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PubMedDate not supplied

Modelling biological depth perception in binocular vision: the local disparity estimation.

This paper presents an approach to solving the correspondence problem in binocular vision and to computing the local horizontal disparity map using a biologically inspired algorithm. A computer application was developed as a tool for implementing, developing, and testing computational models for stereopsis, and also as a framework for integrating the disparity map with other perspective clues. Two models for stereopsis have been implemented. One of them is biologically inspired (it models the behaviour of simple and complex cells from the striate cortex) and the other is the 'classical' model of David Marr and Tomaso Poggio, implemented in order to have a comparison term for the simulation results. The paper details the results obtained on random-dot stereograms and on pairs of real images.

Algorithms↗
PubMed2003

Dynamic interactions of eye and head movements when reading with single-vision and progressive lenses in a simulated computer-based environment.

PURPOSE: To assess dynamic interactions of eye and head movements during return-sweep saccades (RSS) when reading with single-vision (SVL) versus progressive-addition (PAL) lenses in a simulated computer-based business environment. METHODS: Horizontal eye and head movements were recorded objectively and simultaneously at a rate of 60 Hz during reading of single-page (SP; 14 degrees horizontal [H]) and double-page (DP; 37 degrees H) formats at 60 cm with binocular viewing. Subjects included 11 individuals with normal presbyopic vision aged 45 to 71 years selected by convenience sampling from a clinic population. Reading was performed with three types of spectacle lenses with a different clear near field of view (FOV): a SVL (60 degrees H clear FOV), a PAL-I with a relatively wide intermediate zone (7.85 mm; 18 degrees H clear FOV), and a PAL-II with a relatively narrow intermediate zone (5.60 mm; 13 degrees H clear FOV). RESULTS: Eye movements were initiated before head movements in the SP condition, and the reverse was found in the DP condition, with all three lens types. Duration of eye movements increased as the zone of clear vision decreased in the SP condition, and they were longer with the PALs than with the SVL in the DP condition. Gaze stabilization occurred later with the PALs than with the SVL in both the SP and DP conditions. The duration of head movements was longer with the PAL-II than with the SVL in both the SP and DP conditions. Eye movement peak velocity was greater with the SVL than the PALs in the DP condition. CONCLUSIONS: Eye movement and head movement strategies and timing were contingent on viewing conditions. The longer eye movement duration and gaze-stabilization times suggested that additional eye movements were needed to locate the clear-vision zone and commence reading after the RSS. Head movements with PALs for the SP condition were similarly optically induced. These eye movement and head movement results may contribute to the reduced reading rate and related symptoms reported by some PAL wearers. The dynamic interactions of eye movements and head movements during reading with the PALs appear to be a sensitive indicator of the effect of lens optical design parameters on overall reading performance, because the movements can discriminate between SVL and PAL designs and at times even between PALs.

Aged↗
PubMed1988

Color vision defects in ocular hypertension and glaucoma. Quantification with a computer-driven color television system.

In order to detect early defects of color vision caused by increased intraocular pressure, a computer graphics device and color monitor system were used to measure color contrast sensitivity. The system determines the threshold chrominance of a colored grating in which there is no change in luminance. The study included 13 control subjects aged 10 to 57 years and 19 patients with ocular hypertension or glaucoma aged 20 to 58 years. In the 13 eyes with visual field loss, color contrast sensitivity was profoundly reduced when the grating colors fell on a tritan color confusion line. In the eyes without visual field loss, tritan color contrast sensitivity was reduced to an average level considerably below the extreme limits of the control group. These results were compared with those of other color vision tests and diagnostic criteria for glaucoma. The findings suggest that among the tests used, color contrast sensitivity testing was able to discriminate most effectively between patients who had retinal damage and the normal population.

Color Perception Tests↗
PubMed2004

Computer assisted telephone interviewing (CATI) for health surveys in public health surveillance: methodological issues and challenges ahead.

This article describes methodological issues, challenges, and a vision for using computer assisted telephone interviewing (CATI) in a comprehensive public health surveillance system in the 21st century. Methodological issues include funding of surveys, survey frequency, sample size considerations, response rates, and types of bias to be considered in questionnaire design. Challenges include the recognition of the merits and limitations of CATI, and the potential for greater use in surveillance of public health issues in health regions requiring rapid and regular data. The vision of a CATI survey-based, rapid, flexible, cost-effective public health surveillance system is described. It is concluded that further discussion and views on improvements with regard to CATI methodological and practical issues will help build a better CATI survey-based public health surveillance system for the future.

