis etc. Goldmann's theory of binocular vision helps to understand different forms of strabismus, e.g. the statistical interplay of fixation and fusion for microtropia, the fixation mechanism for the congenital strabismus syndrome, the use of binocular stereopsis only for near explains intermittent divergence.

Depth Perception↗
PubMed1990

Performance consequences of two types of stereo picture compression.

Two algorithms for stereo picture compression were evaluated. According to one algorithm, consistent with the fusion theory of depth perception, the reduction of information in the two pictures was about equal. The other algorithm, consistent with the suppression theory of depth perception, was based on very deep compression of one picture and minimal reduction of information in the second picture. Subjects performed depth decisions and object decisions on the compressed picture. They were able to perform both tasks on the compressed pictures, though performance generally was worse than in the un-compressed control conditions. In both tasks performance was better for an uneven division of information between the two pictures. These results are consistent with the suppression theory of depth perception.

Adult↗
PubMed2000

Stereoscopic vision: what's the first step?

Neurons in primary visual cortex respond to binocular disparity, the raw material of stereoscopic depth perception. Although these neurons are probably essential to depth perception, a recent study has shown that they are unable to compute depth itself.

Animals↗
PubMed1995

Mechanisms of stereoscopic processing: stereoattention and surface perception in depth reconstruction.

Consideration of the range of phenomena from studies of human stereopsis suggests that a five-stage model is required to provide a complete account of the processes involved, within which any stereoattention mechanism must operate. The information from the disparity field of the optical projections to the two eyes (stage 1) goes to a set of parallel Keplerian arrays of disparity detectors, each array selective for a different spatiotemporal property of the visual images (stage 2). Global interactions produce a cyclopean depth image that is cleaned of the spurious ghost images in the Keplerian arrays (stage 3) and that may then be processed for its (hypercyclopean) from elements (stage 4). Finally, there must be a stage of integration of the stereoscopic depth cues with monocular and kinesthetic depth cues to form the overall map of perceived distance (stage 5). The fact that multiple cyclopean surfaces may be perceived as transparent implies that the stereoscopic system is not limited by a singular-surface constraint. However, it is unclear whether multiple surfaces can be seen simultaneously or whether only one surface is seen at a time by a selective-attention process, with the others perceived as a purely inchoate (qualitative) depth impression. New experiments on cueing of ambiguous stereocorrugations by singular flat planes suggest that selective stereoattention is a powerful mechanism. In fact, the results show that attention can be focused not just in horopteral planes but in a variety of depth configurations. Moreover, this attention focus may act as a tracking mechanism to allow perception of smooth cyclopean stereomotion, which has a frequency response up to approximately 5 Hz (in contrast to the approximately 15 Hz limit for detecting planar disparity shifts as jerky appearance and disappearance effects). Finally, the spatial limits of stereosurface reconstruction are explored with cyclopean targets to show some interesting asymmetries of the surface-wrapping process that may represent object-oriented constraints on depth reconstruction.

Attention↗
PubMed1996

Non-syncopal falls in the elderly in relation to home environments.

Methods of prevention of falls in the home may differ for healthy and frail individuals. We therefore sought to determine whether measures of health and functioning in older persons are more useful in predicting falls at home not involving home hazards (non-environmental falls) than falls at home related to home hazards (environmental falls), and whether these relationships differ among those who fell once and those who fell multiple times during follow-up. Data for this analysis are from a 1-year prospective cohort study of 325 community-dwelling volunteers aged 60-93 years who had fallen during the year before baseline. In general, associations were stronger between poor functional ability and non-environmental falls than between poor functional ability and environmental falls. Independent predictors of non-environmental first falls during follow-up included Parkinson's disease (adjusted odds ratio (AOR) 7.66, 95% confidence interval (95% CI) 1.15-51.1) and being home alone 10 or more hours per day (AOR 2.36, 95% CI 1.20-4.61); independent predictors of environmental first falls during follow-up included arthritis (AOR 2.60, 95% CI 1.32-5.09) and poor depth perception (AOR 0.73, 95% CI 0.59-0.89, for each unit increase in depth perception score). Also, associations between poor function and falls were generally stronger among participants who fell repeatedly than among individuals who fell only once during the follow-up year. In conclusion, poor function predisposes to non-environmental falls at home in older persons and, to a lesser extent, environmental falls in those who fall repeatedly. Certain functional characteristics such as poor depth perception may predispose to environmental falls to a greater extent than do other disabilities.

Accidental Falls↗
PubMed1982

Simultaneous and successive contrast effects in the perception of depth from motion-parallax and stereoscopic information.

