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Results for “Vision, Monocular”

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At least 253 records · Page 14Linked to original sources

PubMed2006

Vehicle detection by means of stereo vision-based obstacles features extraction and monocular pattern analysis.

This paper presents a stereo vision system for the detection and distance computation of a preceding vehicle. It is divided in two major steps. Initially, a stereo vision-based algorithm is used to extract relevant three-dimensional (3-D) features in the scene, these features are investigated further in order to select the ones that belong to vertical objects only and not to the road or background. These 3-D vertical features are then used as a starting point for preceding vehicle detection; by using a symmetry operator, a match against a simplified model of a rear vehicle's shape is performed using a monocular vision-based approach that allows the identification of a preceding vehicle. In addition, using the 3-D information previously extracted, an accurate distance computation is performed.

Algorithms↗

PubMed1996

Infant peripheral vision: the development of monocular visual acuity in the first 3 months of postnatal life.

Quantitative data on the early morphological development of the human retina show that the peripheral region is relatively more mature than the central region. These results have stimulated researchers to compare the development of visual functions in the central and peripheral regions of the visual field. Here, we used preferential looking to evaluate 1-, 2- and 3-month-old infants' central and peripheral (10 degrees and 30 degrees) monocular visual acuity. There were three findings: (i) both central and peripheral acuities were poor at 1 month, improved over the age range tested, but were still about 3 octaves worse than adults' acuity; (ii) at all ages monocular acuity decreased with increasing eccentricity; (iii) 2- and 3-month-olds showed higher acuity for gratings in the temporal than in the nasal visual field at 30 degrees. The implications of these results for issues in visual development are discussed.

Adult↗

PubMed1996

Monocular contrast sensitivity in 3- to 36-month-old human infants.

A recently developed psychophysical "card" technique was used to evaluate monocular contrast sensitivity in ninety 3-, 6-, 12-, 24-, and 36-month-old human infants. Results showed that for 3-, 6-, 24-, and 36-month-olds, monocular contrast sensitivity functions were very similar to binocular contrast sensitivity functions estimated in a previous experiment. However, at 12-months, monocular contrast sensitivity functions were significantly lower (about 1 octave) than binocular contrast sensitivity functions, a trend also observed in developmental studies of visual acuity. This asymmetry suggests that the neural substrate underlying the development of monocular and binocular spatial vision undergoes different rates of development, at least during the months surrounding the end of the first postnatal year.

Aging↗

PubMed1992

Stereolatency: a stereopsis test for everyday depth perception.

An instrument is described which tests for the use of stereopsis by measuring how long it takes for depth perception to begin (its latency) after a transition from monocular to binocular vision. Starting at 1 s, the duration of binocular vision is reduced progressively toward a limit of 16 ms (or increased to a limit of 4 s) until the latency of stereopsis is found. The preliminary period of monocular vision acts as a probe for suppression of either eye and allows time for accommodation and vergence to stabilize before binocular vision begins. Typical results are presented.

Depth Perception↗

PubMed1986

Different rates and amounts of vision function recovery during orthoptic therapy in an older strabismic amblyope.

Orthoptic therapy was instituted in an 11-year-old patient having deep amblyopia, constant small-angle esotropia with anomalous retinal correspondence, and a past history of minimal success with such therapy. This combination of factors pointed toward a poor prognosis for substantial recovery of vision function. Rate of recovery of several monocular and binocular vision functions was monitored during the course of 18 months of intensive orthoptic therapy. Results showed marked improvement in several monocular vision functions, suggesting presence of considerable residual neural plasticity of multiple sites in the visual pathways of this older amblyope.

Accommodation, Ocular↗

PubMed2002

Changes in cyclotorsion and vertical eye alignment during prolonged monocular occlusion.

When binocular vision is prevented with monocular occlusion, the two eyes assume a position of rest related to the combination of underlying tonic innervation of the oculomotor system, cross-coupled accommodative-vergence input and vergence responses to perceptual cues for spatial location relative to the head. When the latter two are controlled, the covered eye has been shown in the majority of subjects to turn outward (exophoria) and upward (hyperphoria) after prolonged monocular occlusion. The present study investigates the change in torsional eye alignment and its relation to vertical eye alignment after eight hours of monocular occlusion. The results revealed an excyclophoria during occlusion in four out of five subjects. The patched eye also became elevated in two subjects and depressed in two others. Thus, during prolonged monocular occlusion, the relative directions of cyclophoria and vertical phoria appear to be independent. In addition, there were non-concomitant changes in vertical phoria with horizontal gaze, toward a state where the adducted eye was elevated relative to the abducted eye. Simulations with Orbit(TM) suggest that these non-concomitant changes in vertical phoria with a concomitant excyclophoria may be based upon orbital mechanics. Excyclophoria appears to be the baseline state of binocular alignment.