Canada↗
PubMed1996

Tension pneumocephalus and tension orbital emphysema following blunt trauma.

We present the first reported case of vision loss due to tension orbital emphysema associated with tension pneumocephalus resulting from blunt trauma. In the setting of trauma, intraorbital air indicates paranasal sinus-orbital communication. Tension orbital emphysema may cause vision loss through optic nerve compression, ischemia, or contusion; or central retinal artery occlusion. Vision impairment after craniofacial injury should prompt urgent computed tomography. Tension orbital emphysema with associated vision impairment requires treatment including direct decompression and, in some cases, high-dose steroids to preserve vision. Increases in sinus pressure from coughing, nose-blowing, or vomiting should be avoided until definitive treatment can be instituted.

Adult↗
PubMed1995

Beyond the computer-based patient record: re-engineering with a vision.

In order to achieve real benefit from the potential offered by a Computer-Based Patient Record, the capabilities of the technology must be applied along with true re-engineering of healthcare delivery processes. University Hospital recognizes this and is using systems implementation projects, such as the catalyst, for transforming the way we care for our patients. Integration is fundamental to the success of these initiatives and this must be explicitly planned against an organized systems architecture whose standards are market-driven. University Hospital also recognizes that Community Health Information Networks will offer improved quality of patient care at a reduced overall cost to the system. All of these implementation factors are considered up front as the hospital makes its initial decisions on to how to computerize its patient records. This improves our chances for success and will provide a consistent vision to guide the hospital's development of new and better patient care.

Computer Communication Networks↗
PubMed1988

[A computer program for registering all daily accumulated data at a school for vision disorders].

Despite increasing medical use of the computer, many clinics have experienced only limited success (or none at all) in computerized registration of patient data. One important reason for this lies in the complicated user interfaces of most programs. The clinician has no time to familiarize himself with the complicated command sequences involved, while necessary acceptance of the new technology by administrative staff is often lacking. This paper shows that computerized registration and interpretation of patient data are well within the bounds of possibility, given the use of newly-developed user-friendly operating systems and suitable personal computers. A concrete example of computerized registration of data in a remedial center is given: a case with squint symptoms for which 176 parameters can be entered.

Documentation↗
PubMed2002

The proximity-fixation-disparity curve and the preferred viewing distance at a visual display as an indicator of near vision fatigue.

PURPOSE: This laboratory study investigates the relation between measures of fixation disparity (FD) (and other optometric measures) and near vision fatigue at a computer workstation. METHODS: Young adult subjects with normal binocular vision performed three blocks of a visual task of 30 min each. In Block A, the viewing distance was 100 cm, as a reference without near vision. In Block B, the viewing distance of 50 cm induced a defined near vision load. In Block C, subjects were free to choose a comfortable viewing distance. This preferred viewing distance was used as an indicator of near vision fatigue because subjects adopting longer viewing distances in Block C had more near vision fatigue at 50 cm in Block B. RESULTS: Subjects with preferred viewing distances longer than average (63 cm) had steeper slopes of FD as a function of viewing distance (100-30 cm), as shown by discriminant analyses. CONCLUSIONS: Thus, this steep proximity-FD curve indicates a weak disparity vergence system that may cause near vision fatigue. This may explain why some young adults prefer longer viewing distances at the computer workstation.

Computer Terminals↗
PubMed2006

Effects of increased complexity of visuo-motor transformations on children's arm movements.

The effects of increasing complexity of visuo-motor transformations on movement were examined in 4-, 6-, and 8-year-old children and adults. Participants performed a 'center-out' drawing task under three increasingly complex conditions: (1) Normal transformation: The target, line path and hand position were fully visible, in the horizontal plane, throughout the movement. (2) Aligned transformation: The target and line path were displayed horizontally above the workspace, with vision of the arm/hand occluded. (3) Vertical transformation: The target and line paths were presented on a vertical computer monitor with vision of the arm/hand occluded. Results showed that with increasing age, movements became faster, straighter, and smoother. The 4- and 6-year-old children were more variable in their specification of movement direction than the 8-year-old children and the adults, and were also more affected by the complexity of the transformation. This suggested that besides the complexity of the visual transformation, the familiarity/experienced environment might also play a role in 'sharpening' the transformation maps represented in movement planning.

Adult↗
PubMed1998

Computer-based training for the treatment of partial blindness.

