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Results for “Spatial orientation”

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PubMed1992

Cognitive and noncognitive processes involved in selective object exploration: comparison between young adult and old rats.

The age effects on locomotor activity, object-oriented exploration, habituation, and response to a spatial change were studied in young adult and old rats using an object exploration test. In this test the spatial response was evaluated by the renewal of exploration of a familiar object after its repositioning. The specificity of the spatial response was determined by comparison with control animals not submitted to a spatial change. Male Wistar rats 6 and 24 months old were used. Results showed a significant decrement in locomotor activity, object exploration, and spatial reactivity in old rats. The habituation curve and the reactivity to a new object were preserved. Detail analyses suggest that the spatial deficit of old rats is due to an incapacity to detect the spatial change and not to their poor locomotor or exploratory activity. These results corroborate those obtained in spatial orientation tasks and support the idea that the lack of spatial response observed in old animals is more related to cognitive impairments than to other factors such as sensory, motor, or motivational differences.

Aging↗

PubMed1995

Dendritic reorganisation in the basal forebrain under degenerative conditions and its defects in Alzheimer's disease. I. Dendritic organisation of the normal human basal forebrain.

In the present study, the dendritic organisation of neurones in the normal human basal forebrain was analysed as a prerequisite for the evaluation of pathological changes occurring in Alzheimer's disease and related conditions (see other Arendt et al. papers in this issue). Neurones in the basal nucleus of Meynert (NbM), the nucleus of the vertical limb of the diagonal band, and the medial septal nucleus were examined after Golgi impregnation. Cells were classified according to the dendritic branching pattern and soma shape as either reticular neurones or multipolar giant neurones. The reticular type of neurones constitutes more than 90% of neurones in the BnM. Cholinergic neurones also belong to this cell type. Reticular neurones were further subdivided into four subtypes. Morphological features and arrangement of reticular basal forebrain neurones were identical to those described for "reticular formation cells" or "isodendritic" neurones. Dendritic trees of reticular neurones show a spatial orientation perpendicular to passing fibres as well as a high degree of overlap, both of which are hallmarks of "open nuclei." The qualitative classification of Golgi-impregnated basal forebrain neurones was substantiated by a computer-based three-dimensional analysis. Topologic and metric parameters of the dendritic tree were calculated for each type of neurone to characterise the degree of dendritic branching, the shape and orientation of the dendritic arborisation, the spatial extension of the dendritic tree, and soma size. The classification criteria were evaluated according to their power of discrimination between different cell types by means of a discriminant analysis. The quantitative approach applied in the present study not only provides an objective measure for the description and comparison of the structure of various types of neurones but also makes it possible to elucidate fine structural changes that might occur under pathologic conditions and that are not evident during qualitative studies alone.

Adult↗

PubMed2005

Visual search for item- and array-centered locations in patients with left middle cerebral artery stroke.

In this study we systematically explored the impact of left hemisphere (LH) lesions on array-centered and item-centered spatial attention. We investigated 16 LH first ever stroke patients, focusing on strokes of the Middle Cerebral Artery (MCA), and 15 healthy control subjects with a parallel and serial search paradigm. None of the LH patients had a hemianopia or neglect. We systematically varied the item-centered (left- or right-side of a single item) and the array-centered position (left or right position in the search array of ten items) of critical features. Lesion sites were evaluated using MRIcro (Version 1.37; Rorden and Brett, 2000). The results show that patients had no specific problem with parallel search. In serial search patients showed a left to right gradient-like increase in response time for array-positions and they omitted more items if the critical feature was located on the right side of the items in the right half of the array. For low performing patients we found an overlapping lesion area around and anterior to the precentral sulcus (Brodmann's area 6 and 44), encompassing the frontal eye field. We conclude that LH MCA strokes may lead to search impairments in spatial attention, in particular in shifting to the right side of the visual field. Impaired rightward shifting moreover reduces the chance of detecting right-sided item features (but not left-sided). This suggests that spatial attention works with different reference frames, with spatial orientation being more basic than analyzing spatial aspects of objects.

Adult↗

PubMed2004

Hemispheric asymmetries for different components of global/local attention occur in distinct temporo-parietal loci.

