PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “spatial localization”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 19 recordsLinked to original sources
PubMed1992

The spatial localization deficit in amblyopia.

There have now been numerous reports of a spatial localization deficit in amblyopia but none so far have tackled (1) the relationship between the contrast sensitivity and spatial localization deficits and (2) whether the spatial localization deficit is best described in units of visual angle or in terms of the underlying filter size. These issues are germane because they lie at the very heart of our understanding of the underlying deficit in amblyopia. To answer these questions we use spatially bandpass stimuli so that we can readily compare detection and localization for the same stimuli at each of a number of spatial scales. For some amblyopes (all strabismics and a minority of anisometropes) the contrast sensitivity defect neither underlies nor covaries with the spatial localization deficit. In the majority of anisometropic amblyopes, the contrast sensitivity loss is a complete description. The spatial localization deficit in amblyopia is of two independent kinds; positional inaccuracy and positional distortion. The positional inaccuracy deficit which can occur in varying degrees in both strabismic and anisometropic amblyopia, affects all spatial scales equally and therefore is best thought of in terms of a constant fraction of the underlying filter size in the space-frequency plane. The positional distortion deficit which can also occur to varying degrees in both strabismic and anisometropic forms can not be easily understood within this metric at least for strabismics.

Amblyopia↗
PubMed1992

Asymmetries in the spatial localization of transformed targets.

This study was designed to examine the contribution of the right cerebral hemisphere in the spatial localization of visual targets for manual aiming. Visual targets were briefly presented to the right and left fields and subjects were required to point either to the target location, or a "mirror" image of the target location with their right or left index finger. Whereas reaction times were faster for left-hand pointing than for right-hand pointing, there was no differential effect of the mirror image transformation. This suggests that left-hand reaction time advantages are more related to right hemisphere involvement in the spatial parameterization of the movement than spatial localization of the target.

Adult↗
PubMed1976

[Contingent negative variation in 10-year-old children. Relations with the type of performance in a task of spatial localization].

CNV magnitude was studied in a task involving spatial localization and discrimination Subjects were 18 children 10 years of age. The CNV amplitude of half the subjects increased when the performance decreased and, in the other half, CNV amplitude decreased when the performance decreased. However, it seems that CNV magnitude increases as task difficulty increases but only above a minimal threshold varying with the subject. The results suggest that CNV amplitude cannot be related to a single psychological factor.

Age Factors↗
PubMed1992

Spatially localized in vivo 1H magnetic resonance spectroscopy of an intracerebral rat glioma.

Surface coil MRI combined with spatially localized spectroscopy was used to noninvasively detect 1H signals from metabolites within an intracerebral malignant glioma in rats. The MRS pulse sequence was based upon two-dimensional ISIS, which restricted 1H signals to a column-shaped volume, combined with one-dimensional spectroscopic imaging, which further resolved the signals into 8 or 16 slices along the major axis of the column. All experiments were executed with adiabatic pulses which induced uniform spin excitation despite the inhomogeneous radiofrequency field distribution produced by the surface coil transmitter. Surface coil MRI and MRS experiments were performed on phantom samples, normal rat brains, and rat brains harboring malignant gliomas. Spatially resolved in vivo 1H spectra of intracerebral gliomas revealed significantly decreased concentrations of N-acetyl-aspartate and creatine and increased lactic acid (or lipids) as compared to the contralateral hemisphere. These results demonstrate that metabolic abnormalities in intracerebral rat gliomas can be spatially resolved in a noninvasive manner using localized in vivo 1H MRS.

Animals↗
PubMed1992

Topography of the evoked potential to spatial localization cues.

Visual tasks that are perceptually diverse might be expected to elicit unique evoked-potential waveforms that exhibit differing topographic maps. To investigate this possibility, multichannel visual-evoked potentials (VEPs) were recorded in response to several dot spatial localization stimuli that are physically similar yet produce different percepts (vernier offsets, steroscopic disparity, bisection, orientation, and relative displacement) to determine if the unique percepts arising from these stimuli reflect the activation of different cortical neural populations. The resulting evoked potentials were all similar in waveform, although the stereoscopic VEPs were relatively delayed. Topographic maps of the evoked-potential activity to each stimulus revealed a late major component with two independent foci: one 7 or more centimeters above the inion lateral to the midline, and the other at least 6 cm lateral to OZ. The scalp localization of both peaks was independent of both the position of the stimulus in the visual field and the particular stimulus cue presented. An asymmetric response to pattern appearance vs. disappearance indicated strong pattern specificity for each stimulus type except unreferenced motion. The timing of the VEP responses and relative insensitivity to retinal locus of stimulation suggest the involvement of higher cortical areas. The two map foci might be interpreted as activation of inferotemporal and parietal cortices whose roles are thought to be visual object interpretation and spatial attention and localization, respectively.

