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PubMed1989

Spatial autocorrelation analysis of migration and selection.

We test various assumptions necessary for the interpretation of spatial autocorrelation analysis of gene frequency surfaces, using simulations of Wright's isolation-by-distance model with migration or selection superimposed. Increasing neighborhood size enhances spatial autocorrelation, which is reduced again for the largest neighborhood sizes. Spatial correlograms are independent of the mean gene frequency of the surface. Migration affects surfaces and correlograms when immigrant gene frequency differentials are substantial. Multiple directions of migration are reflected in the correlograms. Selection gradients yield clinal correlograms; other selection patterns are less clearly reflected in their correlograms. Sequential migration from different directions and at different gene frequencies can be disaggregated into component migration vectors by means of principal components analysis. This encourages analysis by such methods of gene frequency surfaces in nature. The empirical results of these findings lend support to the inference structure developed earlier for spatial autocorrelation analysis.

Computer Simulation↗
PubMed1993

EEG/EP: new techniques.

The topographic analysis of electrical brain activity consists of the extraction of quantitative features which adequately describe the scalp recorded electrical fields of the brain. In the beginning of brain electrical activity mapping most methods centered mainly around the graphical display of multichannel EEG and evoked potential data. Meanwhile quantitative analysis strategies have been developed, and such methods are applied to topographic EEG and evoked potential data enabling the statistical evaluation of the effects of different experimental conditions as well as the comparison of various clinical populations. Major new analysis techniques comprise the computation of global field power and global dissimilarity for determination of components of evoked potential fields, the segmentation of map series by topographical features, time range analysis, FFT approximation for the spatial analysis of EEG frequency bands as well as correlation analysis and spatial principal components analysis (Spatial PCA). Data from experiments dealing with evoked brain activity will illustrate the application of these quantitative methods that also can be used for the analysis of the spontaneous EEG.

Brain↗
PubMed1993

Fluorescence photobleaching with spatial Fourier analysis: measurement of diffusion in light-scattering media.

A new method for the measurement of diffusion in thick samples is introduced, based upon the spatial Fourier analysis of Tsay and Jacobson (Biophys. J. 60: 360-368, 1991) for the video image analysis of fluorescence recovery after photobleaching (FRAP). In this approach, the diffusion coefficient is calculated from the decay of Fourier transform coefficients in successive fluorescence images. Previously, the application of FRAP in thick samples has been confounded by the optical effects of out-of-focus light and scattering and absorption by the sample. The theory of image formation is invoked to show that the decay rate is the same for both the observed fluorescence intensity and the true concentration distribution in the tissue. The method was tested in a series of macromolecular diffusion measurements in aqueous solution, in agarose gel, and in simulated tissue consisting of tumor cells (45% v/v) and blood cells (5% v/v) in an agarose gel. For a range of fluorescently labeled proteins (MW = 14 to 600 kD) and dextrans (MW = 4.4 to 147.8 kD), the diffusion coefficients in aqueous solution were comparable to previously published values. A comparison of the spatial Fourier analysis with a conventional direct photometric method revealed that even for the weakly scattering agarose sample, the conventional method gives a result that is inaccurate and dependent on sample thickness whereas the diffusion coefficient calculated by the spatial Fourier method agreed with published values and was independent of sample thickness. The diffusion coefficient of albumin in the simulated tissue samples, as determined by the spatial Fourier analysis, varied slightly with sample thickness. In contrast, when the same video images were analyzed by direct photometric analysis, the calculated diffusion coefficients were grossly inaccurate and highly dependent on sample thickness. No simple correction could be devised to ensure the accuracy of the direct photometric method of analysis.These in vitro experiments demonstrate the advantage of our new analysis for obtaining an accurate measure of the local diffusion coefficient in microscopic samples that are thick (thickness greater than the microscope depth of focus) and scatter light.

Biopolymers↗
PubMed2001

Spatial distribution analysis on climatic variables in northeast China.

Information ecology is a new research area of modern ecology. Here describes the spatial distribution analysis methods of four sorts of climatic variables, i.e. temperature, precipitation, relative humidity and sunshine fraction in Northeast China. First, digital terrain models was built with large-scale maps and vector data. Then trend surface analysis and interpolation method were used to analyze the spatial distribution of these four kinds of climatic variables at three temporal scale: (1) monthly data; (2) mean monthly data of thirty years, and (3) mean annual data of thirty years. Ecological information system were used for graphics analysis on the spatial distribution of these climatic variables.

