Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “spatial”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,423 records · Page 79Linked to original sources
PubMed2005

[Spatial distribution pattern and space dependence of Contarinia sp. and Erigonidium graminicola in jujube orchard].

With the principles and methodologies of geostatistics, this paper studied the spatial structure and space dependence of Contarinia sp. and its natural enemy Erigonidium graminicola in a jujube orchard at different date. The results indicated that the semivariogram of Contarinia sp. on 8 June, 27 August and 19 October could be described by spherical model, showing an aggregated spatial distribution with the ranges of spatial dependence being 26.3, 7.8 and 22.0 m, and the degrees of spatial dependence being 88.05%, 85.77% and 87.58%, respectively. The semivariogram of Erigonidium graminicola could be also described by spherical model, showing an aggregated distribution with the ranges of spatial dependence being 28.3, 22.5 and 22.2 m, and the degrees of spatial dependence being 90.09%, 87.96% and 85.72%, respectively. It is suggested that Erigonidium graminicola is the dominant natural enemy against Contarinia sp. population in the examined jujube orchard.

Animals↗
PubMed2006

Three-dimensional spatial skill training in a simulated space station: random vs. blocked designs.

BACKGROUND: Astronauts floating inside a spacecraft must be able to recall the direction to surrounding visual landmarks, regardless of their viewing perspective. If 3D orientation skills are taught preflight, should perspective sequences be blocked or randomized? Can standard spatial skill tests predict performance? METHODS: Undergraduates (40 men and 40 women; ages 19-24) learned 3D spatial relationships among landmark pictures in a cubic chamber simulating a space station node. Subjects learned to predict picture directions when told one picture's direction (the one behind them) and the subject's simulated roll orientation, which was changed between trials by rotating pictures. The dependent variable was the proportion of correct predictions. A between group (n=40 per group) independent variable was training type (random vs. blocked sequencing of perspectives). Experiment phase (familiarization, training, transfer, and 2 retention phases) was a within group variable. Subjects also took three standard spatial skill tests: Card Rotation, Cube Comparison, and Group Imbedded Figures. RESULTS: As hypothesized, during training, performance for the random group (0.56) was worse than the blocked group (0.83); during transfer, the random group (0.75) was better than the blocked group (0.56); during retention-i, the random group (0.70) was better than the blocked group (0.55); and during retention-2, the random group (0.76) was better than the blocked group (0.65). Spatial skill tests correlated differently across the two groups, indicating that random sequencing elicits different skills. CONCLUSION: Random presentation enhances 3D spatial skill transfer and retention. Standard spatial tests can predict performance and have the potential to customize training.

Adult↗
PubMed1991

Correlation of chromatic, spatial, and temporal sensitivity in optic nerve disease.

Spearman rank-order correlations (R) were made between the color-mixture threshold, spatial contrast sensitivity, and flicker sensitivity measurements of 38 patients with a variety of optic nerve disorders. Patients had to satisfy the following criteria: greater than 0.5 log unit loss of chromatic or achromatic sensitivity (compared to age-matched normals), central fixation, no congenital color defects, and no ocular media abnormalities. The results of the analysis show a significant correlation between selective losses of high spatial frequency sensitivity (relative to low) and selective losses of red/green and blue/yellow sensitivities [R = -0.680 (P less than 0.001) and R = -0.439 (P less than 0.01), respectively]. A mild correlation was found between selective spatial and selective temporal losses [r = -0.399 (P less than 0.05)] (ie, low temporal frequency losses correlate with high spatial frequency losses and vice versa). A stronger correlation was found between selective red/green and selective blue/yellow sensitivity losses [R = 0.657 (P less than 0.001)]. No correlation was found between selective temporal losses and selective chromatic losses. These findings can be explained in terms of differential losses of three types of fibers: (1) fibers that are particularly sensitive to red/green color, high spatial and low temporal frequencies; (2) fibers signalling blue/yellow color; and (3) fibers that are relatively sensitive to high temporal frequencies and low spatial frequencies.

