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At least 343 records · Page 19Linked to original sources
PubMed2005

Parametric light bullets supported by quasi-phase-matched quadratically nonlinear crystals.

We present a comprehensive analysis of the dynamics of three-dimensional spatiotemporal nonspinning and spinning solitons in quasi-phased-matched (QPM) gratings. By employing an averaging approach based on perturbation theory, we show that the soliton's stability is strongly affected by the QPM-induced third-order nonlinearity (which is always of a mixed type, with opposite signs in front of the corresponding self-phase and cross-phase modulation terms). We study the dependence of the stability of the spatiotemporal soliton (STS) on its energy, spin, the wave-vector mismatch between the fundamental and second harmonics, and the relative strength of the intrinsic quadratic and QPM-induced cubic nonlinearities. In particular, all the spinning solitons are unstable against fragmentation, while zero-spin STS's have their stability regions on the system's parameter space.

Journal Article↗
PubMed2005

Recent advances in sonographic imaging of fetal thoracic structures.

Recent ultrasonographic methods applied in the evaluation of fetal thoracic structures and anomalies are presented. Fetal lung volumetric assessment by 3D ultrasonography, analysis of the thoracic wall by 3D-rendered image and 3D skeletal-mode imaging, intrathoracic vessel evaluation by 3D power Doppler ultrasonography, analysis of heart anatomy and abnormalities by 4D spatiotemporal image correlation, identification of normal and abnormal intrathoracic almost isoechogenic structures by volume contrast imaging and evaluation of the heart and great vessels by 3 and 4D inverse mode will be reviewed.

Heart Defects, Congenital↗
PubMed2005

Spatiotemporal blind source separation approach to atrial activity estimation in atrial tachyarrhythmias.

The analysis and characterization of atrial tachyarrhythmias requires, in a previous step, the extraction of the atrial activity (AA) free from ventricular activity and other artefacts. This contribution adopts the blind source separation (BSS) approach to AA estimation from multilead electrocardiograms (ECGs). Previously proposed BSS methods for AA extraction--e.g., independent component analysis (ICA)--exploit only the spatial diversity introduced by the multiple spatially-separated electrodes. However, AA typically shows certain degree of temporal correlation, with a narrowband spectrum featuring a main frequency peak around 3.5-9 Hz. Taking advantage of this observation, we put forward a novel two-step BSS-based technique which exploits both spatial and temporal information contained in the recorded ECG signals. The spatiotemporal BSS algorithm is validated on simulated and real ECGs from a significant number of atrial fibrillation (AF) and atrial flutter (AFL) episodes, and proves consistently superior to a spatial-only ICA method. In simulated ECGs, a new methodology for the synthetic generation of realistic AF episodes is proposed, which includes a judicious comparison between the known AA content and the estimated AA sources. Using this methodology, the ICA technique obtains correlation indexes of 0.751, whereas the proposed approach obtains a correlation of 0.830 and an error in the estimated signal reduced by a factor of 40%. In real ECG recordings, we propose to measure performance by the spectral concentration (SC) around the main frequency peak. The spatiotemporal algorithm outperforms the ICA method, obtaining a SC of 58.8% and 44.7%, respectively.

Algorithms↗
PubMed1998

Synchronization and control of spatiotemporal chaos using time-series data from local regions.

In this paper we show that the analysis of the dynamics in localized regions, i.e., sub-systems can be used to characterize the chaotic dynamics and the synchronization ability of the spatiotemporal systems. Using noisy scalar time-series data for driving along with simultaneous self-adaptation of the control parameter representative control goals like suppressing spatiotemporal chaos and synchronization of spatiotemporally chaotic dynamics have been discussed. (c) 1998 American Institute of Physics.

Journal Article↗
PubMed2002

Isolation of relevant visual features from random stimuli for cortical complex cells.

A crucial step in understanding the function of a neural circuit in visual processing is to know what stimulus features are represented in the spiking activity of the neurons. For neurons with complex, nonlinear response properties, characterization of feature representation requires measurement of their responses to a large ensemble of visual stimuli and an analysis technique that allows identification of relevant features in the stimuli. In the present study, we recorded the responses of complex cells in the primary visual cortex of the cat to spatiotemporal random-bar stimuli and applied spike-triggered correlation analysis of the stimulus ensemble. For each complex cell, we were able to isolate a small number of relevant features from a large number of null features in the random-bar stimuli. Using these features as visual stimuli, we found that each relevant feature excited the neuron effectively in isolation and contributed to the response additively when combined with other features. In contrast, the null features evoked little or no response in isolation and divisively suppressed the responses to relevant features. Thus, for each cortical complex cell, visual inputs can be decomposed into two distinct types of features (relevant and null), and additive and divisive interactions between these features may constitute the basic operations in visual cortical processing.