Data from brain-damaged and neurologically intact populations indicate hemispheric asymmetries in the temporo-parietal cortex for discriminating an object's global form (e.g. the overall shape of a bicycle) versus its local parts (e.g. the spokes in a bicycle tire). However, it is not yet clear whether such asymmetries reflect processes that (i) bias attention toward upcoming global versus local stimuli and/or (ii) attend/identify global versus local stimuli after they are presented. To investigate these possibilities, we asked sixteen healthy participants to perform a cued global/local attention task while their brain activity was recorded using event-related functional magnetic resonance imaging (fMRI). The results indicated a novel double dissociation. Hemispheric asymmetries for deploying attention toward expected global versus local object features were specific to the intraparietal sulcus (iPs). However, hemispheric asymmetries for identifying global versus local features after they were presented were specific to the inferior parietal lobe/superior temporal gyrus (IPL/STG). This double dissociation provides the first direct evidence that hemispheric asymmetries associated with different components of global/local attention occur in distinct temporo-parietal loci. Furthermore, it parallels an analogous dissociation reported in a recent fMRI study of spatial orienting, suggesting that global/local attention and spatial attention might rely on similar cognitive/neural mechanisms.

Adolescent↗

PubMed1997

Effects of normobaric hypoxic confinement on visual and motor performance.

INTRODUCTION: The use of reduced oxygen levels has been suggested for fire prevention in closed spaces, such as submarines. However, if humans are to work and live in environments with reduced oxygen levels, the effect of hypoxia on human performance must be further assessed. METHODS: In 3, 11- to 14-d confinements a total of 22 subjects were exposed to different levels of normobaric hypoxia (13, 14, and 15 kPa O2), for up to 10 d, with intervening periods of normoxia. In each experiment eight subjects were divided into two teams, working in 6-h shifts around the clock. Subjects performed tests of spatial orientation, visual reaction time, parallel processing and motor skills. Performance tests and questionnaires were administered once or twice in every 24-h period. RESULTS: All of the subjects appeared to tolerate the acute reduction in oxygen partial pressure well. In many of the tests performance improved with time as a result of learning, despite reductions in the oxygen level. No reduction in performance or decrease in rate of learning was observed at any of the oxygen levels tested. CONCLUSIONS: Oxygen levels down to 14 kPa appear not to impair visual and motor performance during rest.

Adult↗

PubMed1998

Global spatial sampling with isotropic virtual planes: estimators of length density and total length in thick, arbitrarily orientated sections.

Existing design-based direct length estimators require random rotation around at least one axis of the tissue specimen prior to sectioning to ensure isotropy of test probes. In some tissue it is, however, difficult or even impossible to define the region of interest, unless the tissue is sectioned in a specific, nonrandom orientation. Spatial uniform sampling with isotropic virtual planes circumvents the use of physically isotropic or vertical sections. The structure that is contained in a thick physical section is investigated with software-randomized isotropic virtual planes in volume probes in systematically sampled microscope fields using computer-assisted stereological analysis. A fixed volume of 3D space in each uniformly sampled field is probed with systematic random, isotropic virtual planes by a line that moves across the computer screen showing live video images of the microscope field when the test volume is scanned with a focal plane. The intersections between the linear structure and the virtual probes are counted with columns of two dimensional disectors. Global spatial sampling with sets of isotropic uniform random virtual planes provides a basis for length density estimates from a set of parallel physical sections of any orientation preferred by the investigator, i.e. the simplest sampling scheme in stereology. Additional virtues include optimal conditions for reducing the estimator variance, the possibility to estimate total length directly using a fractionator design and the potential to estimate efficiently the distribution of directions from a set of parallel physical sections with arbitrary orientation. Other implementations of the basic idea, systematic uniform sampling using probes that have total 3D x 4pi freedom inside the section, and therefore independent of the position and the orientation of the physical section, are briefly discussed.

Journal Article↗

PubMed2006

Location matters: why target location impacts performance in orientation tasks.

This research explores human performance in a spatial orientation task. In three experiments, participants saw a target highlighted in a visual scene and were asked to locate it on a map of the space. Across all of the experiments, the target's location in the visual scene influenced the participants' response times. Generally, response times increased when the target was located farther away from the viewer, when the target was farther to one side or the other, and when more distractors were nearby. However, there were important exceptions to these findings, suggesting that participants encode the location of a target hierarchically, using different features of the space depending on the target's particular location. We conclude that participants perform such tasks by extracting a description from the egocentric view and then transforming that description to allow them to find the target on the map.

