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At least 433 records · Page 24Linked to original sources
PubMed2004

A prospective study of the effect of a unilateral macular hole on sensory and motor binocular function and recovery following successful surgery.

AIMS: To examine the effect of a unilateral full thickness macular hole on sensory and motor binocular function and to study recovery after successful surgical closure. METHODS: Twenty eight consecutive patients undergoing surgery for a unilateral macular hole underwent orthoptic examination, including measurements of Titmus and TNO stereoacuity and motor fusion range before surgery. Twenty three patients had successful anatomical closure. Fifteen of these patients, who had both improved acuity in the operated eye following surgery and were available for further testing, underwent repeat orthoptic assessment 2-7 months after surgery. RESULTS: In all patients stereoacuity was reduced before surgery, but few patients were subjectively aware of a deficit of depth perception affecting their everyday life. In those patients with improved Snellen acuity after surgery, stereoacuity measured by the Titmus stereotest also improved significantly, but not that measured by the TNO test. Two patients were aware of a subjective improvement in depth perception. Motor fusion was markedly reduced compared to normal before surgery, with only limited recovery after surgery. CONCLUSION: A unilateral macular hole notably reduced both stereoacuity and motor fusion. Successful closure improved the deficit in stereoacuity associated with the hole when measured by a stereotest using contoured stimuli. The majority of patients were not subjectively aware of the deficit in stereoacuity or its improvement following surgery.

Aged↗
PubMed1981

Alternative solutions to kinetic stimulus transformations.

It has been assumed that certain stimulus transformations lead directly to depth effects, that is, that such transformations are the necessary and sufficient conditions for kinetically generated depth perception. An alternative is to view such perception as the preferred solution to the problem posed by the transforming stimulus as to what even in the world is producing that transformation. In several experiments it is shown that when other solutions are supportable by the stimulus, those same transformations will no longer lead to depth perception. These other solutions become preferred on the basis of rejection of certain coincidental features of the stimulus that otherwise would have to be accepted were the kinetic depth solution to be maintained. The findings are interpreted as challenging any theory that perception is simply the direct result of stimulation or of extraction of stimulus information and as supporting the Helmkoltzian rule of perception as a construction of the most reasonable representation.

Depth Perception↗
PubMed1985

Complementary spatial locations, width, and disparity.

An alternative analysis is offered for human depth perception in addition to the depth cue of disparity. The new analysis considers locations both proximal and distal to the fixation point and offers an explanation as to why a stimulus presented at one disparity sign may be mistakenly considered to possess the opposite sign. Three descriptions of applications, the Pulfrich phenomenon, an interpretation of the Hornbostel effect (the three-dimensional Necker cube), and the determination of the limits of stereoscopic vision, are discussed. In addition the new analysis discloses a particular advantage of binocular over monocular vision which had not been appreciated formerly. The new analysis offers a powerful analytical tool of simple mathematical form. The means of conversion from the new analysis to and from disparity is included. In addition the similarity between the new approach and the classical lens equation is examined.

Depth Perception↗
PubMed2002

The optical functional advantages of an intraocular low-vision telescope.

An implantable miniaturized telescope (IMT) for low vision has recently been developed. Surgically inserted into only one eye of patients with bilateral central visual loss, the IMT provides a nominal magnification of 3.0x and a field-of-view of 6.6 degrees (9.2 degrees for the 2.2x magnification version). Theoretical concerns have been raised regarding the ability of patients to function with a large interocular magnification difference, the impact of the monocular restriction of the field-of-view, and the impact of this design on depth perception. This article addresses these concerns regarding the design of the IMT in comparison with spectacle-mounted telescopes and combined intraocular lens/spectacle (or combined contact lens/spectacle) telescopic systems. The effective field-of-view (as determined by the combination of both the field-of-view and the field-of-fixation), the effects of head motion and the vestibular reflex, and the disruption of stereo depth perception with a monocular device are considered here. Physiological optics considerations of these issues show that the IMT may have important advantages over other designs of magnification devices for patients with age-related macular degeneration.