Algorithms↗
PubMed2003

Space, place and movement as aspects of health care in three women's prisons.

This paper focuses on prison as a place in which the prisoner seeks health and health services. Drawing on the work of Henri LeFebvre, Edward Casey, Jeffrey Malpas, and Michel Foucault, a spatial analysis examines the constitutive roles of movement, social structure, and power in determining the prisoner's access to health care. The research methodology utilizes quantitative and qualitative analysis of women prisoners' attempts to get treatment for their health problems. The narratives of these often-failed attempts construct prison as a place where health care access is continually thwarted by rules, custodial priorities, poor health care management, incompetence, and indifference. Analysis of spatial practices, representations of space, and spaces of representation demonstrate the imposition of structural ordering, its naturalization, and the role of narrative in questioning the order, thereby creating possibilities for imaginary and real places where the prisoners' health needs can be met. Simultaneously, this analysis illuminates basic ethical questions about the limitations of human connection and medical caring in prison settings, regardless of the personal motivation of the caregiver.

Adult↗
PubMed1995

Disease models implicit in statistical tests of disease clustering.

State and local health departments investigate an increasing number of cluster allegations, for which the selection of appropriate statistical methods is an important problem. Many of the methods for the spatial analysis of health data assume, either implicitly or explicitly, some model of disease occurrence, and comparisons of methods can be difficult when their underlying disease models differ. We review some of the issues involved in the statistical analysis of spatial disease patterns and describe several methods recently proposed to detect areas of increased disease rates. The disease models upon which the methods are based are explicitly described, and they provide a useful basis for comparing alternative clustering methods.

Cluster Analysis↗
PubMed2001

Statistical analysis of spatial pattern: a comparison of grid and hierarchical sampling approaches.

Previous studies have combined random-site hierarchical sampling designs with analysis of variance techniques, and grid sampling with spatial autocorrelation analysis. We illustrate that analysis techniques and sampling designs are interchangeable using densities of an infaunal bivalve from a study in Poverty Bay, New Zealand. Hierarchical designs allow the estimation of variances associated with each level, but high-level factors are imprecisely estimated, and they are inefficient for describing spatial pattern. Grid designs are efficient for describing spatial pattern, and are amenable to conventional analysis. Our example deals with a continuous spatial habitat, but our conclusions also apply in disjunct or patchy habitats. The influence of errors in positioning is also assessed. The advantages of systematic sampling are reviewed, and more efficient hierarchical approaches are identified. The distinction between biological and statistical significance in all analyses is emphasised.

Animals↗
PubMed1994

Epidemiologic analysis of spatial clustering of bovine ephemeral fever outbreaks. II. Principal component analysis.

The principal component analysis (PCA) was applied to analyze a correlation matrix of three variables on epidemic data of bovine ephemeral fever (BEF) outbreaks. These original data were summarized from the official outbreak report of Fukuoka Prefecture. The first and the second principal components of the PCA were interpreted as the infectious potency due to BEF virus and the prevention against BEF virus infection, respectively. The BEF outbreak areas were able to be classified epidemically into 4 groups by using the two principal components. The valuable epidemiological insights can be reasonably obtained from an application of the PCA. The results provided an important information for a further BEF vaccination campaign in the western part of Japan.

Animals↗
PubMed1995

The use of geographical information systems in studies on environment and health.

Geographical information systems (GIS) provide a powerful technology for the spatial analysis of environmental and health data. Major areas of application include the assessment and mapping of environmental exposure, mapping of health outcome, and the analysis of spatial relationships between environment and health. The use of GIS nevertheless brings with it many potential problems and pitfalls. This article reviews some of the recent applications in relation to studies of environment and health, and examines some of the research issues involved.

Bias↗
PubMed1997

[Characteristics of neonatal mortality in the State of Rio de Janeiro, Brazil, in the 1980's: a spatio-temporal analysis].