Adult↗

PubMed1985

Neurophysiological evaluation of the differential response model for orientation and spatial-frequency discrimination.

Recent models have attempted to reconcile low psychophysical orientation and spatial-frequency discrimination thresholds with relatively broad orientation and spatial-frequency tuning of cortical neurons. These models have relied on the ability of the neurons to convert small stimulus changes into reliable response changes. We have examined this ability in a sample of neurons from the cat's striate cortex. We present here data from two cells that reliably signaled the smallest orientation and spatial-frequency differences. Using receiver operating characteristic analysis, we find that these cells could reliably signal orientation differences of 1.84 deg and spatial-frequency differences of 0.073 octave. We compare these single-cell results to cat and human behavioral discrimination thresholds.

Animals↗

PubMed2003

Orientation opponency in human vision revealed by energy-frequency analysis.

Studies of second-order visual processing have primarily been concerned with understanding the mechanisms for detecting spatiotemporal variations in such attributes as contrast, orientation, spatial frequency, etc. Here, we have examined the orientation characteristics of second-order processes using bandpass noise whose Fourier energy is sinusoidally modulated across orientation, rather than across space or time. Sensitivity for detecting orientation-energy modulations was measured as a function of modulation frequency. The sensitivity function was bandpass, with a pronounced peak at an orientation frequency of 4 cycles/pi. An inverse Fourier transform of the sensitivity function revealed a filter profile displaying a centre-surround antagonism across orientation, with an excitatory centre within 6-9 deg and inhibitory lobes at 15-20 deg from the filter's centre. The degree of centre-surround antagonism increased with stimulus size far beyond the spatial range of the first-order filters (more than 64 times the dominant spatial wavelength of the noise carrier). These results suggest that second-order processing involves 'orientation-opponent' channels that extract differences in first-order outputs across orientation over a wide area of the visual field.

Contrast Sensitivity↗

PubMed1998

Mental representations of large and small spatial layouts are orientation dependent.

Previous research on spatial memory indicated that memories of small layouts were orientation dependent (orientation specific) but that memories of large layouts were orientation independent (orientation free). Two experiments investigated the relation between layout size and orientation dependency. Participants learned a small or a large 4-point path (Experiment 1) or a large display of objects (Experiment 2) and then made judgments of relative direction from imagined headings that were either the same as or different from the single studied orientation. Judgments were faster and more accurate when the imagined heading was the same as the studied orientation (i.e., aligned) than when the imagined heading differed from the studied orientation (i.e., misaligned). This alignment effect was present for both small and large layouts. These results indicate that location is encoded in an orientation-dependent manner regardless of layout size.

Female↗

PubMed2006

Spatial updating in virtual reality: the sufficiency of visual information.

Robust and effortless spatial orientation critically relies on "automatic and obligatory spatial updating", a largely automatized and reflex-like process that transforms our mental egocentric representation of the immediate surroundings during ego-motions. A rapid pointing paradigm was used to assess automatic/obligatory spatial updating after visually displayed upright rotations with or without concomitant physical rotations using a motion platform. Visual stimuli displaying a natural, subject-known scene proved sufficient for enabling automatic and obligatory spatial updating, irrespective of concurrent physical motions. This challenges the prevailing notion that visual cues alone are insufficient for enabling such spatial updating of rotations, and that vestibular/proprioceptive cues are both required and sufficient. Displaying optic flow devoid of landmarks during the motion and pointing phase was insufficient for enabling automatic spatial updating, but could not be entirely ignored either. Interestingly, additional physical motion cues hardly improved performance, and were insufficient for affording automatic spatial updating. The results are discussed in the context of the mental transformation hypothesis and the sensorimotor interference hypothesis, which associates difficulties in imagined perspective switches to interference between the sensorimotor and cognitive (to-be-imagined) perspective.

Adolescent↗

PubMedDate not supplied

Definition and determination of acetabular component orientation in cemented total hip arthroplasty.

