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Results for “spatial localization”

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PubMedDate not supplied

[Spatial localization of sources of slow EEG activity by the equivalent dipole method].

Coordinates and moments of equivalent sources of various kinds of slow activity--local, generalized and synchronous (delta- or theta-ranges) -- were estimated on a computer on the basis of a model of single equivalent dipole, by the method of the coordinates descent. Investigation of local delta-activity caused by a volume process in the brain shows that its localization coincides with the peripheral zone of the tumour. Localization of the delta-focus enables to indicate its position not only on the surface, but in the depth of the brain as well. The dipole localization method helps to specify the concept of "secondary" slow waves and to differentiate slow activity of total brain-, brain-stem and local nature.

Bone Neoplasms↗
PubMed1982

Localized effects of spatial frequency adaptation.

The spatially localized threshold-elevation aftereffect of spatial-frequency adaptation was measured by using localized, aperiodic test patterns that have bandpass Fourier transforms. At a given retinal location, the threshold-elevation curves are consistent with the fatigue of size-turned mechanisms with center-surround sensitivity profile. Only a few different sizes of such mechanisms were required to fit the local results. The local aftereffect was also measured as a function of eccentricity near the fovea. The results indicate that the threshold-elevation aftereffect of spatial-frequency adaptation is not spatially homogeneous.

Adaptation, Ocular↗
PubMed1992

Separation discrimination with embedded targets.

Previous research has shown that separation discrimination thresholds are independent of the internal spatial scale (local spatial frequency) of the targets whose separation is being judged. The experiments reported here tested the generality of this conclusion for separation discrimination of targets that were embedded in an array of identical objects, where crowding could enhance the importance of the scale at which the individual target locations are encoded. No effect of the local spatial scale of the targets was found under these conditions.

Contrast Sensitivity↗
PubMed1988

Large-scale relative localization across spatial frequency channels.

Large-scale relative localization accuracy is measured with objects that stimulate different ranges of spatial frequencies. The author has previously made measurements using objects that stimulate only high-spatial-frequency channels or only low-spatial-frequency channels and found no effect of spatial frequency. In the present study, relative localization accuracy, i.e. interval discrimination, is measured with an object pair consisting of a low-spatial-frequency object and a high-spatial-frequency object. Relative localization accuracy for this cross-channel stimulus is as high as for the same-channel stimuli used previously, showing that the relative localization mechanism operates effectively across spatial frequency channels.

Humans↗
PubMed1992

[Localization disorders in squint amblyopia: horizontal line bisection and relative vertical localization].

We used two different procedures for the evaluation of spatial localization errors in strabismic and anisometropic amblyopes, strabismic alternators and normal control subjects: partitioning of horizontal lines and vertical alignment. We found defective spatial localization in the amblyopic eyes of squinters with both procedures. However, in the horizontal partitioning experiment, the control subjects also showed asymmetries between the two hemifields. Thus, there is no good baseline under these conditions for the results of the amblyopic eyes of squinters. Our results show that vertical alignment is the more appropriate procedure to quantify defective spatial localization in strabismic amblyopes.

Discrimination Learning↗
PubMed1986

Spatial cue utilization in chronically malnourished rats: task-specific learning deficits.

Rats whose mothers were maintained on either a 25% casein diet or an 8% casein diet and who were provided the same diet after weaning were tested on delayed spatial alternation or on one of a series of spatial localization problems using the Morris maze (Morris, 1981). Malnourished rats demonstrated perseverative deficits in the form of strings of consecutive errors on the delayed spatial alternation. Performance in the Morris maze indicated spatial localization ability and spatial memory processes were not impaired by chronic malnutrition in rats. The data suggest that complex processing of spatial information that includes flexible use of place cues over short intervals is impaired by malnutrition, while spatial localization per se and spatial mapping are not affected.

Animals↗
PubMed2026

Beyond benchmarking: an expert-guided consensus approach to spatially aware clustering.

