共查询到20条相似文献,搜索用时 15 毫秒
1.
T. M. H. Dijkstra G. Schöner M. A. Giese C. C. A. M. Gielen 《Biological cybernetics》1994,71(6):489-501
When standing human subjects are exposed to a moving visual environment, the induced postural sway displays varying degrees
of coherence with the visual information. In our experiment we varied the frequency of an oscillatory visual display and analysed
the temporal relationship between visual motion and sway. We found that subjects maintain sizeable sway amplitudes even as
temporal coherence with the display is lost. Postural sway tended to phase lead (for frequencies below 0.2 Hz) or phase lag
(above 0.3 Hz). However, we also observed at a fixed frequency, highly variable phase relationships in which a preferred range
of phase lags is prevalent, but phase jumps occur that return the system into the preferred range after phase has begun drifting
out of the preferred regime. By comparing the results quantitatively with a dynamical model (the sine-circle map), we show
that this effect can be understood as a form of relative coordination and arises through an instability of the dynamics of
the action-perception cycle. Because such instabilities cannot arise in passively driven systems, we conclude that postural
sway in this situation is actively generated as rhythmic movement which is coupled dynamically to the visual motion.
Received: 7 September 1993/Accepted in revised form: 2 May 1994 相似文献
2.
M. A. Giese T. M. H. Dijkstra G. Schöner C. C. A. M. Gielen 《Biological cybernetics》1996,74(5):427-437
Human subjects standing in a sinusoidally moving visual environment display postural sway with characteristic dynamical properties. We analyzed the spatiotemporal properties of this sway in an experiment in which the frequency of the visual motion was varied. We found a constant gain near 1, which implies that the sway motion matches the spatial parameters of the visual motion for a large range of frequencies. A linear dynamical model with constant parameters was compared quantitatively with the data. Its failure to describe correctly the spatiotemporal properties of the system led us to consider adaptive and nonlinear models. To differentiate between possible alternative structures we directly fitted nonlinear differential equations to the sway and visual motion trajectories on a trial-by-trial basis. We found that the eigenfrequency of the fitted model adapts strongly to the visual motion frequency. The damping coefficient decreases with increasing frequency. This indicates that the system destabilizes its postural state in the inertial frame. This leads to a faster internal dynamics which is capable of synchronizing posture with fast-moving visual environments. Using an algorithm which allows the identification of essentially nonlinear terms of the dynamics we found small nonlinear contributions. These nonlinearities are not consistent with a limit-cycle dynamics, accounting for the robustness of the amplitude of postural sway against frequency variations. We interpret our results in terms of active generation of postural sway specified by sensory information. We derive also a number of conclusions for a behavior-oriented analysis of the postural system. 相似文献
3.
E. Golomer P. Dupui H. Monod 《European journal of applied physiology and occupational physiology》1997,76(2):140-144
We investigated the effects of maturation on the dynamic body sways of healthy girls. Prepubertal and postpubertal girls
practising professional physical activities requiring a good ability to maintain equilibrium (acrobats and dancers) were asked
to stand on a free seesaw platform and the results compared to those for untrained age-matched girls. This platform (stabilometer)
allows self-induced body sways. Stabilograms were obtained by a double integration of the angular acceleration from the recordings
of the platform sways made with an accelerometer. Fast Fourier transform processing of stabilograms allowed spectral frequency
analysis. The total spectrum energy and the energies of three frequency bands (0–0.5 Hz, 0.5–2 Hz, 2–20 Hz) were determined.
ANOVA showed that, for all groups of different equilibrium activity and independent of visual input, prepubertal girls had
higher energy values than postpubertal girls in the 0- to 0.5-Hz band whereas the opposite was true for 0.5- to 2-Hz band.
Ballet dancers were more dependent than acrobats on visual inputs for the regulation of their postural control but were less
dependent than untrained girls at both ages. Maturation seemed to shift body sways towards higher frequencies and the utilization
of the cues of postural control was different according to the type of equilibrium activity practised by the subjects.
Accepted: 7 February 1997 相似文献
4.
