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PubMed1982

Finely graded binocular disparities from random-dot stereograms.

Rotation of a stereogram around an axis through its centre provides a method of presenting finely graded binocular disparities. Such displays are useful for clinical testing of stereopsis. A comparison between projected- and real-depth thresholds indicated that most of the differences could be accounted for in terms of the change in stereoscopic sensitivity associated with differing errors in the equidistance judgements. The method of disparity display described allows for the direct observation of those attributes of random-dot stereopsis known as global stereopsis and local stereopsis and requires caution in comparison of stereopsis thresholds using these different perceptual criteria.

Adult↗

PubMed1998

Accommodation to perceived depth in stereotests.

The question of whether the eye may accommodate to the stimulus provided by apparent depth in stereograms is considered theoretically in relation to the magnitudes of the disparities and viewing distances found in typical clinical stereotests. It is concluded that, for the relevant range of disparities (< or = 2000 arc sec), any shift in accommodation is likely to be small (< or = 0.15 D). An experimental study with two different clinical stereotests (Lang, TNO) confirms this prediction.

Accommodation, Ocular↗

PubMed1983

Small-field, binocular neurons in the superficial layers of the frog optic tectum.

Binocular neurons with receptive fields about 5 degrees across were recorded just beneath the pia. Most of them responded to dark stimuli in the lower half of their receptive field and to light stimuli above. There was almost no vertical disparity between the left and right fields and the modal value of the horizontal disparity of the population of cells was 1.7 degrees. Because frogs do not verge their eyes it is possible to calculate at what distance the receptive fields through the two eyes are superimposed. This calculation suggests that the neurons are tuned to detect features in the external world about 50 cm away. This is too far for the neurons to be involved in the frog's everyday distance vision. It is more likely that they are concerned with assessing the vertical position of a horizontal surface.

Action Potentials↗

PubMed1988

Dependence of Panum's fusional area on local retinal stimulation.

The range of fusion in the human binocular vision system has been shown by many research groups to be capable of extension. Although each of these research groups tested the extension of fusion under different conditions, the majority agreed that an extension of fusion is possible, and most have noted a variety of variables that contribute to the phenomenon. The extension of fusion may be interpreted in at least two ways. The first is that the range over which fusion is possible is enlarged, and the second is that the range is shifted. Therefore a study of human binocular fusional ranges was performed to clarify the nature of the extension of Panum's fusional area. The following results were obtained: (1) A shift of the fusional area occurs when one of a pair of fused retinally stabilized images is moved into disparate locations on the retinas. Results for one observer demonstrate a corresponding small enlargement of the fusional area. Thus the extension of the fusional area not only involves the recruitment of retinal locations into the fusional area that are not normally in the area but also involves the loss from the fusional area of certain retinal locations that are normally within it. (2) A continually present stimulus fuses over a wider range with a flashed stimulus than with another continually present stimulus.

Humans↗

PubMed2006

Distance impairs postural stability only under binocular viewing.

Prior studies indicate that postural stability under binocular viewing is not better than under monocular viewing. This was tested at the distances of 145 cm [Fox, C.R. (1990). Some visual influences on human postural equilibrium: binocular versus monocular fixation. Perception and Psychophysics, 47 (5), 409-422] and 90 cm [Isotalo, E., Kapoula, Z., Feret, P.H., Gauchon, K., Zamfirescu, F., & Gagey, P.M. (2004). Monocular versus binocular vision in postural control. Auris Nasus Larynx, 31 (1), 11-17]. On the other hand, postural stability is known to decrease with distance increase. We re-examined the effect of binocular versus monocular viewing on postural stability at near and far distances (40 and 200 cm), and for both young (25.7+/-2.7 years), and old subjects (61.2+/-4.6 years). For both groups of subjects, proximity decreased the area of CoP, the standard deviation of antero-posterior sway (SDy) and the variance of speed. The group of elderly presented increased variance of speed at far distance in comparison with young subjects. The novel finding is the interaction between distance and viewing condition. Under binocular viewing, the area of CoP was significantly higher at far distance than at near; in contrast, monocular viewing produced similar CoP values at both distances. Increased instability at far distance when both eyes are viewing is attributed to decreased sensitivity to binocular disparity cues and to visual motion in depth resulting from body sway. Monocular viewing would provide similar stability at far and at near distance, because sensitivity to lateral visual motion, detected monocularly, decreases less with distance than sensitivity to binocularly detected motion in depth. Alternatively, such monocular viewing could increase subject's attention and lead to tighter postural control regardless of the distance.

