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At least 1,225 records · Page 68Linked to original sources
PubMed1998

Cerebral blood flow and oxygen metabolism before and after a stroke-like episode in patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS).

Cerebral blood flow and oxygen metabolism were examined in two patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) using positron emission tomography (PET). Regional cerebral blood flow (rCBF), regional cerebral oxygen metabolic rate (rCMRO2) and regional oxygen extraction fraction (rOEF) were determined with the steady-state technique using oxygen-15-labeled tracers (15O2, C15O2 and C15O). Case 1, a 45-year-old woman, presented with abrupt onset of fluent aphasia. T2-weighted magnetic resonance imaging (MRI) showed a high signal intensity lesion in the left temporoparietal region. The first PET study on day 16 showed increased rCBF and decreased rCMRO2 in the temporal region. In the second PET study, on day 35, rCBF in the temporal region had decreased. Case 2 was a 19-year-old male; the second son of Case 1. He complained of transient blurring of vision, and then generalized tonic-clonic convulsion occurred. A PET study six days before this stroke-like episode demonstrated increased rCBF in both frontal lobes and putamen, where MRI showed lesions after the episode. Focal hyperemia of the lesion antedated and lasted for at least sixteen days after the stroke-like episode in these MELAS patients. These stroke-like episodes appear to be the result of metabolic dysfunction in neural tissue, although the role of an ischemic vascular event cannot be ruled out.

Adult↗
PubMed1995

Eigenvector interpretation of the Farnsworth-Munsell 100-hue test.

We measured the reflectance spectra for the 85 color caps of the Farnsworth-Munsell 100-hue test. Eigenvectors and eigenvalues of a correlation matrix of cone responses were computed, with the cone responses being determined from the 85 test caps, arranged in order (according to color) by means of a linear model. It is shown that the Farnsworth-Munsell 100-hue test can be simulated by use of eigenvectors of the cone responses. The eigenvectors can be interpreted as nonopponent signal and opponent color signals. The normal observer can determine the color of a cap by using two opponent color signals. For color-blind persons (dichromats) one or the other opponent signal is defective, and errors can occur during the test. The simulation results also suggest that eigenvectors can be used to predict results of arrangement tests similar to the Farnsworth-Munsell 100-hue test.

Color Perception↗
PubMedDate not supplied

Pediatric Vision Screener 1: instrument design and operation.

We develop the Pediatric Vision Screener (PVS) to automatically detect ocular misalignment (strabismus) and defocus in human subjects. The PVS utilizes binocular retinal birefringence scanning to determine when both eyes are aligned, with a theoretical accuracy of <1 deg. The device employs an autoconjugate, bull's-eye detector-based system to detect focus. The focus and alignment pathways are separated by both wavelength and data acquisition timing. Binocular focus and alignment are detected in rapid alternating sequence, measuring both parameters in both eyes in <0.5 sec. In this work, the theory and design of the PVS are described in detail. With objective, automated measurement of both alignment and focus, the PVS represents a new approach to screening children for treatable eye disease such as amblyopia.

Adult↗
PubMed1991

Visual search, visual streams, and visual architectures.

Most psychological, physiological, and computational models of early vision suggest that retinal information is divided into a parallel set of feature modules. The dominant theories of visual search assume that these modules form a "blackboard" architecture: a set of independent representations that communicate only through a central processor. A review of research shows that blackboard-based theories, such as feature-integration theory, cannot easily explain the existing data. The experimental evidence is more consistent with a "network" architecture, which stresses that: (1) feature modules are directly connected to one another, (2) features and their locations are represented together, (3) feature detection and integration are not distinct processing stages, and (4) no executive control process, such as focal attention, is needed to integrate features. Attention is not a spotlight that synthesizes objects from raw features. Instead, it is better to conceptualize attention as an aperture which masks irrelevant visual information.

Attention↗
PubMed2004

Escher in color space: individual-differences multidimensional scaling of color dissimilarities collected with a gestalt formation task.

