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PubMed2006

Investigation of geo-spatial hotspots for the occurrence of tuberculosis in Almora district, India, using GIS and spatial scan statistic.

BACKGROUND: The World Health Organization has declared tuberculosis a global emergency in 1993. It has been estimated that one third of the world population is infected with Mycobacterium tuberculosis, the causative agent of tuberculosis. The emergence of TB/HIV co-infection poses an additional challenge for the control of tuberculosis throughout the world. The World Health Organization is supporting many developing countries to eradicate tuberculosis. It is an agony that one fifth of the tuberculosis patients worldwide are in India. The eradication of tuberculosis is the greatest public health challenge for this developing country. The aim of the present population based study on Mycobacterium tuberculosis is to test a large set of tuberculosis cases for the presence of statistically significant geographical clusters. A spatial scan statistic is used to identify purely spatial and space-time clusters of tuberculosis. RESULTS: Significant (p < 0.05 for primary clusters and p < 0.1 for secondary clusters) high rate spatial and space-time clusters were identified in three areas of the district. CONCLUSION: There is sufficient evidence about the existence of statistically significant tuberculosis clusters in Almora district of Uttaranchal, India. The spatial scan statistics methodology used in this study has a potential use in surveillance of tuberculosis for detecting the true clusters of the disease.

Cluster Analysis↗
PubMed2005

Investigation of the influence of spatial coherence of a broad-area laser diode on the interference fringe system of a Mach-Zehnder interferometer for highly spatially resolved velocity measurements.

Laser Doppler anemometry is a method for absolute velocity measurements that is based on a Mach-Zehnder interferometer arrangement and usually employs transverse fundamental-mode lasers. We employed inexpensive and powerful broad-area laser diodes and investigated ways in which an interference fringe system is influenced by the spatial coherence properties of a multimode beam. It was demonstrated that, owing to poor spatial coherence of the beam, interference is suppressed in the marginal regions of the intersection volume. Based on these results, a sensor for highly spatially resolved velocity measurements can be built. The inherent astigmatism of the broad-area diode is corrected by an arrangement of two crossed cylindrical lenses. An interference fringe system of length 200 microm and a relative variation in fringe-spacing of only 0.22% were demonstrated with light emitted from a broad-area laser diode with a 100 microm x 1 microm emitter size. Based on this principle a powerful, simple, and robust laser Doppler sensor has been achieved. Highly spatially resolved measurements of a boundary layer flow are presented.

Journal Article↗
PubMed1989

Independent processing of suprathreshold spatial gratings as a function of their separation in spatial frequency.

Experiments were done to examine the minimum separation with respect to spatial frequency required for two superimposed gratings to be processed independently in the visual system. The contrasts of all stimuli were well above the detection threshold. The lack of independent processing was measured by the observers' failure to see both gratings as separate sinusoids; changes in the apparent contrast or spatial frequency of one grating when the other was present; and changes in the ability to discriminate small differences in the contrast or spatial frequency of one grating when the second grating was present. All measures point to a lack of independent processing when the gratings differ by less than 2 octaves. When they differ by more than 2 octaves, they are seen as separate, apparent spatial frequency is not altered systematically, and discrimination performance essentially is unaffected. However, the apparent contrast of the high-frequency grating varies, depending on whether its bars are seen against the bright bars or against the dark bars of the low-frequency grating.

Contrast Sensitivity↗
PubMed1983

Pictorial misrepresentation of spatial relations of the face by certain chronic alcoholic men: an interpretation implicating spatial aspects of memory.

Specific deficit in the pictorial (and implied mental) representation of subtle spatial relations of the upper part of the pattern of the human face is demonstrated in 22% of 344 chronic alcoholic skid row men as against 12% of 406 controls, based on protocols for a novel Draw-A-Person-With-The-Face-In-Frontal-View Test. This drawing was previously shown to be sensitive to the detection of ability to represent visually subtle yet elementary spatial relations. A speculative interpretation of the present data and of mnemonic techniques described in the literature suggests that accurate mental representation of these spatial relations may be required particularly during the encoding phase of memory processes which appears to be especially inefficient for those with chronic alcoholism. Aside from the brain systems of the frontal and occipital-parietal lobes, the hippocampal mediation of elementary spatial relations particularly may be implicated.