Partial blindness after brain injury has been considered non-treatable. To evaluate whether patients with visual-field defects can profit from computer-based visual restitution training (VRT), two independent clinical trials were conducted using patients with optic nerve (n = 19) or post-chiasmatic brain injury (n = 19). In post-chiasma patients, VRT led to a significant improvement (29.4%) over baseline in the ability to detect visual stimuli; in optic nerve patients, the effects were even more pronounced (73.6% improvement). Visual-field enlargements were confirmed by the observation of a visual-field expansion of 4.9 degrees-5.8 degrees of visual angle and improved acuity in optic nerve patients. Ninety five percent of the VRT-treated patients showed improvements, 72.2% confirmed visual improvements subjectively. Patients receiving a placebo training did not show comparable improvements. In conclusion, VRT with a computer program improves vision in patients with visual-field defects and offers a new, cost-effective therapy for partial blindness.

Blindness, Cortical↗
PubMed1984

Neuropathies of the optic nerve and visual evoked potentials with special reference to color vision and differential light threshold measured with the computer perimeter OCTOPUS.

The contrast evoked potentials (VEPs) to different check sizes were recorded in about 200 cases of discrete optic neuropathies (ON) of different origin. Differential light threshold (DLT) was tested with the computer perimeter OCTOPUS. Saturated and desaturated tests were applied to evaluate the degree of acquired color vision deficiency. Delayed VEP responses are not confined to optic neuritis (RBN) alone and the different latency times obtained from other ON are confluent. The delay may be due to demyelination, to an increasing dominance of paramacular VEP subcomponents or to an increasing dominance of the upper half-field responses. Recording with smaller check sizes has the advantage that discrete dysfunctions in the visual field (VF) center are more easily detected: a correlation between amplitudes and visual acuity is best in strabismic amblyopias, is less expressed in maculopathies of the retina and weak in ON. The absence or reduction of amplitudes to smaller check sizes, however, is an important indication of a disorder in the VF center of ON in an early or recovered stage. Acquired color vision defects of the tritan-like type are more confined to discrete ON, whereas the red/green type is reserved to more severe ON. The DLT of the VF center is reduced in a different, significant and non significant extent in discrete optic neuropathies and the correlation between DLT and visual acuity is weak. A careful numerical analysis is needed in types of discrete ON where the central DLT lies within normal statistical limits: a side difference of the DLT between the affected and the normal fellow eye is always present. Evaluation of visual fatigue effects and of the relative sensitivity loss of VF center and VF periphery may provide further diagnostic information.

Adolescent↗
PubMed2002

Semiautomated analytical image correlation.

Machine vision refers to computer programs consisting of a collection of pattern recognition and digital image processing algorithms (Fabel, G. Motion Control 2000, 53-54). A version of machine vision has been applied to correlating digital images generated by optical microscopy and secondary ion mass spectrometry (SIMS). By suitable application of image processing algorithms, semiautomated correlation between optical and secondary ion images is possible. For correlation of minor constituents evident in secondary ion images but invisible in optical images, correlation is performed by reference to the relative position of minor to major constituents. Precise coordinates of features apparent in one analytical image can be translated into the corresponding coordinates of an analytical image obtained by a different method. In principle, this capability yields a semiautomated system to combine complementary features of disparate imaging methods, such as secondary ion and optical microscopy.

Journal Article↗
PubMed2005

The cocktail party problem.

This review presents an overview of a challenging problem in auditory perception, the cocktail party phenomenon, the delineation of which goes back to a classic paper by Cherry in 1953. In this review, we address the following issues: (1) human auditory scene analysis, which is a general process carried out by the auditory system of a human listener; (2) insight into auditory perception, which is derived from Marr's vision theory; (3) computational auditory scene analysis, which focuses on specific approaches aimed at solving the machine cocktail party problem; (4) active audition, the proposal for which is motivated by analogy with active vision, and (5) discussion of brain theory and independent component analysis, on the one hand, and correlative neural firing, on the other.

Attention↗
PubMed1982

A computational theory of visual surface interpolation.

