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At least 541 records · Page 30Linked to original sources
PubMed1981

Computer analysis of visual field loss and optimization of automated perimetric test strategies.

Preliminary investigations of optimal target distribution patterns of automated perimetry were conducted. In the first study, frequency distributions of visual field defects were determined in glaucoma (260 scotomata) and optic nerve disease (110 scotomata) for approximately 30,000 visual field locations. The frequency distributions in glaucoma and optic nerve disease were different, and suggest guidelines for development of target distribution patterns to achieve optimal detection rates. The second study included computer simulation of 20 target distribution patterns currently used in manual and automated perimetry. Each distribution pattern was processed through the 370 glaucoma and optic nerve disease scotomata to assess detection performance. Both the density and distribution of target locations affected overall detection rates. In addition, some target configurations were more susceptible to false alarms than others. These data provide qualitative information for optimization of target distribution patterns in automated perimetry, and serve as a foundation for future quantitative studies.

Automation↗
PubMed2001

Classification of hybrid crows in quail using artificial neural networks.

In galliforms, calls are strongly determined genetically and no influence of learning has ever been demonstrated. Hybridization is a useful tool for investigating patterns of heritability. The vocal repertoire of the European quail (Coturnix c. coturnix) and of the Japanese quail (C. c. japonica) are similar except for their crows. The European quail possesses two forms of crows and the Japanese quail only one form. We produced hybrids from the following crosses; F(1), F(2) and backcrosses. Visual analysis of spectrograms showed that hybrid crows presented all intermediaries between the three forms of crows produced by the two subspecies. According to the level of analysis of a crow, visual classifications of spectrograms probably include some subjectivity. Artificial Neural Networks (ANN) are now widely used as a powerful classification technique in behavioural sciences. We trained an ANN to recognize the three crows of the two subspecies. Then we analysed its classification of hybrid crows. The ANN revealed important inter-individual variability between the crows of the F(1) and the F(2) crosses. Birds issued from backcrosses produced crows similar to those of the European quail to which they were backcrossed. This study confirms that ANN is a useful tool to classify spectrograms rapidly.

Journal Article↗
PubMedDate not supplied

Software for efficient visualization and analysis of multiple, large, multi-dimensional data sets from magnetic resonance imaging.

Comprehensive magnetic resonance imaging (MRI) protocols create multiple, large, multi-dimensional data sets that are challenging to review and interpret in an efficient manner. We report on a program called CliniViewer that uses a common data file format to display all files originating from the scanner and other post-processing programs in an integrated display matrix. The five rows of images and maps have general themes of Anatomic Images, Echo-Planar Images, Parametric Maps (derived from echo-planar images), Metabolic Images, and Non-Image Data, respectively. Each row of the matrix contains related image windows of individual MR acquisitions or maps derived from such acquisitions.An interpreter can quickly screen all images and then select any image from the display to create a separate daughter window incorporating a set of analysis tools for in-depth examination. Given that the images can be acquired in the same co-registered planes without moving the subject, regional analysis can be performed simultaneously across multiple MR image types and the corresponding maps, thereby integrating anatomic features with parametric properties. Color can be used to highlight parametric values that fall outside normal ranges to quickly identify abnormalities on each map. CliniViewer is an efficient environment for analyzing multiple images and maps from comprehensive clinical imaging protocols, aiding the neuroradiologist in providing an integrated interpretation of all available MR data for efficient clinical decision making. CliniViewer is compared to AnalyzeAVW and NIH Image, two popular MR image analysis tools. CliniViewer allows efficient clinical analysis of multiple images and maps from comprehensive clinical imaging protocols.

Brain↗
PubMed2003

Control system analysis of visually evoked blood flow regulation in humans under normocapnia and hypercapnia.