Adolescent↗
PubMed2002

Relative roles of spatial and intensive cues in the discrimination of spatial tactile stimuli.

Two psychophysical measures of tactile sensitivity--grating-orientation (GO) and smooth-grooved (SG) discrimination--were used to determine tactile spatial acuity with and without an intermediate surface (latex glove) interposed between the contactor and the skin. Measures were made at three locations that varied in sensitivity and in density of innervation of the primary afferent fibers: the index fingerpad (fingertip), palmar surface of the proximal phalanx (fingerbase), and the thenar eminence (palm). Neurophysiological studies have suggested that the density of innervation of SAI fibers is a limiting factor in spatial acuity. In the present study, without a glove, the GO thresholds varied as a function of location. With the glove, increases in the GO thresholds were relatively uniform and modest. Without a glove, however, the SG thresholds were well below the GO thresholds, and changing the site of stimulation had little effect on the threshold. With a glove, the SG thresholds increased by 100% to more than 300% as in comparison with those in the no-glove condition. The largest increases occurred at the less sensitive locations. The results of the GO task are consistent with the view that GO is a valid measure of spatial acuity. The results of the SG task, however, are inconsistent with previous results and suggest that both spatial and intensive factors are involved in this task.

Cues↗
PubMed2001

A dissociation between object manipulation spatial ability and spatial orientation ability.

We developed psychometric tests of spatial orientation ability, in which people are shown a two-dimensional array of objects, imagine taking a perspective within the array, and indicate the direction to a target object from this perspective. Patterns of errors on these tests were consistent with experimental studies of perspective taking. Characteristic errors and verbal protocols supported the validity of the perspective-taking tests, suggesting that people encoded the objects in the display with respect to a body-centered coordinate system when the imagined perspective was more than 90 degrees different from the orientation of the display. By comparing alternative models in a confirmatory factor analysis, we found that the ability to mentally rotate and manipulate an imagined object (as measured by tests of spatial visualization and spatial relations) and the ability to reorient the imagined self (as measured by the perspective-taking tests) are separable spatial abilities.

Adult↗
PubMed2005

[Spatial heterogeneity of Trichiurus japonicus and small-scale fish in East China Sea and their spatial relationships].

Based on the investigation at 121 positions in East China Sea in 2001 Autumn, this paper analyzed the spatial heterogeneity of hairtail (Trichiurus japonicus) and seven kinds of small-scale fish (Setipinna taty, Collichthys lucidus, Champsodon capensis, Amblychaeturichthys hexanema, Acropoma japonicum, Benthosema pterotum and Apogon lineatus), and the spatial relationships among them. The results indicated that the semivariogram curve of hairtail was very similar to those of Apogon lineatus, Amblychaeturichthys hexanema and Acropoma japonicum, with highly significant correlations (P < 0.01), and the semivariograms of Setipinna taty and Collichthys lucidus appeared as pure nugget effect. The others could be described as spherical or exponential model that had high spatial autocorrelation. The ranges of Apogon lineatus, Amblychaeturichthys hexanema and Acropoma japonicum were equal to or beyond that of hairtail (265 km). Hairtail was spatially close to these three species, and thus, the latter might be the main preys of hairtail.

Animals↗
PubMed2005

The development of spatial capacity in piloting and dead reckoning by infant rats: use of the huddle as a home base for spatial navigation.