OBJECTIVE: The spatial distribution of neonatal mortality by age-group (0-23 hours, 1-6 days and 7-27 days) in the State of Rio de Janeiro, Brazil, for two periods of time 1979-81 and 1990-92, is analysed. METHODOLOGY: A methodology was used to perform the spatial analysis which took the counties of Rio de Janeiro as the spatial units and "first-nearest-neighbors" as the neighborhood criterion. For the purpose of detecting anisotropy, the connection matrix was defined through "first-nearest-neighbors" in a particular direction. To understand the spatial behavior of neonatal mortality, social and environmental indicators and indicators of medical assistance by county for both periods of time were constructed. RESULTS AND CONCLUSIONS: At the beginning of the 80's, the neonatal mortality for the age group 7-27 days showed the presence of clusters in the East and Southeast in direct association with the poorest conditions of life in the State, characteristics that had vanished by the next decade. Spatial dependence for the mortality rates for the first day of life, for 1991, was identified clusters in two different regions beings detected, followed by a positive correlation with "number of private hospital beds per inhabitant". Some of the cluster counties were, in particular, death receivers from neighboring counties and showed hospital case fatality rates much greater than the overall mean rate.

Anisotropy↗
PubMed2000

Local stability analysis of spatially homogeneous solutions of multi-patch systems.

Multi-patch systems, in which several species interact in patches connected by dispersal, offer a general framework for the description and analysis of spatial ecological systems. This paper describes how to analyse the local stability of spatially homogeneous solutions in such systems. The spatial arrangement of the patches and their coupling is described by a matrix. For a local stability analysis of spatially homogeneous solutions it turns out to be sufficient to know the eigenvalues of this matrix. This is shown for both continuous and discrete time systems. A bookkeeping scheme is presented that facilitates stability analyses by reducing the analysis of a k-species, n-patch system to that of n uncoupled k-dimensional single-patch systems. This is demonstrated in a worked example for a chain of patches. In two applications the method is then used to analyse the stability of the equilibrium of a predator-prey system with a pool of dispersers and of the periodic solutions of the spatial Lotka-Volterra model.

Animals↗
PubMedDate not supplied

Linear filtering and nonlinear interactions in direction-selective visual cortex neurons: a noise correlation analysis.

Spatial and temporal properties related to direction selectivity of both simple and complex type visual cortex neurons were assessed by cross-correlation analysis of their responses to random ternary white noise. This stimulus consisted of multiple randomly placed bars, each colored white, black, or gray with equal probability, which were rerandomized every 5-10 ms. A first-order cross-correlation analysis of a neuron's spike train with the spatiotemporal history of the stimulus provided an estimate of the neuron's linear spatiotemporal filtering properties. A nonlinear correlation analysis measured the amount of interaction for pair-wise combinations of bars as a function of their relative spatial and temporal separations. The spatiotemporal orientation of each of these functions was quantified using a "motion energy index" (MEI), which was compared to the neurons' direction selectivity measured with drifting sinewave gratings. Both first-order and nonlinear correlation plots usually showed s-t orientation whose sign was consistent with the neuron's direction preference; however, in many cases the MEI for first-order analysis was weak compared to that seen in the nonlinear interactions. The structures of the nonlinear interaction functions were also compared with predictions from a conventional model of direction selectivity based on a simple spatiotemporally oriented linear filter, followed by an intensive nonlinearity ("LN model"). These comparisons showed that some neurons' data agreed reasonably well with such a model, while others agreed poorly or not at all. Simulations of an alternative model which combines signals from idealized lagged and nonlagged front-end linear filters produce noise correlation results more like those seen in the neurophysiological data.

Animals↗
PubMed1988

The effect of exposure duration on the analysis of spatial structure in eccentric vision.

There is some evidence from grating experiments that the transient presentation of a stimulus pattern interferes with the encoding of positional relationships between pattern elements (i.e. the analysis of spatial structure) more in eccentric vision than in central vision. The present study investigated the effect of exposure duration on the analysis of spatial structure in eccentric vision using a task in which the observer discriminated between two mirror symmetric patterns consisting of short line segments. In each trial, the two patterns were flashed for 140 or 500 ms, and the observer had to decide whether the patterns were identical or mirror symmetric. Both constant-size and size-scaled patterns were used in eccentric vision. The longer exposure duration slightly increased the proportion of correct responses in eccentric vision but performance remained distinctly inferior to that in central vision.

Humans↗
PubMed2001

Spatial data analysis by epidermal Langerhans cells reveals an elegant system.

