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PubMed2006

Humans ignore motion and stereo cues in favor of a fictional stable world.

As we move through the world, our eyes acquire a sequence of images. The information from this sequence is sufficient to determine the structure of a three-dimensional scene, up to a scale factor determined by the distance that the eyes have moved. Previous evidence shows that the human visual system accounts for the distance the observer has walked and the separation of the eyes when judging the scale, shape, and distance of objects. However, in an immersive virtual-reality environment, observers failed to notice when a scene expanded or contracted, despite having consistent information about scale from both distance walked and binocular vision. This failure led to large errors in judging the size of objects. The pattern of errors cannot be explained by assuming a visual reconstruction of the scene with an incorrect estimate of interocular separation or distance walked. Instead, it is consistent with a Bayesian model of cue integration in which the efficacy of motion and disparity cues is greater at near viewing distances. Our results imply that observers are more willing to adjust their estimate of interocular separation or distance walked than to accept that the scene has changed in size.

Computer Simulation↗

PubMed1980

Outbreak of methanol and isopropanol poisoning in New Britain, Papua New Guinea.

Between May 22 and 28, 1978, 372 adult male Melanesians consumed a solution of 82% methanol and 18% isopropanol. One hundred and eighteen men were admitted to hospital and a further 251 subjects were treated as outpatients. Eighteen men died. Fourteen of the survivors were blind initially, but only four failed to recover some vision. Diffuse encephalopathy with residual pseudobulbar palsy and dementia occurred in four patients, two of whom remained permanently blind. Estimated quantities of undiluted spirit consumed varied from 25 mL to 750 mL (mean, 100 mL), and symptoms developed on average 30 hours after consumption. A disparity between the amounts of solution consumed and the sequelae was frequently noted. Blindness and death followed the ingestion of 100 mL in one case, while in two other cases, over 500 mL produced no apparent disability. On investigation, it was established that the mixture had been sold by a local pharmacy in the mistaken belief that it was methylated spirits. Regular consumption of methylated spirits by many adult male Melanesians has been a common practice in east New Britain for many years. The difficulties of managing an outbreak of poisoning of this magnitude in the context of a developing country are discussed.

1-Propanol↗

PubMed1979

Dynamic depth reversal stereograms.

A new stimulus was generated to create dynamic stereopsis. Binocular disparity was alternated between crossed and uncrossed conditions, while mean luminance remained constant, to produce a stereoscopic stimulus that appeared to move continuously in depth. These dynamic depth reversal stereograms provided an effective stimulus to elicit the visual evoked potential (VEP). Neural coding of stereopsis was reflected in the cortical response with VEP amplitudes changing as a function of binocular disparity and of image blur in the stereograms.

Child↗

PubMed1990

Neurological implications of aniseikonic tilts and stereoscopic completions through homogeneous visual space.

In 1965, it was first reported that BROKEN visual contours complete themselves in textured stereovision across empty or homogeneous space and that they do so strongly following directly the optics of crossed versus uncrossed disparities. The importance was then also noted of this completion effect for any neurophysiological model of stereovision. We now extend these measurements with several additional targets and to an analogous aniseikonic target, and confirm that the completion range has a maximum of about 5 degrees. There is much dependence upon target eccentricity and disparity sign, and some on size. That aniseikonic tilts may also be generated over this same range confirms the fact that global neurointegrative processes are of critical importance in all facets of stereovision, and in texture vision in general.

Aniseikonia↗

PubMed1982

[Neurobiological principles of binocular space perception. Historical review on the development of the concept and knowledge].

Binocular vision and space perception are not readily explained on the basis of direct anatomical evidence on the visual system. Galen (2nd century A.D.) localized the mechanism underlying binocular vision into the optic chiasm. Nearly 2000 years later the famous physicist Newton (1704), undoubtedly stimulated by clinical reports on hemianopia and Descartes' (1686) hypothesis on the retinal image projections on the brain, came up with a new hypothesis on the optic chiasm which could explain how information from homonymous visual hemifields could converge from the two eyes to one and the same area in the brain. He predicted that the temporal retinal fibers of both eyes fail to cross. Irrefutable proof of the special arrangement of the optic chiasm was provided by Ramon y Cajal (1899) with the aid of the Golgi method. It took more than 50 years before binocularly oriented cells were discovered in the visual cortex by Baumgartner and colleagues (1958), and before neurons were found in that area by Hubel and Wiesel (1959) which responded to stimulation from corresponding retinal sites of the two eyes. These electrophysiological studies profited by the localization of the cortical visual center in the occipital lobe by Panizza (1856), the identification of the corpus geniculatum laterale as a relais station of the retino-cortical pathway by Monakow (1883, 1885) and the discovery of the projection of homonymous retinal halves upon alternating layers of this structure by Minkowski (1920). Wheatstone opened the road to the understanding of stereoscopic vision by inventing the stereoscope in 1838. He based his research largely upon the the investigation of Aguilonius (1613), Vieth (1818) and Müller (1926) on the horopter. The most elegant evidence on the significance of visual disparity for depth perception came recently from Julesz and his demonstration of "random-dot-stereograms" (1971). Binocular neurons which are sensitive to minimal stimulus disparities within Panum's area (1858) have only recently been observed in the striate cortex by electrophysiological recordings (Barlow et al., 1967; Poggio and Fischer, 1977). These cells were designated as "disparity or depth detectors". They displace the "cyclopean eye" of Helmholtz (1867) and Hering (1879) from its Homeric seat in the forehead to the cortical field whose striations were already noted by Gennari (1782) near the posterior end of the cranium.