The structure of color perception can be examined by collecting judgments about color dissimilarities. In the procedure used here, stimuli are presented three at a time on a computer monitor and the spontaneous grouping of most-similar stimuli into gestalts provides the dissimilarity comparisons. Analysis with multidimensional scaling allows such judgments to be pooled from a number of observers without obscuring the variations among them. The anomalous perceptions of color-deficient observers produce comparisons that are represented well by a geometric model of compressed individual color spaces, with different forms of deficiency distinguished by different directions of compression. The geometrical model is also capable of accommodating the normal spectrum of variation, so that there is greater variation in compression parameters between tests on normal subjects than in those between repeated tests on individual subjects. The method is sufficiently sensitive and the variations sufficiently large that they are not obscured by the use of a range of monitors, even under somewhat loosely controlled conditions.

Color Perception↗
PubMed2004

Characteristics of attention and visual short-term memory: implications for visual interface design.

Although the human retina can code many object images simultaneously, observers are often aware of only a tiny fraction of this information. These processing limitations of the visual brain have evolved to prioritize particularly relevant features of a scene while ignoring other irrelevant features. However, such selectivity has its drawbacks. In information-rich environments, such as driving a car or landing an aircraft, vision can fail to cope, and accidents can result. Accordingly, much recent research in psychophysics and ergonomics has examined how display characteristics affect our ability to process multiple features of the visual environment simultaneously. The majority of these experiments has found that performance can be optimized by combining several features into one visual 'object'. In contrast, several recent studies from my own laboratory have found the opposite pattern, indicating that information sources can often be more efficiently processed when they belong to separate objects. Indeed, these data suggest that the number of objects has no general effect on our perceptual performance. Instead, I argue for a two-pathway approach to understanding human visual capacities, and suggest that this approach may have important implications for a diverse range of display technologies, including cockpit displays.

Attention↗
PubMed1998

Gaze angle: a possible mechanism of visual stress in virtual reality headsets.

It is known that some Virtual Reality (VR) head-mounted displays (HMDs) can cause temporary deficits in binocular vision. On the other hand, the precise mechanism by which visual stress occurs is unclear. This paper is concerned with a potential source of visual stress that has not been previously considered with regard to VR systems: inappropriate vertical gaze angle. As vertical gaze angle is raised or lowered the 'effort' required of the binocular system also changes. The extent to which changes in vertical gaze angle alter the demands placed upon the vergence eye movement system was explored. The results suggested that visual stress may depend, in part, on vertical gaze angle. The proximity of the display screens within an HMD means that a VR headset should be in the correct vertical location for any individual user. This factor may explain some previous empirical results and has important implications for headset design. Fortuitously, a reasonably simple solution exists.

Data Display↗
PubMed1995

[A new method for objective vision assessment using infrared nystagmography].

Objective assessment of visual acuity (VA) is necessary in cases of malingering or poor cooperation in subjective VA evaluation. Based on Ohm's idea of the suppression of experimentally evoked optokinetic nystagmus (OKN), a new objective visual acuity test is presented. A commercially available system for monitoring eye movement (OBER2) allows the test to be performed on a standard PC with a minimum amount of time. A grating pattern moving horizontally on the screen evokes OKN, which is recorded by infrared nystagmography. Superimposed black optotypes of increasing size (brake marks) suppress OKN as soon as they are recognized. Eighty-two normal eyes with VA artificially reduced by different Bangerter dispersion foils (VA 0.04-1.6) and 152 eyes with visual disturbances (VA 0.04-1.0) of various etiologies were examined. The test allowed estimation of the least VA in steps of > or = 1.0, > or = 0.25, > or = 0.1, > or = 0.05. None of the eyes examined had a VA below these values when the OKN was suppressed by the referring brake mark.

Electronystagmography↗
PubMed2004

[The value of multifocal ERG in diagnosis of discrete macular dystrophies].

