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At least 307 records · Page 17Linked to original sources
PubMed2004

A preliminary report on the role of spatial frequency analysis in the perception of breast cancers missed at mammography screening.

RATIONALE AND OBJECTIVES: Because several factors are involved in cancer detection, a malignant lesion that is visible on a mammogram will not necessarily be reported by the radiologist reading the case. Indeed, a significant fraction of screening-detected cancers are visible in retrospect, and were perceived by the radiologist when the case was read, but were either reported as benign findings or dismissed as variations of normal breast tissue. In this preliminary report the spatial frequency characteristics of clinically missed lesions are investigated by analyzing the mammogram acquired when the lesion was sent for biopsy and the most recent prior mammogram. For control purposes, the contralateral breast is also analyzed, when this breast is lesion free. MATERIALS AND METHODS: A database of 70 mammogram cases was assembled. Each case contained eight films: craniocaudal (CC) and mediolateral oblique (MLO) of the breast where a biopsy-proven lesion was found, CC and MLO of the contralateral breast, and CC and MLO of both breasts in the most recent prior mammogram. The dictated reports for all of these cases were obtained. Both benign and malignant lesions were used. The films were digitized and an region of interest surrounding each lesion was segmented from the image for processing using wavelet packets to extract spatial frequency information. The corresponding area was also segmented from the prior mammogram and from the contralateral breast, when this breast was lesion-free. Analysis of variance was used to determine if statistically significant differences existed between the derived features of cancer in the current and prior mammograms. RESULTS: The data suggests that malignant lesions reported in the prior mammogram as being benign differed from correctly reported malignant lesions and from correctly reported benign lesions. They also differed from nonreported malignant lesions. In addition, the spatial frequency representation of cancer significantly differed in the current and prior cases from the representation of normal breast tissue. CONCLUSION: Spatial frequency analysis may be useful to differentiate malignant lesions that are reported as benign and correctly reported benign lesions.

Algorithms↗
PubMed2004

Spatial and temporal analysis of the local response to wounding in Arabidopsis leaves.

We studied the local response to wounding in Arabidopsis thaliana leaves using a two-step microarray analysis. A microarray containing 3500 cDNA clones was first screened to enrich for genes affected by wounding in the immediate vicinity of the wound (4 h post wounding). 359 non-redundant putative wound responsive genes were then spotted on a smaller wound-response array for detailed analysis of spatial expression (local, adjacent and systemic), timing of expression (0.5, 4, 8, 17 h), and effect of hormone treatments (methyl jasmonate, ethylene and abscisic acid). Our results show that genes that respond early at the site of the wound also respond throughout the plant, with similar kinetics. Early-induced genes which respond systemically encode predominantly signal transduction and regulatory factors (36%), and the expression of many of them is also controlled by methyl jasmonate (about 35% of the 36%). Genes specific to the wound site and the wounded leaf have a slower response to wounding and are mainly metabolic genes. At the wound, many genes of the lignin biosynthesis pathway were induced. In silico analysis of the 5' promoter regions of genes affected by wounding revealed G-box-related motifs in a significant proportion of the promoters. These results show that the establishment of a systemic response to wounding is a priority for the plant, and that the local response at the wound site is established later. Ethylene and abscisic acid are involved in the local response, regulating repression of photosynthetic genes and expression of drought responsive genes respectively.

Abscisic Acid↗
PubMed2000

Analysis of spatial patterns of phase in neocortical gamma EEGs in rabbit.

Arrays of 64 electrodes (8 x 8, 7 x 7 mm) were implanted epidurally on the surface of the visual, auditory or somatosensory cortex of rabbits trained to discriminate conditioned stimuli in the corresponding modality. The 64 electroencephalographic (EEG) traces at all times displayed a high degree of spatial coherence in wave form, averaging >90% of the variance in the largest principal components analysis component. The EEGs were decomposed with the fast Fourier transform (FFT) to give the spatial distributions of amplitude and phase modulation (AM and PM) in segments 128 ms in duration. Spatial (2-dimensional) and temporal (1-dimensional) filters were designed to optimize classification of the spatial AM patterns in the gamma range (20-80 Hz) with respect to discriminative conditioned stimuli. No evidence was found for stimulus-dependent classification of the spatial PM patterns. Instead some spatial PM distributions conformed to the pattern of a cone. The location and sign (maximal lead or lag) of the conic apex varied randomly with each recurrence. The slope of the phase gradient varied in a range corresponding to that of the conduction velocities reported of axons to extend parallel to the cortical surfaces. The durations and times of recurrence of the phase cones corresponded to those of the optimally classified spatial AM patterns. The interpretation is advanced that the phase cones are manifestations of state transitions in the mesoscopic dynamics of sensory cortices by which the intermittent AM patterns are formed. The phase cones show that the gamma EEG spatial coherence is not due to volume conduction from a single deep-lying dipole generator nor to activity at the site of the reference lead on monopolar recording. The random variation of the apical sign shows that gamma AM patterns are self-organized and are not imposed by thalamic pacemakers. The half-power radius of the phase gradient provides a useful measure of the soft boundary condition for the formation and read-out of cooperative cortical domains responsible for binding sensory information into the context of prior experience in the process of perception.