Langerhans cells are dendritic cells situated in the mammalian epidermis. In human epidermis, the concentration is between 460 and 1000 mm(-2). Langerhans cells fulfill an essential role in skin immune responses. Numerous scientific reports on Langerhans cells have appeared, but with no systematic research on the pattern of the spatial distributions. On the contrary, in certain fields, a spatial distribution is an important theme, and spatial data analysis has a long history. We hypothesized that epidermal Langerhans cells were set in the best formation for their immuno-surveillance by a sophisticated mechanism. To prove this hypothesis, we have imported spatial data analysis into the study of epidermal Langerhans cells. Here, we show that the distribution is completely regular; the pattern of Voronoi divisions fits the territories; the random packing model simulates their bone marrow derivation; a repulsive interaction is demonstrated and a repulsive potential function is estimated. Spatial data analysis-based computer simulation will be a new method of Langerhans cell study. In addition, this procedure shows promise for future distribution research of certain cells.

Animals↗
PubMed2000

Spatial correlation analysis of the pharmacological conversion of sustained atrial fibrillation in conscious goats by cibenzoline.

The nonlinear spatial redundancy and the linear spatial correlation function were used to investigate to what extent non-linearity was involved in the coupling of atrial regions and how organization in activation patterns of sustained atrial fibrillation (AF) had been modified by administration of the class IC agent cibenzoline in the experimental model of sustained AF in instrumented conscious goats. Electrograms were measured in five goats during sustained AF and when the fibrillation interval had been prolonged to about 25%, 50% and 85% (CIB25, CIB50, CIB85) with respect to control. The nonlinear association length and linear correlation length were estimated along the principal axes of two-dimensional correlation maps estimated from the spatial redundancy and the spatial correlation function, respectively. The estimated short axis association length in the right atrium increased already shortly after the start of infusion (CIB25, +61%), and remained significantly different from control during the experiment, including the effects of non-simultaneous interaction. At CIB85 the association length had almost become twice as long with respect to control (increase from 16 to 29 mm, 89%), while in the left atrium changes were less pronounced (increase from 9 to 12 mm, +32%). The linearized association length which was estimated using multivariate surrogate data increased more gradually and was less sensitive to changes in spatial organization. The results of the spatial correlation analysis suggest that the drug-induced nonlinearity in the spatio-temporal dynamics of sustained AF is related to activation patterns which are characterized by extended uniformly propagating fibrillation wavefronts (AF type I). We conclude that cibenzoline enhanced the spatial organization of sustained AF associated with a transition from type II to type I AF activation patterns. This may destabilize the perpetuation of AF since an increase in association length is equivalent to a reduction of atrial tissue mass available to support reentrant circuits. The results are consistent with the hypothesis that larger association lengths result from fewer and larger reentrant circuits. It is argued that effects of diminished curvature of fibrillation wavefronts are anti-arrhythmic under conditions of suppressed excitability imposed by cibenzoline. Termination of AF may be mediated by a mechanism resembling a bifurcation of the dynamics which sets in when the ends of fractionated wavefronts cannot sufficiently curve anymore to maintain a positive balance of newly generated wavelets needed to sustain AF.

Animals↗
PubMed1995

Spatial autocorrelation analysis reveals that A, B and O allele frequency surfaces on the Indian subcontinent are highly fractured.

Spatial autocorrelation analysis performed on published data pertaining to caste and tribal populations of the Indian subcontinent has revealed that the surfaces of A, B and O allele frequencies are highly fractured. The only significant spatial autocorrelation was observed in respect of the A allele frequency among caste populations.

ABO Blood-Group System↗
PubMed1987

Diversity of some gene frequencies in European and Asian populations. III. Spatial correlogram analysis.

The gene frequencies at eight loci in some European and Asian human populations have been subjected to spatial autocorrelation analysis, using Geary's c coefficient. Contrary to what is expected for markers affected only by gene flow and genetic drift, the spatial correlograms show distinct modes of gene frequency variation: there are significant clinal patterns (at the GLO and ESD loci), significant non-clinal patterns (AK, ADA, 6-PGD and GPT) and marginally significant patterns (PGP and SOD). Any hypothesis on the evolution of these polymorphisms should account for the observed heterogeneity of their geographical distributions.

Asia↗
PubMed1983

The boundary value problem in spatial statistical analysis.

"The primary objective of this paper is to investigate procedures for detecting and handling existing border biasing in spatial statistical analysis." Six conventional solutions to the boundary value problem are criticized, and three alternate statistical solutions are proposed.

Demography↗