Adolescent↗
PubMed1989

Spatial and behavioral correlates of hippocampal neuronal activity.

The firing rate of hippocampal neurons in rats was related both to spatial location and to multiple behavioral variables as rats performed 2 kinds of tasks that rely on hippocampal function: a spatial navigation task similar in performance demands to the radial-arm maze task and a simultaneous cue odor-discrimination task. In the place task, most cells had distinct single or multiple place fields, that is, neurons increased firing when the rat was in a particular location or locations. However, in most of these cells, firing rate also varied systematically in relation to behavioral variables, including the speed, direction, and turning angle of the rat as it moved through the place field. In addition, the activity of most cells was time-locked to task-relevant approach movements. In the odor task, most cells fired as the rat sampled discriminative cues or when it executed specific, task-relevant approach movements. Some cells fired selectively in relation to which odors were presented, the configuration of odor cues, the locus of the response, or a combination of these variables. Many cells with spatial correlates in the place task also had striking behavioral correlates when rats performed the odor task in the same environment, and the locus of the increased firing associated with behavior in the odor task was not the same as the place field in the place task. Thus, while the complex stimuli that compose spatial cues are reflected in hippocampal neuronal activity, hippocampal processing is not limited to the representation of spatial location. Rather, the domain of hippocampal representation includes both spatial and nonspatial relations among multiple cues and the actions directed in relation to these cues, across cue modalities, and across behavioral paradigms.

Animals↗
PubMed1989

Changes in spatial tuning of the pattern electroretinogram with age.

Experimental and clinical studies have demonstrated that the electroretinogram in response to periodical patterns alternating in contrast at constant mean luminance (pattern reversal ERG, P-ERG), is correlated with ganglion cell activity. Senile functional changes of these neurons might be therefore investigated by the P-ERG technique. Steady-state P-ERGs (8 Hz) in response to sinusoidal gratings of different spatial frequencies (0.6-6.8 c/d) were recorded in normal subjects ranging over 50 year age span. The P-ERG amplitude as a function of stimulus spatial frequency shows a maximum between 1.2-1.7 c/d and attenuation at higher and lower spatial frequencies (spatial tuning). The P-ERGs of the older subjects are reduced in amplitute, as compared to those of the younger ones, over the whole range of spatial frequency. This reduction is more marked at intermediate spatial frequencies resulting in a shallower tuning.

Adult↗
PubMed1988

Does impaired contrast sensitivity explain the spatial uncertainty of amblyopes?

We investigated the possibility that the spatial imprecision of amblyopic eyes can be accounted for by the relative insensitivity to contrast that has been documented for these eyes. Thresholds for the discrimination of spatial misalignment, a measure of spatial uncertainty, were determined for three amblyopes and one normal for targets ranging in contrast from detection threshold to 99%. We found that spatial uncertainty was greater in amblyopic eyes than non-amblyopic eyes for targets equally above contrast threshold, and when the targets were presented at threshold contrast to the nonamblyopic eyes and at 99% contrast to the amblyopic eyes. Our results fail to support the possibility that the spatial imprecision of amblyopic eyes can, in general, be attributed to reduced contrast sensitivity. Different neural abnormalities are presumed to limit amblyopes' performance on different spatial tasks.

Amblyopia↗
PubMed1987

A quantitative investigation into the effects of pupil diameter and defocus on contrast sensitivity for an extended range of spatial frequencies in natural and homatropinized eyes.

