[Work adaptation and rehabilitation problems for workers with monocular vision].
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Adaptation, Psychological↗
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Results for “Vision, Monocular”
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Picture perception and monocular vision: a reply to Hagen.
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Humans↗
Monocular double vision in strabismus.
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Diplopia↗
Is there an interaction between perceived direction and perceived aspect ratio in stereoscopic vision?
In monocular vision, the horizontal/vertical aspect ratio (shape) of a frontoparallel rectangle can be based on the comparison of the perceived directions of the rectangle's edges. In binocular vision of a typical three-dimensional scene (when occlusions are present), this is not the case: Frontoparallel rectangles would be perceived in a distorted fashion if an observer were to base perceived aspect ratio on the perceived directions of the rectangle's edges. We psychophysically investigated stereoscopically perceived aspect ratios of frontoparallel occluding and occluded rectangles for various distances and fixation depths. We found that observers did not perceive the distortions that would be predicted on the basis of the above-mentioned comparison of the perceived visual directions of the edges of the rectangle. Our results strongly suggest that the mechanism that determines perceived aspect ratio is dissociated from the mechanism that determines perceived direction. The consequences of the findings for the Kanizsa, Poggendorff, and horizontal/vertical illusions are discussed.
Depth Perception↗
Spatial perception in normal and strabismic subjects: role of stereopsis and monocular clues.
PURPOSE: To evaluate the roles of binocular vision, monocular clues, and experience in spatial perception in a prospective, nonrandomized, case-control study. METHODS: A test was created consisting of three wood blocks arranged along the frontal plane inside Panum area. To produce some degrees of horizontal disparity, blocks were moved along a sagittal plane. Thirteen normal subjects (control group) and 13 nonamblyopic strabismic subjects (study group) were asked to identify, both under binocular and monocular vision, the position of the blocks in a series of 12 randomized presentations (phase 1). In phase II of the trial, a letter E in three different sizes, acting as a monocular clue, marked the three blocks. In both phases, the number of correct answers to the test during binocular and monocular vision was recorded. RESULTS: Binocular normal responses appeared greater than monocular normal responses and strabismic binocular responses in both phases (p < 0.001). Binocular strabismic responses and monocular answers of both groups appeared similar. CONCLUSIONS: In our experimental model, spatial orientation of strabismic subjects in binocular vision is substantially identical to that of normal subjects in monocular vision. Monocular clues were used in the same manner in both groups of subjects, and experience seemed to play no role in spatial localization of visual objects.
Adolescent↗
Enhancement of vision by monocular deprivation in adult mice.
Plasticity of vision mediated through binocular interactions has been reported in mammals only during a "critical" period in juvenile life, wherein monocular deprivation (MD) causes an enduring loss of visual acuity (amblyopia) selectively through the deprived eye. Here, we report a different form of interocular plasticity of vision in adult mice in which MD leads to an enhancement of the optokinetic response (OKR) selectively through the nondeprived eye. Over 5 d of MD, the spatial frequency sensitivity of the OKR increased gradually, reaching a plateau of approximately 36% above pre-deprivation baseline. Eye opening initiated a gradual decline, but sensitivity was maintained above pre-deprivation baseline for 5-6 d. Enhanced function was restricted to the monocular visual field, notwithstanding the dependence of the plasticity on binocular interactions. Activity in visual cortex ipsilateral to the deprived eye was necessary for the characteristic induction of the enhancement, and activity in visual cortex contralateral to the deprived eye was necessary for its maintenance after MD. The plasticity also displayed distinct learning-like properties: Active testing experience was required to attain maximal enhancement and for enhancement to persist after MD, and the duration of enhanced sensitivity after MD was extended by increasing the length of MD, and by repeating MD. These data show that the adult mouse visual system maintains a form of experience-dependent plasticity in which the visual cortex can modulate the normal function of subcortical visual pathways.
Animals↗
The microvascular system of the optic nerve in control and enucleated rats.