OBJECTIVE: Among other factors, the cerebral blood flow (CBF) is regulated in accordance to the arterial CO(2) tension and the cortical activity. The CO(2) test is commonly used to measure the vascular reserve capacity. Most functional imaging studies rely on the activity-flow coupling (AFC). We aimed to combine both challenges in order to increase the insight into mechanisms of CBF regulation. METHODS: Fifteen healthy students underwent a functional transcranial Doppler test using a visual stimulation paradigm: firstly under normocapnia and secondly under conditions of hypercapnia. Hypercapnia was induced by breathing a carbogene gas mixture of 5% CO(2) and 95% O(2). The entire time course of flow velocity adaptation in the posterior cerebral artery (PCA) was analyzed mathematically using a control system approach. RESULTS: Resting CBF velocities increased by nearly 26% under conditions of hypercapnia, whereas the slight increase in arterial blood pressure (ABP) and the decrease in the Pourcelot-Pulsatility index (PI) were statistically not significant. From the control system parameters which were time delay, rate time, gain, attenuation and natural frequency, only the parameter rate time, indicative for the initial steepness of flow velocity increase, showed a statistically significant decrease, consistently for the peak systolic and enddiastolic flow velocity data. As concluded from the unchanged gain parameter the absolute amount of blood flow evoked by the same visual stimulus increased also by 26%. CONCLUSION: Evaluated by Doppler measurements hypercapnia seems to influence the AFC in two ways: It decreases the steepness of the initial increase in blood flow velocity and enhances the absolute amount of blood flow evoked by the same stimulus.

Adult↗
PubMed2002

Three-dimensional analysis and visualization of regional MR signal intensity distribution of articular cartilage.

The aim of this study was to develop a technique for analyzing and visualizing the regional, three-dimensional signal intensity distribution of articular cartilage in MR images, as a potential surrogate marker of structural or biochemical alterations in early osteoarthritis. Exemplary MR-images of human patellae were acquired at a resolution of 1.5 x 0.31 x 0.31 mm(3), using a gradient-echo sequence with water excitation, and by combining three data sets to secondary images of proton density. After segmentation of the cartilage outlines, these were transferred to the other images. Contiguous slices were automatically divided into sub-regions that extend from the surface to the bone interface (layers) as well as from medial to lateral (sections). The signal intensity was then calculated and projected onto a three-dimensional representation of the articular surface, either by averaging through the depth (sections) or by visualizing the signal intensity at distinct levels in depth (layers). The exemplary data indicate that the reproducibility for regional analyses is in the same range as for the entire patellar cartilage, and that the distribution patterns of proton density delineated with MRI are in agreement with the literature. In conjunction with suitable MR protocols, this post-processing technique has potential to allow for detection and quantification of early degenerative processes in cartilage, before macro-morphological lesions occur.

Adult↗
PubMed1999

Vector analysis of visual evoked potentials elicited by pattern reversal and photic stimuli.

OBJECTIVE: The 2D VEPs to pattern reversal (PR) and LED goggle were studied in order to obtain a stable parameter for the functional assessing of posterior visual pathways regardless of the stimulus type used. DESIGN AND METHODS: Apex c latency, bc segment amplitude (V), and bc vector orientation angle (theta) in voltage space were computed from VEPs recorded in 50 normal human beings and two patients with left posterior brain lesions, in an orthogonal Fpz-Oz and T3-T4 montage and displayed as a two channel Lissajous' trajectory. The effects of stimulus type and stimulated eye were analyzed in the normal group by a two-way ANOVA. RESULTS: The stimulated eye had no effect on any parameter. Apex c latency was slightly longer, and V was greater and more variable in the responses to goggle stimuli, but there was no significant difference in theta, oriented to mid-occipital scalp with very low variability for both stimulus types. The patients showed significant deviations of theta towards the affected hemisphere. CONCLUSIONS: The bc vector orientation (theta) is a stable parameter for the evaluation of the posterior visual pathways using both pattern reversal and LED stimuli, specially the latter, useful in unconscious or uncooperative patients.

Adolescent↗
PubMedDate not supplied

The use of m-sequences in the analysis of visual neurons: linear receptive field properties.

We have used Sutter's (1987) spatiotemporal m-sequence method to map the receptive fields of neurons in the visual system of the cat. The stimulus consisted of a grid of 16 x 16 square regions, each of which was modulated in time by a pseudorandom binary signal, known as an m-sequence. Several strategies for displaying the m-sequence stimulus are presented. The results of the method are illustrated with two examples. For both geniculate neurons and cortical simple cells, the measurement of first-order response properties with the m-sequence method provided a detailed characterization of classical receptive-field structures. First, we measured a spatiotemporal map of both the center and surround of a Y-cell in the lateral geniculate nucleus (LGN). The time courses of the center responses was biphasic: OFF at short latencies, ON at longer latencies. The surround was also biphasic--ON then OFF--but somewhat slower. Second, we mapped the response properties of an area 17 directional simple cell. The response dynamics of the ON and OFF subregions varied considerably; the time to peak ranged over more than a factor of two. This spatiotemporal inseparability is related to the cell's directional selectivity (Reid et al., 1987, 1991; McLean & Palmer, 1989; McLean et al., 1994). The detail with which the time course of response can be measured at many different positions is one of the strengths of the m-sequence method.