Two forms of spatial navigation, piloting using external cues and dead reckoning using self-movement cues, are manifest in the outward and homeward trips of adult rats exploring from a home base. Here, the development of these two forms of spatial behavior are described for rats aged 14-65 days using a new paradigm in which a huddle of pups or an artificial huddle, a small heat pad, served as a home base on an open circular table that the rats could explore. When moving away from both home bases, the travel distance, path complexity, and number of stops of outward trips from the home base increased progressively with age from postnatal day 16 through 22. When returning to the home bases, the return trips to the home base were always more direct and had high travel velocities even though travel distance increased with age for the longest trips. The results are discussed in relation to the ideas that: (1) the pups pilot on the outward portion of their excursion and dead reckon on the homeward portion of their excursion, and (2) the two forms of navigation and associated spatial capacity are interdependent and develop in parallel and in close association with locomotor skill.

Animals↗
PubMed1990

Hippocampal mossy fibers and radial-maze learning in the mouse: a correlation with spatial working memory but not with non-spatial reference memory.

One hundred and eight male mice from nine different inbred strains were tested for two aspects of learning in an eight-arm radial maze. In the first experimental arrangement of the maze, measuring spatial working memory, clear strain differences were found on the fifth day of training. Furthermore, this type of learning showed a high positive correlation with the size of the intra- and infrapyramidal hippocampal mossy fiber terminal field as revealed with Timm's staining. In the second experiment, in which non-spatial reference memory was tested, significant strain differences were found for the learning variables, but there were no significant covariations with the sizes of the intra- and infrapyramidal mossy fiber terminal fields. These results, combined with previous data, suggest that heritable variations of the hippocampal intra- and infrapyramidal mossy fiber projection influence processes determining spatial learning capabilities in mice.

Animals↗
PubMed2004

Increased attention to spatial context increases both place field stability and spatial memory.

The hippocampal formation is critical for the acquisition and consolidation of memories. When recorded in freely moving animals, hippocampal pyramidal neurons fire in a location-specific manner: they are "place" cells, comprising a hippocampal representation of the animal's environment. To explore the relationship between place cells and spatial memory, we recorded from mice in several behavioral contexts. We found that long-term stability of place cell firing fields correlates with the degree of attentional demands and that successful spatial task performance was associated with stable place fields. Furthermore, conditions that maximize place field stability greatly increase orientation to novel cues. This suggests that storage and retrieval of place cells is modulated by a top-down cognitive process resembling attention and that place cells are neural correlates of spatial memory. We propose a model whereby attention provides the requisite neuromodulatation to switch short-term homosynaptic plasticity to long-term heterosynaptic plasticity, and we implicate dopamine in this process.

Animals↗
PubMed1991

Spatial segregation between populations of ponto-cerebellar neurons: statistical analysis of multivariate spatial interactions.

This study applies terms and methods for describing spatial interactions between multivariate spatial point patterns, which are, to our knowledge, new in neurobiology. We consider two categories of points, type 1 and 2, distributed within a certain reference volume (such as a nucleus of the brainstem or a cortical area). The points may, for example, represent different categories of labelled cells or axonal fields of termination. We say that there is spatial neutrality between points of type 1 and 2 if the types are signed by random labelling. If a mechanism drives the two point categories together, we say that the point patterns are positively associated. Conversely, if a mechanism drives type 1 and 2 points apart, we say that they are segregated. By comparing two cumulative distribution functions of distances between points, we can distinguish neutrality, positive association, and segregation. One function, H12(t), is the cumulative distribution function of the distance t between a pair of randomly selected points of type 1 and 2. The other, H00(t), is the corresponding function for a pair of points randomly selected without reference to type. Plots of the estimated difference between these two functions give an indication of positive association, neutrality, or segregation. A statistical test, based on simulations of random (neutral) distributions, can be used to see whether deviations from neutrality are significant. We apply the analysis described above to a major pathway of the brain, namely the ponto-cerebellar projection. Different types of cells in the pontine nuclei are retrogradely labelled with the fluorescent tracers Rhodamine-B-isothiocyanate, Fluoro-Gold, and Fast Blue. The tracers are injected in adjacent or more distant folia of the cerebellar paraflocculus. The location of the somata of labelled cells are recorded and the total distribution reconstructed in three dimensions and displayed on a dynamic graphics workstation. We ask whether different units (folia) in the paraflocculus receive information from the same population, from two different positively associated populations, or from segregated cell populations. We find a statistically significant tendency for cell populations projecting to adjacent folia to be positively associated, although there are few cells containing multiple labels. Populations of neurons projecting to folia wider apart are significantly segregated. From inspections of the reconstructions, using real-time rotations, we find that the swarms of labelled neurons tend to accumulate in shells or lamellae in the pons. Within the lamellae, the cells are aggregated in clusters and bands with empty holes (containing unlabelled ponto-cerebellar cell bodies, presumably projecting to other cerebellar targets) in between.(ABSTRACT TRUNCATED AT 400 WORDS)

