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 253 records · Page 14Linked to original sources
PubMed1996

Spatial locations gone awry: object and spatial memory deficits in children with fetal alcohol syndrome.

Hippocampus vulnerability following gestational alcohol exposure has been demonstrated neuroanatomically and behaviorally in animal models of fetal alcohol syndrome (FAS). There has been no similar demonstrations in humans. The Smith and Milner (1981) Memory for 16 Objects task has been used to explore the effects of right vs left temporal lobectomy with varying degrees of damage to the hippocampus. In the present experiment, this same task was administered to 15 children with FAS (mean age 10.03, S.D. = 2.33) and 15 control children (mean age 10.02, S.D. = 2.31). Similar to patients with right temporal lobectomies and a large excision to the hippocampus, children with FAS were able to perform immediate but not delayed object recall, had a general spatial memory deficit (P < 0.05), and significantly distorted the spatial array (P < 0.05). Although these results are consistent with an interpretation of hippocampal dysfunction, gestational alcohol exposure is known to result in a wide-ranging spectrum of neuropsychological deficits that vary in both extent and severity. Visuospatial deficits on the Beery test of Visuomotor Integration and Clock Drawing are suggestive of the other neural regions that may be involved in producing the behavioral deficits in children with FAS.

Adolescent↗
PubMed1992

Spatial and temporal effects of spatial attention on human saccadic eye movements.

A spatial cueing paradigm was used to (a) investigate the effects of attentional orienting on spatial and temporal parameters of saccadic eye movements and (b) examine hypotheses regarding the hierarchical programming of saccade direction and amplitude. On a given trial, the subjects were presented with one of three peripheral cues: a "valid" cue provided correct information, a "neutral" cue no information and an "invalid" cue incorrect information about the location of the subsequent target (the cue was valid on about 50% of the trials). 100 or 500 msec after the cue onset (stimulus onset asynchrony, SOA), the eye movement target was presented at one of six possible locations (from -11.25 degrees to +11.25 degrees, at 3.75 degrees spacing). The results showed a significant effect of cueing on saccade latencies at the 100 msec, but no effect at the 500 msec SOA. The cueing benefits were restricted to the cued location; no other locations within the cued or uncued hemi-field were facilitated. The invalid trial latencies showed: (a) no advantage for targets on the same side as the cue relative to the opposite side, (b) no advantage for targets more proximal to the cue and (c) no advantage for targets sharing the same eccentricity as the cue. In a second experiment, subjects responded to the target by giving a simple manual response [simple reaction time (RT)] while keeping the eyes stationary. The results showed a significant cueing effect on simple RTs both at the 100 msec and, in contrast to saccadic eye movements, the 500 msec SOA. There were specific benefits for targets at the cued location relative to other targets within the same and opposite hemi-fields. Further, in contrast to saccades, there was a general advantage for targets within the same ("cued") hemi-field over targets in the opposite hemi-field. These findings suggest that, for saccadic eye movements (overt orienting), direction and amplitude are programmed holistically; whereas in covert orienting (with eyes stationary), motor parameters (e.g. for directed hand movements) are programmed in a more hierarchical fashion.

Attention↗
PubMedDate not supplied

Spatial cueing, sensory gating and selective response preparation: an ERP study on visuo-spatial orienting.

Event-related brain potentials (ERPs) were recorded in a visuo-spatial attention task where the position of an imperative stimulus was indicated either validly or invalidly by a central arrow (trial-by-trial cueing). Subjects had to perform choice RT tasks with the response being dependent either on the identity of the target stimulus or on its position. When target identity was relevant for response selection, validly cued stimuli elicited amplitude enhancements of the early, sensory-evoked P1 and N1 components at lateral posterior sites. The N1 validity effect was limited to scalp sites ipsilateral to the visual field of stimulus presentation. Although these effects were found only when the sensory discrimination task was considerably difficult, they are in line with models assuming that modulations of sensory-perceptual processing ("sensory gating") are induced by spatial cueing. However, when target location was response-relevant, N1 amplitude enhancements were consistently elicited by invalidly cued letters. CNV and LRP measures indicated that the arrow elicited response-related processing in the cue-target interval. Such processes occurred even when the cue contained no information about an upcoming response. Two consecutive lateralization phases were distinguishable in the LRP, with experimentally induced response assignments becoming effective only during the second phase.

Adult↗
PubMed2004

Aged neuropeptide Y transgenic rats are resistant to acute stress but maintain spatial and non-spatial learning.