Depth Perception↗
PubMed1999

Binocular neurons in V1 of awake monkeys are selective for absolute, not relative, disparity.

Most neurophysiological accounts of disparity selectivity in neurons of the primary visual cortex (V1) imply that they are selective for absolute retinal disparities. By contrast, a number of psychophysical observations indicate that relative disparities play a more important role in depth perception. During recordings from disparity selective neurons in area V1 of awake behaving monkeys, we used a disparity feedback loop () to add controlled amounts of absolute disparity to a display containing both absolute and relative disparities. This manipulation changed the absolute disparity of all the visible features in the display but left unchanged the relative disparities signalled by these features. The addition of absolute disparities produced clear changes in the neural responses to unchanged external stimuli, which were well predicted by the measured change in absolute disparity: in 45/53 cases, the neuron maintained a consistent firing pattern with respect to absolute disparity so that the manipulation created no significant change in the absolute disparity preferred by the neuron. No neuron in V1 maintained a consistent relationship with relative disparity. We conclude that the relative disparity signals used in primate depth perception are constructed outside area V1.

Action Potentials↗
PubMed2000

Visual impairment and risk of hip fracture.

As part of a case-control study, the Auckland Hip Fracture Study (1991-1994), the authors examined associations between impaired vision and risk of hip fracture. Subjects (911 cases and 910 controls aged 60 years or older) completed a questionnaire and had vision measurements taken, including measurements of visual acuity and stereopsis (depth perception). Binocular visual acuity worse than 20/60 was statistically significantly associated with increased risk of hip fracture after adjustment for age, sex, proxy response, hours of activity per week, and height (odds ratio (OR) = 1.5; 95% confidence interval (CI): 1.1, 2.0), as was having poor vision (less than 20/100) in both eyes (OR = 2.4; 95% CI: 1.0, 6.1). Having no depth perception was associated with increased risk (OR = 6.0 95% CI: 3.2, 11.1), as were categories of decreasing stereopsis (trend p = 0.0001), self-reported poor vision (OR = 1.4; 95% CI: 1.0, 1.9), not wearing glasses at the time of the fall (OR = 1.2; 95% CI: 1.0, 1.6), and increasing time since the last eye examination (trend p = 0.03). The population attributable risk of hip fracture due to poor visual acuity or stereopsis was 40%. Visual factors are important fall-related factors which influence risk of hip fracture. Risk of hip fracture may be decreased by correcting refractive error, improving stereopsis, and administering regular eye examinations.

Accidental Falls↗
PubMed1993

Effects of stereoscopic and rotational displays in a three-dimensional path-tracing task.

A series of three experiments investigated the effectiveness of stereoscopic and rotational display techniques for the purpose of establishing human factors guidelines for the design of three-dimensional (3D) displays. In the described experiments, depth perception was evaluated by examining accuracy in a 3D path-tracing task, with stimulus displays resembling the structure of cerebral angiograms. The first experiment allowed subjects to control rotation in dynamic displays. The results indicated that performance improved using either technique relative to viewing two-dimensional (2D) displays. However, rotational displays were superior to stereoscopic displays, and performance was best when both techniques were combined. The second experiment compared subject-controlled rotation with observation of continuously rotating displays at different rates of rotation. Performance declined at faster rotation rates; however, there were no advantages of subject-controlled rotation. In the third experiment, performance in rotational displays was no better than that in stereoscopic displays enhanced with multiple static viewing angles. However, performance was always best when both 3D techniques were jointly implemented. The results are discussed in terms of the visual information available using either 3D display technique and are related to the weighted additive model of depth perception.

Adult↗
PubMed1991

The visual and driving performance of monocular and binocular heavy-duty truck drivers.