OBJECTIVE: To describe the spatial orientation of the cemented acetabular component in cemented total hip arthroplasty, based on a ventrodorsal and lateral radiographic projection of the pelvis. METHODS: Equations were derived by using trigonometric relationships that describe the radiographic rotation about the longitudinal pelvic axis (alpha), transverse pelvic axis (beta), acetabular inclination (phi), acetabular inclination corrected for longitudinal pelvic rotation, version (phiC), acetabular version (theta), acetabular version corrected for longitudinal pelvic rotation (thetaC), acetabular inclination corrected for transverse pelvic rotation (phi(beta)), and acetabular version corrected for transverse pelvic rotation (theta(beta)) RESULTS: Alpha was calculated by using the equation alpha = sin(-1) (x/y) where x is the transverse distance between the dorsal spinous processes and the center of the pubis on a ventrodorsal radiograph and y is the distance from the pubis to the dorsal aspect of the first coccygeal vertebra perpendicular to the long axis of the pelvis on a lateral radiograph. Phi was calculated from the long axis (LA) and short axis (SA) of the ellipse formed by the radiopaque acetabular marker ring by using the equation phi = sin(-1) (SA/LA). phiC was calculated by using the equation phiC = phi +/- (alpha - tan(-1) (tan alpha cos thetaC)). Theta was determined as previously described. ThetaC was calculated by using the equation thetaC = tan(-1) (tan theta cos alpha). Theta(beta) and theta(beta) were calculated with the equations phi(beta) = tan(-1) (tan theta cos beta) and theta(beta) = theta - tan(-1) (sin beta), respectively. Beta could not be accurately determined from ventrodorsal and lateral pelvic radiographs. CONCLUSIONS AND CLINICAL RELEVANCE: These techniques allow for more accurate postoperative radiographic assessment of acetabular component positioning. This information can then be used in retrospective or prospective analyses examining that effects of implant positioning on clinical outcome.

Acetabulum↗

PubMed2002

On the determination of the angular orientation of a vertebra.

In this paper we consider the spatial orientation of vertebrae. We take the view that, in determining their rotation angles from X-rays, the procedure applied by Drerup yields the most reliable empirical results, viz. the three angles through which a vertebra rotates about its own symmetry axes in a specific sequence. With a view to the further use of this information to analyze deformations or the motion of a spine we recommend that the Drerup angles be converted into the well-known Eulerian angles. How this can be done is the subject of this report.

Algorithms↗

PubMed1979

Computer analysis of vectorcardiograms in myocardial infarction with special reference to polar vector and planarity of the QRS and T loops.

Spatial characteristics of the QRS and T loops in 110 patients with old myocardial infarction were analysed in comparison with 221 normal subjects. Measured were (1) QRS and T polar vectors, (2) initial 20- and 30-msec segmental QRS polar vectors, and (3) length, width, thickness, and ratios of width/length and thickness/length of the QRS and T loops in edgewise and broadside projections. Broadside and edgewise projections were obtained by transformation of the reference frame of the Frank lead system to a patient's own frame based on the polar vector. The recognition rates of abnormality in the QRS and T polar vectors were 66% and 60% of a total of 110 patients with myocardial infarction. The initial 30 msec segmental QRS polar vector showed the highest recognition rate of abnormality in myocardial infarction, i.e., 87% in anterior myocardial infarction, 100% in extensive anterior myocardial infarction and 78% in inferior myocardial infarction. The initial segmental QRS polar vector was abnormally deviated posteriorly and superiorly in inferior myocardial infarction. In anterior myocardial infarction, the initial segmental polar vector was directed inferiorly in more than 50% of the cases, while the vector in normal subjects was located superiorly and to the left. The QRS loop of anterior myocardial infarction was significantly smaller in the width and width/length ratio and significantly larger in the thickness and thickness/length ratio than those of the normal. Poor planarity of the QRS loop was one of the characteristics of myocardial infarction, especially of extensive anterior myocardial infarction. The T loop of myocardial infarction was significantly larger in the width/length ratio than that of the normal. More than 50% of the cases with anterior myocardial infarction showed abnormally wide T loops. The polar vector was a useful index to characterize the spatial orientation and sense of rotation of the spatial loop. In addition, the initial segmental QRS polar vector represented the mild localized abnormalities of the spatial loop. The loop configuration in space was characterized in edgewise and broadside projections.

Acute Disease↗

PubMed2005

A role for terrain slope in orienting hippocampal place fields.