Humans↗

PubMed2005

Monocular transparency and unpaired stereopsis.

Howard and Duke [Howard, I. P. & Duke, P. A. (2003). Monocular transparency generates quantitative depth. Vision Research, 43, 2615-2621] recently proposed a new source of binocular information they claim is used to recover depth in stereoscopic displays. They argued that these displays lack conventional disparity and that the metrical depth experienced results from transparency rather than occlusion relations. Using a variety of modified versions of their stimuli, we show here that the conditions for transparency are not required to elicit the depth experienced in their stereograms. We demonstrate that quantitative and precise depth depended not on the presence of transparency but horizontal contours of the same contrast polarity. Depth was attenuated, particularly at larger target offsets, when horizontal contours had opposite contrast polarity for at least a portion of their length. We also show that a demonstration they used to control for the role of horizontal contours can be understood with previously identified mechanisms involved in the computations associated with stereoscopic occlusion. These results imply that the findings reported by Howard and Duke can be understood with mechanisms responsible for the computation of binocular disparity and stereoscopic occlusion.

Contrast Sensitivity↗

PubMed2006

Monocular transparency and unpaired stereopsis.

Contrast Sensitivity↗

PubMed2005

Prevalence of blindness and low vision in an Italian population: a comparison with other European studies.

AIM: The scientific literature contains recent data on the prevalence of blindness and low vision for a few European countries, but most of these studies have been focused exclusively on the elderly sector of the populations. The purpose of the present study was to provide age-specific estimates of the prevalence and causes of visual loss in an Italian population aged 40 years and over. METHODS: In total, 847 of the 1,200 citizens >40 years of age (70.6%) in the island community of Ponza underwent complete standardized ophthalmological examinations. Visual acuity (VA) was measured using a standard logarithmic chart. World health organization (WHO) definitions of blindness and low vision were adopted (respectively, VA>1.3 logMAR or a visual field <10 degrees around central fixation, and VA >0.5 to 1.3 logMAR or a visual field <20 degrees around central fixation). Prevalence rates based on presenting VAs were also calculated. RESULTS: The overall best-corrected prevalence rates were 0.6% (presenting, 0.8%) for better eye blindness, 2.1% (presenting, 6.7%) for better eye low vision, 1.8% (presenting, 2.6%) for monocular blindness, 5.0% (presenting, 11.2%) for monocular low vision. Cataract, glaucoma, degenerative myopia, and AMD were the main causes of better eye visual loss. CONCLUSION: Age-specific prevalence rates in Ponza are fairly consistent with those for other European countries with similar socio-economic conditions and public healthcare systems. A substantial percentage of visual losses remains uncorrected despite the availability of potentially curative therapy. Greater emphasis needs to be placed on educating the public regarding the importance of good vision.

Adult↗

PubMed2004

Distortions of distance and shape are not produced by a single continuous transformation of reach space.

We investigated whether distortions of perceived distance and shape could be captured by a single continuous one-to-one transformation of the underlying space. In Experiment 1, the participants reached to touch points around the perimeter of spherical targets viewed at five different distances, to yield simultaneous measures of perceived distance and shape. Different participants reached while using dynamic monocular, static binocular, or dynamic binocular vision. Thin plate spline (TPS) analysis was applied so as to transform a Cartesian grid in such a way as to carry the original target points to the mean reach locations. In all cases, discontinuities appeared in the transformed grid from folding of the space. In Experiment 2, the participants reached to points that lay at the same locus in reach space, but on different portions of the visible target spheres (e.g., front vs. side). The participants reached to different locations when the points were different with respect to shape (e.g., front vs. side) but reached to the same locations when the points were the same with respect to shape (left vs. right side). TPS analysis revealed discontinuities from holes torn in the underlying space. The results show that perceived distance and perceived shape entail different distortions and cannot be captured by a single continuous transformation of reach space.

Adult↗

PubMed1992

Proteoglycan synthesis by scleral chondrocytes is modulated by a vision dependent mechanism.

