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PubMed2006

A screen magnifier using "high level" implementation techniques.

This paper presents the architecture of, and the techniques used to build, a screen magnifier for visually impaired people that uses the "high-level" features of the Microsoft Windows operating system. The magnifier uses information from the Desktop Window as its source and overlays this with a topmost, transparent, layered window that contains the magnified image. Issues concerning cursor enlargement, tooltip suppression, and focus tracking are discussed. A stable magnifier results that does not need to use the "dirty" low-level techniques that are typically used to build screen magnifiers. The only known problem of the magnifier is that it fails to suppress the original, unmagnified cursor of the few applications that use custom cursors.

Communication Devices for People with Disabilities↗

PubMedDate not supplied

Binary-space-partitioned images for resolving image-based visibility.

We propose a novel 2D representation for 3D visibility sorting, the Binary-Space-Partitioned Image (BSPI), to accelerate real-time image-based rendering. BSPI is an efficient 2D realization of a 3D BSP tree, which is commonly used in computer graphics for time-critical visibility sorting. Since the overall structure of a BSP tree is encoded in a BSPI, traversing a BSPI is comparable to traversing the corresponding BSP tree. BSPI performs visibility sorting efficiently and accurately in the 2D image space by warping the reference image triangle-by-triangle instead of pixel-by-pixel. Multiple BSPIs can be combined to solve "disocclusion," when an occluded portion of the scene becomes visible at a novel viewpoint. Our method is highly automatic, including a tensor voting preprocessing step that generates candidate image partition lines for BSPIs, filters the noisy input data by rejecting outliers, and interpolates missing information. Our system has been applied to a variety of real data, including stereo, motion, and range images.

Algorithms↗

PubMedDate not supplied

Correcting interperspective aliasing in autostereoscopic displays.

An image presented on an autostereoscopic system should not contain discontinuities between adjacent views. A viewer should experience a continuous scene when moving from one view to the next. If corresponding points in two perspectives do not spatially abut, a viewer will experience jumps in the scene. This is known as interperspective aliasing. Interperspective aliasing is caused by object features far away from the stereoscopic screen being too small, which results in visual artifacts. By modeling a 3D point as a defocused image point, we can adapt Fourier analysis to devise a depth-dependent filter kernel that allows filtering of a stereoscopic 3D image. For synthetic 3D data, we use a simpler approach, which is to smear the data by a distance proportional to its depth.

Algorithms↗

PubMedDate not supplied

Comparing 2D vector field visualization methods: a user study.

We present results from a user study that compared six visualization methods for two-dimensional vector data. Users performed three simple but representative tasks using visualizations from each method: 1) locating all critical points in an image, 2) identifying critical point types, and 3) advecting a particle. Visualization methods included two that used different spatial distributions of short arrow icons, two that used different distributions of integral curves, one that used wedges located to suggest flow lines, and line-integral convolution (LIC). Results show different strengths and weaknesses for each method. We found that users performed these tasks better with methods that: 1) showed the sign of vectors within the vector field, 2) visually represented integral curves, and 3) visually represented the locations of critical points. Expert user performance was not statistically different from nonexpert user performance. We used several methods to analyze the data including omnibus analysis of variance, pairwise t-tests, and graphical analysis using inferential confidence intervals. We concluded that using the inferential confidence intervals for displaying the overall pattern of results for each task measure and for performing subsequent pairwise comparisons of the condition means was the best method for analyzing the data in this study. These results provide quantitative support for some of the anecdotal evidence concerning visualization methods. The tasks and testing framework also provide a basis for comparing other visualization methods, for creating more effective methods and for defining additional tasks to further understand the tradeoffs among the methods. In the future, we also envision extending this work to more ambitious comparisons, such as evaluating two-dimensional vectors on two-dimensional surfaces embedded in three-dimensional space and defining analogous tasks for three-dimensional visualization methods.

Algorithms↗

PubMedDate not supplied

Dynamic range reduction inspired by photoreceptor physiology.

A common task in computer graphics is the mapping of digital high dynamic range images to low dynamic range display devices such as monitors and printers. This task is similar to the adaptation processes which occur in the human visual system. Physiological evidence suggests that adaptation already occurs in the photoreceptors, leading to a straightforward model that can be easily adapted for tone reproduction. The result is a fast and practical algorithm for general use with intuitive user parameters that control intensity, contrast, and level of chromatic adaptation, respectively.

Algorithms↗

PubMedDate not supplied

Visualization task performance with 2D, 3D, and combination displays.

