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PubMed1996

Excitatory binocular neurons are lost following prismatic binocular dissociation in infant monkeys.

Four infant rhesus monkeys had prismatic dissociation of binocular vision by viewing the world through prisms. Those monkeys tested previously for ability to utilize horizontal disparity cues in detection of dynamic random dot stereograms, were found here to have few excitatory binocular neurons in visual cortex (V1). Each eye was well represented in the monocular ability to drive cortical neurons, whilst stimulus orientation tuning appeared normal in the monocular neurons, but somewhat less sensitive in the remaining binocular neurons. Binocular dissociation early in life constitutes conditions unfavorable for the maintenance of neural connections delivering binocular excitation to the visual cortex.

Aging↗
PubMed2000

Contrast thresholds and fixation disparity during 5-Hz sinusoidal single- and dual-axis (vertical and lateral) whole-body vibration.

The present study assumed that whole-body vibration, transmitted through the seat, impairs spatial retinal resolution and oculomotor alignment parallel to the vibration axis. More specifically, that the decrement increases gradually from single-axis lateral via single-axis vertical and dual-axis linear to dual-axis circular motion. Twenty participants (19-26 years of age) with good vision volunteered for the experiment where in three sessions one of the following three conditions, contrast threshold, nonius bias or fixation disparity, for vertically and horizontally oriented test patterns was determined during five experimental conditions. The latter comprised a control (a(z) = a(y) = 0) and four conditions where 5-Hz sinusoidal motion of 1.2 ms(-2) rms were applied separately, either in the vertical or in the lateral direction, or simultaneously in both directions, once without and once with a phase shift of 90 degrees, thus causing dual-axis linear or circular motion. Contrast thresholds for horizontal gratings and the variability of vertical fixation disparity increased significantly whenever the participants were exposed to vertical motion (alone or combined with lateral motion). These effects may result in an increased difficulty in properly recognizing characters and graphic patterns containing horizontal lines and in the development of asthenopic complaints.

Adult↗
PubMed1996

Imaging a Computational Process in the Visual Cortex.

Visual perception is a computational process reconstructing the 3D visual world based on the 2D images viewed by the two eyes, which inherently contains ill-posed problems due to information deficiency. A typical example is the correspondence problem in finding partner points between the two retinal images. A neural network model for solution of the correspondence problem was proposed by Marr (1982, Vision. San Francisco: Freeman and Co.), constructed of groups of neurons selectively responsive to different disparities of visual stimuli shown to the two eyes. This model solves the correspondence problem as a relaxation process of excitation working between the neuronal groups responding to the same disparity antagonized by inhibition working between those responding to different disparity. Optical recording of responses evoked in the rat visual cortical slice by electrical stimulation of the white matter demonstrated the relaxation process of excitation antagonized by inhibition. Copyright 1996 Elsevier Science Ltd.

Journal Article↗
PubMed2004

True three-dimensional displays that allow viewers to dynamically shift accommodation, bringing objects displayed at different viewing distances into and out of focus.

Under natural viewing conditions, viewers do not just passively perceive. Instead, they dynamically scan the visual scene by shifting their eye fixation and focus between objects at different viewing distances. In doing so, the oculomotor processes of accommodation (eye focus) and vergence (angle between lines of sight of two eyes) must be shifted synchronously to place new objects in sharp focus in the center of each retina. Accordingly, nature has reflexively linked accommodation and vergence, such that a change in one process automatically drives a matching change in the other. Conventional stereoscopic displays force viewers to try to decouple these processes, because while they must dynamically vary vergence angle to view objects at different stereoscopic distances, they must keep accommodation at a fixed distance--or else the entire display will slip out of focus. This decoupling generates eye fatigue and compromises image quality when viewing such displays. In an effort to solve this accommodation/vergence mismatch problem, we have built various prototype displays that can vary the focus of objects at different distances in a displayed scene to match vergence and stereoscopic retinal disparity demands and better simulate natural viewing conditions. By adjusting the focus of individual objects in a scene to match their stereoscopic retinal disparity, the cues to ocular accommodation and vergence are brought into agreement. As in natural vision, the viewer brings different objects into focus by shifting accommodation. As the mismatch between accommodation and vergence is decreased, natural viewing conditions are better simulated and eye fatigue should decrease.

Accommodation, Ocular↗
PubMed2001

Further consideration of size illusions in random dot stereograms.

