PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Spatial orientation”

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 631 records · Page 35Linked to original sources
PubMedDate not supplied

[Stereotaxic microsurgical resection of intracranial tumors guided by imaging and assisted by computer].

INTRODUCTION: The microsurgical techniques for resection of intracranial lesions are limited where anatomical references do not exist or cannot be used as guides in the dissection of deeply located lesions or in more superficial eloquent areas. The stereotaxic guide, guided by imaging gives precise volumetric and geometric definition in intracranial lesions. Its application in the resection of intracranial tumors has special characteristics due to their biological condition and varied localization. OBJECTIVES: Spatial orientation during surgery is essential. We show this application of stereotaxic surgery in the Centro Internacional de Restauración Neurológica (CIREN) in La Havana, Cuba, between May 1994 and February 1988, describing 65 microsurgical operations done using stereotaxis in 62 patients with intracranial cerebral tumors. PATIENTS AND METHODS: The procedure was divided into three stages: acquiring an image, computerized axial tomography and surgical planning, with the STASSIS planning system and microsurgical procedures, including systems of stereotaxis: Leksell, Micromar and Estereoflex. RESULTS: Of the total, 27 of these patients had glial tumors, 33 non-glial tumors and only 2 had non-neoplastic lesions of different sites and sizes. A total of 30 resections were done. Surgical morbidity was minimal and there was no surgical mortality. CONCLUSIONS: The main advantages of this method are: exact localization of the site for craniotomy, easy spatial orientation and ease in distinguishing the delimitation between the tumour and the healthy tissue. It has been shown that Estereoflex may be used in cerebral microsurgery.

Adolescent↗
PubMed1979

The electroencephalogram (EEG) as a research tool in human behavior genetics: psychological examinations in healthy males with various inherited EEG variants. II. Results.

The results of psychological examinations on 298 adult male probands with various inherited EEG variants are described. They may be summarized as follows: 1) The low-voltage (N) group scored high in intelligence tests, especially in spatial orientation. Personality scores revealed this group as 'normal', extravert, group-dependent, and not very energetic. 2) The borderline low-voltage (NG) group showed slight weakness in abstract thinking, short-time memory, and motor skills and a relatively strong tendency to have 'neurotic' complaints. Reaction time and motor skills were poor. 3) The occipital fast alpha-variants (BO) group performed very well in tests of abstract thinking and motor skills. 4) The monotonous alpha (R) group showed average performance in most intelligence scores but above-average in short-time memory and in precision under stress conditions. Personality scores indicated high spontaneous activity and toughmindedness. 5) The BG (fronto-precentral beta-group) category showed very low MMPI scores, indicating little neurotic tendency. Intelligence could be above average. 6) The diffuse beta (BD) group scored low in intelligence tests, especially in spatial orientation, and had a high error rate in tests measuring concentration and precision. Most differences were relatively small; the whole range of test scores could be found in all EEG groups.

Adult↗
PubMed2003

Optokinetic stimulation in microgravity: torsional eye movements and subjective visual vertical.

INTRODUCTION: Microgravity provides unique sensory inputs to the vestibular and oculomotor systems. We sought to determine the effects of long-term spaceflight on sensing of spatial orientation. METHODS: Two cosmonauts participated in experiments on human vestibulo-visual interactions during a long-term mission (178 d) in the MIR station in 1995. During circular optokinetic stimulation (OKS) the tonic torsional eye position (torsional beating field, TBF) and the subjective visual vertical (SVV) were recorded on several days of the space mission as well as pre- and post-flight. A reference data set was obtained from healthy subjects on Earth, in whom the TBF was measured in upright and in prone positions. RESULTS: Neither cosmonaut showed changes in the SVV or the TBF values during the first days in microgravity. On flight day 149, cosmonaut A showed an increase of both values, which continued to rise by 4- and 10-fold until the end of the flight (TBF: 8.1 degrees; SVV: 216.8 degrees). This cosmonaut reported that the increase was accompanied by a loss of spatial orientation. In contrast, cosmonaut B's values remained at pre-flight levels (TBF: 1.6 degrees; SVV: 4.4 degrees). Post-flight values of the TBF did not significantly differ from pre-flight values for either cosmonaut. Subjects showed an increase of the TBF by more than a factor of 2 in prone position (range -7.7 degrees to +10.2 degrees) compared with upright position (range -3.7 degrees to +3.4 degrees). CONCLUSIONS: Pre-flight, post-flight and during the first part of the flight, both cosmonauts exhibited values similar to those of normal subjects in an upright position. The increased TBF values of cosmonaut A from flight day 110 on were within the range of the normal subjects in prone (face-down) position, when the gravity vector cannot be used to stabilize the TBF against the rotating stimulus (the axis of rotation is parallel to the gravity vector). The increasing deviations of cosmonaut A's SVV values in-flight suggest the presence of an internal body reference system, which weakened throughout the flight and thus lost its stabilizing effect.

