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At least 1,135 records · Page 63Linked to original sources
PubMed2005

Spatial analysis of respiratory disease on an urbanized geothermal field.

Chronic exposure to hydrogen sulfide (H(2)S) in the parts per billion-parts per million range occurs in the population of Rotorua, a city built upon an actively degassing geothermal field in the Taupo Volcanic Zone, New Zealand. H(2)S is acutely toxic at high concentrations but little is understood of the health effects of chronic, low-level exposure. In Rotorua, H(2)S emissions and ambient concentrations are heterogeneous and approximately 30% of the greater urban area's population live upon or <4 km downwind of the geothermal field. Spatial analysis of disease incidence clustering using a spatial scan statistic is a powerful tool with which to investigate the spatial relationship which may exist between H(2)S and respiratory disease. This paper reports findings from a spatial cluster analysis of 11 years of hospital discharge data at the census area unit resolution. Results indicate that the relative risk (RR) of incidence of noninfectious respiratory diseases may be substantially higher among residents living in the geothermal area than have been reported previously. RR >5 for chronic obstructive pulmonary disease and its associated conditions are found in clusters which are spatially coincident with the geothermal field. Future work which investigates neurological and circulatory disease groups at the same or better spatial resolution may provide further insight into the chronic health effects of H(2)S exposure than these preliminary findings indicate.

Adolescent↗
PubMed2005

Risk factors and spatial patterns of hookworm infection among schoolchildren in a rural area of western Côte d'Ivoire.

This study is aimed at investigating the risk factors for hookworm infection among schoolchildren in a rural area of western Côte d'Ivoire and predicting and mapping the spatial distribution of infection. We used demographic and socio-economic data from a cross-sectional survey of 6-16-year-old schoolchildren from 56 schools. Infection with hookworm was determined by microscopic examination of stool samples employing the Kato-Katz technique and an ether-concentration method. Environmental data were derived from satellite images and digitised maps. Bayesian variogram models were applied to investigate the variation of hookworm infection in relation to demographic, socio-economic and environmental factors. The overall hookworm infection prevalence, based on the pooled microscopic diagnoses, was 43.3% and ranged from 5.4 to 79.1% in the schools surveyed. Bivariate analyses showed that sex, age, socio-economic status, elevation, rainfall and land cover were significantly associated with the spatial distribution of hookworm infection. The final multivariate spatial model consisted of the covariates age, sex, socio-economic status, elevation and land cover. When assuming non-stationary underlying spatial dependency, the results of the model suggested that spatial correlation depended on the location only marginally. We conclude that, at the current resolution, it seems more reasonable to target interventions based on well-established epidemiologic risk factors, rather than on spatial factors.

Adolescent↗
PubMed2006

An ERP study of visual change detection: effects of magnitude of spatial frequency changes on the change-related posterior positivity.

In event-related brain potential (ERP) studies using a visual S1-S2 matching task, change stimuli elicit a posterior positivity at around 100-200 ms. In the present study, we investigated the effects of magnitude of spatial frequency changes on change-related positivity. Each trial consisted of two sequentially presented stimuli (S1-S2), where S2 was either (1) the same as S1 (i.e., NO-change, p=.40), (2) different from S1 in spatial frequency only (SF-change, .40), (3) different in orientation only (OR-change, .10), or (4) different in both spatial frequency and orientation (BOTH-change, .10). Further, three magnitude conditions (Large, Medium, and Small) were used to examine the effect of the magnitude of the spatial frequency change. Participant's (N=12) task was to respond to S2 with a change in orientation (from vertical to horizontal, or from horizontal to vertical) regardless of the spatial frequency of the stimulus. Changes in the spatial frequency elicited change-related positivity at a latency range of about 120-180 ms, which was followed by a central negativity (N270) and a late positive component (LPC). The amplitude of the change-related positivity tends to be enhanced as the magnitude of the change is increased. These results support the notion that the change-related positivity reflects memory-based change detection in the human visual system.

Adult↗
PubMed2005

Object-centred spatial reference in 4-month-old infants.