BACKGROUND: Multifocal ERG is being extensively applied to numerous retinal disorders. It has gained particular clinical value in retinal disorders developing without morphological alterations. PATIENTS AND METHODS: We investigated a series of 4 patients, aged 10, 18, 29, and 49 years, respectively. When examined, they complained of photophobia and slowly progressive bilateral loss of vision, visual acuity ranging from 0.7 to 0.1. RESULTS: Ophthalmoscopic examination showed no or minimal alterations such as subtle granular changes in the fovea. Photopic-scotopic full-field ERG was normal. Multifocal ERG, in contrast, showed markedly reduced signal amplitudes within the central 10 degrees. CONCLUSIONS: Based on the results of multifocal ERG, we were able in each case to consider with a high degree of probability the diagnosis of progressive foveal cone dystrophy. This is to emphasize the sensitivity of multifocal ERG in disorders affecting primarily the macula, without morphological changes, as cone (-rod) dystrophy, early Stargardt dystrophy, etc. The uttermost advantages of multifocal ERG are its innocuity, its applicability to children and the very early sensitivity to changes in retinal function.

Adolescent↗
PubMed2004

Distortions of distance and shape are not produced by a single continuous transformation of reach space.

We investigated whether distortions of perceived distance and shape could be captured by a single continuous one-to-one transformation of the underlying space. In Experiment 1, the participants reached to touch points around the perimeter of spherical targets viewed at five different distances, to yield simultaneous measures of perceived distance and shape. Different participants reached while using dynamic monocular, static binocular, or dynamic binocular vision. Thin plate spline (TPS) analysis was applied so as to transform a Cartesian grid in such a way as to carry the original target points to the mean reach locations. In all cases, discontinuities appeared in the transformed grid from folding of the space. In Experiment 2, the participants reached to points that lay at the same locus in reach space, but on different portions of the visible target spheres (e.g., front vs. side). The participants reached to different locations when the points were different with respect to shape (e.g., front vs. side) but reached to the same locations when the points were the same with respect to shape (left vs. right side). TPS analysis revealed discontinuities from holes torn in the underlying space. The results show that perceived distance and perceived shape entail different distortions and cannot be captured by a single continuous transformation of reach space.

Adult↗
PubMed1985

Brain theory and cooperative computation.

"Top-down" brain theory, based upon functional analysis of cognitive processes in terms of interacting schemas, is distinguished from "bottom-up" brain theory based on analysis of the dynamics of neural nets. "Cooperative computation" is proposed as the style of interaction of neural subsystems at various levels. Perceptual schemas are introduced as the building blocks for the representation of the perceived environment, and motor schemas serve as control systems to be coordinated into programs for the control of movement. A cooperative computation view of the design of machine vision systems is exemplified both by an algorithm for computing optic flow which offers interesting insights into the evolution of hierarchical neural structures, and by an analysis of knowledge representation for machine interpretation of visual scenes. The interaction between top-down analysis and detailed neural modelling is illustrated by the study of visuomotor coordination in frogs and toads.

Animals↗
PubMed2005

Synthetic vision systems: the effects of guidance symbology, display size, and field of view.

Two experiments conducted in a high-fidelity flight simulator examined the effects of guidance symbology, display size, and geometric field of view (GFOV) within a synthetic vision system (SVS). In Experiment 1, 18 pilots flew highlighted and low-lighted tunnel-in-the-sky displays, as well as a less cluttered follow-me aircraft (FMA), through a series of curved approaches over rugged terrain. The results revealed that both tunnels supported better flight path tracking and lower workload levels than did the FMA because of the availability of more preview information. Increasing tunnel intensity had no benefit on tracking and, in fact, degraded traffic awareness because of clutter and attentional tunneling. In Experiment 2, 24 pilots flew a lowlighted tunnel configured according to different display sizes (small or large) and GFOVs (30 degrees or 60 degrees). Measures of flight path tracking and terrain awareness generally favored the 60 degrees GFOV; however, there were no effects of display size. Actual or potential applications of this research include understanding the impact of SVS properties on flight path tracking, traffic and terrain awareness, workload, and the allocation of attention.

Adult↗
PubMed2006

Stereo and motion parallax cues in human 3D vision: can they vanish without a trace?