Animals↗
PubMedDate not supplied

[Etiology, occurrence and types of the internal carotid artery loop].

Internal carotid loop was studied in 99 patients out of 1638 cases subjected to angiography. The presence of a loop was arbitrarily accepted when in the tortuous part of the artery one of its segments was situated below the preceding segment. For the spatial analysis of the tortuous part of the artery and its image in the plane of the radiogram a model was used simulating various variants of the course of the internal carotid artery. On the ground of the analysis of the spatial configuration of the arterial loops and the variability of the loop model in the plane of the radiogram six types of the loop were isolated. The loops were found in 9.2% of patients with bilateral angiography and 5.7% of those with unilateral angiography. In adults the loop was present in 5.4% of cases, and in children in 8.9% (statistically significant difference p less than 0.05). It is assumed that the loop in children is a congenital anomaly, while in adulthood besides the congenital etiology an acquired form of the loop is to be taken into account.

Adolescent↗
PubMed2002

Electrophysiology of spatial scene analysis: the mismatch negativity (MMN) is sensitive to the ventriloquism illusion.

OBJECTIVES: The ventriloquism effect is the tendency to underestimate the spatial separation between synchronous auditory and visual signals moderately separated in space. If, as it is thought, this effect is pre-attentive, it could modulate the mismatch negativity (MMN) that indexes the automatic, pre-attentive detection of deviant auditory stimuli rarely occurring in a sequence of standard stimuli. We assessed the existence of an MMN evoked by auditory and visual signals made up of standard sounds coming from the same location as the visual signal and deviant sounds coming from lateral deviations (20 or 60 degrees). As first observed in a behavioral study, a ventriloquism effect occurred for 20 degrees spatial separation but not for 60 degrees. METHODS: Cortical evoked potentials were recorded using the oddball paradigm on 8 adults in auditory alone and audiovisual conditions. RESULTS: In the auditory alone condition, each spatial localization contrast elicited a significant MMN. In the audiovisual condition, a significant MMN was only evoked for the 60 degrees contrasts. CONCLUSIONS: The MMN evoked by spatial separation contrasts (20 and 60 degrees) in the auditory alone condition was suppressed by the corresponding audiovisual condition only when the latter yielded a ventriloquism effect, suggesting that this effect occurs at an early perceptual level.

Acoustic Stimulation↗
PubMed1997

Spatial statistical analysis of Chinese cancer mortality: a comparison study of the D statistic.

In this paper, we study a nonparametric spatial pattern test statistic, the D statistic. The D statistic is an effective test statistic for testing spatial patterns in regional health data. Comparison studies of the D statistic with fixed weights and random weights are illustrated on the atlas of the Chinese cancer mortality rates and on other cancer atlas. Some social, economic and environmental reasons for statistically significant spatial autocorrelations of the Chinese cancer mortality rates were given in the discussion section. The method for calculating the mean and the variance of the randomly weighted D statistic is given in the appendix.

China↗
PubMed1981

Cortical anatomy, size invariance, and spatial frequency analysis.

In a recent application of an algorithm developed in computer and optical pattern recognition, Cavanagh has suggested that a composite of spatial frequency mapping and complex logarithmic mapping would provide translationally, rotationally, and size-invariant mechanism for human vision. In this work, Cavanagh has not made explicit the fact that this transformation is composite, that is, that the first step (global Fourier analysis) perceptually, anatomically, and physiologically inconsistent with primate vision, but that the second step (complex logarithmic mapping) is actually embodied in the anatomy of the primate retinostriate projection. Moreover, it is the complex logarithmic remapping step which is entirely responsible for the computational simplification of the symmetries of size and rotation invariance. These facts, which have been extensively discussed in a recent series of papers, are briefly reviewed and illustrated. Furthermore, it is shown that the architecture of the retinostriate map may provide an example of computational anatomy in vision, such that the spatial representation of a stimulus in the brain may be of direct functional significance to perception, and to the nature of certain visual illusions.