Contrast sensitivity was measured in 12 subjects for different spatial frequencies of sinusoidal grating patterns, generated by oscilloscope, for pupil diameters 2-8 mm and for defocus of +1-4 D, following homatropine eyedrops. Changes in pupil diameter, without correction for the change in retinal illumination, had no significant effect on contrast sensitivity, except at 0.5 and 1 c deg-1 when a significant reduction occurred with the 2 mm pupil. Defocus caused a large reduction in contrast sensitivity at spatial frequencies higher than the peak of the contrast sensitivity function (3 c deg-1) and a smaller reduction below the peak. In both individual and group results, there was no significant effect of defocus in causing a disproportionately greater reduction in contrast sensitivity at higher spatial frequencies nor were the zero mimina predicted by optical theory observed. The results were confirmed in eight subjects viewing with the natural eye, though the reduction in contrast sensitivity caused by +1 D defocus was not significant: this was attributed to the relaxation of accommodation in response to defocus. To predict the performance of the visual system, multiple regression equations were derived to incorporate terms for pupil diameter, defocus and spatial frequency. These equations reflected the lack of effect of pupil diameter, while defocus caused a 51% loss in contrast sensitivity per dioptre at higher spatial frequencies (3-38 c deg-1) and a 19% reduction at low spatial frequencies.

Accommodation, Ocular↗
PubMed1985

Spatial aberrations and acuity in strabismus and amblyopia.

Spatial uncertainty and distortion were quantified from judgement of the horizontal position of a flashed 0.5 deg vertical line with respect to a flanking reference target in strabismics with and without reduced acuity. Spatial uncertainty was outside the range of 30 normal eyes in all of 23 strabismic amblyopic eyes (visual acuity = 20/40 or worse) and in 20 of 22 squinting eyes with 20/30 or better acuity. Abnormal spatial distortion was found in 16 amblyopic and 10 squinting eyes. In the deviated eyes of the strabismics, the extent of spatial uncertainty and distortion correlated with visual acuity. Spatial aberrations were not accounted for by strabismics' unsteady or eccentric fixation, nor were they mimicked in normal eyes when visual acuity was artifically reduced. The authors suggest that spatial uncertainty and distortion represent the primary abnormalities in strabismics and produce deficits of visual acuity according to their severity.

Amblyopia↗
PubMed1983

Spatial characteristics of static and dynamic stereoacuity in strabismus.

The spatial and temporal organization of stereoscopic depth perception were compared in normal and strabismic observers. The minimum and maximum disparities for stimulating static and dynamic stereopsis in strabismus were examined as a function of spatial separation of disparate stimuli. Disparities and their spacing were produced by spatial modulation of two vertical lines viewed haploscopically. Most strabismics had normal upper disparity limits but elevated static and dynamic stereothresholds. Moderate stereothreshold elevations (100 arc sec) were constant for spatial separations greater than 15 arc min. Two new types of spatial crowding effects upon stereopsis were observed. The first type resulted from the constant elevation of the disparity threshold. The second type consisted of a reduced maximum disparity limit for stereopsis. In both cases, the constriction of the range of perceivable depth produced a reduction in the spatial and temporal frequency limits for depth perception. Clinical tests of stereoacuity that crowd stimuli closer than 0.25 degree underestimated the strabismic patients' potential stereoacuities by a factor of 2 to 4. Similarly, tests of dynamic stereopsis that use temporal frequencies greater than 1 Hz will underestimate optimal dynamic stereoacuity.

Depth Perception↗
PubMed1982

Spatial summation and conduction latency classification of cells of the lateral geniculate nucleus of macaques.