In an immersive virtual reality environment, subjects fail to notice when a scene expands or contracts around them, despite correct and consistent information from binocular stereopsis and motion parallax, resulting in gross failures of size constancy (A. Glennerster, L. Tcheang, S. J. Gilson, A. W. Fitzgibbon, & A. J. Parker, 2006). We determined whether the integration of stereopsis/motion parallax cues with texture-based cues could be modified through feedback. Subjects compared the size of two objects, each visible when the room was of a different size. As the subject walked, the room expanded or contracted, although subjects failed to notice any change. Subjects were given feedback about the accuracy of their size judgments, where the "correct" size setting was defined either by texture-based cues or (in a separate experiment) by stereo/motion parallax cues. Because of feedback, observers were able to adjust responses such that fewer errors were made. For texture-based feedback, the pattern of responses was consistent with observers weighting texture cues more heavily. However, for stereo/motion parallax feedback, performance in many conditions became worse such that, paradoxically, biases moved away from the point reinforced by the feedback. This can be explained by assuming that subjects remap the relationship between stereo/motion parallax cues and perceived size or that they develop strategies to change their criterion for a size match on different trials. In either case, subjects appear not to have direct access to stereo/motion parallax cues.

Adult↗
PubMed2004

Mirror vision: perceived size and perceived distance of virtual images.

We investigated spatial perception of virtual images that were produced by convex and plane mirrors. In Experiment 1, 36 subjects reproduced both the perceived size and the perceived distance of virtual images for five targets that had been placed at a real distance of 10 or 20 m. In Experiment 2, 30 subjects verbally judged both the perceived size and the perceived distance of virtual images for five targets that were placed at each of five real distances of 2.5-45 m. In both experiments, the subjects received objective-size and objective-distance instructions. The results were that (1) size constancy was attained for a distance of up to 45 m, (2) distance was readily discriminated within this distance range, although virtual images produced by the mirror of strong curvature were judged to be farther away than those produced by the mirrors of less curvature, and (3) the ratio of perceived size to perceived distance was described as a power function of visual angle, and the ratio for the convex mirror was larger than that for the plane mirror. We compared the taking-into-account model and the direct perception model on the basis of a correlation analysis for proximal, virtual, and real levels of the stimuli. The taking-into-account model, which assumes that visual angle is transformed into perceived size by taking perceived distance into account, was supported by an analysis for the proximal level of stimuli. The direct perception model, which assumes that there is no inferential process between perceived size and perceived distance, was partially supported by an analysis for the distal level of the stimuli.

Adult↗
PubMed1980

Sensory-specific and fractional disorders of recent memory in man. II. Unilateral loss of tactile recent memory.

Three patients were found to have unilateral tactile recent memory loss on examination. In two patients the loss occurred in the right hand and was accompanied by a disorder of verbal recent memory; in the third patient the loss occurred in the left hand and was not accompanied by any other disturbance in recent memory. An acute unilateral lesion, either structural or functional, in the medial temporal lobe contralateral to the tactile recent memory disturbance was the common denominator in all three cases. The proper methods for diagnosing a unilateral tactile disturbance of recent memory and other forms of fractional disorders of recent memory are discussed. Based on computerized tomography scans and behavioral and anatomical data in man and monkey, an anatomical explanation is offered to account for the syndromes of right and left unilateral tactile recent memory loss. The possible existence of other forms of fractional disturbances of recent memory and the role of the cerebral commissures in recent memory functions are discussed.

Adult↗
PubMed1989

Utility of the affected sib pair method to detect linkage of a sex-linked dominant disease with a sex-linked recessive trait.

Use of affected sib-pairs for linkage determination of a sex-linked dominant disease with a recessive X-chromosome marker will require extremely large sample sizes, particularly when the marker is marginally polymorphic. In addition, this method should not be used without caution on data collected for a traditional LOD score analysis, without considering the parental mating types involved in the informative families. Nevertheless, ascertainment adjustment and correction for dependence of multiple pairs of affected sib-pairs in families suggests that this method provides linkage inference concordant with that of the traditional LOD score analysis.

Color Vision Defects↗