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At least 307 records · Page 17Linked to original sources

PubMed1997

Planning an action.

The motor control of a sequence of two motor acts forming an action was studied in the present experiment. The two analysed motor acts were reaching-grasping an object (first target) and placing it on a second target of the same shape and size (experiment 1). The aim was to determine whether extrinsic properties of the second target (i.e. target distance) could selectively influence the kinematics of reaching and grasping. Distance, position and size of both targets were randomly varied across the experimental session. The kinematics of the initial phase of the first motor act, that is, velocity of reaching and hand shaping of grasping, were influenced by distance of the second target. No kinematic difference was found between movements executed with and without visual control of both hand and targets. These results could be due to computation of the general program of an action that takes into account extrinsic properties of the final target. Conversely, they could depend on a visual interference effect produced by the near second target on the control of the first motor act. In order to dissociate the effects due to second target distance from those due to visual interference, two control experiments were carried out. In the first control experiment (experiment 2) subjects executed movements directed towards spatial locations at different distances from the first target, as in experiment 1. However, the near second target was not presented and subjects were required to place the object on an arbitrary near position. Distance of the second (either real or arbitrary) target affected the reaching component of the first motor act, as in experiment 1, but not the grasp component. In the second control experiment (experiment 3), the pure visual interference effect was tested. Subjects were required to reach and grasp the object and to lift it in either presence or absence of a second near stimulus. No effect on the initial phase of the first motor act was observed. The results of the this study suggest a dissociation in the control of reaching and grasping, concerning not only visual analysis of extrinsic properties of the immediate target but also visual analysis of the final target of the action. In other words, the notion of modularity for the motor control can be extended to the construction of an entire action.

Adult↗

PubMed1999

Failure of bacteriophage typing to detect an inter-hospital outbreak of methicillin-resistant Staphylococcus aureus (MRSA) in Zagreb subsequently identified by random amplification of polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE).

OBJECTIVE: To establish the extent of inter-hospital spread of methicillin-resistant Staphylococcus aureus (MRSA) in Zagreb and to determine the most suitable method for typing local strains. METHODS: We analyzed a collection of 33 MRSA isolates from three Zagreb hospitals together with five unrelated British MRSA isolates by antibiogram typing, bacteriophage typing, randomly amplified polymorphic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE) after digestion with Smal restriction endonuclease. Bacteriophage typing was done with the international set of S. aureus typing phages. RAPD and PFGE profiles were analyzed visually and by using the 'GelCompar' computer program. RESULTS: Antibiogram typing provided eight profiles. Thirty (91%) of the 33 Croatian strains of MRSA were non-typable by phage typing. Visual analysis of RAPD products identified six, and visual analysis of PFGE fragments nine, distinct profiles. Computer analysis of RAPD data separated British isolates from the Croatian ones, but did not cluster the visually determined RAPD types. PFGE computer analysis separated British isolates and clustered isolates in concordance with visual interpretation. Thirty-one of the 38 isolates (82%) were visually grouped in the same clusters by both molecular methods. The dominant strain was present in each of the three hospitals. CONCLUSIONS: Bacteriophage typing was unhelpful for the analysis of Croatian MRSA, since most strains were untypable with the international set of bacteriophages. RAPD and PFGE were more successful in typing the organisms and showed evidence of inter-hospital spread of one predominant MRSA strain in all three Zagreb hospitals. Thus RAPD and PFGE proved to be a useful aid in elucidating the epidemiology of MRSA infection in Zagreb hospitals and should be established in Croatia for typing MRSA.

Journal Article↗

PubMed2002

Dynamics of visual feature analysis and object-level processing in face versus letter-string perception.