The microvascular system of the optic nerve of the rat was examined morphometrically to determine the effect of enucleation of one eye at birth on the microvascular development in the contralateral optic nerve. For this purpose, two groups of rats were used: three were unilaterally enucleated on the day of birth and studied on postnatal Day 28; three littermates were used as controls. Using plastic embedded semithin sections, we analyzed various parameters and compared the results statistically. The average diameter of microvessels up to 7.5 microns was found to be 4.7 +/- 0.2 micron in controls and 5.3 +/- 0.5 micron in experimental rats. The density of microvessels expressed as the mean number of sectioned capillaries per tissue area was 137 +/- 25/mm2 in the control group and 169 +/- 32/mm2 in the experimental group. The intravascular volume fraction percentage (Vv), which represents the volume fraction of the capillary network per unit of optic nerve volume (mm3/mm3%), was 0.06% in the controls and 0.10% in the enucleated rats. Total length of capillaries per unit of volume (Lv) averaged 1050 +/- 112 and 2235 +/- 195 mm/mm3 in control and experimental groups, respectively. The internal capillary surface area available for metabolic exchange expressed per volume unit (Sv) was 15.5 +/- 2.1 and 37.2 +/- 2.8 mm2/mm3 in control and experimental groups, respectively. These results, together with the lack of ultrastructural modifications in the vascular walls of microvessels, suggest that these rearrangements of the capillary system in the enucleated group could be triggered by an increase in the optic nerve metabolism resulting from monocular vision.
Animals↗
Cyclopean and disconjugate adaptive recovery from post-saccadic drift in strabismic children before and after surgery.
Post-saccadic drift has been analyzed in strabismic children 11-18 yr old, before and after surgery. Before surgery all the subjects had a large multi-component post-saccadic drift. A disconjugate compensation of the drift was not active, but an optimized cyclopean compensation occurred, aimed at minimizing the drift size in both eyes, either with binocular or monocular vision. The drift was directed toward the static offset of the eyes. One week after surgery the drift increased in most cases but the cyclopean compensation still occurred. One week later, a partial disconjugate compensation decreased the drift to levels lower than before surgery. In one subject surgery produced very big three-component drift, exceeding 20 deg. One year after the drift was decreased to < 1 deg. A mathematical model is presented accounting for most of the results.
Adaptation, Ocular↗
Peripheral fading with monocular and binocular viewing.
This study measured the fading times of peripheral targets as a function of whether viewing was monocular or binocular, and of brightness contrast. Data from a binocularly normal group showed Troxler fading to be significantly faster with monocular (i.e., patched) than with binocular viewing. In contrast, one-eyed observers showed significantly longer fading times than the two-eyed observers viewing monocularly and equivalent times to their binocular viewing. A control experiment showed that these findings were not due to worse fixation stability, larger pupil sizes, or an unusually large blinking rate in the enucleated group. The enucleated group actually exhibited a slight miosis, equivalent fixation stability, and a normal blinking rate. In both experiments, the times to fading of all observers were a function of brightness contrast. We conclude that in binocularly normal observers patching or closing one eye does not produce monocular vision but rather a condition of weak binocular rivalry, and that the absence of inhibitory binocular interactions in the enucleated group may explain, in part, their resistance to fading and their superior performance in other contrast-defined tasks.
Adolescent↗
The axial misalignment between ocular lens and cornea observed by MRI (I)--at fixed accommodative state.
Lens tilt and decentration relative to the corneal axis are two of the factors which cause aberration in human eyes. Although many techniques have been developed to quantitatively measure these factors, however, they are mostly confined in 2D observations. To extend the view from 2D to 3D, MR imaging technique becomes a good candidate due to its capability of 3D-image reconstruction and with fairly good spatial resolution for that purpose. In this study a total of six eyes of six young students at this Institute were examined by using a 1.5T MRI machine incorporating with a commercial 3-in. surface coil at Taipei Veterans General Hospital. From a 45 degrees flipped reflective mirror, the subject could focus to a target at a distance of 60 cm from the eye for MR imaging in monocular vision. Quadric surface models were used to fit cornea and lens surfaces in the post image processes. Tilts of the two lens surfaces and the decentration of lens centre with respect to corneal axis were determined through coordinate transformations. One month later, retest was carried out on five of the six subjects. The results show that the average tilts of anterior and posterior lens surfaces, and lens decentration are 3.7+/-2.5 degrees, 3.3+/-1.4 degrees and 0.11+/-0.07 mm (H), -0.06+/-0.38 mm (V), respectively, for the test; 2.1+/-2.4 degrees, 1.9+/-1.8 degrees and -0.02+/-0.28 mm (H), -0.45+/-0.28 mm (V) for the retest. No statistically significant difference (by Wilcoxon Signed Ranks test) is revealed for the tilts of both lens surfaces (p(phia)=0.375, p(phip)=0.225) and for decentration (p(H)=0.343, p(V)=0.345) between test and retest in this longitudinal observation. The surface shapes of the ocular anterior components do not seem to be unified by only one type but ellipsoid, elliptic paraboloid, hyperboloid and paraboloid are all possible. Changes in shape type in the ocular anterior components were also found when measured in a period of one month.