Animals↗

PubMed1980

Actual measurement of fixation disparity and its use in diagnosis and treatment.

An instrument and technique are described which, for the first time, enable the eye care practitioner to measure the angle of fixation disparity. A forced vergence fixation disparity curve can be quickly measured in the office. Research findings and patient examples are used to show how a fixation disparity curve is analyzed to diagnose and prescribe for an oculomotor imbalance.

Eyeglasses↗

PubMed1985

Motion perception during dichoptic viewing of moving random-dot stereograms.

The relation between binocular and monocular motion perception was investigated. A random-dot stereogram (30 X 30 deg arc), containing a central figure seen in front of the background in stereoscopic vision, was viewed dichoptically by human subjects without a fixed visual frame of reference. The images seen by the right and left eye were moved laterally according to a triangular wave form, in counterphase, but with variable amplitude ratios. Under this condition only purely lateral movement and no motion in depth of the stereogram as a whole was perceived, while stereoscopic vision of the figure-background relation was maintained. The magnitude of the binocularly perceived lateral motion, signalled by manual tracking of the perceived displacement, equalled the algebraic mean of the monocular motion percepts. As a special case, when the two images forming the stereogram were moved with equal velocities but in opposite directions they were perceived as a completely stationary, fused image in stereoscopic depth. Only the addition of a stationary reference (a bar or grating seen by both eyes) resulted in the perception of motion in depth. We conclude that a visual frame of reference is essential for perception of motion in depth but not for perception of lateral movements. Moreover, it seems likely that not absolute binocular disparity (retinal locus differences) but relative binocular disparity (differences in angular distance between two or more corresponding features in the two retinal images) is a cue for perception of depth.

Convergence, Ocular↗

PubMed2005

Repeated visual hallucinations in Parkinson's disease as disturbed external/internal perceptions: focused review and a new integrative model.

Visual hallucinations (VH) in Parkinson's disease (PD) are a chronic complication in 30 to 60% of treated patients and have a multifaceted phenomenology. Flickering, faultive impressions, and illusionary misperceptions precede the core syndrome of stereotyped, colorful images. The patient variably recognizes these images as hallucinations, being rarely irritated or frightened and more often amused as a bystander. Although studies on VH in PD focus on several research domains, no comprehensive, unified theory has been developed to study their pathophysiology. We have adapted Hobson's work on the states of consciousness and propose a model integrating seemingly disparate data on VH. We suggest that VH should be considered as a dysregulation of the gating and filtering of external perception and internal image production. Contributive elements and anatomical links for the model include poor primary vision, reduced activation of primary visual cortex, aberrant activation of associative visual and frontal cortex, lack of suppression or spontaneous emergence of internally generated imagery through the ponto-geniculo-occipital system, intrusion of rapid eye movement dreaming imagery into wakefulness, errative changes of the brainstem filtering capacities through fluctuating vigilance, and medication-related overactivation of mesolimbic systems. Different etiologies likely produce different phenomenologies and the prognosis may not be uniform. This new conceptual framework permits an anatomical view of VH and suggests new, testable hypotheses regarding their pathophysiology and therapy.

Brain Chemistry↗

PubMed2005

Toward an understanding of the neural processing for 3D shape perception.

