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At least 1,351 records · Page 75Linked to original sources
PubMed1997

A simple integrative method for presenting head-contingent motion parallax and disparity cues on intel x86 processor-based machines.

Rogers and Graham (1979) developed a system to show that head-movement-contingent motion parallax produces monocular depth perception in random dot patterns. Their display system comprised an oscilloscope driven by function generators or a special graphics board that triggered the X and Y deflection of the raster scan signal. Replication of this system required costly hardware that is no longer on the market. In this paper the Rogers-Graham method is reproduced with an Intel processor based IBM PC compatible machine with no additional hardware cost. An adapted joystick sampled through the standard game-port can serve as a provisional head-movement sensor. Monitor resolution for displaying motion is effectively enhanced 16 times by the use of anti-aliasing, enabling the display of thousands of random dots in real-time with a refresh rate of 60 Hz or above. A color monitor enables the use of the anaglyph method, thus combining stereoscopic and monocular parallax on a single display without the loss of speed. The power of this system is demonstrated by a psychophysical measurement in which subjects nulled head-movement-contingent illusory parallax, evoked by a static stereogram, with real parallax. The amount of real parallax required to null the illusory stereoscopic parallax monotonically increased with disparity.

Computer Terminals↗
PubMed1997

The PsyScope experiment-building system.

PsyScope is a system for building behavioral experiments on the Apple Macintosh computer using a graphic user interface that requires no computer programming. The program supports a wide variety of experimental designs, multimedia formats, and stimulus control. A freeware version is available at the author's web site.

Computer Communication Networks↗
PubMed1999

The design of telepresence systems: the task-dependent use of binocular disparity and motion parallax.

The effect of different visual depth cues presented through a head-mounted display in a dark (no pictorial cue) environment was investigated. The relative effects of binocular disparity, motion parallax, and a combination of the 2, were assessed for 3 tasks at 2 viewing distances. These tasks (which varied in the minimum amount of information they required) were a nulling task, setting a triangle to be equilateral and matching the base-to-apex magnitude of 2 triangles at different distances. Performance within the tasks varied considerably but was most accurate for the nulling task. Differences between viewing conditions may be due to a failure in the assessment of absolute viewing distance. It is argued that these results are task specific. Although there was some variation between different cue types, they appear to be largely interchangeable within the tasks. These results have implications for system designers selecting an appropriate display device for a telepresence system.

Adult↗
PubMed2005

Rats are able to navigate in virtual environments.

Virtual reality (VR) systems are useful tools that enable users to alter environmental settings and the location of landmarks in an accurate and fast way. Primates have been shown to be able to navigate in virtual environments. For rodents, however, all previous attempts to develop VR systems in which rats behave in the same way as in corresponding 3-D environments have failed. The question arises as to whether, in principle, rodents can be trained to navigate in a properly designed virtual environment (VE), or whether this peculiarity is limited to primates and humans. We built a virtual reality set-up that takes the wide-angle visual system of rats into account. We show for the first time that rats learn spatial tasks in this VE quite readily. This set-up opens up new opportunities for investigations of information processing in navigation (e.g. the importance of optic flow or vestibular input).

Animals↗
PubMed2004

Viewing zones in three-dimensional imaging systems based on lenticular, parallax-barrier, and microlens-array plates.

The viewing zone of autostereoscopic imaging systems that use lenticular, parallax-barrier, and microlens-array plates as the viewing-zone-forming optics is analyzed in order to verify the image-quality differences between different locations of the zone. The viewing zone consists of many subzones. The images seen at most of these subzones are composed of at least one image strip selected from the total number of different view images displayed. These different view images are not mixed but patched to form a complete image. This image patching deteriorates the quality of the image seen at different subzones. We attempt to quantify the quality of the image seen at these viewing subzones by taking the inverse of the number of different view images patched together at different subzones. Although the combined viewing zone can be extended to almost all of the front space of the imaging system, in reality it is limited mainly by the image quality.

Algorithms↗
PubMed1997

Computerized simulation of color appearance for dichromats.