Animals↗
PubMed1990

Quantitative analysis of walking in patients with knee osteoarthritis: a method of assessing the effectiveness of non-steroidal anti-inflammatory treatment.

Most therapeutic tests of osteoarthritis treatments are assessed by criteria based either on fundamental data or on clinical data, which is often subjective. A quantified analysis of locomotion can be used to determine the spatiotemporal indices (stride length and duration), kinematic indices (walking speed, velocity peak), and symmetry criteria that are relevant to the assessment of locomotor handicaps in patients with osteoarthritis. This study examined the progression of locomotor abilities in 11 subjects aged 49-69 (mean 60.9) years with knee osteoarthritis before and after treatment with a non-steroidal anti-inflammatory drug. Naproxen sodium (1100 mg) was given once a day for seven days. The condition before and after treatment was evaluated by quantitative analysis of locomotion, estimation of pain on a visual analogue scale, and assessment of the degree of functional disability. Significant improvement in locomotor indices (proportional increase in walking speed 17.8%) and in degree of pain (proportional decrease 27%) as estimated on the analogue scale was found after non-steroidal anti-inflammatory drug treatment. The lack of a significant correlation between the decrease in pain experienced by the patients and the objective improvement of their functional capabilities emphasises the need in further studies of new treatments to accompany the patients' own assessments of self improvement with a quantitative analysis of the way in which they walk.

Aged↗
PubMed1996

The visual perception of rigid motion from constant flow fields.

Four experiments investigated observers' judgments of rigidity for different types of optical motion. The depicted structural deformations were of two types: (1) those with nonparallel image trajectories that are detectable from the first-order spatiotemporal relations between pairs of views; and (2) those with parallel image trajectories that can only be detected from higher order relations among three or more views. Patterns were composed of smooth flow fields in Experiments 1 and 3, and of wire frame figures in Experiments 2 and 4. For both types of display, the nonrigidity detectable from the first-order spatiotemporal structure of the motion sequence was much more salient than the deformation detectable only from the higher order spatiotemporal structure. These results indicate that observers' judgments of rigidity are based primarily on a two-view analysis, but that some useful information can be obtained under appropriate circumstances from higher order spatiotemporal relations among three or more views.

Adult↗
PubMed2005

What is novel in the novelty oddball paradigm? Functional significance of the novelty P3 event-related potential as revealed by independent component analysis.

To better understand whether voluntary attention affects how the brain processes novel events, variants of the auditory novelty oddball paradigm were presented to two different groups of human volunteers. One group of subjects (n=16) silently counted rarely presented 'infrequent' tones (p=0.10), interspersed with 'novel' task-irrelevant unique environmental sounds (p=0.10) and frequently presented 'standard' tones (p=0.80). A second group of subjects (n=17) silently counted the 'novel' environmental sounds, the 'infrequent' tones now serving as the task-irrelevant deviant events. Analysis of event-related potentials (ERPs) recorded from 63 scalp channels suggested a spatiotemporal overlap of fronto-central novelty P3 and centro-parietal P3 (P3b) ERP features in both groups. Application of independent component analysis (ICA) to concatenated single trials revealed two independent component clusters that accounted for portions of the novelty P3 and P3b response features, respectively. The P3b-related ICA cluster contributed to the novelty P3 amplitude response to novel environmental sounds. In contrast to the scalp ERPs, the amplitude of the novelty P3 related cluster was not affected by voluntary attention, that is, by the target/nontarget distinction. This result demonstrates the usefulness of ICA for disentangling spatiotemporally overlapping ERP processes and provides evidence that task irrelevance is not a necessary feature of novelty processing.

Acoustic Stimulation↗
PubMed2026

GenOT: generative optimal transport enables spatiotemporal interpolation and generation in cross-platform spatial transcriptomics.

Spatial transcriptomics technologies have revolutionized the analysis of spatial gene expression, yet integrating spatial information and generating data across heterogeneous samples remain challenging. We present GenOT, a generative framework combining multi-scale graph self-supervised contrastive learning with optimal transport barycenter theory for efficient cross-slice and cross-platform spatiotemporal interpolation. The core innovation of GenOT lies in introducing an optimal transport barycenter-based interpolation algorithm, which mathematically models spatial distribution differences across heterogeneous samples to reconstruct spatiotemporal gene expression dynamics. Extensive evaluations demonstrate that GenOT consistently outperforms existing approaches in spatial domain identification, cross-platform interpolation, and developmental trajectory reconstruction.

Spatial Transcriptomics↗
PubMed2004

NUTMEG: a neuromagnetic source reconstruction toolbox.