Animals↗
PubMed2001

Virtual 2-D gel electrophoresis: visualization and analysis of the E. coli proteome by mass spectrometry.

Mass spectrometric surface analysis of isoelectric focusing gels provides an ultrasensitive approach to proteome analysis. This "virtual 2-D gel" approach, in which mass spectrometry is substituted for the size-based separation of SDS-PAGE, provides advantages in mass resolution and accuracy over classical 2-D gels and can be readily automated. Protein identities can be postulated from molecular mass (+/-0.1-0.2% for proteins of <50 kDa in size) and pI (+/-0.3 pH unit) and confirmed by MALDI in-source decay of the intact protein (providing sequence spanning up to 43 residues) or by peptide mass mapping following gel-wide chemical cleavage. Additionally, posttranslational modifications such as fatty acid acylation can be detected by the mass-resolved heterogeneity of component hydrocarbon chains. Sensitivity was evaluated by comparing the number of proteins detected by this method to equivalently loaded silver-stained 2-D gels. In the 5.7-6.0 pH range, E. coli is predicted to contain 435 proteins; virtual 2-D gels found 250 proteins ranging from >2 to <120 kDa in size present at levels to tens of femtomoles, as compared to the 100 proteins found by silver-staining 2-D gels. Extrapolating this result to the total theoretical proteome suggests that this technology is capable of detecting over 2500 E. coli proteins.

Amino Acid Sequence↗
PubMed2000

Visualization and analysis of electroosmotic flow in hairless mouse skin.

PURPOSE: To identify the physiological structures in hairless mouse skin responsible for the generation of electroosmotic flow during iontophoresis. Also, to determine the effects of changing the pH of the contacting solution on the magnitude of electroosmotic flow in these structures. METHODS: Localized diffusive and iontophoretic fluxes of a neutral molecule, hydroquinone (HQ), across hairless mouse skin were quantified using scanning electrochemical microscopy (SECM). The iontophoretic flux was determined as a function of the direction of the applied current and pH of the contacting solution. RESULTS: SECM images of HQ transport recorded during iontophoresis at moderate current densities (+/-0.1 mA/cm2) demonstrate that electroosmotic flow is localized to hair follicles. The direction of flow is from anode to cathode at pH > 3.5 and from cathode to anode at pH <3.5. CONCLUSIONS: Electroosmotic flow through hair follicles is an efficient and controllable means of transporting small, electrically neutral molecules across hairless mouse skin. Transport through the appendages is sensitive to the pH of the solution in contact with the skin. The isoelectric point of hair follicles, pI, is estimated to be 3.5 from the dependence of electroosmotic flow on the solution pH.

Animals↗
PubMed2001

Multiple dipole analysis of visual event-related potentials during oddball paradigm with silent counting.

In order to cope with the non-uniqueness of multiple equivalent current dipole source (ECD) solutions, a priori knowledge about P300 generators of visual event-related potentials (ERPs) during an oddball paradigm with silent counting task was incorporated into the multiple ECD localization method. Four-ECD solutions for the target P300 were selected which had the left frontal ECD. The rest of the ECDs were localized to the inferior parietal lobule, the hippocampal formation and subcortical region. By comparing the present results with those on the visual ERPs with button-pressing task, the P300 dipoles common to both the tasks were located at the frontal cortices, the hippocampal formation and the thalamus, suggesting that these structures are the main P300 generators.

Adult↗
PubMed2003

Electrophysiological analysis of visual function in mutant mice.

The mouse has become a key animal model for ocular research. This situation reflects the fact that genes implicated in human retinal disorders or in mammalian retinal function may be readily manipulated in the mouse. Visual electrophysiology provides a means to examine retinal function in mutant mice, and stimulation and recording protocols have been developed that allow the activity of many classes of retinal neurons to be examined and which take into account unique features of the mouse retina. Here, we review the mouse visual electrophysiology literature, covering techniques used to record the mouse electroretinogram and visual evoked potential, and how these have been applied to characterize the functional implications of gene mutation or manipulation in the mouse retina.

Animals↗
PubMed1994

Computational modeling and elementary process analysis in visual word recognition.

