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Results for “Spatial orientation”

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At least 487 records · Page 27Linked to original sources

PubMed1992

Three dimensional vector analysis of the spatial components and voltage magnitudes of the P300 response during different attentional states and stimulus modalities.

The spatial orientation and vector magnitude of the P300 event related potential (ERP) were investigated under both passive and active attentional states using stimuli presented to two sensory modalities. Three orthogonal electrode pairs were used to establish a tri-axial reference frame. By combining the separate single channel data recordings into a Cartisian coordinate system, both the spatial orientation and the vector magnitude of the P300 response could be derived and described as a hypothetical dipole. Results suggested that changes in amplitudes, recorded with individual electrode pairs, can be attributed largely to changes in the spatial orientation of a rotating P300 response dipole, and not simply to the altered magnitude of the response. The combined-axes P300 response occurs in two separate spatial domains, depending on stimulus modality and attentional state.

Acoustic Stimulation↗

PubMedDate not supplied

Space vestibulo-neuroscience in the new century: why proceed in semi-darkness?

With advancing technology, neuroscientists have explored vestibular transducer microstructure and molecular processes, neural pathways of interaction between vestibular visual and proprioceptor systems and neurochemical processes of adaptive change. Progress in space vestibulo-neuroscience will be fostered by focus on interactions among the systems involved in whole-body movement relative to the earth. Description of perceptual and sensorimotor reactions to complex accelerative stimuli during goal-directed and passive movement is crucial to conceptualizing the functional significance of various interactions and viable theory. The vestibulo-ocular reflex is now quantifiable in three dimensions, but description of the dynamics of spatial orientation perception has progressed very little in the 20th century. Much is known about perception of static body tilt, but the dynamics of tilt and movement perception (beyond rotation about an earth-vertical axis) remains relatively unexplored. Innovative procedures and departure from accepted psychophysics are needed. Models developed to predict the dynamics of spatial orientation under complex conditions must be consistent with information at all levels (neural, sensorimotor, and perceptual). To close our eyes to any one aspect of the spatial orientation reaction is to proceed in semi-darkness unnecessarily.

Animals↗

PubMed1982

Binocular rivalry: suppression depends on orientation and spatial frequency.

In binocular rivalry the time during which different stimuli are perceived depends--amongst other things--on their spatial frequency (sf) contents, on contrast and on orientation. Limiting the sf-range of both periodic and aperiodic stimuli in different ways (while keeping the contrast constant) decreased their predominance. This result seems to corroborate the concept of spatial frequency channels in human vision. Decreasing the contrast also decreased predominance. Thus blurred patterns are suppressed by sharply focused ones because of both their lower contrast and their loss of high sf's. This has consequences for the therapy of strabismic amblyopia. Obliquely oriented patterns were almost as dominant as vertical ones and much more than horizontal ones. Instead of a conventional "oblique-effect" we found a "vertical-effect".

Adolescent↗

PubMedDate not supplied

The accuracy of experimentally determined angiographic right ventricular volume.

The purpose of this investigation was to validate in vivo the accuracy of videoangiocardiographic right ventricular volume determination. Thus the stroke volume of the right ventricle as difference of enddiastolic and endsystolic volume was determined simultaneously (n = 70) by videoangiocardiography and with an electromagnetic flowmeter in 7 open-chested pigs with an average weight of 18.5 kg. Model volumes, calculated with the multiple slices and the area-length methods on the basis of mono- and biplane angiographic right ventricular projections, were corrected conventionally and with factors appropriate for cardiac phase and spatial orientation. The correlation between electromagnetic and angiographic stroke volume was the lowest (r = 0.802) when monoplane and highest (r = 0.949) when biplane methods were used. A systematic error could be prevented (y = -0.3 + 1.0 x; Syx = +/- 1.96 ml) by applying correction factors appropriate for cardiac phase and spatial orientation. The statistical error was independent of the correction used. The correlation coefficient for the optimal corrected monoplane method based on the lateral projection was r = 0.861 and for the ap plane r = 0.930. Right ventricular stroke volume can be determined videoangiocardiographically without systemic error and with an acceptable statistical error, if spatial orientation and cardiac phase are considered. If only monoplane equipment is available, the approjection is preferable.