An appreciation of object-centred spatial relations involves representing a 'within-object' spatial relation across changes in the object orientation. This representational ability is important in adult object recognition [Biederman, I. (1987). Recognition-by-components: A theory of human image understanding. Psychological Review, 94, 115-147; Marr, D., & Nishihara, H. K. (1978). Representation and recognition of the spatial organisation of three-dimensional structure. Proceedings of the Royal Society of London, Series B (Biological Sciences), 200, 269-294; Tarr, M. J., & Pinker, S. (1990). When does human object recognition use a viewer-centred reference frame? Psychological Science, 1, 253-256] and is also thought to be a fundamental component of the mature object concept [Piaget, J. (1954). The Construction of Reality in the Child. Routledge & Kegan-Paul: London, UK. (Originally published in French in 1937)]. An experiment is reported in which eighteen 4-month-old infants were familiarised to a specific spatial relation within an object, across six different orientations of the object. On subsequent test trials the object was presented to the infants in an entirely novel orientation. Between successive test trials the within-object spatial relation was alternated between novel and familiar. The infants demonstrated significant sensitivity of their looking to both the novelty of the stimuli and the order in which novel and familiar stimuli were presented. It is concluded that by 4 months of age infants are able to form object-centred spatial frames of reference. These findings are discussed in the light of our current understanding of the development of object representation during infancy.

Attention↗
PubMed2006

Spatial and temporal variability of water repellency in a sandy soil contaminated with tar oil and heavy metals.

Water repellency can induce preferential flow and thus affect water flow and contaminant transport at hazardous waste sites. Since the spatial patterns of water repellency are mostly unknown, it is problematic to use numerical transport models to predict leachate composition. In this study, the spatial variability of soil water repellency was studied at an industrial site contaminated with tar oil, chromium, copper and arsenic. The persistence of water repellency was assessed by the water drop penetration time (WDPT), and the degree of water repellency was quantified by the ethanol percentage (EP) test. Measurements were made at the soil surface along 3.5-12.1 m long transects at different times between March and October 2002. The spatial variability of WDPT, EP, water content, and organic matter content was quantified by variogram analyses. Both the persistence and the degree of water repellency varied seasonally, with the highest water repellency during the summer months. The correlation lengths of WDPT values ranged between 16 and 406 cm, whereas EP values showed no spatial correlation. For field-moist samples, a critical soil water threshold, below which water repellency prevails, was estimated to be 2.5-4%. For oven dry samples, the WDPT values were dependent on the water content prior to drying. The wide range of correlation lengths and the temporal dynamics of spatial repellency patterns suggest that simulations of solute leaching must consider the spatial and temporal variability of soil hydrophobic properties.

Arsenic↗
PubMed2006

The change in spatial distribution of upper trapezius muscle activity is correlated to contraction duration.

The aim of the study was to confirm the hypothesis that the longer a contraction is sustained, the larger are the changes in the spatial distribution of muscle activity. For this purpose, surface electromyographic (EMG) signals were recorded with a 13 x 5 grid of electrodes from the upper trapezius muscle of 11 healthy male subjects during static contractions with shoulders 90 degrees abducted until endurance. The entropy (degree of uniformity) and center of gravity of the EMG root mean square map were computed to assess spatial inhomogeneity in muscle activation and changes over time in EMG amplitude spatial distribution. At the endurance time, entropy decreased (mean+/-SD, percent change 2.0+/-1.6%; P<0.0001) and the center of gravity moved in the cranial direction (shift 11.2+/-6.1mm; P<0.0001) with respect to the beginning of the contraction. The shift in the center of gravity was positively correlated with endurance time (R(2)=0.46, P<0.05), thus subjects with larger shift in the activity map showed longer endurance time. The percent variation in average (over the grid) root mean square was positively correlated with the shift in the center of gravity (R(2)=0.51, P<0.05). Moreover, the shift in the center of gravity was negatively correlated to both initial and final (at the endurance) entropy (R(2)=0.54 and R(2)=0.56, respectively; P<0.01 in both cases), indicating that subjects with less uniform root mean square maps had larger shift of the center of gravity over time. The spatial changes in root mean square EMG were likely due to spatially-dependent changes in motor unit activation during the sustained contraction. It was concluded that the changes in spatial muscle activity distribution play a role in the ability to maintain a static contraction.

Adult↗
PubMed2004

Spatial patterns of recreation impact on experimental campsites.

Management of camping impacts in protected areas worldwide is limited by inadequate understanding of spatial patterns of impact and attention to spatial management strategies. Spatial patterns of campsite impact were studied in two subalpine plant communities in the Wind River Mountains, Wyoming, USA (a forest and a meadow). Response to chronic disturbance and recovery from acute disturbance were both assessed. Previously undisturbed sites were camped on at intensities of one and four nights/year, for either one or three consecutive years. Recovery was followed for three years on sites camped on for one year. Percent bare ground, assessed in 49 contiguous 1 m2 quadrats, increased with increasing use frequency, particularly on the forest sites. Magnitude of impact varied spatially within campsites, with impact decreasing as distance from the center of the campsite increased. On the more fragile forest sites, this radial impact pattern developed rapidly and remained after three years of recovery. Concentration of camping activities around a centrally located small cooking stove was the apparent cause of this pattern. Maximum variation in magnitude of impact occurred at intermediate levels of campsite use and disturbance. The magnitude, variability and spatial pattern of impact varied with the spatial scale of analysis. Generally, results of these controlled experiments are consistent with earlier studies of campsites and validate the management implications derived from those studies. Even where campers use low-impact techniques, low levels of camping use can cause substantial impact and it is important to concentrate use. On resistant sites, however, it is possible that low levels of use can be sustained with minimal resultant impact.