Neurones in the human inferior occipitotemporal cortex respond to specific categories of images, such as numbers, letters and faces, within 150-200 ms. Here we identify the locus in time when stimulus-specific analysis emerges by comparing the dynamics of face and letter-string perception in the same 10 individuals. An ideal paradigm was provided by our previous study on letter-strings, in which noise-masking of stimuli revealed putative visual feature processing at 100 ms around the occipital midline followed by letter-string-specific activation at 150 ms in the left inferior occipitotemporal cortex. In the present study, noise-masking of cartoon-like faces revealed that the response at 100 ms increased linearly with the visual complexity of the images, a result that was similar for faces and letter-strings. By 150 ms, faces and letter-strings had entered their own stimulus-specific processing routes in the inferior occipitotemporal cortex, with identical timing and large spatial overlap. However, letter-string analysis lateralized to the left hemisphere, whereas face processing occurred more bilaterally or with right-hemisphere preponderance. The inferior occipitotemporal activations at approximately 150 ms, which take place after the visual feature analysis at approximately 100 ms, are likely to represent a general object-level analysis stage that acts as a rapid gateway to higher cognitive processing.

Acoustic Stimulation↗

PubMed1989

Sequential ideal-observer analysis of visual discriminations.

Visual stimuli contain a limited amount of information that could potentially be used to perform a given visual task. At successive stages of visual processing, some of this information is lost and some is transmitted to higher stages. This article describes a new analysis, based on the concept of the ideal observer in signal detection theory, that allows one to trace the flow of discrimination information through the initial physiological stages of visual processing, for arbitrary spatio-chromatic stimuli. This ideal-observer analysis provides a rigorous means of measuring the information content of visual stimuli and of assessing the contribution of specific physiological mechanisms to discrimination performance. Here, the analysis is developed for the physiological mechanisms up to the level of the photoreceptor. It is shown that many psychophysical phenomena previously attributed to neural mechanisms may be explained by variations in the information content of the stimuli and by preneural mechanisms.

Attention↗

PubMed1984

Visualization and analysis of right heart blood flow patterns by contrast echocardiography.

UNLABELLED: The clinical utility of visualization of blood flow patterns across the tricuspid valve (TV) and pulmonary valve (PV) by M-mode contrast echocardiography was studied in 38 patients with documented valvular or congenital heart disease and in 15 controls. Diastolic turbulence was observed in the TV outflow side in three patients with tricuspid stenosis. Turbulent flow was also detected during systole in patients with septal defects (atrial septal defect in four patients and ventricular septal defect in one patient) in the right ventricular outflow tract and in three atrial septal defect patients also in the inflow tract, presumably because of increased volume of flow. Tricuspid regurgitation (11 patients) was characterized by retrograde laminar jet throughout systole, while in pulmonary regurgitation (six patients) retrograde flow was initially laminar although later on it might become turbulent. In pulmonary hypertension (29 patients) antegrade flow occurred approximately to mid-systole and then was interrupted by retrograde laminar flow which contributed to the mid-systolic closure of the pulmonary valve and pulmonary regurgitation in some cases. CONCLUSIONS: contrast echocardiography is a useful technique to analyse right heart blood flow patterns and may aid the diagnosis of various right heart abnormalities.

Captopril↗

PubMed1997

Visualization and analysis of chromatin by scanning force microscopy.

The use of the scanning force microscope (SFM) to visualize and analyze chromatin fiber structures is presented. Protocols to prepare chromatin fibers for SFM imaging of fibers in air and in buffer are first discussed. Next, the conditions for acquiring high-quality SFM images such as optimal instrumental parameters, appropriate deposition substrates, and adequate procedures of sample deposition are described. It is shown that analysis and quantitation of the SFM images support an irregular, three-dimensional arrangement of nucleosomes in the native chromatin fiber. This structure is lost in linker histone-depleted fibers, which show, instead, a beads-on-a-string structure. Molecular modeling of the chromatin fiber structures and computer simulation of the SFM imaging process indicate that the natural variability of the linker length may be the major determinant of the structural irregularity of the native chromatin fiber. Removal of linker histones (H1/H5) may change the amount of DNA wrapped around the histone octamer, which in turn may induce the transition from a three-dimensional irregular helix to an extended beads-on-a-string structure. Studies of trinucleosomes indicate that both the average successive nucleosome center-to-center distance and the average angle between two successive linkers increase upon the removal of linker histone.