Angiocardiography↗

PubMed1986

Total internal reflection fluorescence. Measurement of spatial and orientational distributions of fluorophores near planar dielectric interfaces.

The fluorescence collected from a fluorophore which is near a planar interface and is excited by a laser beam that is totally internally reflected at the interface depends on the direction of the absorption and emission transition dipole moments of the fluorophore with respect to the interface, on the distance from the fluorophore to the interface, on the angle of incidence and polarization direction of the exciting beam, and on properties of the collection optics. Expressions are derived for the excitation and subsequent emission and collection of fluorescence from a population of fluorophores near a planar interface. Presented is a general model-independent method of obtaining characteristic parameters of the spatial and orientational distribution of the population of fluorophores, from a measure of the fluorescence collected as a function of the polarization and the incidence angle of the totally internally reflected laser beam. The method is illustrated with several simulation calculations.

Lasers↗

PubMed2000

Unmasking the mechanisms for Vernier acuity: evidence for a template model for Vernier acuity.

The goal of this study was to evaluate the mechanisms underlying Vernier acuity, over a range of spatial scales using narrow-band Vernier stimuli and oblique masking. Specifically, the test stimuli consisted of a pair of vertical ribbons of horizontal cosine grating with a vertical Vernier offset between the ribbons. These stimuli have two important advantages for studying Vernier acuity: (1) they are relatively well localized in vertical spatial frequency, and (2) they are localized in their horizontal extent (width). We measured the orientation, spatial frequency and width tuning of Vernier acuity over a wide range of ribbon spatial frequencies, using a simultaneous oblique masking paradigm. Our masking results suggest that the mechanisms underlying Vernier acuity are tuned to the orientation, spatial frequency and width of the ribbon stimuli. The peak of the bimodal orientation tuning function varies systematically with the spatial frequency of the ribbon. The peak of the spatial frequency tuning function varies systematically with both the ribbon spatial frequency, and the ribbon width (i.e. the grating length). A 'template' model, in which the 'mechanism' is a windowed version of the stimulus is able to account for many features of the data, including results which cannot be easily accounted for by standard multi-scale filter models. Specifically, the template model can account for: (i) the bimodal orientation tuning function, (ii) the systematic variation in the peak of the orientation and spatial frequency tuning functions with spatial frequency, and (iii) the systematic effect of ribbon width on spatial frequency tuning.

Contrast Sensitivity↗

PubMed1999

Reliability of an ear-bow arbitrary face-bow transfer instrument.

STATEMENT OF PROBLEM: Accuracy of techniques for recording the orientation of the maxillary arch to the articulation of the temporomandibular joints has been reported. The variability contributed by the dentist and the equipment within a technique may also contribute to technical error. PURPOSE: This study investigated the variability of a group of dentists who used an arbitrary ear-face-bow instrument to mount a maxillary cast. MATERIAL AND METHODS: The same maxillary cast on a single experimental subject was mounted on an articulator with a common arbitrary ear-face-bow instrument. This cast was equipped with 4 reference points for the measurement of changes of spatial orientation of the cast, which were determined through coordinate measurements with a machinist's microscope. A repeated measures analysis of variance was used to determine statistically significant changes in spatial orientation with a Wilks' Lambda test to compare mean values. RESULTS: A confidence interval of 95% demonstrated that any dentist might expect a range of +/-1.2 mm error in using this instrument/articulator combination. The 3 dentists did not demonstrate any significant differences in the spatial orientation of their mountings in the vertical or horizontal directions. However, there were significant differences in their mountings in linear distance changes of the patient's posterior right side. CONCLUSION: A range of inherent error attributable to the operator using this instrument was recorded.

Analysis of Variance↗

PubMedDate not supplied

Training effects on intelligence of older persons.

In the present study, we tried to answer two main questions: (1) do the elderly of low educational level improve their performance in ability tests when they are trained in inductive reasoning, spatial orientation, or everyday problem solving? (2) If such training were effective, what will the level of training transfer be? Ninety elderly participated in this study (36 women, 54 men; mean age = 67.87); 93.2% of them had less than 4 years of education. The study was based on an experimental-control group design with three main parts: pre-test, cognitive training (three training conditions - Inductive Reasoning, Spatial Orientation and Everyday Problem Solving vs. placebo control) and two post-tests with 3 months of interval. The results indicate that the elderly of low educational level improve their performance both in the domain and transfer test in two of the three training conditions: inductive reasoning and spatial orientation. Results are discussed in relation to other topics related to research studies.