Afterimage↗
PubMed2000

Spatial correlation analysis of atrial activation patterns during sustained atrial fibrillation in conscious goats.

In this study we applied both linear and nonlinear spatial correlation measures to characterize epicardial activation patterns of sustained atrial fibrillation in instrumented conscious goats. It was investigated if nonlinearity was involved in the spatial coupling of atrial regions and to what extent fibrillation was organized in the experimental model of sustained atrial fibrillation (AF) in instrumented goats. Data were collected in five goats during experiments to convert AF by continuous infusion of cibenzoline. Spatial organization during AF was quantified with the linear spatial cross correlation function and the nonlinear spatial cross redundancy which was calculated using the Grassberger-Procaccia correlation integral. Two different types of correlation were evaluated to distinguish simultaneous interaction from non-simultaneous interaction, for instance resulting from propagation of fibrillation waves. The nonlinear association length and the linear correlation length were estimated along the principal axes of iso-correlation contours in two-dimensional correlation maps of the nonlinear spatial redundancy and the linear spatial correlation function, respectively. To quantitatively assess the degree of nonlinearity, the association length was also estimated from the linearized spatial redundancy using multivariate surrogate data. The differences between the nonlinear and linearized association lengths indicated that a nonlinear component in the spatial organization of AF predominantly existed in the right atrium. The degree of organization characterized by association length along the short principal axis was higher in the right atrium (15 +/- 7 mm) than in the left atrium (8 +/- 4 mm). The spatial extension of coherent atrial patches was estimated from a surface of association equal to the area spanned by the principal axes of iso-correlation contours from the redundancy, including the effects from non-simultaneous interaction. Interpreting this area as the spatial domain of a fibrillation wavelet, the results suggest that the mapped region was activated on average by two wavelets in the left atrium and by one wavelet in the right atrium. Therefore, the activation pattern of sustained AF in goats was relatively organized, consistent with type II of AF. It is suggested that the surface of association is a measure of the number of independent wavelets present in the atria during sustained AF, and that larger association lengths result from fewer and larger reentrant circuits.

Animals↗
PubMed2003

Genetic analysis of spatial foraging patterns and resource sharing in bumble bee pollinators.

Conservation biologists, evolutionary ecologists and agricultural biologists require an improved understanding of how pollinators utilize space and share resources. Using microsatellite markers, we conducted a genetic analysis of space use and resource sharing at several spatial scales among workers of two ecologically dissimilar bumble bee species (Bombus terrestris and B. pascuorum) foraging in an urban landscape (London, UK). At fine scales, the relatedness of workers visiting small patches of flowers did not differ significantly from zero. Therefore, colonies shared flower patches randomly with other colonies, suggesting that worker scent-marks deterring visits to unrewarding flowers have not evolved as signals benefiting nestmates. To investigate space use at intermediate scales, we developed a program based on Thomas & Hill's maximum likelihood sibship reconstruction method to estimate the number of colonies utilizing single sites. The average number of colonies (95% confidence limits) sending workers to forage at sites of approximately 1 ha in area was 96 colonies (84-118) in B. terrestris and 66 colonies (61-76) in B. pascuorum. These values are surprisingly high and suggested that workers travelled far from their colonies to visit the sites. At the landscape scale, there was little or no genetic differentiation between sites. We conclude that urban habitats support large bumble bee populations and are potentially valuable in terms of bumble bee conservation. In addition, bumble bee-mediated gene flow in plants is likely to occur over large distances and plant-bumble bee conservation requires landscape-scale action.

Alleles↗
PubMed1994

Cartographic system for spatial distribution analysis of corneal endothelial cells.