Adult↗

PubMed1991

Strabismus presenting after cataract surgery.

Strabismus presenting after cataract surgery is etiologically related to a heterogenous group of disorders. Clinical data from 63 patients so affected revealed four broad etiologic categories: 1) pre-existing disorders that preceded the cataract surgery, but were rendered asymptomatic by the occluding cataract (e.g., thyroid eye disease, cranial nerve palsy, myasthenia); 2) disorders precipitated by prolonged occlusion by a cataract (e.g., sensory deviations, decompensation of heterophorias, and central disruption of binocular vision); 3) disorders resulting from surgical trauma to extraocular muscles and orbital soft tissues. Traumatic injury to the inferior rectus muscle secondary to retrobulbar anesthesia injection, a specific subset, is postulated to result from a Volkmann's type ischemic contracture, a well-known osseofascial compartment syndrome occurring in peripheral skeletal muscles. 4) Disorders related to resulting aphakia/pseudophakia and associated optical aberrations (e.g.; anisophoria, ocular dominance reversal, and color/brightness disparity). The diagnostic and therapeutic implications of these findings are discussed.

Adult↗

PubMed2005

Visual search improvement in hemianopic patients after audio-visual stimulation.

One of the most effective techniques in the rehabilitation of visual field defects is based on implementation of oculomotor strategies to compensate for visual field loss. In the present study we develop a new rehabilitation approach based on the audio-visual stimulation of the visual field. Since it has been demonstrated that audio-visual interaction in multisensory neurons can improve temporally visual perception in patients with hemianopia, the aim of the present study was to verify whether a systematic audio-visual stimulation might induce a long-lasting amelioration of visual field disorders. Eight patients with chronic visual field defects were trained to detect the presence of visual targets. During the training, the visual stimulus could be presented alone, i.e. unimodal condition, or together with an acoustic stimulus, i.e. crossmodal conditions. In the crossmodal conditions, the spatial disparity between the visual and the acoustic stimuli were systematically varied (0, 16 and 32 degrees of disparity). Furthermore, the temporal interval between the acoustic stimulus and the visual target in the crossmodal conditions was gradually reduced from 500 to 0 ms. Patients underwent the treatment for 4 h daily, over a period of nearly 2 weeks. The results showed a progressive improvement of visual detections during the training and an improvement of visual oculomotor exploration that allowed patients to efficiently compensate for the loss of vision. More interesting, there was a transfer of treatment gains to functional measures assessing visual field exploration and to daily-life activities, which was found stable at the 1 month follow-up control session. These findings are very promising with respect to the possibility of taking advantage of human multisensory capabilities to recover from unimodal sensory impairments.

Acoustic Stimulation↗

PubMed2001

A threshold explains modulation of neural responses to opposite-contrast stereograms.

Disparity-sensitive neurons respond to contrast-inverted stereograms (aRDS) that do not evoke depth percepts. This is in conflict with the idea that such neurons are the direct correlate of depth perception. However, the output of neurons responding to aRDS may be further processed: neurons at later processing stages show weaker responses to aRDS than early stage neurons. Here, we show that such a response hierarchy emerges in a three-layered neural network. A numerical analysis demonstrates that threshold operations can largely explain the network's behavior as well as the electrophysiological data. An extension of the energy neuron model for disparity-sensitive neurons predicts increased responses to aRDS for an identifiable sub-class of cells and can thus be tested in electrophysiological experiments.