Adaptation, Physiological↗
PubMed1998

Vibration-induced postural posteffects.

It generally is known that vibration of various muscles in free-standing subjects evokes a spatially oriented postural response. Furthermore, it recently has been shown that when a vibratory stimulus is terminated, a powerful involuntary contraction of the previously vibrated muscle often occurs that, under the isotonic condition, is accompanied by movement of a limb. The aim of this study was to explore effects of a low-amplitude mechanical vibration, applied in a seated position, on the standing posture. The 30-s vibration was applied bilaterally at the ankle level to anterior or posterior tendons and at the cervical level in front or back of the neck, at one site only at a time. Center of pressure trajectories were monitored during quiet stance for </=19 min after the offset of vibration, and these measurements were compared with a previbration control trial. The results clearly indicate that vibration produced in all subjects strong, long-lasting dynamical modification of posture mainly in the anterior-posterior direction. Spatial orientation of the induced postvibratory shift in posture was dependent on the vibration side. We conclude that sustained Ia sensory inflow, evoked by vibration, has a powerful after-effect on the motor system at the postural level.

Adult↗
PubMed1983

Arrangement of hexons and polypeptide subunits in the adenovirus capsid.

With direct analysis of electron micrographs and with Markham's rotational integration technique we have demonstrated that in the adenovirus capsid the triangular profile of the hexon-end facing are formed by one polypeptide each and the sides by two neighbouring polypeptides. The mutual rotational and spatial orientation of the three hexon polypeptide subunits has been determined in relation to each other and to the pentons. Two polypeptides of the peripentonal hexons are oriented towards the penton. A "one-to-one" pattern was found in relation to two peripentonal hexons, "one-to-two" to two of the three neighbouring hexons and "two-to-two" to one hexon. "One-to-two" orientation is the general rule in the GONs. The mutual orientation between the hexons of the neighbouring GONs being in connection with each other and that of the polypeptide subunits of the peripentonal hexons is characterized by the regular alternation of the "one-to-two", "one-to-one" and "two-to-two" orientation. The mutual orientation between the hexons at different points of the capsid has been studied in model experiments and was characterized by the angle enclosed by the longitudinal axis of the given hexon and that of the other hexon in open position towards the virion surface, if the longitudinal axis of the hexons of the triangular faces are perpendicular to the plane of the face and those of the edge-hexons perpendicular to the plane of the edge and the longitudinal axis of the penton faces in radial direction the centre of the virion. In this way the longitudinal axes of the peripentonal hexons enclose with that of the penton an angle of approximately 32 degrees and with each other approximately 36 degrees. The longitudinal axis of the edge-forming hexons shows a deviation of approximately 21 degrees in relation to the longitudinal axes of hexons situated on the neighbouring triangular faces. We present on a tentative virus model the mutual rotational and spatial orientation of all the polypeptide subunits of the adenovirus-building hexon capsomers. This corresponds to the two-, three- and fivefold rotational symmetry characteristic of the icosahedral capsid.

Adenoviruses, Human↗
PubMed1989

Morphometric versus densitometric assessment of coronary vasomotor tone--an overview.

The main advantage of the morphometric approach is that the spatial orientation of the vessel with respect to the image intensifier is not very important. Its most severe limitations are that reasonable accuracy can only be obtained with circular lumina, and that accuracy decreases rapidly with the vessel diameter. The densitometric approach is much less dependent on the shape of the lumen and on the correct identification of the vessel wall in the image. A further essential advantage is that one measures directly the cross-sectional area of the vessel instead of a 'diameter' of low haemodynamic relevance. Severe requirements must however be met if the potential accuracy of densitometry is to be fully exploited. The morphometric approach seems thus preferable for absolute or relative diameter measurements on intact vessels, while densitometry is superior in case of irregular or small lumina. Morphometric calibration using the injection catheter can induce non-negligible errors in both approaches. Grid calibration is probably more accurate, but also more tedious. In the densitometric approach, '3D-calibration' by help of a cube of known size allows also determination of the spatial orientation of the vessel in space. This solution requires however biplane imaging.

Angiography, Digital Subtraction↗
PubMed1994

The use of an unbaited radial maze in neurotoxicology: II. Sensory inputs, general malaise and locomotor activity.