Journal Article↗

PubMed2005

Patients' self-evaluation after 4-12 weeks following xenon or propofol anaesthesia: a comparison.

BACKGROUND AND OBJECTIVE: The aim of this study was to assess postoperative patients' self-evaluation after xenon anaesthesia compared to total intravenous anaesthesia with propofol. METHODS: 160 patients aged 18-60 yr, ASA I-II undergoing elective surgery took part in this randomised-controlled trial. After approval by the local Ethics Committee and as soon as the patients had given their written informed consent, they were randomly allocated to either the xenon (n = 80) or propofol (n = 80) group. In both groups remifentanil was used as opioid. The postoperative patients' self-evaluation was assessed with a double-blind telephone poll. Early spatial orientation, patients' self-evaluation of anaesthesia, choice of the same anaesthesia for future operations and recall of uncomfortable feelings after anaesthesia were determined. RESULTS: 116 Patients were analysed, 63 in the xenon and 53 in the propofol group. The two study groups were comparable with respect to age, weight, height, gender and ASA classification. The two groups indicated similar values in the early spatial orientation at the onset of recovery and thereafter. Patients' self-evaluation of anaesthesia with main emphasis at high marks and repetition of the same anaesthesia if necessary were similar in both groups. Recalls of uncomfortable feelings were comparable but not for postoperative pain and appetite/thirst which appeared with a significantly higher incidence in the xenon group. CONCLUSIONS: Patients' self-evaluation and memory of early spatial orientation following xenon anaesthesia are comparable to propofol.

Adolescent↗

PubMed2000

Assessment of a three-dimensional operating system with skill tests in a pelvic trainer.

OBJECTIVES: To compare the performance of laparoscopic skill assisted by a traditional two-dimensional (2D) and a three-dimensional (3D) endoscopic video system in a pelvic trainer. MATERIALS AND METHODS: The 3D imaging system (DeepVision((R)), Automated Medical Products Corp.) consists of a traditional single lens optic laparoscope, a light source, an endoscopic camera (Stryker), a DeepVision processor and a DeepVision monitor. The 2D images could be obtained with the same system without turning on the DeepVision processor. Thirty-four medical personnel with no laparoscopic surgical experience were enrolled to perform two skill tests, the object-pick-up and spatial orientation test in a trainer box. They were randomly divided into two groups, one group performed the test under 2D conditions first and 3D later, and another group performed the test under 3D conditions first and 2D later. The duration needed to complete the skill tests was recorded and the differences on performance time under 2D and 3D conditions were calculated for each participant. Two-way ANOVA was used to analyze the statistic difference on the performance time in two conditions. RESULTS: The duration needed to complete the initial skill tests was similar among 2D and 3D conditions. For both tests, the average performance time decreased significantly for the second attempt regardless of 2D or 3D conditions. Statistic analysis disclosed significant difference for learning factor (p < 0.001 for object-pick-up test and p < 0.01 for spatial orientation test), but no significant difference between 2D and 3D conditions (p = 0.276 for object-pick-up test and p = 0.327 for spatial orientation test). CONCLUSION: A significant decrease of the performance time at the second attempt reflected the importance of a learning process in laparoscopic surgery. It appears that no significant benefits were obtained by this 3D operating system for surgeons without laparoscopic surgical experience.

Humans↗

PubMed1998

Modeling of facet articulation as a nonlinear moving contact problem: sensitivity study on lumbar facet response.