Action Potentials↗

PubMed2005

Voluntarily controlled bi-stable slant perception of real and photographed surfaces.

We have quantified voluntarily selected perceived slant of real trapezoidal surfaces (a 'reverse-perspective' scene) and their photographed counterparts (pictorial space). The surfaces were slanted about the vertical axis and observers estimated slant relative to the frontal plane. We were particularly interested in those cases in which binocular disparity and monocular perspective provided conflicting slant information. We varied the monocularly and binocularly specified surface slants independently across stimulus presentations. To eliminate texture and shading cues we used sand-blasted aluminium trapezoidal surfaces illuminated from all directions. When disparity-specified slant and perspective-specified slant were conflicting, observers were able to perceive the surfaces in two ways: they perceived either a trapezoid or a rectangle. Our main finding is twofold. First, when subjects chose to perceive the trapezoid, the slant estimates followed the disparity-predicted slant with only a slight underestimation, as if they selected a pure binocular representation of slant governed only by disparity. Second, when subjects chose to perceive the rectangle their estimates for real surfaces were similar to those for photographed surfaces, as if they selected a representation of slant governed by perspective foreshortening.

Humans↗

PubMed1999

Binocular phase interactions in area 21a of the cat.

1. Binocular interactions related to retinal disparity were investigated in single neurons in area 21a of extrastriate cortex in the anaesthetized cat using sinusoidal luminance gratings. 2. The responses of approximately two-thirds of neurons were profoundly modulated by a relative phase difference between identical drifting gratings presented to each eye. This modulation included both facilitatory and inhibitory interocular interactions. The selectivity for binocular disparity was about twice as sharp as the selectivity for monocular spatial position. 3. Significant phase modulation was retained in many neurons at interocular orientation differences exceeding 45 deg. The response suppression associated with stimulation at a phase shift 180 deg from the optimum was stronger than the response suppression to an interocular orientation difference of 90 deg. 4. The proportion of phase modulated neurons and the potency of modulation in area 21a neurons exceed that reported for phase-selective complex cells in area 17. Neurons in area 21a show sharp disparity tuning that is relatively insensitive to changes in orientation and monocular position, which suggests that this extrastriate region has a role in stereoscopic depth perception.

Analysis of Variance↗

PubMed2006

Neural basis for stereopsis from second-order contrast cues.

Humans and animals use visual cues such as brightness and color boundaries to identify objects and navigate through environments. However, even when these cues are not available, we can effortlessly perform these tasks by using second-order cues such as contrast variation (envelope) of patterns on surfaces. Previously, numerous psychophysical studies examined properties of binocular depth processing based on the contrast-envelope cues and suggested the existence of a stereo system that uses these cues. However, its physiological substrate has not been identified yet. Here, we show that a subset of cortical neurons in cat area 18 show binocular interactions for the contrast-envelope stimuli. These neurons are capable of representing a variety of depths in the three-dimensional space based on the information available from contrast cues alone. Furthermore, these neurons show similar disparity-tuning curves for borders defined by both luminance and contrast cues. This cue-invariant tuning is consistent with a linear binocular convergence model for monocular luminance and contrast-envelope processing pathways.

Animals↗

PubMed1978

Visual evoked responses and visual symptoms in multiple sclerosis.

