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Results for “Spatial orientation”

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At least 757 records · Page 42Linked to original sources

PubMed2005

Drift in ocular torsion during sustained head tilt.

PURPOSE: A head tilt towards the shoulder (roll) induces an ocular counter-roll (OCR), i.e. torsion in the opposite direction to the head. How this counter-rolled position is maintained during a static head tilt is in debate. In a previous study, we reported an OCR-increasing drift subsequent to the head tilt. This finding is in contrast to other reports where no such response was found. The primary aim of this study was to repeat the experiment during a prolonged head-tilt test and to describe the OCR characteristics. A secondary aim was to investigate the influence of spatial visual cues on OCR. METHODS: Five male subjects performed a head tilt (30 degrees ) towards the right shoulder while the eye position was recorded during a 10-minute interval. In test 1, the subjects viewed a target with no cues for spatial orientation. The same head-tilt paradigm was repeated in test 2 with a visual target with spatial cues. Two samples of data were extracted from the start and the end of the recordings for statistical analysis. RESULTS: Subsequent to the head tilt, a slow OCR-increasing drift in the opposite direction to the head roll was found in all subjects. On average, this drift lasted for 30 sec (+/- 5) in test 1 and for 55 sec (+/- 18) in test 2. The drift was then found to change its direction, i.e. the eyes were rotated in the same direction as the head roll. When measured after 10 minutes, the OCR was significantly decreased. CONCLUSIONS: The OCR during static head tilt is not constant. During the first minute there is a gradually increasing OCR. Thereafter, the amplitude of the OCR decreases gradually. These changes are influenced to some extent by spatial visual cues. Possible mechanisms are adaptive responses in otolithic afferents as well as central nervous memory functions related to the semicircular canal system.

Adult↗

PubMed1975

Gradual changes of ECG waveform during and after exercise in normal subjects.

The directions and magnitudes of time-normalized P, QRS, and ST vectors, and other ECG parameters were analyzed during and after multistage exercise in 56 ostensibly healthy men aged 23 to 62. By selective averaging with a digital computer system a single representative beat was obtained from each stage. Measurements were taken from this beat. During exercise, the interval between the spatial maximum of the P wave and the onset of the QRS complex decreased while the magnitude of the P wave increased. The direction of the P vectors did not change. This pattern corresponds to the electrocardiographic manifestations of predominant right atrial overload. No significant changes in the QRS duration were observed. Also the magnitude and spatial orientation of the maximum QRS vectors remained constant. The interval between the QRS onset and the maximum spatial magnitude of the T wave shortened. The terminal QRS vectors and the ST vectors gradually shifted toward the right, and superiorly. The T magnitude lessened during exercise. In the first minute of the recovery period the P and T magnitudes markedly increased. Afterward all measurements gradually returned to the resting level. Mechanisms which may explain the observed ECG changes during and after exercise are discussed, including changes in the blood conductivity and intracardiac blood volume. Age did not contribute to the variance of the ECG measurements, but a significant reduction of this variance could be otained in some ST-segment measurements by relating them to heart rate with linear regression equations (P less than or equal to 0.05). Therefore it is expected that the sensitivity of the exercise ECG for detection of ischemic heart disease would be increased when heart rate dependent normal limits for ST-segment measurements are used. Different criteria should be employed for the interpretation of the ECG during and after exercise.

Adult↗

PubMed1993

Do changes in cell shape affect suspension conductivity?

The conductivity of a suspension containing uniformly oriented asymmetric cells depends on the shape of the cells. Whether the shape of cells with random spatial orientation also affects the conductivity of a suspension is not clear. A highly sensitive apparatus was used to register the dynamic changes in conductivity of erythrocyte suspension, upon induced morphological transformation discocytes<-->spherocytes). The results obtained with a sensitivity of up to 0.06% show that the drastic change of cell shape itself did not affect the suspension conductivity.

Electric Conductivity↗

PubMed2000

Simple mechanisms organise orientation of escape swimming in embryos and hatchling tadpoles of Xenopus laevis.