We describe a series of experiments that compare 2D displays, 3D displays, and combined 2D/3D displays (orientation icon, ExoVis, and clip planes) for relative position estimation, orientation, and volume of interest tasks. Our results indicate that 3D displays can be very effective for approximate navigation and relative positioning when appropriate cues, such as shadows, are present. However, 3D displays are not effective for precise navigation and positioning except possibly in specific circumstances, for instance, when good viewing angles or measurement tools are available. For precise tasks in other situations, orientation icon and ExoVis displays were better than strict 2D or 3D displays (displays consisting exclusively of 2D or 3D views). The combined displays had as good or better performance, inspired higher confidence, and allowed natural, integrated navigation. Clip plane displays were not effective for 3D orientation because users could not easily view more than one 2D slice at a time and had to frequently change the visibility of individual slices. Major factors contributing to display preference and usability were task characteristics, orientation cues, occlusion, and spatial proximity of views that were used together.

Adult↗

PubMedDate not supplied

An approach to the perceptual optimization of complex visualizations.

This paper proposes a new experimental framework within which evidence regarding the perceptual characteristics of a visualization method can be collected, and describes how this evidence can be explored to discover principles and insights to guide the design of perceptually near-optimal visualizations. We make the case that each of the current approaches for evaluating visualizations is limited in what it can tell us about optimal tuning and visual design. We go on to argue that our new approach is better suited to optimizing the kinds of complex visual displays that are commonly created in visualization. Our method uses human-in-the-loop experiments to selectively search through the parameter space of a visualization method, generating large databases of rated visualization solutions. Data mining is then used to extract results from the database, ranging from highly specific exemplar visualizations for a particular data set, to more broadly applicable guidelines for visualization design. We illustrate our approach using a recent study of optimal texturing for layered surfaces viewed in stereo and in motion. We show that a genetic algorithm is a valuable way of guiding the human-in-the-loop search through visualization parameter space. We also demonstrate several useful data mining methods including clustering, principal component analysis, neural networks, and statistical comparisons of functions of parameters.

Algorithms↗

PubMedDate not supplied

Presumed and confirmed striatocapsular brain infarctions in six dogs.

OBJECTIVE: To describe the clinical and diagnostic features of the canine sensorimotor syndrome caused by striatocapsular brain infarctions (SCI). ANIMALS STUDIED: Six dogs with diagnostic imaging or postmortem evidence of SCI. PROCEDURES: Medical records of dogs with SCI were retrospectively reviewed and the signalment, history, clinical signs, antemortem clinicopathologic test results, diagnostic imaging findings, case outcomes, and pathologic findings recorded. RESULTS: All dogs had an acute onset of nonprogressive homonymous visual field deficits and contralateral general proprioceptive (GP) deficits. Contralateral hemiparesis and facial hypalgesia were noted in 5/6 dogs. CT scans were normal in 2/4 dogs, and revealed poorly defined hypoattenuating lesions in the subcortical white matter in two dogs. MRI exams were performed in 5/6 dogs and revealed unilateral, variably sized, striatocapsular lesions consistent with nonhemorrhagic infarctions. Diagnostic imaging (6/6) and postmortem examinations (2/6) suggested that SCI resulted from lesions in the vascular territories of the rostral choriodal (6/6) and lenticulostriate arteries (2/6). Diseases predisposing to infarction were not identified in 5/6 dogs. Improvements in mentation, behavior, proprioceptive deficits, and hemiparesis were seen in surviving dogs, but persistent, symptomatic sensory deficits were noted during the follow-up period. CONCLUSIONS: SCI should be considered as a differential diagnosis for dogs with acute onset, nonprogressive homonymous hemianopia, contralateral GP deficits or hemiparesis, and facial hypalgesia. MRI is the preferred modality for the antemortem imaging diagnosis of SCI. Although partial recovery occurred in all surviving dogs, visual and facial sensory disturbances persisted.

Animals↗

PubMed2006

Visual control of action without retinal optic flow.

In everyday life, the optic flow associated with the performance of complex actions, like walking through a field of obstacles and catching a ball, entails retinal flow with motion energy (first-order motion). We report the results of four complex action tasks performed in virtual environments without any retinal motion energy. Specifically, we used dynamic random-dot stereograms with single-frame lifetimes (cyclopean stimuli) such that in neither eye was there retinal motion energy or other monocular information about the actions being performed. Performance on the four tasks with the cyclopean stimuli was comparable to performance with luminance stimuli, which do provide retinal optic flow. The near equivalence of the two types of stimuli indicates that if optic flow is involved in the control of action, it is not tied to first-order retinal motion.