This study compared the performance of 40 monocular and 40 binocular tractor-trailer drivers on measures of both visual and driving performance. On the visual measures, the mononuclear drivers were significantly deficient in contrast sensitivity, visual acuity under low illumination and glare, and binocular depth perception. They were not significantly deficient in static or dynamic visual acuity, visual field of individual eyes, or glare recovery. Driving measures of visual search, lane keeping, clearance judgment, gap judgment, hazard detection, and information recognition showed no differences between monocular and binocular drivers. Monocular drives were poorer than binocular drivers only in sign reading distance in both daytime and nighttime driving. This decrement correlated significantly with the binocular depth perception measure. There were large individual differences within each group for most of the visual and driving performance measures. It was concluded that monocular drivers have some significant reductions in selected visual capabilities and in certain driving functions dependent on these abilities, compared with binocular drivers. However, monocular drivers are not significantly worse than binocular drivers in the safety of most day-to-day driving functions. Implications of these findings and the large individual differences within each group are discussed.

Adult↗
PubMed2000

[Visual evoked potentials and recognizing depths during changes in gaze direction].

PURPOSE: The neurophysiological mechanism underlying a phenomenon of depth perception that can not be explained by only the horizontal binocular retinal disparity was analyzed by means of visual evoked cortical potentials (VECPs). METHODS: A pair of pictures showing fourteen vertical lines with the same magnitude of horizontal retinal disparity were presented to eight normal subjects stereoscopically. Subjects were required to view the pair while changing the visual line direction. VECPs were measured while changing both the visual line directions and the sizes of the horizontal retinal disparity. RESULTS: The subjects perceived all lines as having the same magnitude of depth when they viewed the center position of the pictures stereoscopically (centro-version viewing). Shifting their visual line direction to the left end (laevo-version viewing), the depth magnitude of each line decreased gradually with increase of retinal eccentricity. Next, while maintaining the laevo-version the subjects were asked to make all lines of the same depth by changing the disparity magnitude of each line manually. Viewing this new version of the picture in the centro-version, the further each line was separated from the line located in the center, the greater was the magnitude of its depth. However, no significant differences in amplitudes of VECPs, corresponding to those pictures were found. CONCLUSIONS: Our results suggest that differences of recognizable depth perception between the centro- and the laevo-version viewing occur in a higher order visual center than in the occipital and parietal zone when analyzing horizontal retinal disparity.

Adult↗
PubMed2005

Osteoarthritis of the knees increases the propensity to trip on an obstacle.

Tripping on an object is the most frequent cause of falls. We examined the effects of painful osteoarthritis of the knee on obstacle avoidance success rates in older adults. Obstacle avoidance success rates, pain, body mass index, visual acuity, contrast sensitivity, depth perception, and single-leg stance duration were evaluated in 17 patients with painful osteoarthritis of the knees (age range, 59.6 +/- 8.1 years) and 14 age-matched healthy control subjects (age range, 61.1 +/- 10.0 years). The patients with osteoarthritis of the knees had a 37% lower obstacle avoidance success rate, a 54% lower single-leg stance duration, and a 24% greater body mass index than the control subjects. Age, visual acuity, contrast sensitivity, and depth perception were not different between the two groups. Obstacle avoidance success rates and single-leg stance durations decreased linearly as pain increased in the patients with osteoarthritis of the knees. Obstacle avoidance success rates also decreased linearly as single-leg stance duration decreased in the patients with osteoarthritis of the knees. Osteoarthritis of the knees reduced obstacle avoidance success rates, supporting epidemiologic studies that have found osteoarthritis to be a risk factor for falls. This study showed that pain associated with osteoarthritis of the knees increased the propensity to trip on an obstacle (the greater the pain the greater the propensity to trip and fall) and underscores the importance of treating pain associated with osteoarthritis.

Accidental Falls↗
PubMed1998

Display duration and stereoscopic depth discrimination.