Evoked Potentials, Visual↗
PubMed1977

Spatial localization with paralyzed eye muscles.

Four subjects suffering from a unilateral peripheral paralysis of the 3rd or the 6th nerves have been studied in spatial localization tasks, with their normal eye occluded. When peripheral targets were presented in the hemifield corresponding to the paralysis, the saccadic eye movements (recorded from the normal occluded eye) were of an exaggerated amplitude. 'Staircase' oculomotor patterns, closely similar to those occurring in 'open-loop' visual stimulation, could also be observed. Our patients also presented the classical hypermetric misreaching when attempting to point by hand at visual targets in an otherwise dark room. This effect (past-pointing) was likely to be due to a monitoring of the exaggerated oculomotor signal: in one subject past-pointing disappeared when reaching at the targets on the basis of the sole retinal cues. Finally, the classically described illusory visual effects of ocular paralysis were limited to a feeling of instability during self-motion.

Abducens Nerve↗
PubMed1992

Spatial localization and auditory lateralization: binaural cues and their absence.

In 1990 Cheatham suggested there might be a right-ear advantage for the perception of speech and music for right-handed individuals, which confirms Kinsbourne's observation of a general right-ear advantage. These findings, however, contrast with Segalowitz and Plantery's work that supports attentional bias in lateralized processing of these stimuli. The attentional bias model has also been criticized by Bryden on the basis of its circularity. At present there has not been sufficient evidence to settle this debate empirically. The author suggests that the controversy may best be resolved by disentangling the folklore surrounding spatial localization and auditory lateralization to reexamine this field in light of recent empirical findings by Bryden and by Porac, Coren, and Duncan, who inferred an inherent rightward bias to many kinds of stimulation, including auditory, in right-handed individuals. The present focus is that Cheatham's 1990 data lend themselves more readily to the rightward bias that occurs in right-handed subjects and not to previous structural or attentional models.

Attention↗
PubMed1992

Spatial localization without visual references.

To explain the veridical percept of the spatial ordering of objects and the generation of eye movements to peripheral targets, Lotze (1885 Microcosmos. Edinburgh: T. & T. Clark) proposed that there is a position label (local sign) for each retinal element. To estimate the precision of local sign information, we measured absolute localization thresholds at various eccentricities in the nasal visual field, in the complete absence of visual references. To eliminate perception of the visual surround, observers viewed a large display screen through a neutral density filter (2.0 log unit) in a dark room. The fixation target was extinguished at various times (interstimulus intervals or ISIs) prior to the onset of the test stimulus. In general, our results show that localization thresholds are proportional to the target eccentricity at all ISIs. At each eccentricity, localization thresholds are elevated after the extinction of the visual reference compared to thresholds when the reference is present. However, relative to the referenced threshold, unreferenced thresholds are elevated by a greater proportion at smaller eccentricities than at larger eccentricities. Our threshold vs ISI data can be adequately modeled on the basis of an intrinsic positional uncertainty, which increases with eccentricity, and additive and multiplicative sources of noise. The additive noise appears to reflect primarily the increasing scatter in eye position when the fixation target is extinguished. Our model's estimate of intrinsic positional uncertainty in the isoeccentric direction appears to reflect primarily the intrinsic positional uncertainty of the peripheral retina (the local sign), being very similar to cumulative cone position uncertainty and to the spacing between ON-P beta ganglion cells. In the isoeccentric direction, the estimated precision of the local sign mechanism across eccentricities is slightly better than the precision of saccadic endpoints, suggesting that noise in the motor system must also contribute to the scatter of saccadic endpoints in the isoeccentric direction. Interestingly, in the radial direction, we find a surprising similarity in our observers' positional uncertainty and the precision of saccadic endpoints.