In this article we address the major issue of space vision, how the brain represents the 3D shape of objects in the real world, on the basis of psychophysics and neurophysiology. In psychophysics, Gibson found texture gradients and width gradients, as well as the gradient of binocular disparity, as the major cues for surface orientation in depth. Marr proposed that a surface-based representation is the main step towards 3D shape representation. In our neurophysiological studies of the monkey parietal cortex, we have found visual-dominant neurons in area AIP with selectivity in 3D shape of the objects, and also surface-orientation-selective (SOS) neurons in the caudal intraparietal (CIP) area. SOS neurons responded selectively to surface orientation in depth presented in random dot stereograms with a disparity gradient. Many of the SOS neurons responded selectively also to texture gradients and linear perspective, and their responses were enhanced by the combination of these cues. We also found axis-orientation-selective (AOS) neurons in area CIP, responding selectively to the orientation of the longitudinal axis of elongated objects in depth. We present preliminary data here to demonstrate that some of AOS neurons that prefer intermediate thickness are shape-selective, and they are likely to discriminate surface curvature. These data suggest that neurons in and around area CIP may have the capacity to represent 3D shape.

Animals↗

PubMed1992

Detection and processing of vertical disparity by the human observer.

Based on the distinction between uniocular vertical magnification and vertical disparity, the induced size effect experiments were reinterpreted and new experiments done to show that vertical disparity signals can produce other stereoptic depth effects. The direction and efficiency of utilization of vertical disparity signals depend on the quadrant of the visual field and the stimulus position within it.

Humans↗

PubMed2004

A preference for phase-based disparity in a neuromorphic implementation of the binocular energy model.

The relative depth of objects causes small shifts in the left and right retinal positions of these objects, called binocular disparity. This letter describes an electronic implementation of a single binocularly tuned complex cell based on the binocular energy model, which has been proposed to model disparity-tuned complex cells in the mammalian primary visual cortex. Our system consists of two silicon retinas representing the left and right eyes, two silicon chips containing retinotopic arrays of spiking neurons with monocular Gabor-type spatial receptive fields, and logic circuits that combine the spike outputs to compute a disparity-selective complex cell response. The tuned disparity can be adjusted electronically by introducing either position or phase shifts between the monocular receptive field profiles. Mismatch between the monocular receptive field profiles caused by transistor mismatch can degrade the relative responses of neurons tuned to different disparities. In our system, the relative responses between neurons tuned by phase encoding are better matched than neurons tuned by position encoding. Our numerical sensitivity analysis indicates that the relative responses of phase-encoded neurons that are least sensitive to the receptive field parameters vary the most in our system. We conjecture that this robustness may be one reason for the existence of phase-encoded disparity-tuned neurons in biological neural systems.

Action Potentials↗

PubMed1998

Identifying crash involvement among older drivers: agreement between self-report and state records.

Older drivers have a high crash rate per vehicle mile of travel. Coupled with the growth of the number of older drivers on the road, this has generated interest in the identification of factors which place older drivers at increased risk. However, much of the existing research on medical and functional risk factors for crash involvement has generally been inconsistent. Methodological differences between studies have been hypothesized as being partly responsible for such inconsistencies. The source of information used to identify crash-involved drivers has been identified as one such difference. This paper reports on the agreement between self-report and state record for identifying crash involved-older drivers. We also sought to determine whether the prevalence of visual and cognitive impairment differs across crash-involved drivers identified by either or both sources. Finally, we assessed whether risk factors for crash involvement differed when crash-involved drivers were identified by either self-report or state records. Results indicated that there was a moderate level of agreement between self-reported and state-recorded crash involvement (kappa = 0.45). However, we did find significant differences between crash-involved drivers identified via state records and/or self-report with respect to demographic (age, race), driving (annual mileage, days per week driven), and vision impairment (acuity, contrast sensitivity, peripheral visual field sensitivity, useful field of view). We also found that the possibility for biased measures of association is real. Useful field of view impairment was associated with both self-reported and state-recorded crash involvement; however, the magnitude of the associations was disparate. Moreover, glaucoma was identified as a significant risk factor when considering state-recorded crashes but not self-reported crashes. While validation of these findings is required, research designed to identify risk factors for crash involvement among older drivers should carefully consider the issue of case definition, particularly if self-report is used to identify crash-involved older drivers.

Accidents, Traffic↗

PubMed1988

Planarity and segmentation in stereoscopic matching.

The matching of stereograms which contain periodic patterns suggests ways in which the stereo correspondence problem may be solved in human vision. The stereograms seem to be segmented by coarse-scale features. Within each segment a set of matches approximating a plane is chosen. In regions with periodic patterns there may be many such planar sets, and the disparity of coarse-scale features seems to guide the choice of a particular set. This emphasis on planarity may reflect the occurrence of correlation-like operations in cortical neurons. An attractive possibility is that segmentation effectively delimits areas of the visual field within which disparities are likely to be slow changing (eg local tangent planes to surfaces) so that the correlation sums evaluated in a segment can give the best estimate of depth. A mechanism of this kind cannot account for all of stereo matching, since not all visual objects are well described by ensembles of planes. But it is likely to be a component of the matching system which is particularly important where images are 'noisy' and averaging is needed to extract reliable disparities.