Amidines↗
PubMed1984

The effects of large orientation and spatial frequency differences on spatial discriminations.

We have examined two questions: (1) can the finest orientation discrimination be achieved only between stimuli with similar spatial frequency content? and likewise, (2) can the lowest spatial frequency discrimination thresholds be achieved only with parallel gratings? In 2 AFC tests we found that neither type of discrimination was affected by stimulus differences along the other dimension. However, some small decreases in method of adjustment matching accuracy were associated with large differences along the secondary dimensions. Considering the neurophysiological implications, these data suggest that fine orientation and spatial frequency discrimination can occur even though separate populations of neurones in the primary visual cortex may be activated by the two stimuli to be discriminated.

Discrimination, Psychological↗
PubMedDate not supplied

Spatial-frequency adaptation: evidence for a multiple-channel model of short-wavelength-sensitive-cone spatial vision.

The frequency selective effects of spatial adaptation were measured with vertically-oriented, cosine stimuli upon an intense long-wavelength (yellow) field, which isolated the short-wavelength-sensitive (S) cones. Consistent with isolated-S-cone spatial threshold and masking results, the adaptation measurements demonstrate S-cones input to multiple, orientation selective, spatial frequency mechanisms. Moreover, the adaptation measurements show the minimum number of S-cone mechanisms is three. The frequency tuning of each mechanism was derived from the S-cone threshold and masking results. Two of the tuning curves are bandpass with peak sensitivities in a vicinity of 0.7 and 1.4 c/deg, respectively. These two closely resemble tuning curves derived from results with luminance-modulated stimuli. Confined to the range of frequencies examined (0.25-2.83 c/deg), the third tuning curve is lowpass with a high-frequency cutoff of roughly 2.0 c/deg. However, subsequent measurements of orientation selectivity demonstrate the third mechanism to have bandpass frequency tuning as well.

Adaptation, Ocular↗
PubMed1995

Phase-reversal discrimination in one and two dimensions: performance is limited by spatial repetition, not spatial frequency content.

Lawden [(1983) Vision Research, 23, 1451-1463] used vertical gratings containing two frequencies (F, nF) in phase discrimination (F + nF against F - nF) and compound detection (F + nF against F) experiments, where thresholds were measured by manipulating the contrast of the nF component. When n was varied, Lawden found a phase-plateau of moderate breadth where phase discrimination thresholds were about half of those measured in compound detection. I present the results of similar experiments, using one-dimensional (gratings) and two-dimensional (plaids). In a sine-plaid condition, the 1F grating was split into two 1F plaid components at +/- 45 deg from vertical while the nF component remained a vertical grating. In a square-wave plaid (SqW-plaid) condition the plaid components were square waves. For each of these conditions, the horizontal spatial repetition (SR) of the plaid is given by (F/square root of 2); it is half an octave lower than the spatial frequency (SF) of the oblique components but it is not represented in the stimulus spectrum. By plotting phase discrimination relative to compound detection a phase-plateau was found for all three conditions. When these data were plotted as a function of SF ratio (nF/F) the curves describing the two plaid conditions were found to be leftward translations of that describing the grating condition. However, when the results were plotted as a function of SR ratio (nF/SR), the three functions lay on top of each other. The finding that phase-reversal discrimination is not governed by the Fourier attributes of the stimulus per se, rules out an explanation in terms of a linear, broad-band, phase-sensitive mechanism. Rather, the results imply that information is combined across the set of SF- and orientation-tuned mechanisms before the decision variable. These interactions appear to be governed by the spatial (not Fourier) attributes of the luminance profile of the stimulus. A modified version of Bennett's [(1993) Perception & Psychophysics, 53, 292-304] phase discrimination model is presented as a post-hoc account of the data.

