Binocular rivalry of equiluminant targets.
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Contrast Sensitivity↗
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Interocular suppression in normal and amblyopic subjects: the effect of unilateral attenuation with neutral density filters.
In normal subjects, binocular rivalry suppression takes time to build up (Wolfe, 1986a). The time courses of interocular suppression are different and heterogeneous in amblyopic subjects (de Belsunce & Sireteanu, 1991). In the present study, we found that, in normal observers, progressive reduction of one eye's stimulus luminance with neutral density filters produces time courses similar to those of amblyopic subjects. Conversely, in amblyopes, attenuation of the dominant eye's stimulus produces time courses similar to those of normal observers. Under conditions of balancing of the two eyes, amblyopes experience alternating suppression, similarly to binocular rivalry of normals.
Adult↗
Do background luminances interact during binocular fusion?
The question investigated in the experiments reported here was whether monocular background luminances sum during binocular fusion. Fusion was made explicit by using a random-dot stereogram (RDS) as a background stimulus. In the presence of the RDS, differential luminance thresholds were somewhat higher than in the uniform field: a full-field, binocular dot array acted as a mask for a full-field luminance change, but global depth had no effect at threshold. The amount of the binocular advantage at threshold was compared to the basic "threshold response," that is, the change in threshold resulting from raising the background luminance by a factor of 2. It was found that the amount of the binocular advantage was equivalent, on the average, to some 75% of the threshold response--significantly less than the 100% predicted by "simple summation." The amount of the binocular advantage varied substantially among observers and eyes, whereas the threshold response obeyed Weber's law in all cases: the variability was eye-, rather than threshold-dependent. Monocular thresholds did not decrease when taken with the nontest eye occluded rather than viewing a fused background. The proposition that the adaptation state of the visual system is increased during binocular fusion (Cogan, 1982) was not supported. Yet occluding the nontest eye, rather than presenting the test stimulus monocularly against a fused background, did change monocular thresholds in some eyes and observers. These findings are interpreted as evidence for a complex binocular background interaction involving both summation and inhibition.
Attention↗
Some visual influences on human postural equilibrium: binocular versus monocular fixation.
The importance of vision for postural equilibrium has long been known; traditionally, this visual contribution to the control of posture has been analyzed primarily in terms of optical and retinal phenomena. Recently, however, there has been some suggestion that binocular and monocular fixation of identical stimuli have differential effects. Three experiments were conducted in order to measure self-generated movement (sway during quiet standing) of the body's center of gravity while field structure, ankle proprioception, and binocular/monocular fixation were varied. Field structure was varied from total darkness, to the presence of single and multiple LEDs in the dark, to full field structure (i.e., the richness of the feed back information was varied). Ankle proprioception was varied by changing foot position from side-by-side to heel-to-toe positions. Results indicate that (1) ankle-joint input is a significant factor in reducing sway, (2) binocular fixation attenuates sway relative to monocular fixation, under otherwise identical visual conditions, and (3) this difference persists in total darkness. Taken together, the data indicate that the visual influence on postural equilibrium results from a complex synergy that receives multimodal inputs. A simple optical/retinal explanation is not sufficient.
Adolescent↗
Is the anisotropy of perceived 3-D shape invariant across scale?
A number of studies have resulted in the finding of a 3-D perceptual anisotropy, whereby spatial intervals oriented in depth are perceived to be smaller than physically equal intervals in the frontoparallel plane. In this experiment, we examined whether this anisotropy is scale invariant. The stimuli were L shapes created by two rods placed flat on a level grassy field, with one rod defining a frontoparallel interval, and the other, a depth interval. Observers monocularly and binocularly viewed L shapes at two scales such that they were projectively equivalent under monocular viewing. Observers judged the aspect ratio (depth/width) of each shape. Judged aspect ratio indicated a perceptual anisotropy that was invariant with scale for monocular viewing, but not for binocular viewing. When perspective is kept constant, monocular viewing results in perceptual anisotropy that is invariant across these two scales and presumably across still larger scales. This scale invariance indicates that the perception of shape under these conditions is determined independently of the perception of size.
Adult↗
Monocular discrimination of rigidly and nonrigidly moving objects.
We measured thresholds for the monocular discrimination of rigidly and nonrigidly moving objects defined by motion parallax. The retinal projections of rigidly moving objects are subject to certain constraints. By applying smooth 2-D transformations to the projections of rigidly moving objects, we created stimuli in which these constraints were affected. Thresholds for (generic) nonrigid transformations that in theory can be detected from rigid ones by processing pairs of views depended not only on the extent to which the rigidity constraints were affected, but also on the structure and the movement of the simulated object. Nonrigid transformations under which every three successive views had a rigid interpretation were not discriminable from rigid transformations, except in cases where the distortions were very large. Under the rigidity assumption, this would mean that a large class of nonrigidly moving objects is erroneously perceived as rigidly moving.
Adult↗
Binocular vision.
Sensory correspondence, which forms the foundation for binocular vision, is a central activity of the cortex at the perceptual level and can occur with or without an anatomic proximity of corresponding points on the same cerebral hemisphere. Dysjunctive eye movement (fusional movements) can occur only with an anatomic proximity of corresponding points on the same cerebral hemisphere.