Chromatin↗

PubMed2004

[Evaluation of regional wall motion abnormalities of the heart--comparison with doppler tissue echocardiography, MR-tagging and levocardiography].

PURPOSE: To compare the visual analysis of magnetic resonance imaging (MRI) with the tagging technique and Doppler tissue echocardiography with invasive ventriculography in detecting and quantifying regional left ventricular wall motion abnormalities. MATERIALS AND METHODS: Sixteen patients with coronary artery disease and a history of prior myocardial infarction underwent invasive ventriculography, Doppler tissue echocardiography and MR-tagging within one week. Regional wall motion abnormalities (WMA) were detected in all patients. WMA were graded as normal = 1; hypokinetic = 2; akinetic = 3; or dyskinetic = 4. For agreement between MRI, echocardiography, and ventriculography the kappa coefficient (kappa) according to Cohen was calculated. RESULTS: The kappa coefficient (kappa) was 0.962 for agreement between MRI and echocardiography and 0.602 for agreement between MRI and ventriculography as well as between echocardiography and ventriculography. CONCLUSION: Reliable analysis of regional left ventricular wall motion abnormalities is feasible using visual analysis of MR-tagging. MRI and Doppler tissue echocardiography detect more WMA than invasive ventriculography and grade them as more severe.

Aged↗

PubMed1994

Enhanced maximal binding capacity (Bmax) of second messenger ligand in the acute phase of cerebral ischemia--direct visualization by digital image analysis.

Autoradiographic visualization of the Bmax (maximal binding capacity) and Kd (dissociation constant) of [3H]phorbol 12,13-dibutyrate (PDBu) and [3H]forskolin (FK) was performed after 30-min unilateral carotid artery occlusion in the gerbil brain. These parameters and the local cerebral blood flow (CBF) were measured at the level of the caudate-putamen in the same brain using a digital image processing technique developed in our laboratory. The local CBF was measured at the end of the experiment. [3H]PDBu and [3H]FK were utilized as specific ligands to assess the activities of protein kinase C (PKC) and adenylate cyclase (AC), respectively. The local CBF on the occluded side was severely reduced and ranged from 0.2 to 9.0 ml/100 g/min, whereas the local CBF on the non-occluded side exhibited a moderate reduction except in the midline regions. The Bmax values of PDBu and FK were significantly increased not only on the occluded side but also on the non-occluded side in the ischemia group as compared to the corresponding values in the sham group. In contrast, the Kd value of each ligand remained unchanged in the ischemia group. These findings suggest that both the adenylate cyclase and protein kinase C systems may be significantly and diffusely activated in the initial stage of brain ischemia. Thus, severe hemispheric cerebral ischemia in the acute phase may induce severe perturbation of the second messenger systems in extensive bilateral regions.

Acute Disease↗

PubMed2003

Theatre: A software tool for detailed comparative analysis and visualization of genomic sequence.

Theatre is a web-based computing system designed for the comparative analysis of genomic sequences, especially with respect to motifs likely to be involved in the regulation of gene expression. Theatre is an interface to commonly used sequence analysis tools and biological sequence databases to determine or predict the positions of coding regions, repetitive sequences and transcription factor binding sites in families of DNA sequences. The information is displayed in a manner that can be easily understood and can reveal patterns that might not otherwise have been noticed. In addition to web-based output, Theatre can produce publication quality colour hardcopies showing predicted features in aligned genomic sequences. A case study using the p53 promoter region of four mammalian species and two fish species is described. Unlike the mammalian sequences the promoter regions in fish have not been previously predicted or characterized and we report the differences in the p53 promoter region of four mammals and that predicted for two fish species. Theatre can be accessed at http://www.hgmp.mrc.ac.uk/Registered/Webapp/theatre/.