Contrast Sensitivity↗
PubMed1994

Relationship between spatial integration and spatial spread of contrast energy in detection.

Detection efficiencies were measured for two kinds of grating stimuli. The stimuli of the first kind were uniform square shaped cosine gratings of various sizes but of constant spatial frequency. The stimuli of the second kind were composed of nine small grating patches of the same spatial frequency arranged into a square array. The array size was varied by changing the inter-patch distance. The efficiencies for the two kinds of stimuli obeyed the same decreasing function of area defined by the respective outlines of the grating patch array and the uniform grating. The result means that detection efficiency is not determined by the retinal area stimulated, but by the distances between different parts of stimulus, i.e. the spatial spread of contrast energy, which can be described by a radial moment measure computed from the image.

Contrast Sensitivity↗
PubMed1986

The effects of hippocampal lesions upon spatial and non-spatial tests of working memory.

A series of experiments examined the proposal that the primary effect of hippocampal damage in rats is to disrupt working memory. Although extensive hippocampal lesions produced a severe impairment in forced-choice alternation--a test of spatial working memory--the same lesions did not impair the acquisition of a non-spatial test of working memory--delayed non-matching-to-sample. This test of object recognition required the rats to select that arm in a Y-maze which contained unfamiliar stimuli. Rats with hippocampal lesions were able to learn and perform this task at normal rates, even with retention delays of as long as 60 s. Two additional experiments helped confirm that the animals had indeed learnt a non-spatial test of working memory. The final experiment examined whether hippocampal lesions resulted in an increased sensitivity to proactive interference. It was found that repetition of test stimuli within a session, which increased interference, did attenuate recognition performance but there was no evidence that the animals with hippocampal lesions were differentially affected.

Animals↗
PubMed1993

Role of the parahippocampal region in spatial and non-spatial memory: effects of parahippocampal lesions on rewarded alternation and concurrent object discrimination learning in the rat.

Rats with aspiration or excitotoxic (NMDA) lesions of the parahippocampal region were trained on a series of behavioral tasks which consisted of: (1) a test of spatial memory (discrete trial rewarded alternation), (2) a black-white discrimination, and (3) a test of non-spatial memory commonly used in primate models of amnesia (visual concurrent object discrimination). Rats in both lesion groups were severely impaired on the concurrent discrimination, even though they were able to learn the black-white discrimination normally. Animals with aspiration lesions were also impaired on the spatial memory task, whereas those with NMDA lesions did not differ from controls. The results indicate that concurrent object discrimination is a particularly sensitive measure of hippocampal/parahippocampal functions and suggest that these structures in the rat may serve mnemonic functions which are qualitatively similar to those of human and non-human primates.

Animals↗
PubMed1996

The bailiwick of visuo-spatial working memory: evidence from unilateral spatial neglect.

An accurate representation of the visual environment is crucial for successful interaction with objects in that environment. The means by which that representation is formed in working memory is a major focus of the issues and research discussed in this paper. The discussion draws on experimental studies of healthy adults and of patients with impairments of visual perceptual processing or of visuo-spatial mental representation. These disorders are most commonly linked with the disorder referred to clinically as unilateral spatial neglect. We discuss the observed dissociation between perceptual neglect and representational neglect, and the phenomenon of implicit processing of information in the neglected hemifield. In so doing we explore the implications of the findings from this literature for the development of theories of visuo-spatial working memory.

Attention↗