Avoidance Learning↗

PubMed1992

New method based on random luminance masking for measuring isochromatic zones using high resolution colour displays.

A new method of measuring normal hue discrimination ellipses and dichromatic zones using a high resolution colour monitor is described. The test involves the detection of chromatic bars on a grey background (x = 0.305, y = 0.323) having a luminance of 34 cd m-2. Elements of the background matrix of square checks are varied randomly in luminance in space and time to provide random luminance masking (RLM) which compensates for differences in the relative luminous efficiency of different observers. The measurement technique provides a rapid and comprehensive colour vision test. Typical results are presented for normal trichromats, protanopes and deuteranopes without RLM and with the RLM set of 25%. The size of the discrimination ellipse in normal observers is the same in both viewing conditions, but the use of the RLM technique reveals the extent of the isochromatic zones in colour deficient observers.

Color Perception Tests↗

PubMed1982

A method for quantitative scoring of the Farnsworth Panel D-15.

The Farnsworth Dichotomous test or Panel D-15 is used extensively for the evaluation of colour discrimination in congenital and acquired colour vision defects. This qualitative assessment of colour vision defect type and severity is based on the hue confusions which are represented diagrammatically on the Panel D-15 score sheet. This paper presents a new proposal for quantitatively scoring the Panel D-15 based on those hue confusions made by the subject. Such a quantitative score can be used to establish relationships with other visual functions or experimental conditions. The application of the scoring technique to clinical results is illustrated.

Color Perception Tests↗

PubMed1986

A new method for exact measurements of visual acuity. Determination of threshold curves for the resolving power of the eye by computerized curve fitting.

The paper presents a new test method for investigations of threshold curves for the resolving power of the eye and for exact measurements of visual acuity. This method measures static visual acuity within confidence limits of 9% compared to the acuity steps in Snellen notation of 33% to 50%. Furthermore, the method introduces the slope of the threshold curve as a parameter of suggested importance in the judgement of visual capability. The test mathematic is based on a method described by Finney (1952) for calculations on dose-response curves. To calculate the results and the test statistics an iterative curve fitting programme was designed to be run on a micro-computer. By connecting the presentation system and the response panel to the same computer the test could be performed almost automatically. The new test method was used to study visual acuity measured by projected ortotypes compared to acuity when measured by printed ortotypes. Tests using projected ortotypes were found to equal traditional acuity measurements, but the test results stressed the need for perfect and adjusted optics when projecting systems are used in visual acuity test.

Computers↗

PubMed1993

Long-term dysfunctions of neural stereoscopic mechanisms after unilateral extraocular muscle proprioceptive deafferentation.

1. Neural correlates of the permanent deficits in depth perception that occur when extraocular muscle proprioceptive (EMP) afferents are interrupted unilaterally in kittens were investigated by performing extracellular recordings in the primary visual cortex (area 17) in adulthood. Unilateral section of the ophthalmic branch of the trigeminal nerve (V1 nerve) were performed in 11 cats when they were between 5 and 12 weeks of age (uni-V1 group). Electrophysiological results were compared with those obtained in 17 normal adult cats (control group). 2. Binocular interactions were assessed by testing the sensitivity of cortical neurons to dichoptic presentations of moving sine-wave gratings whose interocular positional phase relationship was randomly varied. The amplitude modulation between the minimum and the maximum binocular responses defined the dynamic range. The degree of binocular suppression or facilitation was assessed by comparing these binocular response limits with the optimal monocular responses evoked through either eye at the best spatial frequency. The variability of both monocular and binocular responses was estimated by using the variation coefficient. 3. In uni-V1 cats, both the dynamic range and the degree of binocular suppression were significantly less pronounced than in controls, whereas binocular facilitation was not affected. The variability of the binocular responses was significantly increased, unlike monocular responses, whose variability was similar to control values. 4. From Fourier analysis of the poststimulus time histograms, two clear-cut categories of cells emerged that were differentially affected in the uni-V1 group. The "modulated" cells showed significantly less binocular suppression than in controls, and the "unmodulated" cells had binocular responses that were significantly more variable than in controls. Results from "simple" cells were similar to those of modulated cells, and results from "complex" cells were similar to those of unmodulated cells. However, in the unmodulated population, which was composed of both simple and complex cells, it was shown that the increase of variability was due to that of complex cells. 5. A nonparametric statistical test was applied on the interocular phase shift tuning curves to determine the minimum stimulus change necessary to elicit a significant change in the neural response. Two categories of cells were determined: the "discriminative" cells (80% in controls but 45% in uni-V1 cats) combined pronounced binocular suppression and dynamic range with relatively low variability. The reverse was true in the case of "nondiscriminative" cells (20% in controls and 55% in uni-V1 cats). 6. In uni-V1 cats, about half of the cells were monocularly activated.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1991

Effect of endocrine therapy on a brain metastatic lesion of prostatic carcinoma.