Prolonged inspection of a three-dimensional corrugated surface resulted in a successive contrast effect, or aftereffect, of depth, whereby a subsequently-viewed physically-flat test surface appeared to be corrugated in depth with the opposite phase to the adapting surface. The aftereffect occurred both when the depth was specified by motion parallax, in the absence of all other sources of depth information, and when it was specified solely by stereoscopic information. The depth aftereffect was measured by 'nulling' the apparent depth in the test surface with physical relative motion or binocular disparity until the test surface appeared flat. Up to 70% of the depth in the adapting surface was necessary to null the aftereffect. Simultaneous contrast effects in the perception of three-dimensional surfaces were used to investigate the spatial interactions that exist in the processing of motion-parallax and stereoscopic information. A physically vertical surface appeared to slope in depth in the opposite direction to the slope of a surrounding surface. In this case up to 50% of the slope of the inducing surface was necessary to null the contrast effect. Similar results were again obtained for motion-parallax and stereoscopic depth.

Adaptation, Ocular↗
PubMed1984

Information about three-dimensional shape and direction of illumination in a square-wave grating.

A homogeneous grey picture and a 'Mondrian' type of picture were illuminated by a projector with square-wave gratings of thirty different contrast values used as slides. Ten observers reported whether the picture appeared three-dimensional (3-D) (pleated) or flat. 3-D responses in this situation indicate colour constancy 'at the cost of' nonveridical depth perception. The frequencies of 3-D responses were significantly higher for the structured picture than for the homogeneous grey one. In reports of the direction from which the apparent 3-D object appeared to be illuminated there was a significant preference for responses "from above" when the grating was horizontally oriented. With vertical orientation there was no preference for "from the left" or "from the right". The results from the first experiment contradict traditional cue theories of depth perception since the projection of the borders between the fields of the structured picture was invariant and expected to inform about the flatness of the picture. They are, however, in line with a model for perceptual analysis of reflected light into common and relative components proposed earlier by Bergström. The difference in perceived direction of illumination between horizontally and vertically orientated gratings is discussed in connection with human ecology.

Color Perception↗
PubMed2001

Visual risk factors for falls in older people.

OBJECTIVES: To determine the tests most predictive of falls in community-dwelling older people from a range of visual screening tests (high and low contrast visual acuity, edge contrast sensitivity, depth perception, and visual field size). To determine whether one or more of these visual measures, in association with measures of sensation, strength, reaction time, and balance, can accurately predict falls in this group. DESIGN: Prospective cohort study of 12 months duration. SETTING: Falls and Balance Laboratory, Prince of Wales Medical Research Institute. PARTICIPANTS: 156 community-dwelling men and women age 63 to 90 (mean age 76.5, standard deviation = 5.1). MEASUREMENTS: Screening tests of vision, sensation, strength, reaction time and balance, falls. RESULTS: Of the 148 subjects available at follow-up, 64 (43.2%) reported falling, with 32 (21.7%) reporting multiple falls. Multiple fallers had decreased vision, as indicated by all visual tests, with impaired depth perception, contrast sensitivity, and low-contrast visual acuity being the strongest risk factors. Subjects with good vision in both eyes had the lowest rate of falls, whereas those with good vision in one eye and only moderate or poor vision in the other eye had elevated falling rates-equivalent to those with moderate or poor vision in both eyes. Discriminant analysis revealed that impaired depth perception, slow reaction time, and increased body sway on a compliant surface were significantly and independently associated with falls. These variables correctly classified 76% of the cases, with similar sensitivity and specificity. CONCLUSION: The study findings indicate that impaired vision is an important and independent risk factor for falls. Adequate depth perception and distant-edge-contrast sensitivity, in particular, appear to be important for maintaining balance and detecting and avoiding hazards in the environment.

Accidental Falls↗
PubMed1975

Relationship between monocular and binocular depth acuity.

Estimates of monocular and binocular depth acuity were obtained on two samples of subjects with adequate visual acuity and capacity for stereopsis. Both a method of average error and a modified method of limits were employed to secure the estimates. Eight ratios of binocular to monocular depth acuity ranged from 2.4:1 to 4.2:1 at a distance of 15 ft. The results contradict the familiar generalization that binocular depth perception is about 20 times as acute as monocular depth perception.

Adolescent↗
PubMed1993

Neurological and behavioral effects of a unilateral frontal cortical lesion in fetal kittens. II. Visual system tests, and proposing an "optimal developmental period" for lesion effects.