Absolute latency, interocular difference in latency, and waveform of visual evoked responses (VER) to checkerboard reversal stimuli recorded from the midline of the skull were studied in 104 multiple sclerosis patients, 25 to 50 years of age, classified according to visual symptomatology. Group 1 had strong evidence of past or present optic neuritis. Patients with blurring of vision, diplopia, and undefined visual complaints were assigned to group 2, while group 3 contained patients with no visual symptoms but suspected diagnosis of multiple sclerosis on other grounds. The three parameters explored showed consistent association with the degree of visual involvement, as assessed by clinical impression, but their discriminatory power was diverse. Absolute latency was significantly longer in group 1 patients compared with groups 2 and 3, but it did not discriminate between the last two, whereas interocular difference in latency proved to be sensitive to differences between symptomatic (diplopia, blurring) and asymptomatic groups (2 and 3). Waveshapes were grouped into three categories based upon degree of distortion of the major positive peak, and their relative distribution among the three patient groups was found to be associated with symptomatology. We suggest that, in the production of symptoms such as diplopia, a temporal disparity of afferent impulses might be involved in much the same way that spatial incongruities between both eyes lead to impaired function. In this regard, interocular difference in latency rather than absolute latency would be a more accurate predictor of symptom development. The analysis of VER waveshape suggests, in addition, the importance of inhomogeneous involvement of the visual pathways in the production of symptoms during the evolution of multiple sclerosis.

Adult↗

PubMed2005

Human functional neuroimaging connectivity research in dependence.

Functional and effective connectivity are relatively new techniques in the analysis of functional neuroimaging studies in humans. They have previously been used in studies of 'normal' psychological and neurological processes such as vision before gradually transferring into use in pathological disease states such as schizophrenia. These techniques are now beginning to extend into the field of substance misuse and dependence. So far, most functional neuroimaging studies in this field have shown consistent patterns of activation in several brain regions, and theories are emerging based upon these and animal models. Studies of brain connectivity can now begin to help further unravel the tangle of disparate brain regions and their connections that underpin the psychopharmacological processes of dependence.

Brain↗

PubMed1999

Electrophysiological evidence of cortical fusion in children with early-onset esotropia.

PURPOSE: To investigate sensory fusion responses in infants and children with early-onset esotropia to gain insights into the sequence of events that leads to strabismus. METHODS: Sensory fusion was tested by measuring visual evoked potential (VEP) responses to dynamic random dot correlograms (DRDCs) in a group of children (n = 23) with early-onset esotropia. Thirteen children were tested before surgical alignment, and 13 children were tested after surgical alignment (three children were tested before and after surgery). If the angle of strabismus was larger than 5 prism diopters, it was corrected with Fresnel prisms (Fresnel Prism and Lens, Scottsdale, AZ). RESULTS: Five (38%) of the 13 children who were tested before surgery showed detectable VEP responses to correlogram stimuli compared with 11 (85%) of the 13 children who were tested after surgical alignment. There were no significant statistical differences between VEP responses to DRDCs from the postsurgery group and VEP responses from an age-matched control group with normal binocular vision. CONCLUSIONS: The presence of cortical sensory fusion in children with early-onset esotropia suggests that a congenital defect of sensory fusion cannot be the root cause of esotropia in most children. The data suggest that sensory fusion, when measured by VEP responses to DRDCs, is more robust than stereopsis to abnormal binocular experience and support the notion that pathways processing correlated/anticorrelated stimuli may not completely overlap with pathways processing disparity information.

Child↗

PubMed1986

Binocular vision and spatial perception in 4- and 5-month-old infants.

Four experiments investigated the relation between the development of binocular vision and infant spatial perception. Experiments 1 and 2 compared monocular and binocular depth perception in 4- and 5-month-old infants. Infants in both age groups reached more consistently for the nearer of two objects under binocular viewing conditions than under monocular viewing conditions. Experiments 3 and 4 investigated whether the superiority of binocular depth perception in 4-month-olds is related to the development of sensitivity to binocular disparity. Under binocular viewing conditions in Experiment 3, infants identified as disparity-sensitive reached more consistently for the nearer object than did infants identified as disparity-insensitive. The two groups' performances did not differ under monocular viewing conditions. These results suggest that, binocularly, the disparity-sensitive infants perceived the objects' distances more accurately than did the disparity-insensitive infants. In Experiment 4, infants were habituated to an object, then presented with the same object and a novel object that differed only in size. Disparity-sensitive infants showed size constancy by recovering from habituation when viewing the novel object. Disparity-insensitive infants did not show clear evidence of size constancy. These findings suggest that the development of sensitivity to binocular disparity is accompanied by a substantial increase in the accuracy of infant spatial perception.