We propose an algorithm that transforms a digitized color image so as to simulate for normal observers the appearance of the image for people who have dichromatic forms of color blindness. The dichromat's color confusions are deduced from colorimetry, and the residual hues in the transformed image are derived from the reports of unilateral dichromats described in the literature. We represent color stimuli as vectors in a three-dimensional LMS space, and the simulation algorithm is expressed in terms of transformations of this space. The algorithm replaces each stimulus by its projection onto a reduced stimulus surface. This surface is defined by a neutral axis and by the LMS locations of those monochromatic stimuli that are perceived as the same hue by normal trichromats and a given type of dichromat. These monochromatic stimuli were a yellow of 575 nm and a blue of 475 nm for the protan and deutan simulations, and a red of 660 nm and a blue-green of 485 nm for the tritan simulation. The operation of the algorithm is demonstrated with a mosaic of square color patches. A protanope and a deuteranope accepted the match between the original and the appropriate image, confirming that the reduction is colorimetrically accurate. Although we can never be certain of another's sensations, the simulation provides a means of quantifying and illustrating the residual color information available to dichromats in any digitized image.

Algorithms↗
PubMed2006

Impact of Zernike-fit error on simulated high- and low-contrast acuity in keratoconus: implications for using Zernike-based corrections.

This study examines the extent to which a Zernike-based optical correction can restore acuity in keratoconus as a function of disease severity and contrast level. Increasingly complete Zernike corrections in the presence of Zernike-fit error were simulated. Acuity for keratoconic eyes with <60 D maximum corneal power reached 20/13 with a fifth-order Zernike correction under high-contrast conditions and exhibited a loss of 0.1 logMAR (minimum angle of resolution) (from 20/32 to 20/40) for low-contrast conditions. Acuity for keratoconic eyes with >60 D maximum corneal power approached 20/13 with sixth-tenth-order corrections under high-contrast conditions but did not return to similar levels with a tenth-order correction for low-contrast conditions. The results suggest that fit error affects visual performance for more difficult tasks and that restoring high-contrast acuity (20/16 or better) using a fifth-order Zernike correction is not limited by Zernike=fit error for over 88% of keratoconus cases.

Computer Simulation↗
PubMed1997

Artificial looming yields improved performance over lateral motion: implications for stereoscopic display techniques.

In the natural world, a number of visual cues indicate that an item is quickly approaching the perceiver. Binocular disparity is one cue for depth, and it has been demonstrated that abrupt changes in disparity, artificially unaccompanied by correlated depth cues, are capable of causing the perception of looming for the observer. An experiment involving 38 undergraduates, using a computer-controlled stereoscopic display, examined the ability of above-threshold changes in disparity (artificial looming) to facilitate response time and accuracy for observers engaged in an object-enumeration task within a cluttered display. Compared with performance using the same stimuli without disparity information (lateral motion), participants were more accurate regardless of the disparity level (9, 12, 24, or 48 minutes of arc) and faster at the two lowest levels of disparity. Participants showed the classic subitizing function, suggesting that target stimuli presented with motion information were segregated from otherwise identical distractor items. It is proposed that binocular disparity information can act as a valid location cuing method in stereoscopic computer displays in which form and color information are to be preserved.

Computer Graphics↗
PubMed1998

Localization of virtual objects in the near visual field.

We examined errors in the localization of nearby virtual objects presented via see-through helmet-mounted displays as a function of viewing conditions and scene content in four experiments using a total of 38 participants. Monocular, biocular, and stereoscopic presentation of the virtual objects, accommodation (required focus), participants' age, and the position of physical surfaces were examined. Nearby physical surfaces were found to introduce localization errors that differ depending on the other experimental factors. These errors apparently arise from the occlusion of the physical background by the optically superimposed virtual objects, but they are modified by participants' accommodative competence and specific viewing conditions. The apparent physical size and transparency of the virtual objects and physical surfaces, respectively, are influenced by their relative position when superimposed. The design implications of the findings are discussed in a concluding section. Head-mounted displays of virtual objects are currently being evaluated as aids for mechanical assembly and equipment maintenance. Other applications include telesurgery, surgical planning, telerobotics, and visualization aids for robotic programming.

Accommodation, Ocular↗
PubMed1999

Good vibrations: tactile feedback in support of attention allocation and human-automation coordination in event-driven domains.

Observed breakdowns in human-machine communication can be explained, in part, by the nature of current automation feedback, which relies heavily on focal visual attention. Such feedback is not well suited for capturing attention in case of unexpected changes and events or for supporting the parallel processing of large amounts of data in complex domains. As suggested by multiple-resource theory, one possible solution to this problem is to distribute information across various sensory modalities. A simulator study was conducted to compare the effectiveness of visual, tactile, and redundant visual and tactile cues for indicating unexpected changes in the status of an automated cockpit system. Both tactile conditions resulted in higher detection rates for, and faster response times to, uncommanded mode transitions. Tactile feedback did not interfere with, nor was its effectiveness affected by, the performance of concurrent visual tasks. The observed improvement in task-sharing performance indicates that the introduction of tactile feedback is a promising avenue toward better supporting human-machine communication in event-driven, information-rich domains.