Accommodation, Ocular↗
Mobility of normal observers under conditions of reduced visual input.
The importance in mobility performance of the rate of presentation of visual information, binocular versus monocular vision, the use of multiple rather than single reference points, and local motion parallax was investigated in two experiments. In each experiment ten subjects walked a triangular mobility course in a totally darkened room; the only visible targets were light emitting diodes (LEDs), mounted on poles, at the apices of the triangle. The LEDs were mounted so that one or two could be used in a trial; if two were used the distance between them was varied horizontally (in experiment 1) and vertically (in experiment 2). The subjects walked around the course under a range of conditions, including two 'optimal trials' in full light. The LEDs were flashed for 1 ms at frequencies of 0.5, 1 and 5 Hz in experiment 1 and at 1 and 5 Hz in experiment 2. Mobility was measured with the use of an ultrasonic locator system which measured the subject's position on the course 10 times per second. The mean velocity of the subject in traversing the course was significantly reduced when the flash rate was slower, when the subject had one eye occluded, or when there was only one LED on the pole; when the spacing between the LEDs was varied, either vertically or horizontally performance was unaffected. These results imply that the frequency of updating of visual information is important in determining mobility performance, as are binocular cues, but that local motion parallax is not important. The number of LEDs on each pole had a significant effect on mobility performance an 'object' (two lights) gave more information than a point reference.
Adult↗
Monocular acuity in the presence and absence of fusion.
Because little is known about monocular acuity during binocular fusion, acuity of the right eye was measured in binocularly normal subjects, with the fellow eye open or fully occluded. The target was flashed for 65 ms or presented sinusoidally for 1 s. Subjects had both eyes optimally focused, or the right eye defocused by +3.00 D. Monocular acuities were equivalent during fusion or occlusion when both eyes were optimally focused. Acuity of the defocused eye was reduced when the fellow eye was open compared to when it was occluded. Suppression of the blur, therefore, produced a measurable reduction in recognition thresholds. As monocular acuity was not measurably affected by the fellow eye when each eye was in focus, the finding that monocular vision is improved with the fellow eye occluded should be ascribed to something other than suppression or more sensitive spatial measures of the suppression should be obtained.
Humans↗
Perception of verticality after recent cerebral hemispheric stroke.
BACKGROUND AND PURPOSE: Perception of the subjective visual vertical (SVV) is affected by cerebral hemispheric lesions. Knowledge of this disturbance is of interest for the study of its possible relation to balance disturbances. There is still uncertainty about the possible effects of a visual field defect and of the side and site of the lesion. This study was conducted to assess SVV with the head upright or tilted and to explore its relation to a visual field defect, visuospatial neglect, and the site of lesion. METHODS: Forty patients with hemiplegia after a recent hemispheric stroke (20 with left and 20 with right stroke) were studied. The site of the lesion was determined on CT scan, with special attention focused on the vestibular cortex. A neurological examination with determination of the visual field and visual neglect was conducted before SVV was tested. Subjects sat in a dark room and adjusted a luminous rod to the vertical position. Measures were repeated with binocular and monocular vision and with the head upright or tilted to the right or left. RESULTS: SVV was abnormally deviated in 23 of 40 patients (57%). The deviation was significantly greater among patients with a right or left hemispheric lesion than among healthy controls (-2.2 degrees and 1.5 degrees versus 0.2 degrees ); the same applied to the range of uncertainty (7.6 degrees and 4.7 degrees versus 1.9 degrees ). SVV deviation was not significantly related to the location of the lesion but was closely related to visuospatial neglect. The "E" effect observed in controls with the head tilted, ie, an SVV shift in the direction opposite to the head tilt, was not observed in hemiplegic patients with the head tilted toward the nonparetic side. CONCLUSIONS: Recent hemispheric stroke affects SVV perception, which is closely correlated to visuospatial neglect. It is suggested that the E effect might be mediated by the stretching of the somatosensory structure of the neck.
Brain↗
The analysis of disparity evoked potentials by a new form of static random-dot stereograms.
PURPOSE: A new form of static random-dot stereograms free of monocular clues was designed as stimulus to elicit disparity evoked potentials. METHODS: Disparity evoked potentials were recorded in 40 stereo-normal subjects. The stimulator was a white-black static random-dot stereograms generated by a computer and had no monocular clues. Every subject was tested in disparity stimulus, zero disparity stimulus, monocular stimulus and wearing prism condition. RESULTS: A characteristic wide positive wave at about 250 ms was consistently recorded in disparity stimulus, which may be regarded as evidence of the presence of stereopsis. In contrast, recordings for zero disparity stimulus, monocular vision, stimulus and wearing prism condition all demonstrated a markedly difference from recording for disparity stimulus.