Conservation of Natural Resources↗
PubMed2004

A design and application of a multi-agent system for simulation of multi-actor spatial planning.

Multi-agent Systems (MAS) offer a conceptual approach to include multi-actor decision making into models of land use change. The main goal is to explore the use of MAS to simulate spatial scenarios based on modelling multi-actor decision-making within a spatial planning process. We demonstrate MAS that consists of agents representing organizations and interest groups involved in an urban allocation problem during a land use planning process. The multi-actor based decision-making is modelled by generating beliefs and preferences of actors about the location of and relation between spatial objects. This allows each agent to confront these beliefs and preferences with it's own desires and with that of other agents. The MAS loosely resembles belief, desire and intentions architecture. Based on a case study for a hypothetical land use planning situation in a study area in the Netherlands we discuss the potential and limitations of the MAS to build models that enable spatial planners to include the 'actor factor' in their analysis and design of spatial scenarios. In addition, our experiments revealed the need for further research on the representation of spatial objects and reasoning, learning and communication about allocation problems using MAS.

Communication↗
PubMed2005

The spatial resolutions of the apposition compound eye and its neuro-sensory feature detectors: observation versus theory.

For 100 years three ideas dominated efforts to understand the apposition compound eye. In Müller's theory, the eye viewed the panorama through an array of little windows without overlaps and without gaps, with no details within windows. Spatial resolution then depended on the interommatidial angle (Deltaphi) and the number of ommatidia. In the second proposal, the insect detected the temporal modulation of the light, which was limited by the aperture of the lens and the wavelength, assuming good focus. Modulation is the change of intensity in the receptor, usually caused by motion of a spatial contrast in the stimulus. Thirdly, motion was detected from the successive temporal modulations at adjacent visual axes. Recently, two more principles arose. The light-sensitive elements, called rhabdomeres, project through the nodal point of the lens to the outside world, and the resolution was limited by their grain size, like the pixels in a digital camera. Finally, detection of contrast and colour was limited by the signal/noise ratio (SNR) which was improved by brighter light and more visual pigment. These five physical principles provide satisfying explanations of eye function but they all originated from theory. Actual measurements of resolution depend on the operation of the test. The visual system of the honeybee recognizes a limited variety of simple cues, but there is no evidence that the pattern of ommatidial stimulation is re-assembled, or even seen. The known cues are: the temporal modulation of groups of receptors, the direction and angular velocity of motion, some measure of the spatial disruption of the pattern or the length of edge (related to spatial frequency and contrast), colour, the intensity, the position of the centre and the size of large well-separated areas of black or colour, the angle of orientation of a bar or grating, radial or tangential edges, and bilateral symmetry. Neurons connected to more than two adjacent ommatidia collaborate in the detection of cues, and the resolution depends on the neuro-sensory feature detectors at work at the time. Although some behavioural and electrophysiological measurements give a spatial resolution similar to the interommatidial angle, different spatial properties of neuro-sensory detectors predominate at different light intensities and with a diurnal rhythm. During the long history of this topic, the belief that the resolution ought to be Deltaphi has frequently been overturned by experimental measurement.

Animals↗
PubMed2004

Spatially resolved multidimensional NMR spectroscopy within a single scan.

We have recently demonstrated that the spatial encoding of internal nuclear magnetic resonance (NMR) spin interactions can be exploited to collect multidimensional NMR spectra within a single scan. Such experiments rely on an inhomogeneous spatial excitation of the spins throughout the sample, and lead to indirect-domain peaks via a constructive interference among the spatially resolved spin-packets that are thus created. The shape of the resulting indirect-domain echo peaks approaches a Sinc function when the chemical's distribution is uniform, but will depart from this function otherwise. It is hereby shown that a Fourier analysis of either the diagonal- or the cross-peaks resolved in these single-scan two-dimensional (2D) NMR experiments can in fact provide a weighted spatial distribution of the analyte originating such peak, thus opening up the possibility of completing spatially resolved multidimensional NMR measurements within a fraction of a second. Principles of this new mode of analysis are discussed, and examples where the potential of spatially resolved ultrafast 2D NMR spectroscopy is brought to bear are presented. Potential extensions of this approach to higher dimensions are also briefly addressed.