Many amphibian tadpoles hatch and swim before their inner ears and sense of spatial orientation differentiate. We describe upward and downward swimming responses in hatchling Xenopus laevis tadpoles from stages 32 to 37/38 in which the body rotates about its longitudinal axis. Tadpoles are heavier than water and, if touched while lying on the substratum, they reliably swim upwards, often in a tight spiral. This response has been observed using stroboscopic photography and high-speed video recordings. The sense of the spiral is not fixed for individual tadpoles. In 'more horizontal swimming' (i.e. in directions within +/-30 degrees of the horizontal), the tadpoles usually swim belly-down, but this position is not a prerequisite for subsequent upward spiral swimming. Newly hatched tadpoles spend 99 % of their time hanging tail-down from mucus secreted by a cement gland on the head. When suspended in mid-water by a mucus strand, tadpoles from stage 31 to 37/38 tend to swim spirally down when touched on the head and up when touched on the tail. The three-dimensional swimming paths of stage 33/34 tadpoles were plotted using simultaneous video images recorded from the side and from above. Tadpoles spiralled for 70 % of the swimming time, and the probability of spiralling increased to 1 as swim path angles became more vertical. Tadpoles were neutrally buoyant in Percoll/water mixtures at 1.05 g cm(-)(3), in which anaesthetised tadpoles floated belly-down and head-up at 30 degrees. In water, their centre of mass was ventral to the muscles in the yolk mass. A simple mathematical model suggests that the orientation of tadpoles during swimming is governed by the action of two torques, one of which raises the head (i.e. increases the pitch) and the other rotates (rolls) the body. Consequently, tadpoles (i) swim belly-down when the body is approximately horizontal because the body is ballasted by dense yolk, and (ii) swim spirally at more vertical orientations when the ballasting no longer stabilises orientation. Measurements in tethered tadpoles show that dorsal body flexion, which could produce a dorsal pitch torque, is present during swimming and increases with tailbeat frequency. We discuss how much of the tadpole's behaviour can be explained by our mathematical model and suggest that, at this stage of development, oriented swimming responses may depend on simple touch reflexes, the organisation of the muscles and physical features of the body, rather than on vestibular reflexes.

Animals↗

PubMed2006

The study of hemispheric specialization for categorical and coordinate spatial relations in animals.

This article reviews some of the most representative studies in the animal literature pertaining to the processing of categorical and coordinate spatial relations and of their hemispheric control. Although the processing of coordinate and categorical cognition has been studied directly with nonhuman primates, experiments on cerebral asymmetries in avian spatial orientation are also reviewed. It turns out that Kosslyn's model concerning the existence of two types of spatial representations each with a specific lateralization pattern has received some support in nonhuman primates and is only weakly verified in the avian studies. Procedural differences might explain some but certainly not all of the discrepancies between the human and the animal literature. It is especially the laterality hypothesis of a left hemisphere advantage in relational cognition and a right hemispheric superiority in judging absolute distances that is not supported by the animal data. Studies specifically addressing Kosslyn's hypotheses and bearing on the use of similar stimuli, procedures and methods between the species tested are needed in order to lead to firm conclusions about the existence of coordinate versus categorical processing systems in animals.

Animals↗

PubMed2002

Solution structure of calcium-saturated cardiac troponin C bound to cardiac troponin I.

Cardiac troponin C (TnC) is composed of two globular domains connected by a flexible linker. In solution, linker flexibility results in an ill defined orientation of the two globular domains relative to one another. We have previously shown a decrease in linker flexibility in response to cardiac troponin I (cTnI) binding. To investigate the relative orientation of calcium-saturated TnC domains when bound to cTnI, (1)H-(15)N residual dipolar couplings were measured in two different alignment media. Similarity in alignment tensor orientation for the two TnC domains supports restriction of domain motion in the presence of cTnI. The relative spatial orientation of TnC domains bound to TnI was calculated from measured residual dipolar couplings and long-range distance restraints utilizing a rigid body molecular dynamics protocol. The relative domain orientation is such that hydrophobic pockets face each other, forming a latch to constrain separate helical segments of TnI. We have utilized this structure to successfully explain the observed functional consequences of linker region deletion mutants. Together, these studies suggest that, although linker plasticity is important, the ability of TnC to function in muscle contraction can be correlated with a preferred domain orientation and interdomain distance.