Animals↗
Stage I intraoperative adjustment of eye muscle surgery under general anesthesia.
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Anesthesia, General↗
Acquired central fusion disruption following cataract extraction.
Central sensory and motor fusion of images, once established, is usually maintained throughout life. Under certain circumstances, this ability may be lost. This gives rise to the syndrome known as horror fusionis, or acquired disruption of central fusion. We report the development of central fusion disruption in three patients with uniocular mature senile cataract. We postulate that this is the result of prolonged sensory deprivation in the cataractous eye. The loss of fusion results in a particularly troublesome type of intractable diplopia, characterized by the inability to either fuse or suppress images. To the best of the authors' knowledge, this is the first report of central fusion disruption following cataract surgery for senile cataract.
Aged↗
Development of compensating exotropia with anomalous retinal correspondence after early infancy in congenital homonymous hemianopia.
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Cerebral Palsy↗
Cyclofusion in normal and superior oblique palsy subjects.
PURPOSE: To evaluate the cyclofusional status in normal and acquired superior oblique palsy subjects. To know the extent to which cyclodeviations can be tolerated asymptomatically. METHOD: Incyclovergence and excyclovergence break points and recovery points were evaluated in 40 normal subjects and 17 cases of acquired superior oblique palsy. A Polaroid dissociation stereoprojector was used with special torsional slides at fixation distances of 1 meter and 6 meters. In addition, maximum intorsion tolerated (MIT) and maximum extorsion tolerated (MET), ie, the torsion that allowed baseline horizontal fusion, were studied. The evaluation was repeated in the palsy group 1 month after recovery, which was spontaneous in 8 cases, and after surgery in 9 cases. RESULT: The normal values for incyclovergence and excyclovergence were in the range of 12 degrees (break point) and 8 degrees (recovery point). In the case of superior oblique palsy, only the incyclovergence recovery point was significantly diminished (p=.004), which improved after recovery to near normal values. The intorsion tolerance (MIT) and extorsion tolerance (MET) also showed deterioration in the palsy group. After recovery, the MIT normalized but the MET did not recover at 1-meter distance fixation. The maximum torsional tolerance values appear to be more critical. CONCLUSION: The cyclofusional vergence under physiological conditions are better than reported earlier. But MIT and MET are better indicators of cyclofusional potential. These low values demand more precise alignment of the torsion in weakening or strengthening surgery of the oblique muscles.
Eye Movements↗
[Binocular rivalry in half-occluded region is weakened by eye movement].
To investigate the effect of eye movement on suppression of binocular rivalry in the half-occluded region, which is the monocular region made by occlusion, the amount of binocular rivalry in the half-occluded region was measured in the eye movement condition and the fixating condition. In the eye movement condition, the observer moved their eyes between the occluder and the occluded object. In the fixating condition, the observers fixated the occluder (the fixating-the-occluder condition) or the occluded object (the fixating-the-occluded-object condition). Following facts were found: (a) the amount of binocular rivalry in the half-occluded region reduced more in the eye movement condition than in the two fixating conditions, (b) there was no significant difference in the amount of binocular rivalry in the half-occluded region between the two fixating conditions. These results suggested that eye movement is one of the factors to suppress binocular rivalry in the half-occluded region in natural viewing situations.
Eye Movements↗
Increased synchronization of neuromagnetic responses during conscious perception.
In binocular rivalry, the observer views two incongruent images, one through each eye, but is conscious of only one image at a time. The image that is perceptually dominant alternates every few seconds. We used this phenomenon to investigate neural correlates of conscious perception. We presented a red vertical grating to one eye and a blue horizontal grating to the other eye, with each grating continuously flickering at a distinct frequency (the frequency tag for that stimulus). Steady-state magnetic fields were recorded with a 148 sensor whole-head magnetometer while the subjects reported which grating was perceived. The power of the steady-state magnetic field at the frequency associated with a grating typically increased at multiple sensors when the grating was perceived. Changes in power related to perceptual dominance, presumably reflecting local neural synchronization, reached statistical significance at several sensors, including some positioned over occipital, temporal, and frontal cortices. To identify changes in synchronization between distinct brain areas that were related to perceptual dominance, we analyzed coherence between pairs of widely separated sensors. The results showed that when the stimulus was perceived there was a marked increase in both interhemispheric and intrahemispheric coherence at the stimulus frequency. This study demonstrates a direct correlation between the conscious perception of a visual stimulus and the synchronous activity of large populations of neocortical neurons as reflected by stimulus-evoked steady-state neuromagnetic fields.
Adult↗
Development of rivalry and dichoptic masking in human infants.
