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Results for “Spatial Analysis”

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At least 1,207 records · Page 67Linked to original sources
PubMed1978

[Multimeasurement analysis of the quantitative spatial organization of epicardial lymphatic capillaries under normal conditions].

Principles of quantitative-spatial organization of the epicardial lymphatic capillaries have been studied in 26 normal dogs' hearts. Multimeasurable systemic models have been constructed to demonstrate how quantitative indices of metrical properties of the capillaries depend on the cardiac size. The possibility is discussed to apply the data obtained in the study of microcirculatory pathology of different genesis.

Animals↗
PubMed1998

A new concept for EEG/MEG signal analysis: detection of interacting spatial modes.

We propose a new concept for analyzing EEG/MEG data. The concept is based on a projection of the spatiotemporal signal into the relevant phase space and the interpretation of the brain dynamics in terms of dynamical systems theory. The projection is obtained by a simultaneous determination of spatial modes and coefficients of differential equations. The resulting spatiotemporal model can be characterized by stationary points and corresponding potential field maps. Brain information processing can be interpreted by attraction and repulsion of spatial field distributions given by these stationary points. This allows an objective and quantitative characterization of the brain dynamics. We outline this concept and the underlying algorithm. Results of the application of this method to an event related potential (ERP) study of auditory memory processes are discussed.

Algorithms↗
PubMed1998

Spatial and temporal pattern analysis via spiking neurons.

Spiking neurons, receiving temporally encoded inputs, can compute radial basis functions (RBFs) by storing the relevant information in their delays. In this paper we show how these delays can be learned using exclusively locally available information (basically the time difference between the pre- and postsynaptic spikes). Our approach gives rise to a biologically plausible algorithm for finding clusters in a high-dimensional input space with networks of spiking neurons, even if the environment is changing dynamically. Furthermore, we show that our learning mechanism makes it possible that such RBF neurons can perform some kind of feature extraction where they recognize that only certain input coordinates carry relevant information. Finally we demonstrate that this model allows the recognition of temporal sequences even if they are distorted in various ways.

Action Potentials↗
PubMed1995

Magnitude of sex differences in spatial abilities: a meta-analysis and consideration of critical variables.

In recent years, the magnitude, consistency, and stability across time of cognitive sex differences have been questioned. The present study examined these issues in the context of spatial abilities. A meta-analysis of 286 effect sizes from a variety of spatial ability measures was conducted. Effect sizes were partitioned by the specific test used and by a number of variables related to the experimental procedure in order to achieve homogeneity. Results showed that sex differences are significant in several tests but that some intertest differences exist. Partial support was found for the notion that the magnitude of sex differences has decreased in recent years. Finally, it was found that the age of emergence of sex differences depends on the test used. Results are discussed with regard to their implications for the study of sex differences in spatial abilities.

Aptitude↗
PubMed1995

Geographic variation analysis of the ABO and RH systems in Turkey.

In this study, we report the results of a geographical variation analysis on the gene frequencies of ABO and RH systems in 67 provinces of Turkey. The gene frequencies of A, O and RH(-), were subjected to spatial autocorrelation analysis and significant spatial autocorrelation coefficients were observed for each gene in the first distance class. The average I-correlogram for the three genes displayed a clinal pattern. The results also suggested a marked decrease in genetic similarity in relation to geographic distance.

ABO Blood-Group System↗
PubMed1995

Disease risk near point sources: statistical issues for analyses using individual or spatially aggregated data.

STUDY OBJECTIVE: To examine the statistical issues involved in the analysis of disease risk near point sources of environmental pollution, where data are held at both the individual and group (areal) level. To explore these issues with reference to possible socioeconomic confounding. DESIGN: Statistical review. SETTING: Point sources of environmental pollution. MAIN RESULTS: Except in very specific circumstances unlikely to hold in practice, aggregation of data to the areal level will lead to bias in the estimation of disease risk. CONCLUSIONS: There is no easy solution to the analysis of spatial data when some covariates (for example, age and sex of cases) are known at individual level, whereas others (for example, populations, age-sex distributions, small area deprivation indices) are known only at the areal (ecological) level. The underlying assumptions inherent in the analysis of these data need to be explicitly recognised in order to understand better the limitations of the available methodology as well as to inform interpretation of results. Ideally, the data should be kept as disaggregated as possible, to maximise the information available and minimise potential for bias.