Animals↗

PubMed1993

Quantitative same-day rest-stress technetium-99m-sestamibi SPECT: definition and validation of stress normal limits and criteria for abnormality.

Gender-matched stress normal limits and criteria for abnormality for rest-stress 99mTc-sestamibi same-day myocardial perfusion imaging were developed and validated in 160 patients who were imaged using previously developed optimized acquisition, processing and quantitative protocols. The gender-matched mean and standard deviation of the normal response were calculated using 35 male and 25 female patients with a < 5% likelihood of coronary artery disease. Receiver-operating curve analysis using expert visual interpretation as the "gold standard" was used to determine the optimal criteria for abnormality detection, in terms of standard deviations from the mean and minimum defect size for each of the four major zones of the polar map, in a pilot population consisting of an additional 35 male and 25 female patients with a variety of perfusion defects. The optimum standard deviations resulted in the following true-positive/true-negative rates when quantitative results were compared to visual analysis for the anterior, septal, lateral, and inferior segments in the combined male and female pilot populations: 84%/86%, 70%/75%, 86%/76% and 69%/76%, respectively. The final criteria were then applied to a prospective population consisting of 33 male and 7 female patients. This analysis resulted in the following true-positive/true-negative rates for overall perfusion abnormalities and abnormalities of the LAD, LCX and RCA vascular territories: 97%/67%, 94%/73%, 73%/90% and 72%/91%, respectively. The optimized 99mTc-sestamibi stress normal limits and criteria for abnormality correlate well with expert visual interpretation of stress myocardial perfusion defects.

Coronary Disease↗

PubMed1995

Neutral location cues and cost/benefit analysis of visual attention shifts.

The effects of location cuing on target responses can be examined by comparing informative and neutral cuing conditions. In particular, the magnitudes of costs of invalid location cuing and of benefits of valid location cuing can be determined by comparing invalid and valid cue responses to location-nonspecific neutral cue responses. Cost/benefit analysis is based on the assumption that neutral baseline measures reflect a general warning effect about the impending target's onset but no other specific target information. The experiments we report were carried out to determine the appropriateness of two baseline measures for cost/benefit analyses of direct (nonsymbolic) location cuing effects. We found that a multiple-cue baseline attenuated the benefits of valid cuing, and that a background-flash baseline arbitrarily attenuated costs or benefits depending on flash intensity. It is proposed that a background flash is the more suitable neutral cue because it is target-location-nonspecific, but that its intensity should be adjusted to elicit a target-onset warning signal of the same magnitude as the location cues with which it will be compared.

Attention↗

PubMed1994

The primary treatment trial: changes in the visual field analysis by computer-assisted perimetry.

Computer-assisted perimetry was performed 6-monthly on patients entered into the Primary Treatment Trial using the 30-2 program. Those patients with a minimum of five visual fields had pointwise linear regression analysis (Progressor) carried out. Two consecutive slopes significant at the 0.05 level were taken as evidence for change, either improvement or worsening. Forty-eight patients in the surgery group, 40 in the medical group and 20 in the laser group were suitable for analysis. A comparison of the eyes showing 'improvement' or 'worsening' in the surgery and medicine groups showed no difference between them. This lack occurred despite a significant difference in intraocular pressure between the two groups. The reasons for this lack of difference are discussed.

Diagnosis, Computer-Assisted↗

PubMed2005

Walking perception by walking observers.

People frequently analyze the actions of other people for the purpose of action coordination. To understand whether such self-relative action perception differs from other-relative action perception, the authors had observers either compare their own walking speed with that of a point-light walker or compare the walking speeds of 2 point-light walkers. In Experiment 1, observers walked, bicycled, or stood while performing a gait-speed discrimination task. Walking observers demonstrated the poorest sensitivity to walking speed, suggesting that perception and performance of the same action alters visual-motion processes. Experiments 2-6 demonstrated that the processes used during self-relative and other-relative action perception differ significantly in their dependence on observers' previous motor experience, current motor effort, and potential for action coordination. These results suggest that the visual analysis of human motion during traditional laboratory studies can differ substantially from the visual analysis of human movement under more realistic conditions.