Cells in the lateral geniculate nucleus (LGN) of the macaque monkey were investigated with microelectrodes in an attempt to develop an overall classification scheme. We classified cells in the parvocellular (P) and magnocellular (M) layers according to (non)linearity of spatial summation, shock latency, and chromatic organization of center and surround. We also measured the spatial and temporal tuning to counterphasing and drifting sine wave gratings and tested for periphery effects. Our results showed that no strict laminar segregation existed for any cell property studied. Our results can be summarized as follows: 1. Most P layer cells showed a linear summation (98%) and color-opponent responses (80%), while other cells showed a nonlinear summation (Y-cells, 2%) and broad band responses (28%). In contrast, 37% of the M layer cells were linear summators and the remainder were nonlinear. Therefore, there are overlapping distributions of X- and Y-cells in P and M layers but not a strict segregation. 2. P layer cells had longer shock latencies than M layer cells. X-cells conducted more slowly (2.4 +/- 0.7 msec) than Y-cells (1.6 +/- 0.8 msec), but there were overlapping distributions. Latency shortened gradually, rather than abruptly, with increasing depth. 3. The first harmonic of X- and Y-cell responses was maximally sensitive to spatial frequencies of about 2 cycles/deg. Each type of cell modulated about a mean rate to a drifting grating, although Y-cells had higher distortion than X-cells. Response amplitudes to drifting gratings were higher for MX- and MY- than for PX-cells. No DC elevation to high spatial frequencies was seen. Spatial bandwidths averaged 2 to 5 octaves. X-cells were maximally tuned to temporal frequencies around 11 Hz, and Y-cells were tuned to about 19 Hz;. temporal bandwidths for both averaged 2.8 octaves. 4. Periphery effects were detected in 4% of the X-cells and 25% of the Y-cells. 5. These data indicate that gradual changes occur between dorsal and ventral layers: summation changes from linear to nonlinear; conduction latencies shorten; peak temporal tuning increases; response amplitudes increase; the periphery effect becomes more prevalent. Spatial tuning does not change. No strict laminar segregation or specificity exists for any of the properties that we studied.

Animals↗
PubMedDate not supplied

[The functional organization of the spatial structures of the neuronal receptive fields in field 21 of the cat cerebral cortex].

In result study of structural organization of neural receptive fields (RFs) and their different zones on the prestriate cortex level was shown that neural RFs in this area have hypercomplex structure and consist of some spatial different excitatory zones. Orientation and velocity selectivity and spatial-frequency characteristics of the excitatory zones of the same RF may differ between zones. The number of zones in RFs correlate with RF sizes: the more RF size the more zones number in them (r = 0.05, P < 0.02). About 66% of zones in RFs have approximately identical sizes (12-16 deg) and sizes those zones an dependence as from their number in RFs (r = 0.03, P > 0.05) as from the eccentricity (r = 0.3, P > 0.05). Zones in RF were distributed so that distance their centres was between 56-65 degrees (an average across all 60 degrees). If two or three zones were tested simultaneously the neuron changed own frequency and orientation tuning. Consequently the functional organization of neural RFs of prestriate cortex depend upon number simultaneously tested zones in spatial information processing. Was shown that important properties of prestriate cortex neurons is their ability to integrate and complex processing of spatial information across wide area of the visual field; in the prestriate cortex thus violate of straight retinotopical representation principle of visual field, characteristics of all investigated areas of visual system. The results represented in this review allow suppose that the structural and functional unit of cortex which make integration of spatial information from different compose this information is prestriate cortex neurons and not is no striate cortex modules. Consequently combined of neurons which make images description from different parts of visual field out of dependence of cortical area in turn integrate in neuron networks. Is known that neurons of any level have characteristics different of (from) characteristics of other levels visual system. The interaction of different elements of visual system form ultrastructure of RFs and their different zones in prestriate cortex, and ensure function of networks. So just on prestriate cortex neurons level appear whole system of surrounding world universe system of connections from different cortical areas which is morphological and functional base in process of spatial information integration RFs which have the central and peripheral representation.

Animals↗
PubMed1995

A generalized estimating equations approach for spatially correlated binary data: applications to the analysis of neuroimaging data.

This paper proposes a generalized estimating equations approach for the analysis of spatially correlated binary data when there are large numbers of spatially correlated observations on a moderate number of subjects. This approach is useful when the scientific focus is on modeling the marginal mean structure. Proper modeling of the spatial correlation structure is shown to provide large efficiency gains along with precise standard error estimates for inference on mean structure parameters. Generalized estimating equations for estimating the parameters of both the mean and spatial correlation structure are proposed. The use of semivariogram models for parameterizing the correlation structure is discussed, and estimation of the sample semivariogram is proposed as a technique for choosing parametric models and starting values for generalized estimating equations estimation. The methodology is illustrated with neuroimaging data collected as part of the National Institute of Neurological Disorders and Stroke (NINDS) Stroke Data Bank. A simulation study demonstrates the importance of accurate modeling of the spatial correlation structure in data with large numbers of spatially correlated observations such as those found in neuroimaging studies.