A combined cartographic and morphometric endothelium analyser has been developed by integrating the HISTO 2000 histological imaging and analysis system with a prototype human corneal endothelium analyser. The complete system allows the elaboration and analysis of cartographies of corneal endothelial tissue, and hence the in vitro study of the spatial distribution of corneal endothelial cells, according to their regional morphometric characteristics (cell size and polygonality). The global cartographic reconstruction is obtained by sequential integration of the data analysed for each microscopic field. Subsequently, the location of each microscopically analysed field is referred to its real position on the histologic preparation by means of X-Y co-ordinates; both are provided by micrometric optoelectronic sensors installed on the optical microscope stage. Some cartographies of an excised human corneal keratoconus button in vitro are also presented. These cartographic images allow a macroscopic view of endothelial cells analysed microscopically. Parametric colour images show the spatial distribution of endothelial cells, according to their specific morphometric parameters, and exhibit the variability in size and cellular shape which depend on the analysed area.

Biomedical Engineering↗
PubMed1986

Event-related potentials of the brain and cognitive processes: approaches and applications.

Event-related potentials (ERPs) are recordings of the electric field which the brain produces in fixed time-relation to an event. ERPs open a time and space window onto covert steps of brain information processing which need not be accompanied by overt behavior or private experiences. ERPs are the only noninvasive method which resolves the dynamic pattern of events in the human brain down to the millisecond range. Early ERP components are valuable tools in clinical testing of the afferent sensory systems in the absence of anamnestic or clinical pathology. Later components (e.g. the 'P300') index intermediate, covert steps of information processing and have clarified the time course and the contingencies of processes in attention, decisions and language. ERP waveshapes show electric potential differences between two recording points. Conventional analysis often ignores the fact that there is no unique voltage amplitude or signal latency for a single point, and interprets ambiguous results. Although important insights have emerged with such strategies, full utilization of ERP data requires unambiguous ERP assessment and converging evidence from neuropsychological and cognitive experimentation. Sequences of field distribution maps offer an unbiased display of ERP data. Spatial analysis yields unambiguous values for further comprehensive assessment, and should precede analysis over time. Examples of spatial analysis have shown that different ERP field configurations follow the presentation of noun and verb meaning of homophone words; that the ERP effects to subjective contours resemble those to attention in time course and topography; that the 'cognitive' P300 component reflects the specific stimulus location; and that subliminal information influences the configuration of late ERP fields.

Attention↗
PubMed1981

A variance components approach to categorical data models with heterogeneous cell populations: analysis of spatial gradients in lung cancer mortality rates in North Carolina counties.

A mixed categorical-continuous variable model is proposed for the analysis of mortality rates. This model differs from other available models, such as weighted least squares and loglinear models, in that the within-cell populations are assumed to be heterogeneous in their levels of mortality risk. Heterogeneity implies that, in addition to the sampling variance considered in other available models, there will be a second component of variance due solely to within-cell heterogeneity. Maximum likelihood procedures are presented for the estimation of the model parameters. These procedures are based on the assumption that the distribution function for each cell death count is the negative binomial probability function. This assumption is shown to be equivalent to assuming a mixture of Poisson processes with the differential risk levels among individuals within each cell being governed by a two-parameter gamma distribution. The model is applied to data on lung cancer mortality for 1970-1975 for the 100 counties of North Carolina. The analysis shows that, though a gradient in lung cancer mortality rates exist in space, the gradient is restricted to specific demographic categories identified by race, age and sex.

Adult↗
PubMed2000

A bayesian analysis for spatial processes with application to disease mapping.

In epidemiology, maps of disease rates and disease risk provide a spatial perspective for researching disease aetiology. For rare diseases or when the population base is small, the rate and risk estimates may be unstable. We propose using a Bayesian analysis based on the conditional autoregressive (CAR) process that will spatially smooth disease rates or risk estimates by allowing each site to 'borrow strength' from its neighbours. Covariates may be included in the model in such a way as to establish a possible association between risk factors and disease incidence. Bayesian inferences are implemented from a direct resampling scheme where large samples are generated from the various posterior distributions. The methodology is demonstrated with a simulation that assesses the effect of sample size and the model parameters on inferences for the parameters. Our approach is also used to spatially smooth district lip cancer rates in Scotland using the CAR model with a covariate that allows for exposure to sunlight.

Bayes Theorem↗
PubMed1980

Spatial frequency analysis in early visual processing.

The existence of multiple channels, or multiple receptive field sizes, in the visual system does not commit us to any particular theory of spatial encoding in vision. However, distortions of apparent spatial frequency and width in a wide variety of conditions favour the idea that each channel carries a width- or frequency-related code or 'label' rather than a 'local sign' or positional label. When distortions of spatial frequency occur without prior adaptation (e.g. at low contrast or low luminance) they are associated with lowered sensitivity, and may be due to a mismatch between the perceptual labels and the actual tuning of the channels. A low-level representation of retinal space could be constructed from the spatial information encoded by the channels, rather than being projected intact from the retina.