Spatial omics technologies have revolutionized the study of tissue architecture and cellular heterogeneity by integrating molecular profiles with spatial localization. In spatially resolved transcriptomics, delineating higher-order anatomical structures is critical for understanding how cellular organization affects function. However, the reliability of current benchmarks of spatially aware clustering (SAC) methods is undermined by their narrow focus on Visium and brain tissue datasets and the incorrect interpretation of manual annotation as ground truth. Here we present SACCELERATOR, a community-driven, extensible framework that standardizes data formatting, method integration and metric evaluation, enabling rapid inclusion of new methods and datasets. Our analysis revealed substantial limitations in the generalizability and reproducibility of SAC methods and shows that anatomical labels commonly used as ground truths are often biased, error prone and unsuitable for benchmarking. Rather than ranking methods, we propose a consensus-guided workflow where descriptive spatial metrics highlight high-entropy regions of method disagreement, enabling targeted feedback for tissue experts. Applied to brain and cancer datasets, this approach uncovered biologically meaningful patterns overlooked by individual SAC methods and manual annotations, highlighting the need for iterative, expert-in-the-loop evaluation.

Benchmarking↗
PubMed1993

Type VII collagen gene expression in human umbilical tissue and cells.

BACKGROUND: Type VII collagen is a minor collagen found in anchoring fibrils. It is expressed predominantly by keratinocytes. In this study, we report the localization and spatial distribution of type VII collagen gene expression in the human umbilical cord, a fetal-derived tissue. EXPERIMENTAL DESIGN: Human umbilical cords were examined in indirect immunofluorescence studies, employing a mouse monoclonal anti-human type VII collagen antibody. Endothelial cells were cultured from the vein and grown on chamber slides for the detection of type VII collagen epitopes. In addition, cultured human umbilical vein cells were analyzed by Northern transfer analysis and by polymerase chain reaction for the expression of the corresponding gene. Fibroblast-like cells were isolated from the Wharton's jelly and were analyzed similarly for type VII collagen expression as well. RESULTS: We demonstrate that type VII collagen is expressed by human umbilical tissue and cells. Indirect immunofluorescence studies demonstrate the presence of type VII collagen epitopes in the epithelium surrounding a connective tissue region known as Wharton's jelly. In addition, there was low but detectable immunofluorescence signal associated with endothelial cells of blood vessels within the umbilical cord. In vitro, the fibroblast-like cells cultured from the Wharton's jelly showed prominent type VII collagen signal. This result was supported by the finding of high level of type VII collagen mRNA in these cells. The human endothelial cells from the vein demonstrated weak but detectable staining for type VII collagen, and the corresponding gene expression was shown by polymerase chain reaction analysis of the mRNA of the endothelial cells. CONCLUSIONS: The results show that umbilical tissue and cells, specifically those from the Wharton's jelly, are relatively enriched in type VII collagen. There is differential spatial localization of this collagen in the fetal tissue. The novel finding is that cells, other than epithelial cells such as keratinocytes, are able to express the type VII collagen gene.

Antibodies, Monoclonal↗
PubMed1994

Implications for bcd mRNA localization from spatial distribution of exu protein in Drosophila oogenesis.

Subcellular RNA localization in different cell types leads to asymmetric distribution of proteins in these cells. The localization of bicoid (bcd) messenger RNA to the anterior pole of the developing Drosophila oocyte gives rise in embryogenesis to a steep concentration gradient of the bcd protein, a transcription factor that activates expression of zygotic genes needed for anterior development. The exuperantia (exu) gene is necessary for this localization of bcd mRNA. Here we express a chimaeric gene encoding a fusion between the Acquorea victoria green fluorescent protein (GFP) and the exu protein (Exu) in female germ cells, and find that the fusion protein fluoresces strongly in both live and fixed cells during Drosophila oogenesis. The fusion protein rescues an exu null allele, restoring full fertility to females, and is expressed and localized in a temporal and spatial pattern similar to native Exu. The high sensitivity of the GFP tag provides important new details on the subcellular localization of Exu. The fusion protein is found in particles concentrated at ring canals, where transport occurs between nurse cells and the oocyte. Drugs such as colchicine and taxol that affect microtubule stability alter localization of the particles. We propose that the particles are ribonucleoprotein complexes or vesicles which transport bcd mRNA along microtubules and target it to the anterior oocyte cortex.

Animals↗
PubMed1984

Temporal and spatial regulation of fibronectin in early Xenopus development.