Computational theories of structure-from-motion and stereo vision only specify the computation of three-dimensional surface information at special points in the image. Yet the visual perception is clearly of complete surfaces. To account for this a computational theory of the interpolation of surfaces from visual information is presented. The problem is constrained by the fact that the surface must agree with the information from stereo or motion correspondence, and not vary radically between these points. Using the image irradiance equation, an explicit form of this surface consistency constraint can be derived. To determine which of two possible surfaces is more consistent with the surface consistency constraint, one must be able to compare the two surfaces. To do this, a functional from the space of possible functions to the real numbers is required. In this way, the surface most consistent with the visual information will be that which minimizes the functional. To ensure that the functional has a unique minimal surface, conditions on the form of the functional are derived. In particular, if the functional is a complete semi-norm that satisfies the parallelogram law, or the space of functions is a semi-Hilbert space and the functional is a semi-inner product, then there is a unique (to within possibly an element of the null space of the functional) surface that is most consistent with the visual information. It can be shown, based on the above conditions plus a condition of rotational symmetry, that there is a vector space of possible functionals that measure surface consistency, this vector space being spanned by the functional of quadratic variation and the functional of square Laplacian. Arguments based on the null spaces of the respective functionals are used to justify the choice of the quadratic variation as the optimal functional. Possible refinements to the theory, concerning the role of discontinuities in depth and the effects of applying the interpolation process to scenes containing more than one object, are discussed.

Animals↗
PubMed2004

Wearable systems for health care applications.

OBJECTIVES: Wearable systems can be broadly defined as mobile electronic devices that can be unobtrusively embedded in the user's outfit as part of the clothing or an accessory. In particular, unlike conventional mobile systems, they can be operational and accessed without or with very little hindrance to user activity. To this end they are able to model and recognize user activity, state, and the surrounding situation: a property, referred to as context sensitivity. Wearable systems range from micro sensors seamlessly integrated in textiles through consumer electronics embedded in fashionable clothes and computerized watches to belt worn PCs with a head mounted display. The wearable computing concept is part of a broader framework of ubiquitous computing that aims at invisibly enhancing our environment with smart electronic devices. The goal of the paper is to provide a broad overview of wearable technology and its implications for health related applications. METHODS: We begin by summarizing the vision behind wearable computing. We then describe a framework for wearable computing architecture and the main technological aspects. Finally we show how specific properties of wearable systems can be used in different health related application domains. RESULTS: Wearable computing is an emerging concept building upon the success of today's mobile computing and communication devices. Due to rapid technological progress it is currently making a transition from a pure research stage to practical applications. Many of those applications are in health related domains, in particular, health monitoring, mobile treatment and nursing. CONCLUSIONS: Within the next couple of years wearable systems and more general ubiquitous computing will introduce profound changes and new application types to health related systems. In particular they will prove useful in improving the quality and reducing the cost of caring for the aging population.

Clothing↗
PubMed2003

Computational evidence for a rivalry hierarchy in vision.

Cortical-form vision comprises multiple, hierarchically arranged areas with feedforward and feedback interconnections. This complex architecture poses difficulties for attempts to link perceptual phenomena to activity at a particular level of the system. This difficulty has been especially salient in studies of binocular rivalry alternations, where there is seemingly conflicting evidence for a locus in primary visual cortex or alternatively in higher cortical areas devoted to object perception. Here, I use a competitive neural model to demonstrate that the data require at least two hierarchic rivalry stages for their explanation. This model demonstrates that competitive inhibition in the first rivalry stage can be eliminated by using suitable stimulus dynamics, thereby revealing properties of a later stage, a result obtained with both spike-rate and conductance-based model neurons. This result provides a synthesis of competing rivalry theories and suggests that neural competition may be a general characteristic throughout the form-vision hierarchy.

Evoked Potentials, Visual↗
PubMed1996

Colour contrast thresholds are normal in functional amblyopia.

We evaluated colour contrast thresholds in patients with unilateral functional amblyopia. A computer-controlled colour vision test was used to determine colour contrast thresholds along a blue-yellow tritan axis. Prior to the threshold measurement, a heterochromatic flicker brightness test was performed to ensure isoluminance between the test stimulus and the background for every subject individually. Luminance contrast thresholds were also measured using the same computer-based system. Twenty amblyopic patients were tested. All showed normal tritan colour contrast thresholds both for their amblyopic eye and non-amblyopic fellow eye. Luminance contrast thresholds were elevated in all 6 refractive amblyopic eyes, in 4 of 9 strabismic eyes and in 2 of 5 mixed amblyopic eyes. Colour contrast thresholds are normal in functional amblyopia (with central fixation). Whenever elevated tritan colour contrast thresholds are found in patients with a decreased visual acuity, other causes of visual impairment are to be evaluated.

Adolescent↗