Nine fetal kittens sustained removal of the left frontal cortex during the last third of gestation (E 43-55) and were compared to animals sustaining a similar lesion postnatally (P 8-14) as well as to intact littermates. Beginning after 6 months of age, the animals' visual field and depth perception were assessed. In addition, pupil size as well as eye alignment were measured. On two visual field tests the fetal-lesioned cats showed test dependent decrements for some angles of vision. In terms of depth perception, only the prenatal-lesioned animals showed a higher binocular threshold; they also showed ocular misalignment which may have contributed to their depth perception impairment. Moreover, these animals had a larger ipsilateral pupil. The neonatal-lesioned animals were like normal cats for all tests and measurements. We conclude that, as for the tests reported in the preceding paper, the outcome for visual related behaviors of a prenatal frontal cortical lesion in the cat is also worse than that of a similar lesion sustained neonatally. Dysgenetic anatomical changes of the visual system induced indirectly by the frontal lesion are proposed as a possible explanation for these age-at-lesion differences. Based on the present work as well as on the literature, we propose the existence of an "optimal developmental period" for the best behavioral and anatomical outcome of perinatal brain lesions. We argue that this concept fits contemporary data and can better explain the different age-at-lesion effects of brain injury across animals species than the "Kennard Principle" (or "infant-lesion effect").

Animals↗
PubMed1986

Binocular vision and spatial perception in 4- and 5-month-old infants.

Four experiments investigated the relation between the development of binocular vision and infant spatial perception. Experiments 1 and 2 compared monocular and binocular depth perception in 4- and 5-month-old infants. Infants in both age groups reached more consistently for the nearer of two objects under binocular viewing conditions than under monocular viewing conditions. Experiments 3 and 4 investigated whether the superiority of binocular depth perception in 4-month-olds is related to the development of sensitivity to binocular disparity. Under binocular viewing conditions in Experiment 3, infants identified as disparity-sensitive reached more consistently for the nearer object than did infants identified as disparity-insensitive. The two groups' performances did not differ under monocular viewing conditions. These results suggest that, binocularly, the disparity-sensitive infants perceived the objects' distances more accurately than did the disparity-insensitive infants. In Experiment 4, infants were habituated to an object, then presented with the same object and a novel object that differed only in size. Disparity-sensitive infants showed size constancy by recovering from habituation when viewing the novel object. Disparity-insensitive infants did not show clear evidence of size constancy. These findings suggest that the development of sensitivity to binocular disparity is accompanied by a substantial increase in the accuracy of infant spatial perception.

Adaptation, Psychological↗
PubMed1996

Sensory impairments and physical disability in aged women living at home.

BACKGROUND: Studies of the impact of visual or hearing impairments on physical disability in older people have provided conflicting results. Furthermore, the consequences of the loss of such visual functions as depth perception or contrast sensitivity have rarely been studied. We examined the relationship of visual acuity, depth perception, contrast sensitivity, and hearing difficulty to the ability of older women living at home to accomplish instrumental activities of daily living independently. METHODS: Data on self-reported physical disability and hearing impairment, as well as objective measures of functional vision and physical ability were collected from a sample of 1210 community-dwelling women aged 75 years and older. Multivariate logistic regression modelling was used to assess the strength of the association between physical disability and sensory impairments, controlling for age, education level, motor limitations, and prevalent chronic diseases. RESULTS: Women with low visual acuity or low contrast sensitivity were significantly more likely to be physically dependent than women with good vision. Contrast sensitivity was, however, a better predictor than functional acuity, after controlling for age, education level, motor limitations and chronic medical conditions (adjusted odds ratio: 5.1; 95% confidence interval: 2.0-12.9). Depth perception was not related to physical disability. Women with serious hearing difficulty had significantly increased odds of dependency (4.1; 1. 4-12.1). CONCLUSIONS: Severe sensory impairments are strongly related to physical dependency in older women. It may be useful to add a test of contrast sensitivity to the traditional acuity test to predict better which elderly individuals may have difficulty carrying out routine daily activities.

Activities of Daily Living↗
PubMed1998

Cortical computation of stereo disparity.

Our ability to see the world in depth is a major accomplishment of the brain. Previous models of how positionally disparate cues to the two eyes are binocularly matched limit possible matches by invoking uniqueness and continuity constraints. These approaches cannot explain data wherein uniqueness fails and changes in contrast alter depth percepts, or where surface discontinuities cause surfaces to be seen in depth, although they are registered by only one eye (da Vinci stereopsis). A new stereopsis model explains these depth percepts by proposing how cortical complex cells binocularly filter their inputs and how monocular and binocular complex cells compete to determine the winning depth signals.

Contrast Sensitivity↗
PubMed1989

The power of shadows: shadow stereopsis.

Our ability to localize objects in three-dimensional space relies primarily on the stereoscopic capability of our visual system. It is generally believed that parallax disparities in the retinal images in our two eyes are required for experiencing stereovision. Traditionally, parallax disparities refer to points that are well defined within the objects, such as edges or boundaries. Shadows can create abrupt luminance changes in the scene but are neither edges nor boundaries, and their position varies with the position of the light sources. It is demonstrated that retinal images with no parallax disparity but with different shadows are fused stereoscopically, imparting depth perception to the imaged scene. Shadows are shown to be an important, hitherto undescribed stereoscopic cue for depth perception.

Depth Perception↗