We have developed an analysis toolbox called NUTMEG (Neurodynamic Utility Toolbox for Magnetoencephalography) for reconstructing the spatiotemporal dynamics of neural activations and overlaying them onto structural MR images. The toolbox runs under MATLAB in conjunction with SPM2 and can be used with the Linux/UNIX, Mac OS X, and even Windows platforms. Currently, evoked magnetic field data from 4-D Neuroimaging, CTF, and KIT systems can be imported to the toolbox for analysis. NUTMEG uses an eigenspace vector beamforming algorithm to generate a tomographic reconstruction of spatiotemporal magnetic source activity over selected time intervals and spatial regions. The MEG coordinate frame is coregistered with an anatomical MR image using fiducial locations and, optionally, head shape information. This allows the reconstruction to be superimposed onto an MRI to provide a convenient visual correspondence to neuroanatomy. Navigating through the MR volume automatically updates the displayed time series of activation for the selected voxel. Animations can also be generated to view the evolution of neural activity over time. Since NUTMEG displays activations using SPM2's engine, certain SPM functions such as brain rendering and spatial normalization may be applied as well. Finally, as a MATLAB package, the end user can easily add customized functions. Source code is available at http://bil.ucsf.edu/ and distributed under a BSD-style license.

Electroencephalography↗
PubMed2006

Spatiotemporal patterns of malaria incidence in northern Thailand.

We present a detailed analysis of long-term time series of malaria incidence in northern Thailand. Positive cases for Plasmodium falciparum and P. vivax have been recorded monthly from 1977-2002 at 13 provinces in the region. Time series statistical methods are used to examine the long-term trends and seasonal dynamics of malaria incidence at regional and provincial scales. Both malarial types are declining throughout the region, except in the two provinces that share a large border with Myanmar. The rate of decline in P. vivax has decreased across the region since the end of the 1980s, and this may be a signal of developing resistance or changing vector potential. Both species display a two-peak annual seasonality that may be attributed to patterns of vector occurrence, farming practice and migration of individuals across international borders. In a number of provinces, the importance of the first seasonal peak has grown in recent years, possibly owing to increases in vector densities. The medium-term fluctuations of both species exhibit a clear spatial organisation. There is some evidence of a subtle close to 4-year super annual cycle in P. falciparum, which we suggest is driven by extrinsic factors relating to the climate of the region.

Humans↗
PubMedDate not supplied

[The electroencephalographic correlates of the intellectual abilities of adolescents].

Analysis of correlation between intellectual faculties of schoolchildren and spatiotemporal organization of their brain electrical activity was carried out. The less intelligent teen-agers showed more expressed alpha-activity in the EEG of rest, higher level of EEG coherence, and insignificant restructuring of the rhythmical activity under conditions of "open eyes" as compared with the "closed eyes". In the resting EEG of highly intelligent teen-agers beta-frequencies were more expressed and desynchronization after opening the eyes was clearly detectable.

Adolescent↗
PubMedDate not supplied

Analysis of electrically induced reentrant circuits in a sheet of myocardium.

Understanding the complex spatiotemporal dynamics of action potential propagation in the heart during arrhythmia is exceedingly difficult. This study applies nonlinear dynamics tools to simplify this task. Using the results of a simulation of an electrical induction of reentry in a sheet of myocardium represented as a bidomain, transmembrane voltage maps are processed to obtain: (i) spatial maps of phase angle and phase singularity trajectories, (ii) state scatter plots, and (iii) spatial maps of even phase resetting, wave fronts and wave tails. Tracking the phase singularities allows us to identify the "seeds" of reentry before the reentrant circuit is formed and to characterize the spatiotemporal evolution of the organizing center of the reentrant circuit. The state scatter plots demonstrate the effect of the shock on the instantaneous state of the system. The spatial maps of even phase resetting allow us to identify the shock-induced excitable gaps (regions of regenerative repolarization) as well as the regions directly activated by the shock. These nontraditional approaches to the analysis of electrophysiological phenomena greatly enhance our ability to conceptualize the dynamics of arrhythmias.

Action Potentials↗
PubMed1999

Nonintegrable dynamics of the triplet-triplet spatiotemporal interaction.

In this paper we examine the coupling of two wave triplets sharing two common modes. The analysis is performed in the solitonic sector of the parameter space where uncoupled solutions departing from linearly unstable homogeneous initial conditions evolve into a collection of regularly interspersed, spatiotemporally localized spikes. The uncoupled system is integrable, but coupling destroys integrability. As coupling grows, energy transfer to smaller spatial scales does appear and becomes faster not only in linearly unstable, but also in linearly stable cases. Chaos in low-dimensional subsystems appears to be responsible for the transfer. We perform a series of numerical tests to verify this idea.