We investigated the role of display duration in stereoscopic depth perception. The display consisted of a dynamic random-dot stereogram, with two disparity-defined squares (1.9 degrees x 1.9 degrees), one on the left and one on the right of a central (Nonius) fixation stimulus. The sign of the disparity (crossed or uncrossed) was always the same for both squares, and the magnitude of disparity was 0.25 degree for one square and either 0.125 degree or 0.375 degree for the other square. Participants indicated which square appeared closer. The display duration was varied adaptively between 20 and 1000 ms until participants performed at 75% accuracy. Results confirmed large individual differences in the display duration required for stereoscopic depth perception. Approximately half of the 100 naive participants were able to perform the task at 20 ms, while the remaining participants required up to 1000 ms to perform at criterion. The present study shows that display duration is a critical variable in explaining wide differences in reported abilities of individuals to process stereoscopic depth information.

Adult↗
PubMed1983

Spatial characteristics of static and dynamic stereoacuity in strabismus.

The spatial and temporal organization of stereoscopic depth perception were compared in normal and strabismic observers. The minimum and maximum disparities for stimulating static and dynamic stereopsis in strabismus were examined as a function of spatial separation of disparate stimuli. Disparities and their spacing were produced by spatial modulation of two vertical lines viewed haploscopically. Most strabismics had normal upper disparity limits but elevated static and dynamic stereothresholds. Moderate stereothreshold elevations (100 arc sec) were constant for spatial separations greater than 15 arc min. Two new types of spatial crowding effects upon stereopsis were observed. The first type resulted from the constant elevation of the disparity threshold. The second type consisted of a reduced maximum disparity limit for stereopsis. In both cases, the constriction of the range of perceivable depth produced a reduction in the spatial and temporal frequency limits for depth perception. Clinical tests of stereoacuity that crowd stimuli closer than 0.25 degree underestimated the strabismic patients' potential stereoacuities by a factor of 2 to 4. Similarly, tests of dynamic stereopsis that use temporal frequencies greater than 1 Hz will underestimate optimal dynamic stereoacuity.

Depth Perception↗
PubMed2000

Model complexity: the fit to random data reconsidered.

A recent controversy in the field of depth perception has highlighted an important aspect of model testing concerning a model's complexity, defined as the prior propensity of the model to fit arbitrary data sets. The present article introduces an index of complexity, called the mean minimum distance, defined as the average squared distance between an arbitrary data point and the prediction range of the model. It may also be expressed as a dimensionless quantity called the scaled mean minimum distance. For linear models, theoretical values for the scaled mean minimum distance and the variance of the scaled minimum distance can be readily obtained and compared against empirical estimates obtained from fits to random data. The approach is applied to resolving the question of the relative complexity of the Linear Integration model and the Fuzzy Logic of Perception model, both of which have been the subject of controversy in the field of depth perception. It is concluded that the two models are equally complex.

Humans↗
PubMed2001

The processing of stereoscopic information in human visual cortex: psychophysical and electrophysiological evidence.

Three-dimensional depth perception relies in part on the binocular fusion of horizontally disparate stimuli presented to the left and right eye. The mammalian visual system offers a unique possibility to study electrophysiologically cortical neuronal mechanisms: since the input of the two eyes remains separated up to the level of the visual cortex, evoked potential components that are generated exclusively by cortical structures may be explored when dynamic random-dot stereograms (dRDS) are presented. In a series of independent studies, we determined the scalp topography of dRDS evoked brain activity in different groups of healthy subjects, and we found consistent results. Major differences between stereoscopic and contrast evoked brain activity are seen in the strength of the potential fields as well as in their topography. Our findings suggest that there are fewer neurons in the human visual cortex that are responsive to horizontal disparity, and that higher visual areas like V2 are more engaged with stereoscopic processing than the primary visual cortex. On the other hand, component latencies of evoked brain activity show no effect signifying that the binocular information flow to the visual cortex has a similar time course for both the processing of contrast information and of dRDS stimuli. We could also verify that healthy subjects can learn to perceive 3D structure contained in dRDS. Changes in perceptual ability as measured with psychophysical tests are paralleled by systematic alterations in the topography of stereoscopically evoked potential fields. Stereoscopic VEP recordings may also be of clinical use: in patients with selectively disturbed depth perception but normal visual acuity there is a high correlation between clinical symptoms, perceptual deficiency, and altered VEP amplitudes and latencies.