The behavioral phenotype of five-month-old rats overexpressing neuropeptide Y (NPY) has previously been described [Proc Natl Acad Sci USA 97 (2000) 12852]. In this transgenic rat model, there is central overexpression of prepro-NPY mRNA and NPY peptide in the hippocampus and hypothalamus and decreased Y1 binding sites within the hippocampus. These molecular and neurochemical events led to altered anxiety profile and learning abilities in NPY-overexpressing rats. In the present study, anxiety and learning/memory related behaviors were examined in one-year-old NPY-transgenic rats in order to assess any behavioral changes that may have occurred during the aging process. As observed in 5-month-old overexpressing rats, aged NPY-transgenic animals are resistant to acute physical restraint stress measured by the elevated-plus maze and demonstrate anxiolytic-like activity in the open field. However, in contrast to data in young rats, there was no significant difference between aged wildtype and NPY-transgenic animals in relation to spatial and non-spatial memory as indicated by the (allo- and ego-centric) Morris water maze and object recognition test. It would thus appear that the anxiolytic-like profile observed in young NPY-overexpressing rats is maintained in older animals providing further evidence for a role for NPY in anxious behaviors. However, the cognitive deficits observed in young rats do not appear to occur in older animals suggesting the existence of compensatory mechanisms leading to a reversal of the learning deficits noted in younger animals. These results also provide additional evidence for the mechanistic dissociation between anxiety and cognition-related behaviors modulated by NPY.

Adaptation, Psychological↗
PubMed2006

Spatially uniform sampling in 4-D EPR spectral-spatial imaging.

Four-dimensional EPR imaging involves a computationally intensive inversion of the sampled Radon transform. Conventionally, N-dimensional reconstructions have been carried out with N-1 stages of 2-D backprojection to exploit a dimension-dependent reduction in execution time. The huge data size of 4-D EPR imaging demands the use of a 3-stage reconstruction each consisting of 2-D backprojections. This gives three orders of magnitude reduction in computation relative to a single stage 4-D filtered backprojection. The multi-stage reconstruction, however, requires a uniform angular sampling that yields an inefficient distribution of gradient directions. We introduce a solution that involves acquisition of projections uniformly distributed in solid angle and reconstructs in three 2-D stages with the spatial uniform solid angle data set converted to uniform linear angular projections using 2-D interpolation. Images were taken from the two sampling schemes to compare the spatial resolution and the line width resolution. The degradation in the image quality due to the additional interpolation was small, and we achieved approximately 30% reduction in data acquisition time.

Algorithms↗
PubMed2005

Sustained involvement of a frontal-parietal network for spatial response selection with practice of a spatial choice-reaction task.

With practice, performance on a task typically becomes faster, more accurate, and less prone to interference from competing tasks. Some theories of this performance change suggest it reflects a qualitative reorganization of the cognitive processing required for successful task performance. Other theories suggest this change in performance reflects a more quantitative change in the amount of processing required to perform the task. Neuroimaging research results provide some support for both of these broad theories. This inconsistency may reflect the complex nature of the effect of practice on cognitive and neural processing. Our current experiment addresses this issue by investigating the effect of practice of a relatively easy perceptual-motor task on the frontal-parietal brain network for a specific cognitive process (viz. spatial response selection). Participants were scanned during three functional magnetic resonance imaging sessions on separate days within 4 days while they performed a relatively easy spatial perceptual-motor task. We found sustained activity with practice in right dorsal prefrontal cortex; and sustained but decreasing activity in bilateral dorsal premotor, left superior parietal, and precuneus cortices, supporting a quantitative decrease in difficulty of response selection with practice. Conversely, we found a qualitative change in activity with practice in left dorsal prefrontal cortex. This brain region is outside the response selection network for this task and showed activity only during novel task performance. These results suggest that practice produces both qualitative and quantitative changes in processing. The particular effect of practice depends on the cognitive process in question.

Adult↗
PubMed2006

Spatial summation and spatial discrimination of pain sensation.

