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PubMed1998

Modelling human depth perception in binocular vision: obtaining the horizontal disparity map.

The paper presents a computer application developed as a tool for implementing, developing, and testing computational models for stereopsis. Two models for solving the correspondence problem and computing the stereo disparity map have been implemented. One of them is biologically inspired (it models the behaviour of simple and complex cells from the striate cortex) and the paper details the results obtained on random-dot stereograms and on pairs of real images.

Algorithms↗
PubMed1989

[Recent trends and developments in the clinical study of color vision--the 2-comparison method].

Modern anomaloscopes with four independent light channels (i.e., the Besançon Anomalometer which was presented in 1980 at the DOG) allow accurate examinations of color vision. In our routine clinical examination, we use two metameric equations: the red-green Rayleigh equation and the blue-green Moreland equation. This two-equation method permits the diagnosis of congenital and acquired color vision defects in a precise quantitative way. In both equations the goal of the examination is to measure the absolute matching range. The diagnosis is abnormal color vision if the absolute matching range is shifted and/or enlarged in one or both of the two metameric equations. A computer-controlled clinical examination of color vision, which will make the procedure simpler and shorter for the patient, is presently being developed.

Adolescent↗
PubMed2005

Texture synthesis and perception: using computational models to study texture representations in the human visual system.

Traditionally, texture perception has been studied using artificial textures made of random dots or repeated shapes. At the same time, computer algorithms for natural texture synthesis have improved dramatically. We seek to unify these two fields through a psychophysical assessment of a particular computational model, providing insight into which statistics are most vital for natural texture perception. We employ Portilla and Simoncelli's texture synthesis algorithm, a parametric model that mimics computations carried out in human vision. We find an intriguing interaction between texture type (periodic, structured, or 3-D textures) and image statistics (autocorrelation function and filter magnitude correlations), suggesting different representations may be employed for these texture families under pre-attentive viewing.

Adult↗
PubMed1998

Transient cortical blindness in preeclampsia with indication of generalized vascular endothelial damage.

A 26-year-old woman with twin fetuses of 28 weeks' gestational age had symptoms of preeclampsia and was admitted to the hospital for observation. Nine days later, after reporting a severe headache, the patient experienced loss of vision in both eyes. An emergency computed tomographic brain scan was performed to rule out intracranial hemorrhage, and cesarean delivery was performed. Twelve hours after the operation, the patient's vision improved gradually and returned to normal after 24 hours. The placenta was submitted to pathologic examination, and magnetic resonance imaging was performed 4 days after birth. Recent thrombosis observed in the histologic section of the placenta, ischemic changes in the brain seen in the computed tomographic and magnetic resonance scans, and severe proteinuria manifested clinically suggest vascular endothelial damage as the underlying mechanism in this case of preeclampsia-related transient cortical blindness.

Adult↗
PubMed2002

Computer modeling of airbag-induced ocular injury in pilots wearing night vision goggles.

BACKGROUND: Airbags have saved lives in automobile crashes for many years and are now planned for use in helicopters. The purpose of this study was to investigate the potential for ocular injuries to helicopter pilots wearing night vision goggles when the airbag is deployed. METHODS: A nonlinear finite element model of the human eye was created. Ocular structures such as the fatty tissue, extraocular muscles, and bony orbit were included. The model was imported into Madymo (Mathematical Dynamical Models) and used to determine the worst-case position of a helicopter pilot wearing night vision goggles. This was evaluated as the greatest Von Mises stress in the eye when the airbag was deployed. RESULTS: The worst-case position was achieved by minimizing the distance between the eyes and goggles, having the occupant look directly into the airbag, and making initial contact with the airbag halfway through its full deployment. Simulations with the goggles both remaining fastened to and breaking away from the aviator helmet were performed. Finally, placing a protective lens in front of the eyes was found to reduce the stress to the eye but increase the force experienced by the surrounding orbital bones. CONCLUSION: The finite element model of the eye proved effective for evaluating the experimental parameters.

Accidents, Aviation↗
PubMed2000

A method for using relay lenses with display monitors for vision testing at far and near.