An unbaited 6-arm radial tunnel maze (6-arm RTM) is used in our laboratory to screen for working- and reference memory deficits in rats in the course of neurotoxicological studies. In the 6-arm RTM animals are minimally stressed, and do not need food reward as a reinforcer. Maze behavior is assessed using mean error score of arm repetitions as a measure of 'working memory', left-right discrimination within each arm (expressed as percent "blind-alley" visits) as a measure of 'reference memory' and trial time (time to complete 12 arm entries) as a measure of locomotor activity. As shown for other mazes sensory deficits may affect spatial orientation. Sensory dysfunction are likely to be induced by neurotoxic compounds, while at toxic doses reduced locomotor activity is a common finding. When using the 6-arm RTM in the course of neurotoxicity studies to assess cognitive functions such potentially confounding effects have to be excluded to allow the conclusion of a cognitive impairment. The aim of the following experiments was to assess if visual, vibrissal or olfactory dysfunction, or hypoactivity may affect memory parameters in the 6-arm RTM. Loss of visual, olfactory or vibrissal input alone did not affect any of the maze parameters. Combined loss of visual and vibrissal or olfactory inputs increased mean error score. Loss of olfaction prolonged trial time under both lighting conditions. Acrylamide- and vitamin B6-induced sensorymotor dysfunctions and hypoactivity did not affect mean error score or percent blind-alley visits in the 6-arm RTM. Similarly, gastrointestinal distress and hypoactivity induced by lithium chloride injections did not affect parameters of working or reference memory. Results indicate that in the 6-arm RTM (1) olfactory, visual and, to a minor extent, vibrissal input contribute to the sensory information necessary for spatial orientation and (2) reduced locomotor activity secondary to impaired sensorymotor abilities or drug-induced illness do not influence working or reference memory parameter.

Analysis of Variance↗
PubMed2001

Attention deficits in minimal hepatic encephalopathy.

Minimal hepatic encephalopathy (HE) is characterized by a decrease of psychomotor speed, and deficits in visual perception, visuo-spatial orientation, and visuo-constructive abilities. Attention deficits have also been proposed to be part of the syndrome. Several attempts were made in the past to elaborate suitable psychometric means for the assessment of minimal HE. However, there is still no "gold standard" for the diagnosis of minimal HE. We recently evaluated the so called "PSE-Test" for the assessment of minimal HE, a test battery which does not include a test predominantly aimed at the assessment of attention. We therefore presented a battery of attention tests in addition to the PSE-Test to a group of cirrhotics without clinical signs of HE compared to a healthy control group matched for age and education to determine whether the addition of special attention tests would increase the diagnostic sensitivity of the PSE-Test. It was shown that the patients with a pathological PSE-Test result differed significantly from controls in all attention tests applied, while the patients with normal PSE-Test results achieved attention test results similar to that of the controls. Thus, the PSE-Test results represent attention deficits as well as deficits in motor skills, visuo-spatial orientation, and visual construction.

Adult↗
PubMed2003

Interpretation of a discontinuity in the sense of verticality at large body tilt.

Results of earlier spatial-orientation studies focusing on the sense of verticality have emphasized an intriguing paradox. Despite evidence that nearly veridical signals for gravicentric head orientation and egocentric visual stimulus orientation are available, roll-tilted subjects err in the direction of the long body axis when adjusting a visual line to vertical in darkness (Aubert effect). This has led to the suggestion that a central egocentric bias signal with fixed strength and direction acts to pull the perceived vertical to the subjects' zenith (M-model). In the present study, the subjective visual vertical (SVV) was tested in six human subjects, across the entire 360 degrees range. For comparison, body-tilt estimates from four subjects where collected in a separate series of experiments. For absolute tilts up to approximately 135 degrees, SVV responses showed a gradually increasing Aubert effect that could not be attributed to errors in perceived body tilt but was nicely in line with the M-model. At larger absolute tilts, SVV errors abruptly reversed sign, now showing a pattern concordant with errors in body-tilt estimates but incompatible with the M-model. These results suggest that, in the normal working range, the perception of external space and the perception of body posture are based on different processing of body-tilt signals. Beyond this range, both spatial-orientation tasks seem to rely mainly on a common tilt signal.

Adult↗
PubMed1996

Nature and precision of temporal coding in visual cortex: a metric-space analysis.