Form Perception↗
PubMed2004

Motion-based analysis of spatial patterns by the human visual system.

BACKGROUND: It is known that the visibility of patterns presented through stationary multiple slits is significantly improved by pattern movements. This study investigated whether this spatiotemporal pattern interpolation is supported by motion mechanisms, as opposed to the general belief that the human visual cortex initially analyses spatial patterns independent of their movements. RESULTS: Psychophysical experiments showed that multislit viewing could not be ascribed to such motion-irrelevant factors as retinal painting by tracking eye movements or an increase in the number of views by pattern movements. Pattern perception was more strongly impaired by the masking noise moving in the same direction than by the noise moving in the opposite direction, which indicates the direction selectivity of the pattern interpolation mechanism. A direction-selective impairment of pattern perception by motion adaptation also indicates the direction selectivity of the interpolation mechanism. Finally, the map of effective spatial frequencies, estimated by a reverse-correlation technique, indicates observers' perception of higher spatial frequencies, the recovery of which is theoretically impossible without the aid of motion information. CONCLUSIONS: These results provide clear evidence against the notion of separate analysis of pattern and motion. The visual system uses motion mechanisms to integrate spatial pattern information along the trajectory of pattern movement in order to obtain clear perception of moving patterns. The pattern integration mechanism is likely to be direction-selective filtering by V1 simple cells, but the integration of the local pattern information into a global figure should be guided by a higher-order motion mechanism such as MT pattern cells.

Adult↗
PubMed2004

[Spatial pattern analysis of forest landscape in low coteau of middle Qilian Mountains].

Based on the vegetation map and the relief map, using GIS and Fragstats, the spatial pattern of forest landscape of Xishui reserve in Qilian Mountains were analyzed. The results showed that the distribution of the vegetation was impacted mostly by altitude and aspect, grasslant was mostly distributed on the land of altitude 2,500-2,900 m and aspect of south and southwest, Picea crassifolia forest was always in the land of altitude 2,900-3,300 m and aspect of north, northeast, east and northwest, and shrubbery was in the land of altitude 3,300-3,700 m. The grassland had the biggest area and its connectivity and integrality were the best. The biggest MPFD of Picea crassifolia forest meant that its shape was the most complicated, its mean patch area was small, and the distance between the patches was short. So Picea crassifolia forest was easy to be impacted by some disturbance. The forest suitable land and Sabina przewalskii forest showed more outstretched characteristics than farmland and land with few trees. The mean nearest-neighbor distance of the poplar forest was the biggest in all the landscape elements, so the poplar forest's fragmentized degree was the highest in all the landscape elements.

Conservation of Natural Resources↗
PubMed1998

Factors influencing malaria endemicity in Yunnan Province, PR China (analysis of spatial pattern by GIS). Geographical Information System.

This study is an initial attempt to apply disease mapping through Geographical Information System (GIS) with multiple regression analysis to determine the nature and extent of factors influencing malaria transmission in Yunnan Province, PR China, particularly in border areas. Secondary county-based data covering the period 1990 to 1996 were collected and analyzed. The malaria situation in Yunnan Province as a whole is influenced mainly by the combined effects of the physical environment, the presence of efficient vector species, and mobile population along international borders with Myanmar, Lao PDR and Vietnam.

China↗
PubMed1998

Spatial chemical analysis of dental stain using wavelength dispersive spectrometry.

Six extracted human teeth with naturally-formed neglected stain were analyzed for chemical constituents using wavelength dispersive spectrometry (WDS), an electron microprobe technique. Spatial distribution, within a few microm resolution, of the compositional elements was obtained by line and map analyses, which provided relative concentrations of the elements in stain-enamel complex. Absolute concentrations at different locations across a specimen were obtained from quantitative analysis. Results showed that these neglected stains were highly calcified and contained a significant amount of organic matter (C, N, O, S), with traces of Fe and Cu. The tooth surface underneath the stain layer could be easily distinguished by the higher Ca and P content, as well as by finite amounts of C and S. Corresponding areas of high concentrations between S and Fe/Cu were observed, which suggested the complex of sulfur and metal ions as possible color-forming species. S was found to diffuse into surface enamel in the range of 10 microm.

Calcinosis↗