Calcium↗

PubMed1992

Actin- and tubulin-dependent functions during Saccharomyces cerevisiae mating projection formation.

Several conditional-lethal mutant alleles of the single-copy Saccharomyces cerevisiae beta-tubulin and actin genes were used to evaluate the roles of microtubules and actin filaments in the pheromone-induced extension of mating projections. Mutants defective in tubulin assembly form projections indistinguishable in appearance from those formed by wild-type cells. However, the tubulin mutants are unable to move their nuclei into the projections and to orient the spindle pole body associated with each nucleus toward the projection tip. Actin mutants are defective in spatial orientation of cell-surface growth required for formation of normal mating projections. Migration of nuclei into mating projections and Spa2p segregation to projection tips are also defective in actin mutants. Studies with abp1 null mutants showed that the function of the Abp1p actin-binding protein is either not required for projection formation or there are other proteins in yeast with similar functions. Our findings demonstrate that actin is required to restrict cell-surface growth to a defined region for pheromone-induced morphogenesis and suggest that nuclear position and orientation in mating projections depend on direct or indirect interaction of microtubules with actin filaments.

Actins↗

PubMed1988

Some proprioceptive influences on the perceptual representation of body shape and orientation.

Perception of the surface contour of the body is generally thought to depend on topographically organized neural maps of somatosensation in the thalamus and cortex. Recent neurophysiological studies indicate that these maps are potentially modifiable through alterations in their sensory input. We present evidence that the apparent shape and orientation of the body can be changed within seconds by using muscle vibration to generate proprioceptive misinformation about limb position. Depending on the position of the hands or feet in relation to the rest of the body and to the test chamber, it is possible to generate systematic perceptual distortions of the body and changes in the apparent orientation of the body. Some implications of these observations for the maintenance of an accurate body schema, for spatial orientation, and for the encoding of ocular position are described.

Adolescent↗

PubMed1998

Burst firing and modulation of functional connectivity in cat striate cortex.

We studied the influences of the temporal firing patterns of presynaptic cat visual cortical cells on spike generation by postsynaptic cells. Multiunit recordings were dissected into the activity of individual neurons within the recorded group. Cross-correlation analysis was then used to identify directly coupled neuron pairs. The 22 multiunit groups recorded typically showed activity from two to six neurons, each containing between 1 and 15 neuron pairs. From a total of 241 neuron pairs, 91 (38%) had a shifted cross-correlation peak, which indicated a possible direct connection. Only two multiunit groups contained no shifted peaks. Burst activity, defined by groups of two or more spikes with intervals of </=8 ms from any single neuron, was analyzed in terms of its effectiveness in eliciting a spike from a second, driven neuron. We defined effectiveness as the percentage of spikes from the driving neuron that are time related to spikes of the driven neuron. The effectiveness of bursts (of any length) in eliciting a time-related response spike averaged 18.53% across all measurements as compared with the effectiveness of single spikes, which averaged 9.53%. Longer bursts were more effective than shorter ones. Effectiveness was reduced with spatially nonoptimal, as opposed to optimal, stimuli. The effectiveness of both bursts and single spikes decreased by the same amount across measurements with nonoptimal orientations, spatial frequencies and contrasts. At similar firing rates and burst lengths, the decrease was more pronounced for nonoptimal orientations than for lower contrasts, suggesting the existence of a mechanism that reduces effectiveness at nonoptimal orientations. These results support the hypothesis that neural information can be emphasized via instantaneous rate coding that is not preserved over long intervals or over trials. This is consistent with the integrate and fire model, where bursts participate in temporal integration.

Action Potentials↗

PubMedDate not supplied

[From determination of amino acid residue conformation to reconstruction of the spatial structure of proteins (from the data of nuclear Overhauser enhancement spectroscopy].