1. We recorded single-unit and multi-unit activity in response to transient presentation of texture and grating patterns at 25 sites within the parafoveal representation of V1, V2, and V3 of two awake monkeys trained to perform a fixation task. In grating experiments, stimuli varied in orientation, spatial frequency, or both. In texture experiments, stimuli varied in contrast, check size, texture type, or pairs of these attributes. 2. To examine the nature and precision of temporal coding, we compared individual responses elicited by each set of stimuli in terms of two families of metrics. One family of metrics, D(spike), was sensitive to the absolute spike time (following stimulus onset). The second family of metrics, D(interval), was sensitive to the pattern of interspike intervals. In each family, the metrics depend on a parameter q, which expresses the precision of temporal coding. For q = 0, both metrics collapse into the "spike count" metric D(Count), which is sensitive to the number of impulses but insensitive to their position in time. 3. Each of these metrics, with values of q ranging from 0 to 512/s, was used to calculate the distance between all pairs of spike trains within each dataset. The extent of stimulus-specific clustering manifest in these pairwise distances was quantified by an information measure. Chance clustering was estimated by applying the same procedure to synthetic data sets in which responses were assigned randomly to the input stimuli. 4. Of the 352 data sets, 170 showed evidence of tuning via the spike count (q = 0) metric, 294 showed evidence of tuning via the spike time metric, 272 showed evidence of tuning via the spike interval metric to the stimulus attribute (contrast, check size, orientation, spatial frequency, or texture type) under study. Across the entire dataset, the information not attributable to chance clustering averaged 0.042 bits for the spike count metric, 0.171 bits for the optimal spike time metric, and 0.107 bits for the optimal spike interval metric. 5. The reciprocal of the optimal cost q serves as a measure of the temporal precision of temporal coding. In V1 and V2, with both metrics, temporal precision was highest for contrast (ca. 10-30 ms) and lowest for texture type (ca. 100 ms). This systematic dependence of q on stimulus attribute provides a possible mechanism for the simultaneous representation of multiple stimulus attributes in one spike train. 6. Our findings are inconsistent with Poisson models of spike trains. Synthetic data sets in which firing rate was governed by a time-dependent Poisson process matched to the observed poststimulus time histogram (PSTH) overestimated clustering induced by D(count) and, for low values of q, D(spike)[q] and D(intervals)[q]. Synthetic data sets constructed from a modified Poisson process, which preserved not only the PSTH but also spike count statistics accounted for the clustering induced by D(count) but underestimated the clustering induced by D(spike)[q] and D(interval)[q].

Action Potentials↗
PubMed1998

Interaction of vestibular, somatosensory and visual signals for postural control and motion perception under terrestrial and microgravity conditions--a conceptual model.

This article considers the intersensory interaction mechanisms and biomechanical aspects of human spatially oriented behavior and asks to what extent these are interrelated on earth by gravity and how they might be affected under microgravity. The interactions between vestibular, somatosensory and visual inputs for postural control are obscured by several complications (biomechanics, multi-body dynamics, multimodal feedback control, cognition etc.). However, they can be revealed in psychophysical studies on human self-motion perception. Based on such studies, we present a conceptual model, which we think is valid also for postural control. It accounts for the multi-segmental structure of the body, allowing local control of inter-segmental joints, but uses one global reference system for all segments, which is derived from the intersensory interactions. We hold that, at a sensory level, the system is tied together by linkages between vestibular, visual and somatosensory information which develop through experience of inertial and gravitational reaction forces. On earth these linkages are established even in the absence of active behavior by gravity, allowing the incorporation of one's body and its support into a notion (Gestalt) of ourselves in the environment. Under microgravity, in contrast, the linkages have to be actively established for postural and perceptual stability in the environment (e.g., by grasping a handle on the wall). From this work we recommend that future research under altered gravity conditions should be guided by models that include biomechanics, considerations of intersensory interaction and dynamic control mechanisms. Such an integrative conceptual framework will be helpful for reaching a general understanding of spatially oriented behavior.

Gravitation↗
PubMed1996

Uncertainty experiments support the roles of second-order mechanisms in spatial frequency and orientation discriminations.

Previous studies of spatial frequency and orientation discrimination [Vision Res. 32, 1885 (1992)] suggest the existence of two second-order cortical mechanisms: one that mediates spatial frequency discriminations and sums signals across orientations and one that mediates orientation discriminations and sums signals across spatial frequency bands. The existence of each mechanism is tested in an uncertainty experiment in which the observer does not know which of two hypothetically pooled signals deviates from the standard but must judge whether the deviation is an increment or a decrement. No uncertainty effect is expected if the signals are completely pooled. Observed effects are compared with this expectation and with both theoretical and empirical estimates of the effects expected if the signals are processed separately. Results support the existence of the first mechanism, but not its exclusive role in mediating spatial frequency judgments, and support the exclusive role of the second mechanism in mediating orientation judgments.