A finite element (FE) based scheme for modeling facet articulation in a spinal motion segment is proposed. The algorithm presented models the facet articulation as a nonlinear progressive contact problem. This algorithm is used to perform a nonlinear FE analysis of a complete L3-L4 motion segment. The role of facets in load transmission through a motion segment and its sensitivity to facet geometric parameters (i.e., spatial orientation of the facets and the gap between the facet articular surfaces) on this load transmission are studied. Compression, flexion, extension, and torsion loads are used in this study. The effect of facetectomy on gross segment response and disk fiber strains is studied by comparing the response of FE models of motion segment with and without facets. Large facet loads are obtained when the motion segment is subjected to torsional and large extension rotations, whereas minimal facet loads are observed under compression and flexion loading. Removal of facets reduces the segment stiffness considerably in torsion and results in higher strain levels in disk fibers. The facet load transmission is sensitive to facet geometric parameters, i.e., spatial orientation and initial facet joint gap. The facet loads increase uniformly with decrease in initial gap between the facet articular surfaces under compression, extension, and torsional loads. The sensitivity to spatial orientation angles of the facet is, however, found to vary with the type of loading. This sensitivity may account for the wide variation in the facet response reported in literature.

Biomechanical Phenomena↗

PubMed2006

A gender- and sexual orientation-dependent spatial attentional effect of invisible images.

Human observers are constantly bombarded with a vast amount of information. Selective attention helps us to quickly process what is important while ignoring the irrelevant. In this study, we demonstrate that information that has not entered observers' consciousness, such as interocularly suppressed (invisible) erotic pictures, can direct the distribution of spatial attention. Furthermore, invisible erotic information can either attract or repel observers' spatial attention depending on their gender and sexual orientation. While unaware of the suppressed pictures, heterosexual males' attention was attracted to invisible female nudes, heterosexual females' attention was attracted to invisible male nudes, gay males behaved similarly to heterosexual females, and gay/bisexual females performed in-between heterosexual males and females.

Adult↗

PubMed1976

Psychohysical hallucinations of orientation and spatial frequency.

After inspection of vertical sinusoidal gratings at least three distinct types of subjective or "hallucinated" patterns can be seen on a uniform test field. One type, here called horizontal streaming (H), is already well-known from the work of MacKay. A second type (V) looks like aroughly sinusoidal grating about 1-5 octaves above the adapting spitial frequency. Under optimal conditions a second vertical component appears at about 2 octaves below the adapting frequency. The third category of aftereffect consists of diagonal lines (D) at two orientations (about +/-40 degrees from vertical). The spatial-frequency band at these two orientations appears to be fairly broad, but roughly similar to the adapting frequency. The duration and strength of D increased, while V declined, at higher adapting spatial frequencies. D and V were increasing functions of adapting contrast, while H appeared abruptly only after the highest adapting contrast. H, D, and V are thus all functionally distinct. A schematic model of cortical organization is proposed to account for these phenomena. Pattern channels selective for a given orientation are grouped together with movement channels selective for the orthogonal direction. Antagonism between channels within such "modules" accounts for the streaming effect (H). Inhibition between modules tuned to different orientations and spatial frequencies accounts for the D and V effects: after adaptation of channels in one module, neighbouring module(s) are released from inhibition to produce a spurious response which is seen as a grating-like object in the adapted part of the visual field. During flickering adaptation a "halluncinated" lattice can be seen superimposed on the adapting grating. It apparently consists of Fourier components more remote from the adapting pattern than D and V are. This disinhibitory effect is strong confirmation of the inhibitory model. The regular and highly organized matrix of channels implied by these experiments may constitute a cortical hypercolumn conducting a coarse, piecewise Fourier transformation of the retinal image.

Figural Aftereffect↗

PubMed2000

Tactile situation awareness system: proprioceptive prostheses for sensory deficiencies.