Adaptation, Psychological↗

PubMed2001

The Freiburg Stereoacuity Test: automatic measurement of stereo threshold.

BACKGROUND: There is a need for a stereotest with the following properties: (1) Natural viewing conditions, i.e. stimulus contours visible for each eye alone, but no or hardly any cue for monocular detection, and (2) suitability for threshold determination over a wide range of disparities. To comply with these requirements, we developed the Freiburg Stereoacuity Test. METHOD: The stimulus configuration is shown on a visual display unit (VDU) using phase-difference haploscopy with ferromagnetic liquid crystal shutters. The stereo target consists of a vertical bar that can be presented "in front of' or "behind" a frame. The sizes of the bar and the frame are kept constant relative to the stereo disparity. Anti-aliasing allows for disparities finer than the pixel raster. To mask monocular cues the bar is displaced randomly to the right or left. The stereo threshold was determined in two observers with normal eyes, using first the method of constant stimuli and then the best PEST. Both procedures were repeated with observers wearing scatter transparencies that reduced their visual acuity to about 1/10. In addition, the two observers with insight into the test design and two strabismic patients performed the best PEST procedure with one eye only. RESULTS: With constant stimuli both observers achieved a stereoacuity of 2.6 arcsec and 3.1 arcsec, respectively, taking a hit rate of 75% as the threshold. The best PEST revealed a stereoacuity of 2.5 arcsec and 3.0 arcsec, respectively. The scatter transparencies raised the threshold to 261 and 257, respectively. With one eye only, the two observers with insight into the test design exploited the subtle position cue and reached a coarse pseudostereopsis. The two strabismic patients did not utilise the position cue. CONCLUSION: The Freiburg Stereoacuity Test allows determination of stereoacuity over a wide range of disparities (1-1000 arcsec). Although the stimuli can be seen with each eye alone, monocular depth cues are sufficiently masked. The Freiburg Stereoacuity Test is available at http://www.ukl.uni-freiburg.de/aug/bach/fst/.

Adolescent↗

PubMed1990

3-D model of vascular network in rat skin obtained by stereo vision techniques.

The quantitative analysis of the depth of injury, penetration of therapeutic agents in tissues, and the regeneration of vascular patency after a graded degree of thermal injury requires a knowledge of the shape and spatial configuration of the vascular networks in the tissue. We have applied computational stereo vision techniques to describe the 3-D configuration of microvessels in full thickness rat skin vascular casts produced by perfusion of Yellow Microfil latex solution through the aorta. The principal concern is to describe the 3-D structure of vascular networks using a set of 3-D space curves. This representation is computed by integrating monocular and binocular processing; the 2-D curve representation of blood vessels computed through monocular analysis is integrated with disparity data to yield a space curve representation for each vessel. A connection diagram is also computed to indicate the connections existing among the computed space curve representations.

Algorithms↗

PubMed1986

Static vergence and accommodation: population norms and orthoptics effects.

The steady-state characteristics of the accommodation and vergence systems can be described by a model with six major oculomotor parameters. These include the system biases (tonic vergence and accommodation) and forward-loop gains (vergence and accommodative gains), as well as the interactive system gains (AC/A and CA/C ratios). We investigated these parameters in two populations: (1) 22 visually-normal asymptomatic individuals, and (2) 21 visually-abnormal symptomatic individuals before and after conventional orthoptic therapy. Two parameters related to system gain differentiated between the symptomatic and asymptomatic individuals: the slope of the fixation disparity curve with accommodation open-looped and the slope of the accommodative response/stimulus curve. Following orthoptic therapy, 4 static model parameters and 1 dynamic clinical parameter showed changes toward the normal mean; this included tonic accommodation, slope of the fixation disparity curve with accommodation closed-loop (2.5D), slope of the accommodative response/stimulus curve, the CA/C ratio, and the +/- 2D monocular accommodative flipper rate.

Accommodation, Ocular↗

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