Adult↗
PubMed1995

Optic nerve compression from a basal encephalocele.

A woman developed headaches, transient visual obscurations, anosmia, and decreased visual acuity. Ocular examination showed bilateral pulsatile proptosis and disc edema with choroidal folds. Standardized ophthalmic echography showed absence of bony orbital roofs, prominent dural pulsations, direct apposition of brain parenchyma and orbital tissues, and echographic signs suggesting bilateral optic nerve compression. CT and MRI showed a large defect in the floor of the anterior cranial fossa. The cribriform plate, both orbital roofs, and sphenoid bones were displaced by a large basal encephalocele. Clinical improvement followed reconstruction of the anterior cranial fossa and decompression of both optic nerves.

Adult↗
PubMedDate not supplied

Neuroradiological features of patients with optic nerve hypoplasia.

Optic nerve hypoplasia (ONH) is associated with a wide range of neurological and endocrine disorders. A series of 21 patients is reported. This comprised 17 with ONH in association with manifest neurological and endocrine disturbance, 3 who were blind but who were otherwise normal, and 1 with bilateral impaired visual acuity only. All patients underwent neuroradiological and detailed ophthalmic assessment. A wide range of abnormalities was observed. The most common findings were absent septum pellucidum, hydrocephaly, and porencephaly. Evidence of hypothalamic/pituitary hormone deficiency was present in nine patients, six of whom had demonstrable intracranial radiological abnormalities. All patients except one had bilateral optic nerve hypoplasia. Most patients had poor visual acuities and nystagmus. Astigmatism was also common. Two conditions which have not previously been reported in association with optic nerve hypoplasia were found: an intracranial arachnoid cyst and an intracranial epidermoid cyst.

Abnormalities, Multiple↗
PubMed1999

[Introduction of the project "Westdeutsche Allgemeine Zeitung (WAZ) for visually impaired" (a talking electronic daily newspaper)].

In order to complete the range of topical media, that is currently available for the visually impaired, a working group is developing and testing the "Westdeutsche Allgemeine Tageszeitung (WAZ) for the visually impaired", an auditive electronic daily newspaper. The intention of this project is to take into consideration the needs of the visually impaired, especially of those who acquired the handicap in middle or later age and might feel that not being able to read the daily newspaper anymore reduces their quality of life to a great extent. The central aim therefore is to put the modern computer technology at the disposal of the impaired in a way that enables them to make use of the newspaper without having had previous experience. In a first phase of several months twelve probands in different personal settings will test a first prototype of the newspaper reading machine, a modified and optimated multimedia computer system with modern and speech output, at home. During this period the users will be intensively looked after and undergo psychodiagnostic examination. By means of analysing the data collected in extended talks and questionnaires concrete proposals on how to improve the machine are to be made and a statement about the potential impact of the electronic newspaper on the quality of life of the visually impaired--in the sense of a contribution to their rehabilitation--is to be given.

Adolescent↗
PubMed1999

Processing images by semi-linear predictability minimization.

In the predictability minimization approach, input patterns are fed into a system consisting of adaptive, initially unstructured feature detectors. There are also adaptive predictors constantly trying to predict current feature detector outputs from other feature detector outputs. Simultaneously, however, the feature detectors try to become as unpredictable as possible, resulting in a co-evolution of predictors and feature detectors. This paper describes the implementation of a visual processing system trained by semi-linear predictability minimization, and presents many experiments that examine its response to artificial and real-world images. In particular, we observe that under a wide variety of conditions, predictability minimization results in the development of well-known visual feature detectors.

Environment↗
PubMed1999

Peduncular hallucinosis: an unusual sequel to surgical intervention in the suprasellar region.

Peduncular hallucinations are formed visual images often associated with sleep disturbance, and are caused by lesions in the midbrain, pons and diencephalon. In the present study, we report two patients who developed peduncular hallucinations following surgery in the suprasellar region. In one of these, the peduncular hallucinations were a sequel to endoscopic third ventriculostomy, while in the other, they were due to diencephalon and mid-brain compression by a postoperative clot following excision of a hypothalamic astrocytoma.

Astrocytoma↗