Resolution limitations preclude the use of display monitors for near testing of acuity and contrast sensitivity. Relay lenses can form minified aerial images of the display at any given near viewing distance, but the image will differ in spatial frequency from the display. Equations are presented that can be used to specify the far- and near-viewing distances and the necessary focal length of a lens so that the display and its near aerial image have identical spatial frequencies when viewed by a subject at a fixed location. Modulation transfer function (MTF) calculations show that achromatic doublets will not degrade the resolution across a 300-mm wide display, thereby providing the versatility of display monitors for near vision testing.

Computer Terminals↗
PubMed2004

High-resolution computed tomography study of the cranium of a fossil anthropoid primate, Parapithecus grangeri: new insights into the evolutionary history of primate sensory systems.

Extant anthropoids have large brains, small olfactory bulbs, and high-acuity vision compared with other primates. The relative timing of the evolution of these characteristics may have important implications for brain evolution. Here computed tomography is used to examine the cranium of a fossil anthropoid, Parapithecus grangeri. It is found that P. grangeri had a relatively small brain compared with living primates. In addition, it had an olfactory bulb in the middle of the range for living primates. Methods for relating optic foramen area and other cranial measurements to acuity are discussed. Multiple regression is used to estimate retinal ganglion cell number in P. grangeri. Given currently available comparative data, P. grangeri seems to have had retinal ganglion cell counts intermediate for living primates, overlapping with the upper end of the range for strepsirrhines and possibly with the lower end for anthropoids.

Animals↗
PubMed2003

Blobs strengthen repetition but weaken symmetry.

The human visual system is more sensitive to symmetry than to repetition. According to the so-called holographic approach [J. Math. Psychol. 35 (1991) 151; Psychol. Rev. 103 (1996) 429; Psychol. Rev. 106 (1999) 622], however, this perceptual difference between symmetry and repetition depends strongly on spatial scaling. This was tested in three experiments, using symmetry and repetition stimuli that consisted of black and white patches, with patch size as the critical variable. In Experiment 1, patch size was increased in the entire pattern, yielding fewer but larger patches (or blobs). This is known to have hardly any effect on symmetry but, as found now, it does have a strengthening effect on repetition. In the second experiment, we increased patch size in subpatterns only, yielding salient blob areas. This again strengthens repetition but, as double-checked in experiment 3, it can weaken symmetry. These results agree with the holographic approach, and enable an integration of computational, algorithmic, and implementational aspects of vision.

Adolescent↗
PubMed2004

A unified theory of brightness contrast and assimilation incorporating oriented multiscale spatial filtering and contrast normalization.

Brightness induction includes both contrast and assimilations effects. Brightness contrast occurs when the brightness of a test region shifts away from the brightness of adjacent regions. Brightness assimilation refers to the opposite situation in which the brightness of the test region shifts toward that of the surrounding regions. Interestingly, in the White effect [Perception 8 (1979) 413] the direction of the induced brightness change does not correlate with the amount of black or white border in contact with the gray test patch. This has led some investigators to reject spatial filtering explanations not only for the White effect but for brightness perception in general. Instead, these investigators have offered explanations based on a variety of junction analyses and/or perceptual organization schemes. Here, these approaches are challenged with a critical set of new psychophysical measurements that determined the magnitude of the White effect, the shifted White effect [Perception 10 (1981) 215] and the checkerboard illusion [R.L. DeValois, K.K. DeValois, Spatial Vision, Oxford University Press, NY, 1988] as a function of inducing pattern spatial frequency and test patch height. The oriented difference-of-Gaussians (ODOG) computational model of Blakeslee and McCourt [Vision Res. 39 (1999) 4361] parsimoniously accounts for the psychophysical data, and illustrates that mechanisms based on junction analysis or perceptual inference are not required to explain them. According to the ODOG model, brightness induction results from linear spatial filtering with an incomplete basis set (the finite array of spatial filters in the human visual system). In addition, orientation selectivity of the filters and contrast normalization across orientation channels are critical for explaining some brightness effects, such as the White effect.

Computational Biology↗
PubMed1994

Waardenburg's syndrome and pituitary tumor.