Brain Mapping↗
PubMed2000

[The effect of attention on visual evoked potentials elicited by a newly designed stereogram].

PURPOSE: To investigate whether the visual evoked potentials (VEPs) obtained by a newly designed stereogram were generated by some higher function like depth perception, we examined the effect of attention on the VEPs. SUBJECTS AND METHOD: Eight subjects participated in the experiments. The VEPs were recorded according to the international 10/20 system. The stimulus consisted of circles with or without disparity presented on 4 locations around the fixation point, and they appeared in one of 3 patterns in random order when viewed through red/green spectacles 1. at the same distance as the fixation point, 2. in front of it, or 3. at the back of it. The near pattern was defined as the target. In Experiment 1, the subjects just fixated on the fixation point. In Experiments 2 and 3, they were required to respond to the target by pressing a button and counting the number (target discrimination task). RESULTS: A scalp negative potential with a latency of 170-280 msec was elicited in the lateral occipital area. For each of the 3 patterns the amplitude was greater in Experiments 2 and 3 than in Experiment 1. In Experiments 2 and 3, stimuli with disparity resulted in larger amplitude than without disparity. The target stimulus also evoked larger potentials than non-target stimuli did, although no such effect was apparent in Experiment 1. CONCLUSION: Attention, as well as disparity, increased the VEPs amplitude, which indicates that the potential could be generated by neural activity higher than V 1 including depth perception. Moreover, the potential showed characteristics similar to attention-related potentials modulated by visuo-spatial attention.

Adult↗
PubMed2000

Influence of two-dimensional and three-dimensional imaging on endoscopic bowel suturing.

Several three-dimensional (3-D) video-endoscopic systems have been introduced in surgical practice to enhance depth perception during minimal access surgery (MAS), but the facilitation of endoscopic manipulations by the current 3-D systems remains unproved. The aim of the study was to investigate the influence of 2-D and 3-D imaging modalities on intracorporeal suturing. The standard task consisted of suture closure of 60 mm enterotomies made in porcine small bowel with continuous seromuscular 3/0 Polysorb. Ten experienced surgeons participated in the study. The imaging systems were Storz (2-D), Welch Allyn (3-D), and Zeiss (as both 2-D and 3-D). Each surgeon performed two tasks with each modality in a random sequence. The outcome measures were execution time, suture line leakage pressure, and suture placement score. In addition, the participating surgeons assigned subjective scores on the image quality and the adverse effects of the imaging systems. There was no significant difference in the execution time, leakage pressure, and suture placement score among the various imaging modalities. Depth perception was rated as similar with 2-D and 3-D imaging. Surgeons experienced visual strain with the three systems, but it was rated higher with 3-D imaging. With the current technology, we have not documented any significant difference in task efficiency and quality of endoscopic bowel suturing by trained surgeons between 2-D and 3-D imaging systems.

Analysis of Variance↗
PubMed2004

Sensitivity to linear-speed-gradient of radial expansion flow in infancy.

A radial expansion flow having a linear-speed-gradient (linear-grad) creates robust perception of a rigid object moving-in-depth [Perception 19 (1990) 21]. It has been reported that sensitivity to a linear-grad of radial expansion emerges at 2 months of age [Infant Behavior and Development 17 (1994) 165]. In the present study, we examined the development of sensitivity to the linear-grad of radial expansion after 2 months of age with three experiments. A total of 197 2- to 5-month-old infants participated. The results showed that sensitivity to the linear-grad improves between 2 and 3 months of age (Experiment 1), and that the infants may discriminate between an expansion having linear-grad and that having zero-grad based on their perception of motion-in-depth (Experiments 2 and 3).

Aging↗