Algorithms↗
PubMed2004

Discussion on the choice of separated components in fMRI data analysis by spatial independent component analysis.

By measuring the changes of magnetic resonance signals during a stimulation, the functional magnetic resonance imaging (fMRI) is able to localize the neural activation in the brain. In this report, we discuss the fMRI application of the spatial independent component analysis (spatial ICA), which maximizes statistical independence over spatial images. Included simulations show the possibility of the spatial ICA on discriminating asynchronous activations or different response patterns in an fMRI data set. An in vivo visual stimulation fMRI test was conducted, and the result shows a proper sum of the separated components as the final image is better than a single component, using fMRI data analysis by spatial ICA. Our result means that spatial ICA is a useful tool for the detection of different response activations and suggests that a proper sum of the separated independent components should be used for the imaging result of fMRI data processing.

Algorithms↗
PubMed2006

Assessing the effect of verbal working memory load on visuo-spatial exogenous orienting.

The aim of this study was to assess whether or not loading verbal working memory (WM) affects the exogenous orienting of visuo-spatial attention. Visuo-spatial exogenous orienting was measured under low/high WM load conditions by means of an orthogonal spatial cuing paradigm. Participants had to discriminate the elevation (up versus down) of a visual target preceded by a peripheral spatially-nonpredictive visual cue presented on either the left or right. This elevation discrimination task was carried out in-between a verbal WM test, in which a sequence of six digits (to be remembered for report at the end of the trial) was presented either in numerically ascending or random order (i.e., low and high load conditions, respectively). Participants made significantly more recall errors in the high load than in the low load condition, demonstrating that the verbal WM load manipulation had been effective. However, WM load did not interact with visuo-spatial exogenous orienting (i.e., comparable cuing effects were reported in both load conditions). These results are consistent with the view that peripheral visual onsets automatically capture spatial attention, regardless any concurrent increase of verbal WM load.

Adult↗
PubMed2005

Directing spatial attention in mental representations: Interactions between attentional orienting and working-memory load.

Orienting spatial attention to locations in the extrapersonal world has been intensively investigated during the past decades. Recently, it was demonstrated that it is also possible to shift attention to locations within mental representations held in working memory. This is an important issue, since the allocation of our attention is not only guided by external stimuli, but also by their internal representations and the expectations we build upon them. The present experiment used behavioural measures and event-related functional magnetic resonance imaging to investigate whether spatial orienting to mental representations can modulate the search and retrieval of information from working memory, and to identify the neural systems involved, respectively. Participants viewed an array of coloured crosses. Seconds after its disappearance, they were cued to locations in the array with valid or neutral cues. Subsequently, they decided whether a probe stimulus was presented in the array. The behavioural results indicated that orienting of spatial attention within working memory attenuates the well-known effect of decreasing performance when memory load is increased. So "internal" spatial orienting seems to highlight information or facilitate search within working memory, which leads to advantages in retrieval. Imaging enabled the separation of brain areas supporting spatial orienting functions from those sensitive to working-memory load. Orienting of spatial attention to the contents of working memory activated posterior parietal cortex bilaterally, the insula, and lateral and medial frontal cortices.

Adult↗
PubMed2005

Spatial extent of oxygen metabolism and hemodynamic changes during functional activation of the rat somatosensory cortex.

The spatial extent of the changes in oxy-hemoglobin (HbO), deoxy-hemoglobin (HbR), total hemoglobin concentration (HbT), cerebral blood flow (CBF), and the cerebral metabolic rate of oxygen (CMRO(2)) in response to forepaw and whisker stimulation were compared in the rat somatosensory cortex using a combination of multi-wavelength reflectance imaging and laser speckle contrast imaging of cerebral blood flow. The spatial extents of the response of each hemodynamic parameter and CMRO(2) were found to be comparable at the time of peak response, and at early times following stimulation onset, the spatial extent of the change in HbR was smaller than that of HbO, HbT, CBF, and CMRO(2). In addition, a slight spatial dependence was found in the power law coefficient relating changes in CBF and HbT. Although the CMRO(2) response is a metabolic measure and thus expected to have a more localized response than the hemodynamic parameters, the results presented here suggest that this may not be the case in general, possibly due to the increased sensitivity of optical imaging techniques to superficial cortical layers where the lateral extent of the metabolic and neuronal activation is larger compared to that in layer IV. In addition, we found that the measured spatial extent of the CMRO(2) changes was insensitive to assumptions made in the calculation of the CMRO(2) changes such as baseline hemoglobin concentrations, vascular weighting constants, and wavelength dependence of tissue scattering. Multi-parameter full field imaging of the functional response provides a more complete picture of the hemodynamic response to functional activation including the spatial and temporal estimation of CMRO(2) changes.