Brain↗
PubMed1994

Differential effects on spatial navigation of immunotoxin-induced cholinergic lesions of the medial septal area and nucleus basalis magnocellularis.

The effects on anatomy and behavior of a ribosomal inactivating protein (saporin) coupled to a monoclonal antibody against the low-affinity NGF receptor (NGFr) were examined. In adult rats, NGFr is expressed predominantly in cholinergic neurons of the medial septal area (MSA), diagonal band nuclei, and nucleus basalis magnocellularis (nBM), but also in noncholinergic cerebellar Purkinje cells. Rats with immunotoxin injections to the MSA, nBM, and lateral ventricle were compared to controls on a spatial and cued reference memory task in the Morris maze. Toxin injections to the MSA slightly impaired the initial, but not asymptotic, phase of spatial navigation. Injections to the nBM impaired all phases of spatial navigation. Cued navigation, however, was not affected in either the MSA or nBM group. The ventricular injections severely affected spatial and cued navigation. Acetylcholinesterase (AChE) histochemistry and NGFr and choline acetyltransferase immunohistochemistry revealed a loss of (1) almost all NGFr-positive cholinergic neurons in the MSA and AChE fibers in hippocampus (MSA group); (2) almost all NGFr neurons in the nBM, some in the MSA, most AChE fibers in neocortex and some in the hippocampus (nBM group), and (3) almost all NGFr neurons in the MSA and nBM and their corresponding hippocampal and cortical AChE fibers (ventricular group). Cholinergic nBM projections to the amygdala were largely preserved in all groups. The amount of cholinergic fiber loss in the cortex correlated modestly, but significantly, with the severity of impairment of the asymptotic phase of performance of the spatial task. An unambiguous interpretation of the anatomical locus of behavioral deficits was not possible because of damage to cholinergic striatal interneurons (nBM group) and to noncholinergic cerebellar Purkinje cells (ventricular group). These data suggest that the cholinergic cortical system is critical to the performance of this spatial memory task. Cholinergic denervation of the hippocampus alone, however, is not sufficient to impair markedly performance of this task.

Animals↗
PubMed1994

Spatial correlates of firing patterns of single cells in the subiculum of the freely moving rat.

Hippocampal lesions cause spatial learning deficits, and single hippocampal cells show location-specific firing patterns, known as place fields. This suggests the hippocampus plays a critical role in navigation by providing an ongoing indication of the animal's momentary spatial location. One question that has received little attention is how this locational signal is used by downstream brain regions to orchestrate actual navigational behavior. As a first step, we have examined the spatial firing correlates of cells in the dorsal subiculum as rats navigate in an open-field, pellet-searching task. The subiculum is one of the few major output zones for the hippocampus, and it, in turn, projects to numerous other brain areas, each thought to be involved in various learning and memory functions. Most subicular cells showed a robust locational signal. The patterns observed were different from those in the hippocampus, however, in that cells tended to fire throughout much of the environment, but showed graded, location-related rate modulation, such that there were some localized regions of high firing and other regions with relatively low firing. There were slight quantitative differences between the proximal (adjacent to the hippocampus) and distal (farther from the hippocampus) subicular regions, with distal cells showing slightly higher average firing rates, spatial signaling, and firing field size. This was of interest since these two regions have different efferent connections. Examination of spike trains allowed classification of cells into bursting, nonbursting, and theta (putative interneuron) categories, and this is similar to subicular cell types identified in vitro. Interestingly, the bursting and nonbursting types did not differ detectably in spatial firing properties, suggesting that differences in intrinsic membrane properties do not necessitate differences in coding of environmental inputs. The results suggest that the subiculum transmits a robust, highly distributed spatial signal to each of its projection areas, and that this signal is transmitted in both a bursting and nonbursting mode.

Animals↗
PubMed1993

Spatial modulation transfer function of vision by pattern visual-evoked potentials in patients with early glaucoma.