A new approach to the calculation of the spatial protein structure based on the joint utilization of the theoretical conformational analysis method and nuclear Overhauser enhancement (NOE) spectroscopy data is proposed and verified. The quality in determining various molecule structural parameters is estimated in terms of the expected NOE spectral parameters derived from the X-ray analysis data of the avian pancreatic polypeptide. The proposed approach is shown to correctly determine such structural parameters of protein molecules as local amino acid residue conformations, reciprocal spatial orientation of the C alpha atoms neighbouring along amino acid sequence and reapproached segments of the polypeptide chain. Spatially remote molecule fragments are mainly responsible for the error in determining structural parameters.

Amino Acids↗

PubMed2004

An integrative neural network for detecting inertial motion and head orientation.

The ability to navigate in the world and execute appropriate behavioral responses depends critically on the contribution of the vestibular system to the detection of motion and spatial orientation. A complicating factor is that otolith afferents equivalently encode inertial and gravitational accelerations. Recent studies have demonstrated that the brain can resolve this sensory ambiguity by combining signals from both the otoliths and semicircular canal sensors, although it remains unknown how the brain integrates these sensory contributions to perform the nonlinear vector computations required to accurately detect head movement in space. Here, we illustrate how a physiologically relevant, nonlinear integrative neural network could be used to perform the required computations for inertial motion detection along the interaural head axis. The proposed model not only can simulate recent behavioral observations, including a translational vestibuloocular reflex driven by the semicircular canals, but also accounts for several previously unexplained characteristics of central neural responses such as complex otolith-canal convergence patterns and the prevalence of dynamically processed otolith signals. A key model prediction, implied by the required computations for tilt-translation discrimination, is a coordinate transformation of canal signals from a head-fixed to a spatial reference frame. As a result, cell responses may reflect canal signal contributions that cannot be easily detected or distinguished from otolith signals. New experimental protocols are proposed to characterize these cells and identify their contributions to spatial motion estimation. The proposed theoretical framework makes an essential first link between the computations for inertial acceleration detection derived from the physical laws of motion and the neural response properties predicted in a physiologically realistic network implementation.

Acceleration↗

PubMed1983

Visible persistence: effects of luminance, spatial frequency and orientation.

Square-wave gratings of various space-average luminances, spatial frequencies and orientations were presented briefly to observers, who were asked to adjust a brief visual probe to coincide with the end of the longer-lasting, gradually decaying sensory trace of these stimuli. Visible persistence of 2 and 7 c/deg gratings increased with increasing luminance, and an interaction was found at approx. 6 cd/m2 between luminance and spatial frequency. The persistence curves showed a low-pass frequency characteristic at low mean luminance levels, whereas at high luminances, they presented a band-pass frequency characteristic. Persistence of a 7 c/deg grating was longer at oblique orientations than at horizontal or vertical orientations. These findings were related to properties of transient and sustained channels in human vision.

Afterimage↗

PubMed1993

[Analysis of the behavior of rats in the Morris water-basin: new methodology and pharmacological application].

The Morris water-maze has been designed to test spatial orientation ability, learning and memory processes. In order to improve the analyse of the organization of the trajectory of rats, during the training phase, a computer program was elaborated. The study of the effect of a benzodiazepine, diazepam, was chosen to illustrate and validate this methodological approach. Results showed that rats pre-treated with diazepam (2 mg/kg) presented an impairment of spatial learning associated with the occurrence of a stereotyped circular swimming behaviour.

Animals↗

PubMed1983

The orientation of melittin in lipid membranes. A polarized infrared spectroscopy study.

Polarized infrared spectra of melittin incorporated into macroscopically oriented lipid membranes are reported. From the linear dichroism of the amide I and amide II vibrational bands, the spatial orientation of the melittin helices was determined as being preferentially parallel to the membrane normal, under our experimental condition of low water content and an ordered lipid phase. Considering the various models for the orientation of melittin in lipid membranes proposed in the literature, we conclude that our data are in accord with an arrangement whereby the hydrophobic part of the polypeptide either spans the bilayer in the form of two bent helix segments, or is folded back within one monolayer in the form of a wedge.