Algorithms↗
PubMed2005

Time course of attention reveals different mechanisms for spatial and feature-based attention in area V4.

Attention can facilitate visual processing, emphasizing specific locations and highlighting stimuli containing specific features. To dissociate the mechanisms of spatial and feature-based attention, we compared the time course of visually evoked responses under different attention conditions. We recorded from single neurons in area V4 during a delayed match-to-sample task that controlled both spatial and feature-based attention. Neuronal responses increased when spatial attention was directed toward the receptive field and were modulated by the identity of the target of feature-based attention. Modulation by spatial attention was weaker during the early portion of the visual response and stronger during the later portion of the response. In contrast, modulation by feature-based attention was relatively constant throughout the response. It appears that stimulus onset transients disrupt spatial attention, but not feature attention. We conclude that spatial attention reflects a combination of stimulus-driven and goal-driven processes, while feature-based attention is purely goal driven.

Animals↗
PubMed2005

Loss of memory for auditory-spatial associations following unilateral medial temporal-lobe damage.

The goal of the present experiment was to determine the role of medial temporal-lobe structures in episodic memory of auditory-spatial associations. By using a two-alternative forced choice paradigm in which an association between eight different sounds and their spatial location must be recognized, learning abilities over 10 learning sessions were tested in 19 patients who had undergone a right or a left medial temporal-lobe resection for the relief of intractable seizures as well as in nine normal control participants. The data demonstrated that significant learning took place over the successive sessions for all the participants. In addition, the results showed that patients with left but not right medial temporal-lobe lesion were impaired in this learning task as compared to normal participants, suggesting the predominant implication of left medial temporal-lobe structures in auditory-spatial associative learning. The predominant role of left hemisphere structures in this memory task could be explained by a spatial categorical coding, which was enhanced by the use of eight loud-speakers. This result also suggests that the ability to store an episodic event associated with a rich spatial (or temporal) context depends on the left medial temporal-lobe structures. Thus, this finding provides an interesting parallel with data obtained in the visual modality by documenting for the first time the role of the left medial temporal-lobe in episodic learning of auditory-spatial associations.

Adult↗
PubMed2005

Brain areas involved in spatial working memory.

Spatial working memory entails the ability to keep spatial information active in working memory over a short period of time. To study the areas of the brain that are involved in spatial working memory, a group of stroke patients was tested with a spatial search task. Patients and healthy controls were asked to search through a number of boxes shown at different locations on a touch-sensitive computer screen in order to find a target object. In subsequent trials, new target objects were hidden in boxes that were previously empty. Within-search errors were made if a participant returned to an already searched box; between-search errors occurred if a participant returned to a box that was already known to contain a target item. The use of a strategy to remember the locations of the target objects was calculated as well. Damage to the right posterior parietal and right dorsolateral prefrontal cortex impaired the ability to keep spatial information 'on-line', as was indicated by performance on the Corsi Block-Tapping task and the within-search errors. Moreover, patients with damage to the right posterior parietal cortex, the right dorsolateral prefrontal cortex and the hippocampal formation bilaterally made more between-search errors, indicating the importance of these areas in maintaining spatial information in working memory over an extended time period.

Brain↗
PubMed2005

Exploratory spatial relative risk mapping.

The many faces of disease mapping include maps of disease case locations, regional counts of cases, and disease risk. Another approach is that of mapping the relative risk. Previous methods to map the relative risk were based on regression models of relative risk, given information about geographical locations and established risk factors. However, spatial epidemiological investigations are often exploratory with limited knowledge about the putative risk factors. Indeed, often the primary motivation for the analysis is to identify unknown geographically varying risk factors. An exploratory approach to mapping the spatial relative risk is to scale the risk map using the background risk in the unexposed (or less-exposed) population. Exposure to unknown spatial risk factors is defined via specific cluster analysis. Identification of spatial disease clusters separates the population into those inside and those outside high risk areas (the exposed and unexposed populations). This exploratory approach to relative risk mapping gives the investigator an impression about the importance and geographical distribution of the unknown spatial risk factors. Two examples illustrate the exploratory relative risk mapping approach using a spatial point data set on pseudorabies in pig-herds and a regional count data set on small fox tapeworm infections in red foxes.

Animals↗