We applied subjective and psychophysical methods and pattern visual-evoked potential (VEP) P100peak latency as an objective index to measure spatial modulation transfer function (MTF) in normal subjects and patients with early primary open-angle glaucoma (POAG) in an effort to detect impairment of the spatial MTF of vision. To estimate spatial MTF objectively, the peak latency of the P100 component of pattern VEP was investigated. The mean contrast sensitivity in normal subjects derived from the pattern VEP peak latency was found to be maximum at the check size of 14.4 minutes of arc (i.e., 2.08 cycles per degree of spatial frequency), and the objective spatial MTF curve coincided well with that of the subjective one at all spatial frequencies examined. A statistically significant positive correlation was found between the objective (VEP) contrast threshold and the subjective one. Deterioration of the objective contrast sensitivity derived from the VEP peak latency was found to be much prominent that of the subjective one in patients with early glaucoma.

Adolescent↗
PubMed1993

Spatial guidance of choice behavior in the radial-arm maze.

In 6 experiments, the performance of male rats in a 12-arm radial maze was examined. The focus of study was the extent to which the spatial location of individual baited maze arms was determined before the rat was exposed to the extramaze visual cues corresponding to the arm, and thereby guided the rat toward the location of baited arms. Such spatial guidance of choice behavior implies a spatially organized cognitive representation of maze arms (i.e., a cognitive map). A higher level of spatial guidance was found when visual access to extramaze cues was restricted than when it was unrestricted. There was no evidence of a difference between the level of spatial guidance in the context of working memory performance and reference memory performance. Some evidence that intramaze cues contributed to microchoice guidance was found. However, spatial guidance, under at least some conditions, is best explained in terms of cognitive mapping.

Animals↗
PubMed1997

Spatial relationships among three columnar systems in cat area 17.

In the primary visual cortex, neurons with similar response properties are arranged in columns. As more and more columnar systems are discovered it becomes increasingly important to establish the rules that govern the geometric relationships between different columns. As a first step to examine this issue we investigated the spatial relationships between the orientation, ocular dominance, and spatial frequency domains in cat area 17. Using optical imaging of intrinsic signals we obtained high resolution maps for each of these stimulus features from the same cortical regions. We found clear relationships between orientation and ocular dominance columns: many iso-orientation lines intersected the borders between ocular dominance borders at right angles, and orientation singularities were concentrated in the center regions of the ocular dominance columns. Similar, albeit weaker geometric relationships were observed between the orientation and spatial frequency domains. The ocular dominance and spatial frequency maps were also found to be spatially related: there was a tendency for the low spatial frequency domains to avoid the border regions of the ocular dominance columns. This specific arrangement of the different columnar systems might ensure that all possible combinations of stimulus features are represented at least once in any given region of the visual cortex, thus avoiding the occurrence of functional blind spots for a particular stimulus attribute in the visual field.

Animals↗
PubMed1998

The effects of rotation on spatial attention.

Unilateral spatial neglect can be reduced by cold water caloric stimulation of the contralesional ear. Three hypotheses may account for this response. Caloric stimulation may increase the arousal of the damaged hypoaroused hemisphere. Moving stimuli to ipsilesional space improves the performance of patients with neglect. Caloric stimulation may move viewer-centered spatial maps in an ipsilesional direction. Unilateral neglect may be related to a spatial attentional bias. Vestibular stimulation may temporarily influence this bias. To learn if vestibular stimulation may induce an attentional spatial bias, the authors studied eight normal subjects by having these subjects attempt to bisect lines before and during vestibular stimulation. If caloric stimulation alters neglect because it changes the attentional spatial bias, the authors should be able to induce neglect in normal subjects by pertubating the vestibular system. Vestibular stimulation was induced by spinning a chair and then abruptly stopping the spinning chair. The authors found that after normal subjects were rotated to the left, they misbisected lines to the left but did not misbisect lines after they were rotated to the right. Although these results support the postulate that vestibular stimulation can induce an attentional spatial bias, the authors' results also suggest that there are intrinsic attentional asymmetries.

Adult↗