Journal Article↗
PubMed2001

Importance of temporal cues for tactile spatial- frequency discrimination.

While scanning a textured surface with fingers, tactile information is encoded both spatially, by differential activation of adjacent receptors, and temporally, by changes in receptor activation during movements of the fingers across the surface. We used a tactile discrimination task to examine the dependence of human tactile perception on the availability of spatial and temporal cues. Subjects discriminated between spatial frequencies of metal gratings presented simultaneously to both hands. Tactile temporal cues were eliminated by preventing lateral hand movements; tactile spatial cues were eliminated by using gloves with an attached rubber pin. Analysis revealed separation of the subjects into two groups: "spatiotemporal" (ST) and "latent-temporal" (LT). Under normal conditions, the performance of ST subjects was significantly better than that of the LT subjects. Prevention of lateral movements impaired performance of both ST and LT subjects. However, when only temporal cues were available, the performance of ST subjects was significantly impaired, whereas that of the LT subjects either improved or did not change. Under the latter condition, LT subjects changed strategy to scanning with alternating hands, at velocities similar to the velocities normally used by ST subjects. These velocities generated temporal frequencies between 15 and 30 Hz. The LT subjects were unaware of their improved performance. Nine of ten LT subjects significantly improved their performance under normal conditions when trained to scan gratings using alternating hands and velocities similar to those used by ST subjects. We conclude that (1) temporal cues are essential for spatial-frequency discrimination, (2) human subjects vary in the tactile strategies they use for texture exploration, and (3) poor tactile performers can significantly improve by using strategies that emphasize temporal cues.

Adult↗
PubMed1996

Some methods for dynamic analysis of the scalp recorded EEG.

This paper describes methods for quantifying the spatiotemporal dynamics of EEG. Development of these methods was motivated by watching computer-generated animations of EEG voltage records. These animations contain a wealth of information about the pattern of change across time in the voltages observed across the surface of the scalp. In an effort to quantify this pattern of changing voltages, we elected to extract a single quantifiable feature from each measurement epoch, the highest squared voltage among the various electrode sites. Nineteen channels of EEG were collected from subjects using an electrode cap with standard 10-20 system placements. Two minute records were obtained. Each record was sampled at a rate of 200 per second. Thirty seconds of artifact-free data were extracted from each 2 minute record. An algorithm then determined the location of the channel with the greatest amplitude for each 5 msec sampling epoch. We quantified these spatio-temporal dynamics as scalars, vectors and cluster analytic plots of EEG activity for finger tapping, cognitive effort (counting backwards) and relaxation to illustrate the utility of the techniques.

Algorithms↗
PubMed1995

Progressive ideomotor apraxia: evidence for a selective impairment of the action production system.

We report a patient with slowly progressive bilateral limb apraxia associated with an asymmetrical focal degenerative process of the parietal lobes. Clinical assessment of praxis production suggested a striking deficit in controlling the spatiotemporal attributes of purposeful skilled limb movements, consistent with ideomotor apraxia. The precise nature of the action production impairment was further defined by objective three-dimensional computergraphic analysis of transitive movements which demonstrated significant kinematic deficits in spatial accuracy, timing, spatiotemporal coupling, and joint coordination. Gesture comprehension and discrimination were spared. Furthermore, detailed evaluation of the conceptual praxis system revealed that despite an almost complete inability to perform transitive movements accurately, abstract knowledge of tool function and action was remarkably well preserved. The critical dissociation between intact conceptual knowledge of action and impaired movement execution documented in this case points to a fundamental competence/performance dichotomy in apraxia and provides empirical support for cognitive models of praxis that divide the action system into distinct conceptual and production subcomponents. Within this theoretical framework, our patient's severe ideomotor apraxia is interpreted to represent a selective disruption of the action production system.

Apraxias↗
PubMed2006

Analysis and visualization of cell movement in the developing zebrafish brain.

Detailed reconstruction of the spatiotemporal history of embryonic cells is key to understanding tissue formation processes but is often complicated by the large number of cells involved, particularly so in vertebrates. Through a combination of high-resolution time-lapse lineage tracing and antibody staining, we have analyzed the movement of mesencephalic and metencephalic cell populations in the early zebrafish embryo. To facilitate the analysis of our cell tracking data, we have created TracePilot, a software tool that allows interactive manipulation and visualization of tracking data. We demonstrate its utility by showing novel visualizations of cell movement in the developing zebrafish brain. TracePilot (http://www.mpi-cbg.de/tracepilot) is Java-based, available free of charge, and has a program structure that allows the incorporation of additional analysis tools.

Animals↗