Proteoglycan synthesis was measured in chick sclera at the onset of form-deprivation myopia, as well as in the period immediately following removal of the occluder. Two day-old chicks were monocularly form vision deprived for periods from one to ten days and proteoglycan synthesis was determined after placing posterior scleral buttons in organ culture and measuring 35SO4 incorporation into glycosaminoglycans. Following 24 hrs of form-deprivation, proteoglycan synthesis was 33% higher in myopic eyes as compared with paired control eyes. The rate of proteoglycan synthesis further increased to levels 83% higher than controls after four days of form-deprivation and remained elevated throughout the ten day period of deprivation. Removal of the occluder after 10 days of form-deprivation resulted in a rapid drop in the rate of proteoglycan synthesis to control levels within 24 hrs. Proteoglycan synthesis was also measured in scleral chondrocytes isolated from control and myopic eyes after 10 days of form-deprivation. Proteoglycan synthesis by chondrocytes from myopic eyes did not return to control levels until 48 hrs after plating. Since the rate of proteoglycan synthesis returns to control levels more quickly during the recovery period ex vivo than when scleral chondrocytes from myopic eyes are placed in cell culture, we suggest that a mechanism is present within the eye which rapidly lowers the rate of proteoglycan synthesis in response to form vision.

Animals↗

PubMed1995

Depth relief.

A study is reported of the depth relief in a simple three-dimensional scene consisting of a white, rough sphere on a planar support, illuminated in a natural manner. Viewing conditions included monocular and binocular as well as 'synoptical' viewing. In the synoptical condition the eyes are optically superimposed. The local surface attitude was probed via a gauge figure that had to appear as a circle painted upon the surface of the object. The measurements allow a reconstruction of the depth relief, which can be compared with the (known) range map. Idiosyncratic differences between three subjects were found that are the exact reverse of what was found for these same subjects for the case of pictorial relief reported in an earlier paper. Apparently the subjects put different weights on sources of sometimes conflicting, sometimes corroborative evidence. The relief is deepest for binocular vision, flatter for monocular vision, and flatter still for synoptical vision. Deviations from veridicality that cannot be explained by mere depth scaling exist and may be due to the nature of the monocular cues.

Cues↗

PubMed1999

Binocular and monocular detection of Gabor patches in binocular two-dimensional noise.

Contrast thresholds for detecting sine-wave Gabor patches in two-dimensional externally added random-pixel noise were measured. Thresholds were obtained for monocular and binocular signals in the presence of spatial correlated (identical) and uncorrelated (independent) noise in the two eyes. Measurements were obtained at four different spectral densities of noise (including zero). Thresholds were higher for monocular stimuli than for binocular, and higher in the presence of correlated noise compared to uncorrelated noise. The magnitude of binocular summation, similar in correlated and uncorrelated noise, decreased with increasing noise strength. The independent contributions of internal noise and sampling efficiency to detection were analysed. Sampling efficiencies were higher for binocular than for monocular viewing for both types of noise, with values being higher with uncorrelated noise. Binocular stimuli showed a lower equivalent noise level compared to the mean monocular case for both types of noise.

Contrast Sensitivity↗

PubMed1998

Interocular suppression of a half-occluded region of stereoscopic images.

We assessed the detectability d' of a monocular small gray dot target presented on a half-occluded region of stereoscopic three-dimensional background images by comparing it with that on a two-dimensional (2D) region. For our experiments we used a typical two-alternative temporal forced-choice procedure, in which the target was presented in one of two temporal intervals for approximately 67 ms, and observers selected the interval they believed to have contained the target by pressing the corresponding key. To vary target signal intensity, we changed the target contrast against the background. According to signal-detection theory, we converted the percent-correct data to detectability d' and found that the relationship between d' and the contrast of the target followed Legge's equation. We used Legge's equation to calculate the contrast threshold and found that the contrast threshold of the target on the half-occluded region was higher than that on the 2D region. This elevation of contrast threshold indicates that interocular suppression of the half-occluded region occurs more frequently than that of the 2D region. We also refer to the monocular performance of the human visual system.

Adult↗

PubMed1996

Nonlinear responses of simple cells to Mach band stimuli: evidence from early monocularly deprived cats.