Humans↗
PubMed1992

Ideational fluency in Parkinson's disease.

Recent research on Parkinson's disease (PD) suggests that executive functions are impaired but that visuospatial functions may be spared. This dissociation has been attributed to dysfunction in ascending dopaminergic pathways affecting the prefrontal cortex. We investigated these ideas in a sample of intellectually intact patients with idiopathic, optimally treated PD (N = 20) and in spouse controls (N = 15); the groups were divided into young (age < 60) and old subgroups, each comparable on education, vocabulary level, and Mini-Mental State scores. Six tasks were selected from a set of factor-referenced cognitive tests to measure three abilities: (1) ideational fluency (ability to generate ideas), (2) flexibility of use (ability to shift mental set), and (3) spatial orientation (ability to perceive spatial patterns). PD patients were impaired only on the ideational fluency factor (p = .01). An age-related deficit was seen on the spatial factor (p < .05) with a trend on the flexibility factor (.05 < p < .10). No interactions were significant. The findings suggest that when age and verbal intelligence are controlled, PD patients show no deficit on purely spatial tasks; in contrast, patients seem less able to generate ideas though capable of shifting from one idea to another.

Brain Mapping↗
PubMed2000

Crosslinking between alpha and beta subunits defines the orientation and spatial relationship of some of the transmembrane helices of the proton-translocating pyridine nucleotide transhydrogenase of Escherichia coli.

The proton-translocating pyridine nucleotide transhydrogenase of Escherichia coli is composed of two types of subunits, alpha and beta, organized as an alpha(2)beta(2) tetramer. The protein contains three recognizable domains, of which domain II is the transmembrane region of the molecule containing the pathway for proton translocation. Domain II is composed of four transmembrane helices at the carboxyl-terminus of the alpha subunit and either eight or nine transmembrane helices at the amino-terminal region of the beta subunit. We have introduced pairs of cysteine residues into a cysteine-free transhydrogenase by site-directed mutagenesis. Disulfide bond formation between some of these cysteine residues occurred spontaneously or on treatment with cupric 1, 10-phenanthrolinate. Analysis of crosslinked products confirmed that there are nine transmembrane helices in the domain II region of the beta subunit. The proximity to one another of several of the transmembrane helices was determined. Thus, helices 2 and 4 are close to helix 6 (nomenclature of Meuller and Rydström, J. Biol. Chem. 274, 19072-19080, 1999), and helix 3 and the carboxyl-terminal eight residues of the alpha subunit are close to helix 7. In the alpha(2)beta(2) tetramer, helices 2 and 4 of one alpha subunit are close to the same pair of transmembrane helices of the other alpha subunit, and helix 6 of one beta subunit is close to helix 6 of the other beta subunit.

Amino Acid Sequence↗
PubMed1999

Contrast dependency of foveal spatial functions: orientation, vernier, separation, blur and displacement discrimination and the tilt and Poggendorff illusions.

To examine the effect of reducing luminance contrast in human foveal vision, discrimination thresholds were measured in four tasks and also a numerical measure of two visual illusions were obtained by a nulling technique. The patterns used for all tasks were made very similar to facilitate comparison between them--all featured luminance step edges whose contrast could be varied from near unity down to the detection threshold. Orientation, vernier and blur discrimination thresholds rise on average 5-6-fold when the contrast is reduced from near unity to a Michelson value of 0.03. Jump displacement thresholds are somewhat more robust to contrast reduction, and the curve of separation discrimination versus contrast is much shallower, rising by a factor of about 2. The magnitude of the Poggendorff and tilt illusions changes very little until the inducing contours are barely detectable.

Adult↗
PubMed1989

Cells transmit spatial information by orienting collagen fibers.

Parallel orientation of large cell populations occurs when cells are cultured on thin collagen films if and only if a gel is restrained at two or more edges. The direction in which cell bodies orient is determined by the geometry of the gel. It can be shown that tension exerted by cells on a collagen gel leads to reorientation of collagen fibers in a direction determined by the initial geometry of the collagen gel. Hence, tension generated by cells leads to collagen fiber orientation which, in turn, determines the spatial orientation and morphology of cells. Thus, without cell-to-cell contact, cells can communicate with each other by applying tension to collagen fibers in their extracellular matrix. Information concerning the shape of the environment can be transmitted via such long range forces.

Animals↗