Bee Venoms↗

PubMed1994

Sun compass-based spatial learning impaired in homing pigeons with hippocampal lesions.

The hippocampal formation is known to be critical for spatial cognition, for example, regulating the learning of environmental maps. But how is a spatial map learned, and what is the role of the hippocampal formation in the learning process? The sun compass is perhaps the most ubiquitous, naturally occurring spatial orientation mechanism found in the animal kingdom. The sun compass may also serve as a directional reference that supports spatial learning. We report that homing pigeons with hippocampal lesions were unable to use the sun compass to learn the directional location of food in an outdoor, experimental arena. Homing pigeons with lesions of the caudal neostriatum readily learned the same task, and showed appropriately shifted directional responses following a clock-shift manipulation demonstrating that they were indeed using the sun compass to learn the task. Finally, both hippocampal and control lesioned birds quickly learned a procedurally similar task where a color cue identified the location of food in the same experimental arena. The results indicate that hippocampal lesions impair sun compass use in the context of learning. As such, the results support the hypothesis that the importance of the hippocampal formation in spatial cognition may be related to its participation in a neural process in which information from a directional reference, in this case the sun compass, is used to learn the directional relationship among stimuli in space.

Animals↗

PubMed1989

The young child's representation of depth in drawing: process and product.

Two experiments are reported from a series of studies in which plain blocks of various sizes were presented in various spatial orientations to children aged between 3 and 8 years in an attempt to establish how they represent three-dimensional spatial relations pictorially. The major results were that young children represent depth in the array vertically in the picture plane. Two important findings were that even from an early age drawings contain "view-centered" information and that children differentiate between the relative positions of objects in the array by the temporal order of their drawing. These results show the importance of studying the drawing process as well as its product.

Art↗

PubMed2003

Way-marking behaviour: an aid to spatial navigation in the wood mouse (Apodemus sylvaticus).

BACKGROUND: During their movements in the wild, wood mice (Apodemus sylvaticus) distribute small objects, such as leaves or twigs, which are often visually conspicuous. Our experiments demonstrate that these marks serve as points of reference during exploration. Way-marking, as we call it, may diminish the likelihood of losing an "interesting" location, perhaps following disturbance by, for example, a predator or conspecific. Way-marks, being readily portable, may be a less confusing method of marking ephemeral sites than scent marks. They may also be a safer option for local navigation insofar as scent marks can easily be detected by a predator. RESULTS: In an experiment, conspicuous natural candidate way-marks were removed from a simple arena and wood mice were given white plastic discs instead. The wood mice picked up these discs and re-distributed them about their arena; as the mice moved, they repeatedly re-positioned the discs and usually spent a considerable time near recently repositioned discs. Analysis revealed a statistically significant association between the location of places in which the mice had positioned way-marks and the subsequent pattern of their movements. In a separate analysis, based on the context in which each behaviour occurred, we used the components and sequences of wood mouse behaviour to deduce the motivation behind each activity. One set of behaviour patterns, the elements of which were closely linked by the high transition probabilities amongst them, were interpreted as linked elements of exploration; whenever the mice transported a disc it was in association with these exploratory behaviours. This evidence that transporting discs is set in the motivational context of exploratory behaviour supports the conclusion that way-marking is part of the wood mouse's system of spatial orientation. CONCLUSION: We conclude that way-marking - a behaviour not previously described in mammals other than humans - serves solely as an aid to spatial navigation during exploration.

Animals↗

PubMed2005

Strong orientation effects in ionization of H+2 by short, intense, high-frequency light pulses.

We present three-dimensional time-dependent calculations of ionization of arbitrarily spatially oriented H+2 by attosecond, intense, high-frequency laser fields. The ionization probability shows a strong dependence on both the internuclear distance and the relative orientation between the laser field and the internuclear axis. The physical features are explained in terms of two-center interference effects.

Journal Article↗