PURPOSE: To examine the development of rivalry, dichoptic masking, and binocular interactions in infants more than 5 months of age using the visual evoked potential (VEP). METHODS: VEPs were recorded in 35 infants between 5 and 15 months of age and 23 adults between 13 and 59 years of age. Counterphasing, sinusoidal, 1 cycle/deg gratings were presented dichoptically. Responses from each eye were isolated by "tagging" each half-image with a different temporal frequency (5 or 7.5 Hz). Observers were presented with fixed 80% contrast gratings in each eye in experiment 1. Rivalry was detected on the basis of a negative correlation between the simultaneously measured response amplitudes at the second harmonics of the two eye-tagging frequencies. In a second analysis of the same data, response amplitudes recorded under dichoptic viewing conditions were compared to those obtained in a monocular control condition (dichoptic masking). In experiment 2, a 40% fixed-contrast grating was presented to one eye, whereas the other eye viewed a grating that was swept in contrast from 1% to 67%. Dichoptic masking was measured as the reduction in the fixed-grating response caused by the variable contrast grating. RESULTS: Experiment 1: although adults showed evidence of VEP amplitude alternations between the eyes for cross-oriented half-images (physiological rivalry), infants did not. This immature response to rivalrous stimuli occurred despite the presence of responses at nonlinear combination frequencies recorded with gratings of the same orientation in each eye, a definitive indication of binocular interaction. In addition, both iso- and cross-oriented half-images produced less dichoptic masking in infants than in adults in this experiment. Experiment 2: dichoptic masking in the infants was equivalent to that seen in adults with parallel gratings in the two eyes; however, masking with cross-oriented configurations was approximately five times weaker in the infants relative to the adults. CONCLUSIONS: The authors have identified a set of stimulus conditions under which infants between 5 and 15 months of age fail to demonstrate physiological rivalry despite the presence of binocular interactions. The observed lack of binocular rivalry may be the result of a specific immaturity in dichoptic, cross-orientation suppression.
Adolescent↗
Effect of sustained cyclovergence on eye alignment: rapid torsional phoria adaptation.
PURPOSE: To describe adaptive changes in torsional alignment that follow sustained cyclovergence in healthy humans. METHODS: Eye movements were recorded binocularly from four healthy subjects using dual-coil scleral annuli. Cyclovergence movements were evoked over periods of 30 to 150 seconds using a stereoscopic display, presenting gratings of lines arranged horizontally, vertically, or at 45 degrees, subtending angles of up to 48 degrees. In- and excyclodisparities of 5 degrees were introduced and removed in a single-step fashion. After stimulation, the time course and magnitude of the decay in cyclovergence was compared with the subject either in darkness or viewing a baseline stimulus of zero cyclodisparity. RESULTS: As reported previously, the cyclovergence response to incyclodisparities was greater than to excyclodisparities. After sustained excyclovergence, however, in all subjects and in response to all orientations of the gratings, the decay in darkness was incomplete, implying an adaptive change in torsional alignment. In response to the horizontal gratings, for incyclovergence there was also an incomplete decay in darkness but to a lesser degree than in response to excyclovergence, and in only three of four subjects. The incyclovergence evoked by the oblique and vertical gratings was of small magnitude, and its decay was unaffected by the presence or absence of a visual stimulus. CONCLUSIONS: After sustained cyclovergence, its decay in the absence of a visual stimulus may be incomplete. The residual component may be interpreted, by analogy with horizontal and vertical vergence, as reflecting so-called phoria adaptation for torsional alignment.
Adaptation, Ocular↗
Intermittent exotropia: stimulus characteristics affect tests for retinal correspondence and suppression.
BACKGROUND AND PURPOSE: Prior studies have reported various sensory responses in subjects with intermittent exotropia [X(T)]. These varying responses have been proposed due to differences in stimulus targets, backgrounds, or even a lack of control of binocular alignment. This study investigated the effects of varying target and background stimuli while controlling binocular alignment. METHODS: Eight X(T)s of the divergence excess or basic type were presented dichoptic computer generated visual stimuli while an infra red eye movement monitoring system determined horizontal eye position of each eye. Target and background were varied to assess their effect on sensory responses during latent and manifest exotropia. RESULTS: Most of our X(T)s demonstrated, while tropic, a consistent, i.e., dominant, type of retinal correspondence, i.e. a response that occurred on most tests, independent of the stimulus or background used for testing. Four subjects demonstrated harmonious anomalous retinal correspondence (HARC) while three subjects demonstrated normal retinal correspondence (NRC) with three out of four of the tests. In two out of four stimuli used for testing, one subject demonstrated NRC and another HARC. CONCLUSIONS: Complex backgrounds resulted in the largest number of suppressions, whereas blank backgrounds decreased the number of reported suppressions.
Adaptation, Ocular↗
How do the corresponding eyes avoid disturbing contour overlaps? Historical answers (1859 - 1981).
The visual system has a limited capacity to fuse overlapping impressions. It takes advantage of three principles of organization: (1) The mixing of different impressions resulting in a new entity (compensation principle); examples are the mixing of colors, dark and light at the retina, Fechner's paradox. The twelve researchers whose work is reported here analyzed two other unifying principles: (2) Selection by successive contrasts (polarization principle) and (3) subordination in a hierarchy of vision (differentiation principle).
History, 19th Century↗
Monofixation syndrome. Presbyopia monovision followup.
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Fixation, Ocular↗