The three-dimensional topography of the environment is a potentially important source of orienting information for animals, but little is known about how such features affect either navigational behaviour or the neural representation of place. One component of the neural place representation comprises the hippocampal place cells, which show location-specific firing that can be oriented by directional cues in the environment. The present study investigated whether a simple topographical feature, terrain slope, could provide such orienting information to place cells. Place cells were recorded as rats explored a tilted (30 degrees) square box located in the centre of a dark, curtained and visually symmetrical circular enclosure. The orientation of the tilted surface was varied, first in conjunction with that of a visible cue card (to stabilise the system) and then in the absence of the cue card, when the slope of the box was the only remaining stable polarising cue in the environment. In the latter condition, place fields continued to be reliably oriented by the slope. Thus, terrain slope provides sufficient orienting information to set and probably maintain the orientation of the hippocampal place system. This may explain previous behavioural observations that spatial orientation is improved when slope information is available.

Analysis of Variance↗

PubMed2006

Second-order spatial frequency and orientation channels in human vision.

We compared the number of spatial frequency and orientation mechanisms underlying first- versus second-order processing by measuring discrimination at detection threshold for first- and second-order Gabors to determine the smallest difference in spatial frequency and orientation that permits accurate discrimination at threshold. For second-order gratings, the number of channels is the same as for first-order gratings for spatial frequencies up to about 2 cpd; however, there are fewer second-order channels at higher spatial frequencies. In contrast, the number of labeled channels for orientation is the same for first- and second-order gratings. In conclusion, our findings provide evidence for distinct spatial frequency and orientation labeled detectors in second-order visual processing. We also show that, relative to first-order, there are fewer second-order channels processing higher spatial frequencies. This is consistent with a filter-rectify-filter scheme for second-order in which the second stage of filtering is at lower spatial frequencies.

Contrast Sensitivity↗

PubMed2002

Spatial frequency and orientation tuning dynamics in area V1.

Spatial frequency (SF) and orientation tuning are intrinsic properties of neurons in primary visual cortex (area V1). To investigate the neural mechanisms mediating selectivity in the awake animal, we measured the temporal dynamics of SF and orientation tuning. We adapted a high-speed reverse-correlation method previously used to characterize orientation tuning dynamics in anesthetized animals to estimate efficiently the complete spatiotemporal receptive fields in area V1 of behaving macaques. We found that SF and orientation tuning are largely separable over time in single neurons. However, spatiotemporal receptive fields also contain a small nonseparable component that reflects a significant difference in response latency for low and high SF stimuli. The observed relationship between stimulus SF and latency represents a dynamic shift in SF tuning, and suggests that single V1 neurons might receive convergent input from the magno- and parvocellular processing streams. Although previous studies with anesthetized animals suggested that orientation tuning could change dramatically over time, we find no substantial evidence of dynamic changes in orientation tuning.

Animals↗

PubMed1984

Stimulus specificity of binocular cells in the cat's visual cortex: ocular dominance and the matching of left and right eyes.

Most cells in the striate cortex respond to visual stimulation through either eye. We have examined quantitatively the matching of response specificity for the two eyes. Our intention was to determine the degree to which this matching depends on ocular dominance. We used standard single cell recording techniques and studied responses to sinusoidal gratings of different spatial frequencies, orientations, and contrasts. For all tests, stimuli were randomly interleaved both with respect to the value of each parameter, and the eye which was stimulated. After estimating ocular dominance qualitatively and quantitatively, we measured: response modulation (to help identify whether a cell was simple or complex), orientation and spatial frequency tuning, and contrast response functions (to estimate contrast thresholds). Results show that: (1) Response modulation is well matched between the two eyes, but there is a slight tendency for the dominant eye to respond with less modulation. (2) Optimal orientation and spatial frequency and their respective tuning widths were similar for the two eyes. In general, tuning functions for the two eyes differed mainly in slope. However, in each case, there was a tendency for the dominant eye to have broader tuning widths. (3) In most cases, contrast response functions for the two eyes differed mainly in their slopes. Extrapolation to spontaneous levels suggests that estimated contrast thresholds are relatively independent of ocular dominance although, again, there ws a tendency for the dominant eye to exhibit slightly lower estimated thresholds. These findings demonstrate that response characteristics between the two eyes are generally well matched regardless of relative response strength. There are, however, small but clear differences between the two eyes for all parameters we measured which are related to and demonstrate that ocular dominance influences the degree of matching between the two eyes.

Animals↗