It has been suggested that many geometric illusions are caused by the application of depth or size constancy rules to an image which does not have sufficient cues to establish that the elements lie in a flat plane. Thus, converging lines are taken as depth cues, and the attributed depth provides the basis for adjusting the perceived size of stimulus elements. It this is the case, one should not see a distortion of relative size if the disparity cues provide for strong statification, i.e., localization in depth of the linear perspective cues. This expectation is challenged by demonstrations that show distortions of relative size using random-dot stereograms. In 1971 Julesz provided such examples but did not comment on the implications for theories of depth. Here we redemonstrate these distortion of length and size in autostereograms which contain the Ponzo and Corridor configurations. The illusory distortions can be seen in the cyclopean view even though the linear perspective elements are well stratified. We suggest that the processing of binocular disparity cues, as required for judgments of absolute distance, may involve the dorsal stream of vision, i.e., activity passing into and including the parietal lobe. Pictorial cues, on the other hand, are likely passed through the ventral stream into the temporal lobe. The analysis of depth by this system provides for size constancy and, possibly, the calibration of relative motion.

Cues↗
PubMedDate not supplied

[Interocular accommodative disparities: asymmetry and/or paresis?].

Description of interocular accommodative disparities about 3 cases of young patients, whose occupations require an excellent stereopsis in near vision. Is is a paresis, an asynergy or a constitutional asymmetry? In order to delimit this pathology, the accommodative power of each eye has been measured on a reference population including 100 subjects aged 20 to 35 years. The suitable correction of this anomaly, allows an exact compensation and the recovery of a normal functional comfort.

Accommodation, Ocular↗
PubMedDate not supplied

Mechanisms of binocular interaction in the visual cortex of rodents.

New hypotheses are advanced relating to the functional role and mechanisms of interaction of afferentation from the two eyes in the visual cortex of animals with poorly developed binocular vision. The proposed approach sheds lights on a number of questions, particularly those concerning the relatively large level of disparity of the receptor fields in cortical neurons, the role of non-overlapping fibers in the visual tract, and others. Hypothesis relating to the evolutionary relationships between these mechanisms and the mechanisms of stereopsis are discussed.

Animals↗
PubMed2003

Attention affects the stereoscopic depth aftereffect.

'Preattentive' vision is typically considered to include several low-level processes, including the perception of depth from binocular disparity and motion parallax. However, doubt was cast on this model when it was shown that a secondary attentional task can modulate the motion aftereffect (Chaudhuri, 1990 Nature 344 60-62). Here we investigate whether attention can also affect the depth aftereffect (Blakemore and Julesz, 1971 Science 171 286-288). Subjects adapted to stationary or moving random-dot patterns segmented into depth planes while attention was manipulated with a secondary task (character processing at parametrically varied rates). We found that the duration of the depth aftereffect can be affected by attentional manipulations, and both its duration and that of the motion aftereffect varied with the difficulty of the secondary task. The results are discussed in the context of dynamic feedback models of vision, and support the penetrability of low-level sensory processes by attentional mechanisms.

Adaptation, Ocular↗
PubMed1975

Presumed histoplasmic maculopathy: xenon photocoagulation.

Every investigation into the efficacy and role of photocoagulation in the management of PHM has been handicapped by the lack of a valid control series. In all first eyes, the results of photocoagulation are better than in second eyes. The increased salvage rate of central visual acuityof 20/50 or better in first eyes without photocoagulation is on the order of 15.8 percent to 28.6 percent-versus 25 to 38 percent in first eyes with photocoagulation (an average of 54 percent salvage rate for all first eyes). However, in second eyes, even though the number of eyes is small, it appears that nonphotocoagulated eyes do better than those that have been photocoagulated: 46 percent of nonphotocoagulated second eyes versus 33 percent of second eyes with photocoagulation retain central vision of 20/50 or better. Comparison of our results with some of the other published studies indicates some disparity in results [1-5], arising, most plausibly, from variations in the severity of the maculopathy just prior to photocoagulation. It is our contention that carefully designed prospective studies are needed, in which cases would be randomized for treatment in groups classified according to severity of the process (for example, size of SNV, proximity of SNV to fovea, and amount and location of subretinal hemorrhage). In order to obtain sufficient cases for analysis, a collaborative study may be essential in which the results and analysis of the cases are compiled by an independent party not involved in the treatment of evaluation of the patients. Despite this lack of clinical corroboration, it is my firm belief based on clinical experience that photocoagulation does have a role in the management of this vision-threatning process.