Adolescent↗
The effects of intermittent vision on prehension under binocular and monocular viewing.
The aim of the present study was to examine the effects of intermittent binocular and monocular vision on the preparation and execution of the transport and grasp phases of prehension, and hence the temporal limit of binocular and monocular integration. Participants in two groups (speed or accuracy) performed prehensile movements of two amplitudes (20 and 40 cm) to either a large or small object (6 x 6 x 2 and 6 x 4x 2 cm) under conditions of binocular and monocular viewing. The interval between visual samples was manipulated with liquid crystal goggles (continuous vision, 20on/60off, and 20on/120off ms). A kinematic analysis indicated that participants modified variables associated with the preparation and execution of prehension in the intermittent vision conditions when instructed to emphasize accuracy. Participants instructed to emphasize speed, modified variables associated with the preparation phase only. The impact of intermittent vision was similar under binocular and monocular viewing. Thus, for prehension, it appears that consecutive binocular or monocular samples need to occur less than 60 ms apart in order to be fully integrated for limb control.
Adult↗
Understanding the contribution of binocular vision to the control of adaptive locomotion.
Abstract. Although the contribution of binocular vision to reach-to-grasp movements has been extensively studied, it has been largely ignored in locomotion. The aim of these studies was to explore the role of binocular vision during the approach phase and step over the obstacle and the contribution of head movements to acquisition of depth information under monocular vision. Binocular and monocular vision was manipulated in different phases using either an eye patch or liquid crystal glasses. Head movement relative to the trunk was restricted in the first experiment by a modified Ferno Universal Head Immobilizer attached to a rigid board strapped to the participant's back. Whole body kinematics were collected by placing infrared diodes on anatomical landmarks and using an Optotrak imaging system. Several measures related to head and limb movement were analyzed. Three major findings emerged from these studies. First, binocular vision is important for the acquisition of accurate information about the surrounding environment: accuracy but not precision of limb elevation over the obstacle was adversely affected when binocular vision was unavailable. Second, motion parallax due to self-motion provides the most critical depth information and it can be used to partially compensate for the loss of binocular vision. Although head movement is not essential to augment depth information, it is important for reorientation of the visual field to obtain the necessary information about the moving limbs when visual field is suddenly limited under monocular vision. Third, step over the obstacle is pre-planned based on visual information acquired during the approach phase: changes in visual condition during the adaptive step do not influence the limb trajectory. Collectively these three studies provide unique insights into the contribution of binocular vision during adaptive locomotion.
Adaptation, Psychological↗
Pattern adaptation of relay cells in the lateral geniculate nucleus of binocular and monocular vision-deprived cats.
To test whether the pattern adaptation in thalamus is dependent upon postnatal visual experience during early life, the responses of relay cells to prolonged drifting grating stimulation were recorded extracellularly from the dorsal lateral geniculate nucleus (dLGN) of cats reared with binocular and monocular lid suture. In binocular vision-deprived cats, 68% of cells recorded showed significant adaptation to prolonged grating stimuli within 30 s, with a mean response decrease of 33%, and then stabilized gradually. This adaptation was stronger than that of relay cells in normal cats. In monocular vision-deprived cats, 53% of the cells driven by the deprived eye showed similar adaptation as did 44% of the cells driven by the non-deprived eye. These results indicate that pattern adaptation could be maintained or even enhanced after visual deprivation in early life. It is suggested that pattern adaptation is a general and intrinsic property of the dLGN cells, which may be mainly determined by genetic factors.
Adaptation, Ocular↗
Infant interocular acuity differences and binocular vision.
Monocular acuity, binocular acuity, and stereopsis were assessed with preferential-looking techniques in a sample of 114 normal infants aged 0-11 months in order to examine developmental trends in: (1) interocular differences in acuity, (2) test-retest reliability, (3) the relationship between monocular and binocular measures of acuity, and (4) the relationship between interocular differences in acuity and stereopsis. Mean interocular acuity difference was largest during months 0-5 (approximately 1 octave) and decreased to approximately 0.5 octaves by months 9-11. Test-retest reliability was constant throughout months 0-11 (0.5 octaves). The superiority of binocular acuity over monocular acuity was evident after the 6th month. The presence or absence of stereopsis during months 3-5 was directly related to the magnitude of interocular acuity differences. These age trends suggest that the third to fifth months of life may represent a period of binocular competition in the human visual system which, during normal development, culminates in small interocular acuity differences and the onset of binocular function, including stereopsis.
Age Factors↗