Algorithms↗

PubMed1995

Valproic acid treatment of chronic daily headache.

The efficacy of valproic acid in the treatment of intractable chronic daily headache, unresponsive to traditional prophylactic medications, was examined prospectively in 16 patients. Dosage of the medication was adjusted to maintain serum valproic acid levels between 50 and 100 micrograms/mL, provided there were no significant side effects at that level. Valproic acid prophylaxis was of some benefit in only 2 of 16 patients. One of these two patients discontinued therapy due to side effects. Eight of the 16 patients reported side effects which included nausea, diarrhea, anorexia, lethargy, sleepiness, confusion, blurred vision, and decreased libido. In conclusion, valproic acid was not effective in controlling chronic daily headache in the majority of patients in whom conventional therapy had failed, and 50% of patients reported side effects. There is a significant disparity in the reported efficacy of this drug in treating chronic daily headache. This disparity is most likely due to the poorly-defined nature of this variety of headache. It is, therefore, recommended that more stringent definition of this disorder be developed before therapeutic regimens are evaluated.

Adult↗

PubMed1998

Plaid slant and inclination thresholds can be predicted from components.

We investigated whether stereoscopic slant and inclination thresholds for surfaces defined by two component plaids could be predicted from the interocular differences in their individual component gratings. Thresholds were measured for binocular images defined by single sinusoidal gratings and two component plaids. In both cases thresholds showed a marked dependence on component orientation. For absolute component orientations greater than 45 deg we found that inclination thresholds were smaller than slant thresholds. However, for absolute component orientations less than 45 deg, we found a reversal: slant thresholds were smaller than inclination thresholds. We considered three models that might account for these data. One assumed that thresholds stemmed from interocular position differences of corresponding image points. The other two assumed a combination of position, orientation and/or spatial-frequency differences. The best fits were obtained from those models that explicitly represented orientation differences. From the model combining orientation and spatial-frequency differences, we estimated the relative cue sensitivity to be 1.7:1, respectively. For plaids, we found that thresholds obtained from the individual components could be used to predict thresholds for plaids, even though an additional disparity cue from the contrast beat was available.

Depth Perception↗

PubMedDate not supplied

Serial and parallel processing of visual feature conjunctions.

Treisman and others have reported that the visual search for a target distinguished along a single stimulus dimension (for example, colour or shape) is conducted in parallel, whereas the search for an item defined by the conjunction of two stimulus dimensions is conducted serially. For a single dimension the target 'pops out' and the search time is independent of the number of irrelevant items in the set. For conjunctions, the search time increases as the set becomes larger. Thus, it seems that the visual system is incapable of conducting a parallel search over two stimulus dimensions simultaneously. Here we extend this conclusion for the conjunction of motion and colour, showing that it requires a serial search. We also report two exceptions: if one of the dimensions in a conjunctive search is stereoscopic disparity, a second dimension of either colour or motion can be searched in parallel.

Color↗

PubMed1987

Visual function and pattern visual evoked response in optic neuritis.

The disparity between clinical visual function and pattern visual evoked response (VER) was studied in 53 patients who had suffered an attack of optic neuritis (ON) more than six months before. The visual functions tested included Snellen visual acuity, colour vision, visual field, and contrast sensitivity. The effect of pattern presentation, check size, and luminance was tested by recording VERs with several stimulus configurations. VER amplitudes were found to be associated with the outcome of all four clinical tests, independently of check size, luminance, or the presentation method used. On the other hand VER latencies were hardly ever related to the results of any of the four clinical visual tests. These findings support the idea that VER amplitude provides information about visual spatial perception, while VER latency is more related to the extent of demyelination.

Adolescent↗

PubMed2002

Disparity-selective neurons in area V4 of macaque monkeys.

Area V4 is an intermediate stage of the ventral visual pathway providing major input to the final stages in the inferior temporal cortex (IT). This pathway is involved in the processing of shape, color, and texture. IT neurons are also sensitive to horizontal binocular disparity, suggesting that binocular disparity is processed along the ventral visual pathway. In the present study, we examined the processing of binocular disparity information by V4 neurons. We recorded responses of V4 neurons to binocularly disparate stimuli. A population of V4 neurons modified their responses according to changes of stimulus disparity; neither monocular responses nor eye movements could account for this modulation. Disparity-tuning curves were similar for different locations within a neuron's receptive field. Neighboring neurons recorded using a single electrode displayed similar disparity-tuning properties. These findings indicate that a population of V4 neurons is selective for binocular disparity, invariant for the position of the stimulus within the receptive field. The finding that V4 neurons with similar disparity selectivity are clustered suggests the existence of functional modules for disparity processing in V4.

Animals↗