We describe a 62-year-old male with brain metastasis from prostatic carcinoma, which regressed with medical and surgical endocrine therapies. The patient's presenting complaints were left periocular and deep ocular pain and a defect of the left visual field. During treatment of the above symptoms, macrohematuria, dysuria and pollakiuria occurred. Pathological examination of a transrectal needle biopsy disclosed moderately differentiated adenocarcinoma of the prostate. Computerized tomographic scan (CT) and magnetic resonance imaging demonstrated a brain tumor at the frontal skull base and the region of the frontal lobe suspected to be a metastasis of the prostatic carcinoma. One week after a period of daily administration of estramustine phosphate sodium, the prostate was observed to be softened and slightly decreased in size. The visual field defect and disturbance of urination gradually improved. The prostate decreased to normal size and no tumor mass could be detected on the brain CT after 3 months of treatment.

Adenocarcinoma↗

PubMed1994

An unusual orbital lesion: hepatoma metastatic to the orbit.

The authors describe a case of histologically proven orbital metastasis from a hepatic carcinoma in an 85-year-old patient with rapid onset of proptosis and visual loss. The clinical diagnosis of orbital metastatic lesion was established by standardized echography and CT scan. To the best of our knowledge, this is only the third histologically proven case of hepatoma metastatic to the orbit.

Aged↗

PubMed2001

A competitive-layer model for feature binding and sensory segmentation.

We present a recurrent neural network for feature binding and sensory segmentation: the competitive-layer model (CLM). The CLM uses topographically structured competitive and cooperative interactions in a layered network to partition a set of input features into salient groups. The dynamics is formulated within a standard additive recurrent network with linear threshold neurons. Contextual relations among features are coded by pairwise compatibilities, which define an energy function to be minimized by the neural dynamics. Due to the usage of dynamical winner-take-all circuits, the model gains more flexible response properties than spin models of segmentation by exploiting amplitude information in the grouping process. We prove analytic results on the convergence and stable attractors of the CLM, which generalize earlier results on winner-take-all networks, and incorporate deterministic annealing for robustness against local minima. The piecewise linear dynamics of the CLM allows a linear eigensubspace analysis, which we use to analyze the dynamics of binding in conjunction with annealing. For the example of contour detection, we show how the CLM can integrate figure-ground segmentation and grouping into a unified model.

Brain↗

PubMed2006

Self-replication and self-assembly for manufacturing.

It has been argued that a central objective of nanotechnology is to make products inexpensively, and that self-replication is an effective approach to very low-cost manufacturing. The research presented here is intended to be a step towards this vision. We describe a computational simulation of nanoscale machines floating in a virtual liquid. The machines can bond together to form strands (chains) that self-replicate and self-assemble into user-specified meshes. There are four types of machines, and the sequence of machine types in a strand determines the shape of the mesh they will build. A strand may be in an unfolded state, in which the bonds are straight, or in a folded state, in which the bond angles depend on the types of machines. By choosing the sequence of machine types in a strand, the user can specify a variety of polygonal shapes. A simulation typically begins with an initial unfolded seed strand in a soup of unbonded machines. The seed strand replicates by bonding with free machines in the soup. The child strands fold into the encoded polygonal shape, and then the polygons drift together and bond to form a mesh. We demonstrate that a variety of polygonal meshes can be manufactured in the simulation, by simply changing the sequence of machine types in the seed.

Computer-Aided Design↗

PubMed1997

Judgments of the distance to nearby virtual objects: interaction of viewing conditions and accommodative demand.

Ten subjects adjusted a real-object probe to match the distance of nearby virtual objects optically presented via a see-through, helmet-mounted display. Monocular, binocular, and stereoscopic viewing conditions were used with two levels of required focus. Observed errors may be related to changes in the subjects' binocular convergence. The results suggest ways in which virtual objects may be presented with improved spatial fidelity.

Computer Graphics↗