Computers↗

PubMed1995

Psychovegetative syndrome diagnosis: an automated psychophysiological investigation and mathematical modeling approach.

1. INTRODUCTION. The main purpose of our work was to create the informational expert system of psychovegetative syndrome diagnosis by applying clinical data and estimating the functioning of the central and peripheral part of regulatory apparatus of the human organism, taking into consideration parallel and consecutive sensory, motor, associative, emotional drive systems, and internal body state. We used automatized psychophysiological investigation and mathematical models. For this purpose the following principal tasks have been prepared: the creation of database of quantifiable estimation patient state; the definition and automation of psychophysiological investigation; mathematical modeling of vegetative functions using a non-invasive sample and its connection with real psychophysiological experiment; mathematical modeling of organisms inner medium homeostasis; and the creation of an informational-expert system of psychovegetative syndrome diagnosis. 2. DATABASE OF ESTIMATION OF PATIENTS STATE. The medical records of the DB "PATIENT" contain data on patient psychic and somatoneurological status. 3. AUTOMATED PSYCHOPHYSIOLOGICAL INVESTIGATION. Psychophysiological investigation enables estimation of the functioning of several subsystems of the human organism and establishes an interrelationship between them by means of electrophysiological data and performance parameters. The study of psychophysiological provision of behavior by psychophysiological investigation enables us to get information about adaptational mechanisms of the patient under certain environmental loads. By means of special mathematical provision, the mathematical elaboration of biosignals as performance parameters has been realized; also realized were the formation of received parameters in the database, the estimation of separated parameters in the view of informativity, and the establishment of diagnostic patterns. 4. MATHEMATICAL MODELS FOR ESTIMATION INTERNAL BODY STATE. The proposed mathematical models allow investigation of homeostatic regulation in various intensities of the metabolic processes and external load. This approach in mathematical models allows us to characterize the relations between the central and peripheral parts of the regulatory mechanisms, using non-invasive samples under psychophysiological investigation and the simulation of different surroundings for brain cells functioning. 5. INFORMATION-EXPERT SYSTEM. Proceeding from the principle of psychoneural unity, we characterized the functioning mechanisms of CNS by means of automatized EEG analysis, visually evoked potential analysis, estimated psychic status, and the characteristics of neural system biochemical processes received by mathematical modeling. By using the indices of the viscero-vegetative and somatolocomotor system (as well as parameters received by automatized analysis of ECG), the EEG respiratory signal--from mathematical models of vegetative functions decision support system applied in estimation of a peripheral block of the regulatory system--is reflected in diagnosis of certain syndromes. The informational expert system, proceeding from the functioning of the human organism's regulatory apparatus, diagnosed psychovegetative syndrome and described the mechanisms of its development. 6. CONCLUSION. The informational expert system enables estimation of the functioning of a human organism as a whole and can be introduced in the sphere of practical medicine and professional orientation as well as in laboratories of experimental psychology and neurosciences.

Brain↗

PubMed2005

Distinct neural systems underlie learning visuomotor and spatial representations of motor skills.

Motor skill learning depends upon acquiring knowledge about multiple features of sequential behaviors, including their visuomotor and spatial properties. To investigate the neural systems that distinguish these representations, we carried out functional magnetic resonance imaging (fMRI) as healthy adults learned to type sequences on a novel keyboard. On the initial training day, learning-related changes in brain activation were found in distributed cortical regions, only a subset of which correlated with improvements in movement time (MT), suggesting their preeminence in controlling movements online. Subjects received extended training on the sequences during the ensuing week, after which they returned to the scanner for another imaging session. Relative to performance at the end of the first training day, continued plasticity was most striking in the inferior parietal cortex and new areas of plasticity were uncovered in the caudate and cerebellum. Plasticity in these regions correlated with reaction time (RT), suggesting their role in planning sequences before movement onset. Two transfer conditions probed for "what" subjects learned. The probe for visuomotor learning produced increased activation in visual analysis (left inferior visual cortex) and advance planning (left caudate) systems. The probe for spatial learning produced increased activation in visuomotor-transformation (left dorsal visual pathway) and retrieval (left precuneus) systems. Increased activity in all of these regions correlated with increased RT, but not MT, indicating that both transfer conditions interfered with the neural representation of plans for the sequences, but not processes that controlled their implementation. These findings demonstrated that neuroanatomically dissociable systems support the acquisition of visuomotor and spatial representations of actions.