Adolescent↗
PubMed2001

Configuration specificity in bisection acuity.

Crucial for the perception of form are the spatial relationships between the elements of a visual stimulus. To investigate the mechanisms involved in coding the distance between visual stimuli, thresholds for detecting whether a central marker accurately bisects a spatial interval were compared for a variety of configurations. Thresholds are best when all three members of the bisection configuration are identical. Performance is impaired, often by as much as a factor of two, when the outer delimiters of the spatial interval differ from the central marker in either length, orientation or contrast polarity. Illusory contours act poorly as borders for bisection by a central line. Disparity thresholds are not affected by orientation differences between test and flanking lines. Because in peripheral vision bisection acuity improves with practice, transfer of training between configurations can be used to gauge overlap of neural processing mechanisms. Transfer is complete only between patterns where all markers are similar, reduced when the outer markers differ by 20 degrees in orientation and absent when they are orthogonal. The dependence of bisection discrimination on similarity between the elements of the stimulus demonstrates that the encoding of spatial location and spatial extent are coupled to the coding of other stimulus properties.

Contrast Sensitivity↗
PubMed1999

Position-based motion perception for color and texture stimuli: effects of contrast and speed.

Motion can be perceived either through low-level, motion-energy detection or through tracking the change in position of features. Previously we have shown that, while luminance-based motion likely is detected with velocity-sensitive motion-energy units, patterns defined by texture or binocular disparity ('second-order' stimuli) were tracked by a position-sensitive mechanism (Seiffert & Cavanagh (1998) Vision Research, 38, 3569-3582). Here, we use the same technique, measuring motion amplitude thresholds of oscillating gratings over a range of temporal frequencies and find that the motion of low-contrast equiluminant red/green gratings is also detected with position tracking. In addition, we find that as contrast or speed increases these results change: high-contrast or high-speed equiluminant color or texture-based motion is detected by velocity-sensitive mechanisms. These results help resolve the dispute over the processes which detect the motion of non-luminance based stimuli. Both systems are available, but their relative efficiency changes as a function of contrast and speed. A position-tracking process is more sensitive at low contrasts and low speeds whereas a motion-energy system is more sensitive at high contrasts and high speeds.

Color Perception↗
PubMed1978

Moirés maintained internally by binocular vision.

Moiré patterns in depth are reported when spatially periodic stimuli are viewed stereoscopically. Near-vertical square-wave gratings with horizontal disparity effected by orientation difference produce a 'venetian blind' effect. A single grating is observed divided into horizontal layers, the number of layers being a direct function of orientation difference. Lines within each layer are slanted with respect to the frontoparallel plane, becoming more so with increasing orientation difference. Subjects with stereo deficits report a decreased effect. Quantitative reports implicate stereoscopic mechanisms responsible for this unique, internal preservation of moiré patterns.

Depth Perception↗
PubMed1983

Some recent findings on the development of human binocularity: a review.

Evidence on the development of binocular function in infancy is reviewed. (1) Visual evoked potentials (VEP) may be recorded from infants in response to dynamic random dot stimuli which alternate between positive and negative binocular correlation. Such responses can only arise in neurones receiving binocular input. (2) Infants' looking behaviour may be shown to depend on the presence of binocular disparity in the stimulus (either random-dot or line stereograms). Results of these techniques agree that binocular function normally develops initially between 2 and 4 months of age. Our own data using VEP show a median age of first binocular response of 13 weeks but with marked individual variations. Binocular development involves the interplay of sensory interaction and oculomotor coordination, but it is unlikely that alignment of the two eyes is the dominant constraint determining the onset of binocular vision. It is possible, but not yet established, that the detection of binocular correlation may precede the ability to discriminate stereoscopic disparities. Infants in the first 3 months of life show an asymmetry of monocular optokinetic nystagmus (MOKN). The response to temporalwards field motion which they lack is driven in cat by a pathway via binocular cortex: thus the development of this response in human infants might depend on development of binocularity. However, the correlation across individual infants between the age of onset of binocularity and the age at which symmetrical MOKN is attained is relatively weak. It is possible that the neuroanatomical basis of MOKN control differs between cat and human.

Child Development↗