The aims of this study were to explore: (a) the interrelation between spatial summation (SS) and spatial discrimination (SD) of pain, (b) whether the two phenomena are subserved by different sensory channels. SS and SD of pain were measured with contact heat stimuli delivered at slow (0.50 degrees C/s) and fast (40 degrees C/s) rise times. Pressure nerve block of the radial nerve was employed to assess whether differential activation of C and A delta fibers is obtained by these different rates of rise. Two discrete stimuli (each 3x3 cm) were applied to the forearm with separation distances between them varying from 0 to 30 cm. A single stimulus or two applied simultaneously were employed. For each distance heat-pain threshold (HPT) and suprathreshold pain ratings were obtained and subjects were asked to report the number of pain spots perceived (SD). SS of HPT occurred at separations smaller than 10 cm whereas significant SD occurred only from a separation of 10 cm and up. SS of suprathreshold sensations was completely accounted for by threshold changes. Stimulation rate did not affect SS or SD. Following nerve block, thresholds obtained with the fast rise stimulation increased significantly (HPT rose from 46.2 to 50.5 degrees C) but those obtained with slow rise stimuli were not affected by the block, indicating that C and A delta fibers were activated selectively. The results suggest that: (a) SS and SD are mutually exclusive functions of the nociceptive systems, (b) C and A delta nociceptors are probably similarly involved in these functions.

Adult↗
PubMed2006

Do parietal cortical lesions impair spatial attention or allocentric spatial perception?

It remains unclear whether monkeys with large parietal cortical lesions fail "landmark" tasks because they cannot judge the relative distances between landmark and response locations, or because they fail to attend to, or even to notice, the landmark. Monkeys with small posterior parietal (SPP), large posterior parietal (LPP), superior temporal sulcus (STS), or frontal eye field (FEF) lesions were tested on a landmark task in which the physical salience of the landmark and its location varied. Only the LPP monkeys were impaired, seemingly because they overtly failed to shift attention during each trial, responding to whichever food well they looked at first. A task based on one used with neurological patients was therefore introduced in which the monkeys had to discriminate between two white square plaques each containing a spot, where the spot on the positive stimulus was centrally placed. Solving this task requires an allocentric judgement about the relative location of each spot to the edges of the plaque. Even on the most difficult discrimination, monkeys with large parietal lobe lesions were unimpaired. The deficits previously reported on landmark tasks probably reflect a failure of spatial attention or attention to objects rather than an inability to judge allocentric spatial relationships.

Animals↗
PubMed1998

The effects of nicotine on spatial and non-spatial expectancies in a covert orienting task.

The present study examined how nicotine influences shifts of visuo spatial attention in casual smokers at each of three delays after smoking one cigarette: immediately, 1 h and 24 h. Informative peripheral cues were used to exogenously orient attention to the location where an increase or decrease in the size of a peripheral object was most likely to occur. One size change was more likely to occur than the other and the task was choice (expansion/contraction) reaction time. The performance decrement obtained when the target appeared at an uncued location was smallest in sessions run immediately after smoking (when nicotine levels were highest), suggesting that nicotine may increase the ease with which attention can be disengaged from a cued location. This finding confirms previous research which suggests a specific role for the basal forebrain cholinergic system in visual orienting. In contrast, nicotine was not found to affect non-spatial expectancies based on stimulus-response (expansion/contraction) probability. These findings, together with recent converging evidence, strongly support the proposition that different attentional operations are mediated by different neural subsystems.

Adult↗
PubMed1999

Spatial attention improves performance in spatial resolution tasks.

This study used peripheral precueing to explore the effect of covert transient attention on performance in spatial resolution tasks. Experiments 1 (Landolt-square) and 2 ('broken-line') measured gap resolution and Experiment 3 measured vernier resolution. In all three tasks the target was presented alone in a large number of possible locations, ranging from 1.5-6 degrees of eccentricity in the vertical or horizontal axes. The precue indicated the target location but did not convey information regarding the correct response. Performance decreased as the gap size or the vernier offset size decreased and as target eccentricity increased. Precueing improved performance in terms of RT and accuracy in all three tasks; the eccentricity effect decreased in the cued trials of the gap resolution tasks. These findings support the idea that the performance improvement at attended locations results, to some extent, from an enhanced spatial resolution at the cued location, and not just from distractor exclusion, diminished uncertainty, or decisional factors.

Attention↗
PubMed1998

Estimating spatial resolution of in vivo MR images using spatial modulation of magnetization.

Spatial Modulation of Magnetization is shown to provide a means of estimating perceived spatial resolution directly in vivo. On the first magnetic resonance system tested, resolution in conventional spin echo images was found to be stability limited in the phase encoding direction and voxel limited (via the Nyquist sampling theorem) in the frequency encoding direction both in vitro and in vivo. As the voxel size approaches half the stripe separation, fringes of resolved and unresolved stripes are formed across the image. This phenomenon is explained and described mathematically. On a second magnetic resonance scanner, resolution in the phase encoding direction of fast spin echo images with centrically ordered phase encoding is shown to be voxel limited in substances with long T2, with poorer resolution in substances with short T2. Resolution in fast spin echo images with linearly ordered phase encoding was shown to be voxel limited in the phase encoding direction.