We have previously shown that, cat simple cells respond linearly to edges of variable blur widths: cells with receptive fields (RFs) of even symmetry respond better to a luminance ramp (where Mach bands are observed); cells with RFs of odd symmetry respond better to a luminance step (where no Mach bands are perceived). Our evidence has also indicated the existence of inhibitory interaction between cells with RFs of even and odd symmetry as predicted by the Tolhurst-Ratliff Mach band model. Since monocular deprivation is known to impair cortical inhibitory mechanisms, we studied the responses of simple cells of adult cats monocularly deprived at the age of 8-10 weeks to Mach band stimuli in order to delineate specific changes in inhibitory interactions caused by monocular deprivation. In pattern-deprived cats, particularly for cells driven by the deprived eye, there were many cells that responded contrary to linear models: odd-symmetric cells responded maximally to blurred edges while even-symmetric cells responded maximally to sharp edges. Cells that responded maximally as predicted, responded, similarly to normal cat cells, less than expected at suboptimal widths. All cells in normal and light-deprived cats responded in a linear fashion to sinusoidal stimuli. We conclude, therefore, that intracortical inhibition shapes simple cells' responses to edges. Monocular deprivation impairs this mechanism, thus causing simple cells in monocularly deprived cats to respond nonlinearly to edges. All simple cells responded linearly to gratings since it is not the linear spatiotemporal RF of these simple cells that was impaired under monocular deprivation.

Animals↗

PubMed2000

Neuronal representation of optic flow experienced by unilaterally blinded flies on their mean walking trajectories.

Asymmetries in the optic flow on both eyes may indicate an unintended turn of an animal and evoke compensatory optomotor responses. On a straight path in an evenly structured environment, the optic flow on both eyes is balanced corresponding to a state of optomotor equilibrium. When one eye is occluded an optomotor equilibrium is expected to be reached on a curved path provided that the translatory optic flow component is cancelled by a superimposed rotation. This hypothesis is tested by analysing how the HSE cell, a constituent element of the fly's optomotor system, represents optic flow in behavioural situations. The optic flow as seen on the average trajectory of freely walking monocular flies is reconstructed. This optic flow is used as stimulus of the HSE cell in electrophysiological experiments and as input of a model of the fly's optomotor system. The responses of the HSE cell and of the model fluctuate around the resting potential. On average, they are much smaller than the responses evoked by optic flow experienced on a straight path. These results corroborate the hypothesis that the mean trajectory of monocular flies corresponds to a path of optomotor equilibrium.

Animals↗

PubMed1997

[Evaluation of some vision components after implantation of bifocal and monocular intraocular lenses].

Short and long distance vision as well as vision in twilight conditions and dazzle sensitivity in 2 groups of 30 persons have been compared. In one group Corneal-Dual bifocal intraocular lenses and in the other group monocular lenses were implanted. In the former group 0.75 or nearer vision acuity was obtained without any additional correction, while in the latter group obtention of such vision required additional correction to +/- +2 4.0 D sph. Vision in twilight conditions and dazzle sensitivity were similar in both groups, though clearly lower than normal. The study also presents indications and contraindications for implantation of bifocal lenses.

Adult↗

PubMed2003

Simultaneous mapping of binocular and monocular receptive fields in awake monkeys for calibrating eye alignment in a dichoptical setup.

We developed a modified Wheatstone stereoscope for simultaneous dichoptical and binocular stimulation in awake monkey. We, therefore, extended the conventional two-screen Wheatstone stereoscope to a setup with an additional third screen viewed binocularly via semi-transparent mirrors. With a sparse noise stimulation we mapped classical receptive field (CRF) positions via each screen independently but simultaneously. This was done for multiple recording positions (16 electrodes) at once in primary visual cortex based on multiple unit spike activity (MUA) and local field potentials (LFP), respectively. The technique can be used to (1) quickly and simultaneously determine binocular as well as left and right eye CRFs, including ocular dominance characteristics (net recording time for the given examples: approximately 2 min), (2) precisely adjust dichoptical stimulation by evaluating offsets between monocular and binocular CRF positions (average spatial incongruency between binocular and left/right eye stimulation after calibration: approximately 0.025 degrees visual angle), and (3) investigate left and right eye interaction in forming binocular CRFs. Due to the precise adjustment of the dichoptical and the simultaneous binocular stimulation investigations on the basis of stereo vision can be done with appropriate eye vergence alignment matching normal binocular viewing conditions in awake animals.

Animals↗