Pattern formation and temporal control of gene expression in Xenopus development were investigated using fibronectin as a biochemical marker. We determined the spatial localization of fibronectin in the embryo by immunofluorescence and the temporal program of its expression by biosynthesis studies and Western blotting techniques. At the start of gastrulation, fibronectin is localized on the roof of the blastocoel which serves as the surface upon which mesodermal cells will migrate. However, since we find fibronectin secreted by all parts of the embryo, localization is probably achieved through spatially localized receptors that bind secreted fibronectin. Fibronectin levels and fibronectin synthesis rates increase following the midblastula stage. This increase is independent of transcription and therefore involves activation of maternal RNA for fibronectin. Since this message mobilization also occurs in activated but unfertilized eggs, this event must be regulated separately from the midblastula transition.

Animals↗
PubMed1995

Model-based maximum-likelihood estimation for phase- and frequency-encoded magnetic-resonance-imaging data.

A maximum-likelihood (ML)-based magnetic-resonance-imaging (MRI) reconstruction algorithm is established, based on frequency- and phase-encoded data. The model on which the ML method is based is a superposition of exponentially decaying, sinc-modulated sinusoids, arising from the basic Bloch equations for MR spectroscopy, modified to account for the distribution of resonance frequencies and phases used for spatial localization in the image field. Spatial-localizing gradients are assumed to be known linear functions of spatial coordinate position, with the x-encode (frequency) gradient applied continuously during the full duration of data collection, and the y-encode (phase) gradient applied during varying time periods before data collection. A single-voxel emitter becomes sinc-modulated in the x, y directions at rates proportional to voxel size and gradient strengths in the x-encode and y-encode directions. The full two-dimensional MRI signal becomes a superposition of sinc-modulated, exponentially decaying, single-sinusoid emitters, one for each voxel. The ML estimation of spin-density and spin-spin relaxation decay time images becomes a nonlinear least-squares optimization problem; it is solved using an iterative expectation-maximization algorithm for estimating multiple modulated sinusoids in noise. Phantom studies are presented, demonstrating the accuracy of the model and the application of the algorithm to spin-density and spin-spin relaxation decay time profiles.

Algorithms↗
PubMed1991

[Discrimination difficulties--expression of disordered relative localization?].

Spatial uncertainty was examined according to a procedure suggested by Bedell and Flom (1981) ("triangle procedure") and additionally with a line-division test designed by Kundt. A horizontal line of a length of about 20 degrees and a shorter one of 4.3 degrees was divided into two equal parts. Strabismic amblyopes mark the middle of such a line with less precision and greater uncertainty than visually normal subjects do. Visual acuity was measured by single optotypes (Landolt rings), as well as by line optotypes with spaces of 2.6 min of arc between each other (C-test). Surprisingly, there was little correlation between visual acuity--even line acuity--and localization tasks.

Amblyopia↗
PubMedDate not supplied

Egocentric localization changes following unilateral strabismus surgery.

We measured spatial localization (using an open-loop pointing task) monocularly in each eye of eight patients undergoing unilateral strabismus surgery. Most of these patients had some degree of binocular vision. We found that, in most cases, changes in spatial localization produced by surgery on the operated eye paralleled those found in the other eye, both in magnitude and duration. Unilateral surgery can have central effects on egocentric localization.

Adolescent↗
PubMed1994

Band-selective spin echoes for in vivo localized 1H NMR spectroscopy.

This study describes a new single spin-echo spatial localization sequence, BASSALE or BAnd-Selective Spin echo Acquisition for Localized Editing, that overcomes a number of the limitations of the STEAM and PRESS volume selection pulse sequences. It achieves conformal volume localization in a single shot by spatially tailored suppression of all magnetization outside a 2D region of interest followed by selection of a single orthogonal slice. This separation of spatial localization from the echo formation process has permitted use of a spectrally selective cosine-modulated sinc refocusing pulse to acquire localized 1H spectra with the water suppression efficiency of STEAM and the sensitivity of PRESS. Echoes formed by such spectrally selective pulses have been termed band-selective spin echoes. The BASSALE sequence attains shorter echo times than PRESS, inhibits scalar spin-spin interactions to permit localized editing and T2 relaxometry of metabolites with J-coupled spins (e.g., lactate), is insensitive to homonuclear multiple-quantum and polarization transfer effects, and can be made sensitive or insensitive to spin displacement effects. Applications are shown both with phantoms and in situ in the rat brain.

Amino Acids↗