An attempt is made to isolate the assumptions that make a connectionist approach to visual word recognition distinctive. These include the commitment to distributed representations, the claim that there is no distinction between lexical and nonlexical systems in the naming task, and the claim that it is possible to map from orthography to meaning without using localized representations. It is argued that merely demonstrating that a network model can perform these tasks is not sufficient and that a detailed theory of how the network performs its tasks must accompany the simulation, because a simulation is not equivalent to an explanation. It is argued that further progress requires detailed modeling and experimental study of the elementary processes assumed to be involved in networks and that it is premature to dismiss alternative models of lexical access such as serial search models.

Humans↗
PubMed2005

Validity of the detection of wheelchair propulsion as measured with an Activity Monitor in patients with spinal cord injury.

STUDY DESIGN: Validation study. OBJECTIVES: An accelerometry-based Activity Monitor (AM) has proven to be a valid instrument to quantify mobility-related activities (lying, sitting, standing, walking, cycling, general (noncyclic) movement). The aim of this study was to assess whether, additional to other activities, wheelchair propulsion (hand-rim wheelchair propulsion and handbiking) can be validly detected by the AM in patients with spinal cord injury (SCI). SETTING: Rehabilitation center. METHODS: In all, 10 patients with SCI (aged 19-63 years; five patients with poor triceps strength and five patients with good triceps strength) participated. Patients performed a series of representative daily life activities (involving wheelchair propulsion and nonwheelchair propulsion activities), according to a standard protocol, in a seminatural setting. Continuous registrations of signals from body-fixed accelerometers were made and the AM output (after automatic analysis) was compared with visual analysis of simultaneously made video recordings (reference method). Validity scores (agreement, sensitivity, specificity) between the output of the AM and the video analysis were calculated. RESULTS: Agreement, sensitivity and specificity for the detection of wheelchair propulsion were overall 92 (range, 87-96)%, 87 (76-99)% and 92 (85-98)%, respectively. Sensitivity was smaller in patients with poor triceps strength compared to patients with good triceps strength; 81 (76-89)% and 95 (89-99)%, respectively (P<0.01). Mean overestimation in duration of wheelchair propulsion by the AM was 3.9% (P<0.05). CONCLUSION: Besides already validated other activities, wheelchair propulsion (hand-rim wheelchair propulsion and handbiking) can be validly detected by the AM in patients with SCI, both with good and poor triceps strength. Therefore, the AM offers the possibility to obtain objective and detailed information on all major mobility-related activities performed by patients with SCI. SPONSORSHIP: Stichting Rotterdams Kinderrevalidatie Fonds Adriaanstichting.

Acceleration↗
PubMed2003

Correlation analysis of visual field thresholds and scanning laser ophthalmoscopic optic nerve head measurements in glaucoma.

In a cross-sectional study of 50 consecutive primary open-angle glaucoma cases, full threshold 30-2 visual fields on Humphrey Visual Field Analyser were correlated to stereometric parameters obtained using a scanning laser ophthalmoscope (HRT II). The strength of linear correlation between the stereometric parameters and visual thresholds was used to generate a correspondence map between the optic disc and the visual field. Rim/disc area ratio and cup/disc area ratio correlated with the visual thresholds at the highest number of points in the visual fields. Thresholds at superior hemifield locations correlated best with the rim/disc area ratio and cup/disc area ratio in the inferonasal sector and the ones in the inferior hemifield correlated best with the rim/disc area ratio and cup/disc area ratio in the superotemporal sector. Optic disc parameters correlated better with inferior field locations and non-edge points than superior field locations and edge points. The data indicate that rim/disc area ratio and cup/disc area ratio measurements on HRT II have a good correlation with visual field damage seen on automated visual fields.

Adult↗
PubMed2006

An information theory analysis of visual complexity and dissimilarity.

The subjective complexity of a computer-generated bitmap image can be measured by magnitude estimation scaling, and its objective complexity can be measured by its compressed file size. There is a high correlation between these measures of subjective and objective complexity over a large set of marine electronic chart and radar images. The subjective dissimilarity of a pair of bitmap images can be predicted from subjective and objective measures of the complexity of each image, and from the subjective and objective complexity of the image produced by overlaying the two simple images. In addition, the subjective complexity of the image produced by overlaying two simple images can be predicted from the subjective complexity of the simple images and the subjective dissimilarity of the image pair. The results of the experiments that generated these complexity and dissimilarity judgments are consistent with a theory, outlined here, that treats objective and subjective measures of image complexity and dissimilarity as vectors in Euclidean space.

Computer Simulation↗