A 57-year-old woman with Waardenburg's syndrome presented with a 2-month history of decreased vision in the right eye. Computed tomography and magnetic resonance imaging studies for the brain disclosed a large suprasellar cystic lesion compressing the optic chiasm upwards. The association of Waardenburg's syndrome with pituitary tumor is rare, and may be fortuitous. However, it is interesting to note that both disorders are derived from the same embryological origin.

Adenoma↗
PubMed1997

Computer simulation of neuronal toxicity in the spinal cord.

The use of computers to model biological systems is a relatively new research tool. For example, it is possible to write mathematical systems to model neuronal activity involved in memory and learning and to model blood flow in any organ such as the brain. There is also an interest in designing computer-controlled machines to simulate human activities such as hand movements and vision. One of the most important uses of computer modeling is as a research tool to test hypotheses and aid in formulating new hypotheses. This enables the investigator to apply preliminary tests on several experimental strategies and select for animal experimentation the ones that are most likely to produce unambiguous and interpretable results. In the following article, we describe a computer model of neuron toxicity in the mammalian spinal cord.

Dynorphins↗
PubMed1985

Return of vision following orbital decompression after 36 hours of postoperative blindness.

A 43-year-old woman undergoing repair of an orbital floor fracture had no light perception postoperatively. Computed tomography showed a normal optic nerve and there was no optic canal fracture, intraorbital hematoma, or intraconal expansion. After a two-wall orbital decompression, visual acuity recovered to 20/70 although only an inferior nasal island of vision remained. Ductions were full and there was no blepharoptosis but a 2+ afferent pupillary defect persisted.

Adult↗
PubMed1994

[Examination procedure in automated determination of far and near vision].

BACKGROUND: Although the measurement of visual acuity at distance is more important in ophthalmological practice, the visual acuity at near should be tested additionally. In a recently published paper we showed that with today's computer technology visual acuity at distance can be measured in standardized procedures according to DIN 58220. We describe here an additional, integrated setup, which allows the measurement of visual acuity also at near. METHODS: For testing visual acuity at near, the whole set of optotypes is presented on a transparent overlay mask in front of a computer monitor which is used as a program-controlled light source. A certain optotype is chosen by illuminating its background. The patient's responses are read via a small console by the computer. The test procedure follows the DIN requirements. RESULTS AND CONCLUSIONS: First reliability tests showed that the test arrangement is qualified for rapid and standardized determination of visual acuity at near and at distance under nearly natural viewing conditions.

Adult↗
PubMed1997

An introduction to accurate display timing for PCs under 'Windows'.

As the use of computers for delivering stimuli in vision research has become ubiquitous, there is an obvious need for accurate timing of display monitors without the use of expensive hardware extensions. If a user should decide to program an application in the increasingly common 'Windows' operating system for IBM PCs and compatibles, a software solution for this problem is not obvious any more. The goal is to achieve display durations down to one single video frame. This article describes several approaches and a tested solution designed to run on any PC or compatible under Windows 3.1/95, regardless of the video card used. This creates new possibilities for low-cost, implementation of visual experiments for laboratory and classroom use.

Computer Terminals↗
PubMed1989

Construction of the diagnostic encyclopedia workstation. Computerizing pathology for the pathologist.

The combination of a personal computer and a laser-vision disc player is an adroit tool for storing and retrieving textual information in combination with pictorial information. This paper describes such a system (a "diagnostic encyclopedia workstation"), which provides information to the pathologist engaged in daily diagnostic practice. The system contains a considerable amount of descriptive textual information that might be useful in making diagnoses in histopathology, along with many illustrations; the text is presented in a natural language (English). The descriptive information is divided into 18 categories, including such topics as histology, macroscopy, immunopathology and clinical data; each topic has a separate display in the system. Also present are two types of "decision rules" for making diagnoses (confirmative criteria for a diagnosis under consideration and exclusive criteria for many other diagnoses) and a classifying structure. The present version of this system contains information on about 100 diagnoses in ovarian pathology, illustrated with about 3,000 color slides from about 140 cases. The information and pictures are immediately available. Further characteristics of this system are its flexibility, accessibility and user friendliness; it has been structured so that components of artificial intelligence may be added later.

Artificial Intelligence↗