Adolescent↗

PubMed1985

Spatio-temporal EEG measures and their application to human intracranially recorded epileptic seizures.

We describe analysis methods which involve the computation of band-integrated, intrachannel spectral measures from the EEG. These measures require only very general assumptions, have a simple interpretation and achieve significant data reduction, while providing a quantitative assessment of significant EEG modification at seizure or onset or in the course of seizure evolution. In developing these measures, we experimented with various measures derived from spatio-temporal power spectra. Bandpass (8-30 Hz) integrated relative energy measures appear to be the most useful since they objectively measure paroxysmal modification. Two such measures are illustrated in this report: the band-integrated power z-score (BIPZ), which is a quantitative measure designed to allow significance testing, and the band-integrated power ratio (BIPR), which is a simply calculated qualitative measure that behaves very similarly to the BIPZ measure and may be useful for real-time data screening. In addition to developing these intrachannel measures, we have also developed methods of displaying these measures in a format appropriate to the analysis of interchannel relationships. In a general sense, the displays provide objective information regarding the spatio-temporal dynamics of the EEG in a condensed format which is still readily understandable to the electroencephalographer. This analysis was applied to 29 spontaneous, depth-recorded seizures in 14 patients with the aim of identifying the initial locus of seizure activity in each seizure episode. The initial locus was defined as that location (or set of locations) to first exhibit statistically significant values of the BIPZ measure. The method was very effective in this regard, as shown by correspondence between the conclusions of this automated analysis and conventional visual analysis.

Brain↗

PubMed1989

The implementation of an autoregressive model with exogenous input in a single sweep visual evoked potential analysis.

Based on a model of signal-noise interaction, we present a method for single-sweep analysis of Visual Evoked Potentials. The EEG is represented as an autoregressive process and the single-sweep VEP as a filtered version of a reference signal taken as the running average of 20 consecutive sweeps. The algorithm for model identification and filtering is an ARX (AutoRegressive with eXogenous input) which provides a fast and efficient solution by means of a least squares approach. The choice of reference signal, as well as the complexity of the model, is also discussed. A further advantage of this approach is parameter reduction: all the single-sweep information is contained in 18 model coefficients and the reference signal.

Evoked Potentials, Visual↗

PubMed2005

Centrographic analysis of 1-phase versus 2-phase treatment for Class II malocclusion.

INTRODUCTION: Cephalometric analyses have been used by orthodontists to track growth and monitor treatment effects. Most of these analyses have normative values to which patients are compared, but some "normal" patients vary quite a bit from the normative values. The centrographic analysis is a visual analysis with no angles to measure or normative values to compare. After a reference plane is developed, the relative position of variable landmarks can be seen. METHODS: We used the centroid centrographic analysis to study the effects of 1-phase and 2-phase orthodontic treatment. Phase 1 treatment consisted of bionator (n = 66), headgear/biteplane (n = 69), or observation (n = 65) until a Class I molar relationship was achieved or 2 years had elapsed. After 1 year, all subjects underwent full orthodontic treatment with fixed appliances. RESULTS: Centrographic analysis showed that early treatment has effects on the mandible. However, the differences were not apparent by the end of fixed appliance treatment. CONCLUSIONS: The skeletal effects of phase 1 treatment disappear by the end of fixed appliance treatment.

Activator Appliances↗