Fovea Centralis↗
PubMed1992

Spatial localization of distinct rheumatic disease-associated epitopes and the RNA "cap" of the U1 snRNP particle.

The spatial organization of two rheumatic disease-associated epitopes and the RNA "cap" structure of the U1 small nuclear ribonucleoprotein (snRNP2) was analyzed both in situ and in vitro by two independent interference immuno-assays. Sm and RNP autoantibodies, associated with systemic lupus erythematosus and mixed connective tissue disease, respectively, were used to probe the epitope locations. The Sm epitope on the U1 snRNP structure was localized proximal to the RNP. Experiments with an anti-m7G (mRNA "cap") monoclonal antibody revealed that an in situ association of the Sm and RNP epitopes with the mRNA "cap" structure may exist. Our findings, together with previous observations by others, suggest a model for the spatial arrangement of these rheumatic disease-associated protein epitopes, and the U1 RNA within the U1 snRNP particle.

Antibodies, Monoclonal↗
PubMed1992

[Methods of NMR signal spatial localization for in vivo spectroscopy. A metabolic approach to diseases].

State-of-the-art methods for in vivo localized NMR spectroscopy are described. The methods are presented according to the type of pulse sequences implemented and the number of spatial dimensions which are obtained. The advantages and limitations of methods based either on (i) surface coil, (ii) complex radiofrequency pulse sequences with or without gradients, or (iii) double phase encoding (spectroscopic imaging) are discussed. The specific features of 31P and 1H localized spectroscopy are presented with a description of potential clinical applications of this approach which affords precise biochemical and metabolic information on a variety of organs and tissues in a strictly non-invasive manner.

Humans↗
PubMedDate not supplied

Improvement of precision in spatial localization of radio-opaque markers using the two-film technique.

Radio-opaque markers implanted inside or placed on the skin of patients can be used to detect set-up errors and patient motion. The effects of imaging geometry accuracy for standard radiotherapy equipment on the precision of calculating the positions of radio-opaque spherical markers using two orthogonal radiographic film projections is investigated. Inaccuracies in the imaging geometry are computed from the manually digitized positions of the marker images on each film pair. Actual marker locations are calculated with a precision limited only by the variance in manual digitization by incorporating those imaging geometry inaccuracies into their computation. Results of a phantom study using a grid of markers in a plastic block indicate that submillimeter precision can be obtained for the spatial coordinates of individual markers, and that the precision is not sensitive to the small inaccuracies in imaging geometry present within the mechanical tolerances of modern radiotherapy treatment machines and simulators.

Humans↗
PubMed1992

Effects of unilateral parietal lesions on spatial localization in the rat.

In the first of two experiments, rats with left or right parietal lesions and controls were tested in place and landmark navigation in the water maize. Right parietal lesions resulted in deficits in both tasks, but especially landmark navigation. Lateralized effects appeared mainly in latency to find the platform. Experiment 2 investigated the role of the corpus callosum. Split-brain rats with unilateral parietal lesions were tested on the same two tasks. Place and landmark deficits were particularly severe, but lateralization was weaker. Callosum section had its own effect, impairing the learning of both tasks. There appear to be additive effects of unilateral cortical lesions and bisection of the hemispheres. The impairment from left lesions equaled the right-lesion deficit because of the interruption of compensatory information from the intact right hemisphere and the effect of callosum section itself.

Animals↗
PubMed1979

Spatial localization under conflict conditions: is there a single explanation?

Visual--auditory (VA) and visual--proprioceptive (VP) localization conflict paradigms were varied to explore the comparability of the conflict situations. In experiment 1 various attempts were made to decrease the dominance of visual information over proprioceptive and auditory target information. Pairing auditory with proprioceptive information against conflicting visual information did not lessen the visual dominance, nor did dimming the visual field. A 'cognitive' manipulation, in which the subject was led to doubt the reliability of the visual information, reduced visual dominance over audition but not visual dominance over proprioception. This difference between the two conflict situations was further explored and corroborated in experiment 2. In experiment 3 no attempt was made to lead the subject to believe that paired discrepant targets were related, and the visual dominance of audition was strong while the visual dominance of proprioception did not occur. The apparent differences between the VA and VP conflict situations are discussed with regard to the feability of generating a unitary explanation of localization conflict results. Several further factors are discussed that must be explored before undertaking such a unitary formulation.

Cognition↗