Bias↗
PubMed2004

Spatial filters based on independent component analysis for magnetic noise reduction in the magnetocardiogram.

A spatial filter design method to reduce magnetic noise in the magnetocardiogram (MCG) is introduced. Based on the facts that external magnetic noise appearing on multichannel MCG sensors is independent of the cardiac signals and that there is strong spatial correlation among the channels, the independent component analysis (ICA) method was applied to extract the noise components from the measured MCG signals. After extraction of the noise components in a given time period using ICA, a spatial filter was made to reduce the noise components in subsequently acquired MCG signals. In experimental studies of nine healthy volunteers, the spatial filters improved the signal-to-noise ratio of the MCG signals by about 500% on average. This spatial filtering method can be used for measurements of MCG signals in a magnetically noisy environment.

Artifacts↗
PubMed2005

Generalized spatial structural equation models.

It is common in public health research to have high-dimensional, multivariate, spatially referenced data representing summaries of geographic regions. Often, it is desirable to examine relationships among these variables both within and across regions. An existing modeling technique called spatial factor analysis has been used and assumes that a common spatial factor underlies all the variables and causes them to be related to one another. An extension of this technique considers that there may be more than one underlying factor, and that relationships among the underlying latent variables are of primary interest. However, due to the complicated nature of the covariance structure of this type of data, existing methods are not satisfactory. We thus propose a generalized spatial structural equation model. In the first level of the model, we assume that the observed variables are related to particular underlying factors. In the second level of the model, we use the structural equation method to model the relationship among the underlying factors and use parametric spatial distributions on the covariance structure of the underlying factors. We apply the model to county-level cancer mortality and census summary data for Minnesota, including socioeconomic status and access to public utilities.

Bayes Theorem↗
PubMed2001

Analysing spatially referenced public health data: a comparison of three methodological approaches.

In the analysis of spatially referenced public health data, members of different disciplinary groups (geographers, epidemiologists and statisticians) tend to select different methodological approaches, usually those with which they are already familiar. This paper compares three such approaches in terms of their relative value and results. A single public health dataset, derived from a community survey, is analysed by using 'traditional' epidemiological methods, GIS and point pattern analysis. Since they adopt different 'models' for addressing the same research question, the three approaches produce some variation in the results for specific health-related variables. Taken overall, however, the results complement, rather than contradict or duplicate each other.

Adult↗
PubMed2003

Cerebral lateralization of spatial abilities: a meta-analysis.

There is a substantial disagreement in the existing literature regarding which hemisphere of the brain controls spatial abilities. In an attempt to resolve this dispute, we conducted a meta-analysis to decipher which hemisphere truly dominates and under what circumstances. It was found that across people and situations, the right hemisphere is the more dominant for spatial processing. However, consideration of specific moderator variables yielded a more complex picture. For example, females showed no hemisphere preference while males showed a right hemisphere advantage. Also, no hemisphere preference was indicated for spatial visualization tasks while subjects performing spatial orientation and manual manipulation tasks displayed a predictable right hemisphere preference. These findings are discussed in terms of their implications for exiting theoretical positions as well as future empirical research.

Brain↗
PubMed2005

Mastering time and space: immune cell polarization and chemotaxis.

Many immune cells can detect the direction and intensity of an extracellular chemical gradient, and migrate toward the source of stimulus. This process, called chemotaxis, is essential for immune system function and homeostasis, and its deregulation is associated with serious diseases. Chemotaxis is initiated by chemoattractant binding to heterotrimeric G protein-coupled receptors, which translate the gradients into accurate directional migration. A necessary step in this process is cell polarization, the acquisition of functional and spatial asymmetry. The use of new imaging technologies enables analysis of spatial and temporal changes in the activity of proteins and membrane domains involved in polarization and chemotaxis. We discuss the sometimes contradictory evidence available and the emerging molecular model for immune cell polarity and chemotaxis.

Animals↗