Artifacts↗
PubMedDate not supplied

Refractive astigmatism acts predominantly as a source of high spatial frequency image distortion: the associated lineal distortions can be overcome by using a low pass spatial filter!

PURPOSE: Surprisingly, an important characteristic of astigmatism has been overlooked by ophthalmic and clinical scientists. Apparently, refractive astigmatism is due largely to a form of high spatial frequency image distortion. METHODS: Characteristic astigmatic image distortion can be minimized or eliminated by using a low-pass spatial filter (here, a ground glass plate was employed for this purpose). The ground glass is placed a short distance in front of a visual acuity chart, or it may be used with other tests, such as vernier acuity. RESULTS: This test has been performed by us on large numbers of patients and test subjects. A clinician can try this test for himself/herself. Place a +2.00 D.C. (any axis) lens in front of the eye; the usual distortions will be observed. Locate the ground glass plate as described. The usual distortions associated with the conoid of Stürm will not be visible or will be virtually eliminated, although some image blur will remain. CONCLUSIONS: This technique has significance, e.g., in visual screening programs in developing nations, or in assessing patients with media disorders prior to ophthalmic surgery.

Astigmatism↗
PubMed2002

Spatial updating of locations specified by 3-d sound and spatial language.

Blind and blindfolded sighted observers were presented with auditory stimuli specifying target locations. The stimulus was either sound from a loudspeaker or spatial language (e.g., "2 o'clock, 16 ft"). On each trial, an observer attempted to walk to the target location along a direct or indirect path. The ability to mentally keep track of the target location without concurrent perceptual information about it (spatial updating) was assessed in terms of the separation between the stopping points for the 2 paths. Updating performance was very nearly the same for the 2 modalities, indicating that once an internal representation of a location has been determined, subsequent updating performance is nearly independent of the modality used to specify the representation.

Adult↗
PubMedDate not supplied

[Measuring spatial micro-movement of the femur shaft of endoprostheses in relation to the spatial force system].

A precision measurement method (resolution: 0.1 micron) is described that simultaneously tracks spatial movement of the prosthesis and its bending as a function of the spatial force system (three force and three torque components). With this technique, we examined the effects of complete separation between shaft and cement on bending and micromovement. With regard to mechanical stability a completely tied and a loosened prosthesis differ only in respect to torsional load: the loosened prosthesis bears a 2.5-fold larger torsion flexibility. In both cases the shaft does not move like a rigid body: it bends up or down depending on the way the torque acts. It is the torques (that are produced by the forces) rather than the forces themselves that are responsible for the extent of micromovement and bending. In the completely loosened shaft, the shaft's apex only moves either intrusively or extrusively according to the directions of the torque vector: the horizontal movement cannot be resolved. The data suggest that shafts that are freely mounted into its cement quiver load the cement layer in a less damaging fashion than tied shafts.

Adult↗
PubMed1977

What is the child's own view in a spatial task?: a spatial by temporal interaction affecting errors in perceptual reports.

Children are sometimes called 'egocentric' on the basis of their performance on Piagetian spatial-inference tasks. They often inappropriately substitute their own perceptual report for another observer's. Little is known about what responses are activated in giving perceptual reports. An experiment is presented which tightly controls spatial and temporal stimulus ordering. One condition elicted reports of that aspect of the display which children could not see instead of what they could see. Explanations are considered on the basis of relational coding and temporal responsiveness.

Child↗
PubMed1977

Spatial effects in speech perception in the absence of spatial competition.

Two synthetic speech syllables, differing in pitch, were presented over one loudspeaker situated at one of the following azimuths: 0 degrees (in from of the subject); 45 degrees, 90 degrees, and 135 degrees to the left or to the right; and 180 degrees. The subject's task was to report the high-pitch syllable. The pattern of performance can be described in terms of two component effects: a decreasing anterior-posterior gradient, and right-side advantage. Competition between messages from one direction only appears to be as effective in determining auditory spatial effects as competition between spatially distinct sources.

Adolescent↗
PubMed1987

Spatial frequency and selective attention to spatial location.

The effect of spatial attention on the detectability of gratings of different spatial frequency was measured using a probe technique. Three experiments are reported in which the detectability of full-field probe gratings was measured while subjects analyzed stimuli presented in either the central or the peripheral visual field. Selective attention to peripheral stimuli produced a facilitation at low frequencies and a decrement at high frequencies. These effects disappeared under forced-choice presentation.

Attention↗