UNLABELLED: Pilots and astronauts do not experience spatial disorientation in normal day-to-day terrestrial activities. On the ground, the perception of position and motion is determined by central nervous system integration of concordant and redundant information from multiple sensory channels (somatosensory, vestibular and visual) which collectively yield veridical perceptions. In the acceleration environments experienced by pilots and astronauts, the somatosensory and vestibular senses frequently present false but concordant information concerning the direction of gravity or down. When presented with conflicting sensory stimuli, it is normal for pilots and astronauts to experience episodes of disorientation. Visual instruments and displays developed over the past 70 yr have not solved the problem. A simple solution to maintain spatial orientation is to provide true information using the same sensory channels we use so successfully on Earth. METHODS: The Tactile Situation Awareness System (TSAS) developed by NASA and the U.S. Navy uses a matrix of mechanical tactile stimulators (tactors) applied on the torso and limbs to convey orientation cues (e.g., gravity vector) in an intuitive fashion to the skin. A series of in-flight experiments to validate and test a variety of tactile displays and concepts has been carried out in both helicopters and fixed wing aircraft. RESULTS: Pilots were able to fly complex maneuvers with no instruments or outside visual references (blindfolded) with less than 20 min of training. Recovery from unusual attitudes solely by tactile cues was trivial. Lab tests have shown the TSAS improves performance under conditions of high workload. CONCLUSIONS: When orientation information is presented via intuitive tactile displays spatial orientation is easily maintained in altered sensory conditions including unusual acceleration environments.

Aerospace Medicine↗

PubMed1988

[Rehabilitation of the hemianopsia patient from the viewpoint of the ergotherapist].

Hemianopsia, above all if it is associated with other neuropsychological deficits (neglect, disturbances of spatial orientation) is very disturbing for the patient in daily life. The patient has difficulty dressing, exhibits poor spatial orientation, has difficulty construing spatial relations or reading. Ergotherapy tries to combat all these disorders. There are various methods of treatment at the ergotherapist's disposal: activities of everyday life, such as self-help and household training, functional games, craft skills and neurotraining, which aims in particular at improving intellectual function. In a well-protected environment the patient learns to judge his or her capabilities correctly once again and to make the best of his or her strength or weaknesses in daily life.

Activities of Daily Living↗

PubMed2005

Estimation of the orientation term of the general quadrature transform from a single n-dimensional fringe pattern.

The spatial orientation of the fringe has been demonstrated to be a key point in the reliable phase demodulation from a single n-dimensional fringe pattern regardless of the frequency spectrum of the signal. The recently introduced general n-dimensional quadrature transform (GQT) makes explicit the importance of the fringe orientation in the demodulation process. The GQT is a quadrature operator that transforms cos phi into -sin phi--where phi is the modulating phase--and it is composed of two terms: an orientation factor directly related to the fringe's spatial orientation and an isotropic n-dimensional generalization of the one-dimensional Hilbert transform. We present a method for the determination of the orientation factor in a general n-dimensional case and its application to the demodulation of a single fringe pattern by the GQT. We have tested the algorithm with simulated as well as real photoelastic fringe patterns with good results.

Journal Article↗

PubMed2004

The organization of orientation and spatial frequency in primary visual cortex.

Many studies have demonstrated that the primary visual cortex contains multiple functional maps of visual properties (e.g., ocular dominance, orientation preference, and spatial-frequency preference), but as yet no consistent picture has emerged as to how these maps are related to one another. Three divergent, prior optical-imaging studies of spatial frequency are reanalyzed and critiqued in this article. Evidence is presented that a nonstimulus-specific response biased the interpretation of results in previous studies. In addition to reexamining four prior cat experiments, we carried out one new experiment. Through the use of different methods and a careful removal of the nonspecific response, we are led in all instances to a unique view of cortical organization for spatial-frequency preference. In particular, we find little apparent evidence for a columnar organization for spatial frequency. The response recorded by each image pixel may be viewed as arising from an admixture of low- and high-spatial-frequency populations. For most pixels, the ratio of these populations is 1:1.

Animals↗

PubMed1995

Ontogeny of orientation and spatial learning on the radial maze in mice.

The development of the orientation capacities of C57BL/6 mice has been studied on the radial maze in several procedures allowed to dissociate the different types of cues used by the mouse for solving the task with two intersession delays (2 and 24 hr). The results of the first two studies show that performance is independent of intersession delay regardless of the age of the subject. Mice as early as 23 days old obtain good performances when they can develop an algorithmic strategy or when they dispose of both proximal and distal cues during learning. At 37 days of age, however, mice can efficiently solve the radial maze task with distal cues alone. However, in the third experiment, 23-day-old mice were able to use distal cues for orientation at the end of the learning session if, at the onset, they also had access to proximal cues. These results suggest that, on weaning, mice use several types of information for task performance and that, as they mature, they turn more often to distal cues for orientation.

Aging↗