Anthony P. Scinicariello Kenneth Eaton J. Timothy Inglis J. J. Collins 《Biological cybernetics》2001,84(6):475-480
With galvanic vestibular stimulation (GVS), electrical current is delivered transcutaneously to the vestibular afferents
through electrodes placed over the mastoid bones. This serves to modulate the continuous firing levels of the vestibular afferents,
and causes a standing subject to lean in different directions depending on the polarity of the current. Our objective in this
study was to test the hypothesis that the sway response elicited by GVS can be used to reduce the postural sway resulting
from a mechanical perturbation. Nine subjects were tested for their postural responses to both galvanic stimuli and support-surface
translations. Transfer-function models were fit to these responses and used to calculate a galvanic stimulus that would act
to counteract sway induced by a support-surface translation. The subjects' responses to support-surface translations, without
and with the stabilizing galvanic stimulus, were then measured. With the stabilizing galvanic stimulus, all subjects showed
significant reductions in both sway amplitude and sway latency. Thus, with GVS, subjects maintained a more erect stance and
followed the support-surface displacement more closely. These findings suggest that GVS could possibly form the basis for
a vestibular prosthesis by providing a means through which an individual's posture can be systematically controlled.
Received: 11 May 2000 / Accepted in revised form: 20 November 2000 相似文献
5.
Rafael Laboissière Jean-Charles Letievant Eugen Ionescu Pierre-Alain Barraud Michel Mazzuca Corinne Cian 《PloS one》2015,10(12)
Motion sickness (MS) usually occurs for a narrow band of frequencies of the imposed oscillation. It happens that this frequency band is close to that which are spontaneously produced by postural sway during natural stance. This study examined the relationship between reported susceptibility to motion sickness and postural control. The hypothesis is that the level of MS can be inferred from the shape of the Power Spectral Density (PSD) profile of spontaneous sway, as measured by the displacement of the center of mass during stationary, upright stance. In Experiment 1, postural fluctuations while standing quietly were related to MS history for inertial motion. In Experiment 2, postural stability measures registered before the onset of a visual roll movement were related to MS symptoms following the visual stimulation. Study of spectral characteristics in postural control showed differences in the distribution of energy along the power spectrum of the antero-posterior sway signal. Participants with MS history provoked by exposure to inertial motion showed a stronger contribution of the high frequency components of the sway signal. When MS was visually triggered, sick participants showed more postural sway in the low frequency range. The results suggest that subject-specific PSD details may be a predictor of the MS level. Furthermore, the analysis of the sway frequency spectrum provided insight into the intersubject differences in the use of postural control subsystems. The relationship observed between MS susceptibility and spontaneous posture is discussed in terms of postural sensory weighting and in relation to the nature of the provocative stimulus. 相似文献
6.
G. Schöner 《Biological cybernetics》1991,64(6):455-462
Action-perception patterns are studied theoretically in terms of equations of motion that capture the coordination capacity of the nervous system. We consider intrinsic dynamics in the absence of visual information that contain a single posture state as a fixed point attractor. We couple these intrinsic dynamics to visual information that stabilizes posture in the visual world. This leads to a theory of postural sway induced by an optic flow field (moving room paradigm). The optic flow is parametrized in a simplest approximation by the expansion rate of a relevant perceptual target. We show how temporal stability as the key concept of this theory can lead to prediction and serve as a measure of perceptual coupling. Finally, we discuss the relation of the present theory to biological cybernetics. 相似文献
7.
Taishin Nomura Shota Oshikawa Yasuyuki Suzuki Ken Kiyono Pietro Morasso 《Mathematical biosciences》2013
Ground reaction force during human quiet stance is modulated synchronously with the cardiac cycle through hemodynamics [1]. This almost periodic hemodynamic force induces a small disturbance torque to the ankle joint, which is considered as a source of endogenous perturbation that induces postural sway. Here we consider postural sway dynamics of an inverted pendulum model with an intermittent control strategy, in comparison with the traditional continuous-time feedback controller. We examine whether each control model can exhibit human-like postural sway, characterized by its power law behavior at the low frequency band 0.1–0.7 Hz, when it is weakly perturbed by periodic and/or random forcing mimicking the hemodynamic perturbation. We show that the continuous control model with typical feedback gain parameters hardly exhibits the human-like sway pattern, in contrast with the intermittent control model. Further analyses suggest that deterministic, including chaotic, slow oscillations that characterize the intermittent control strategy, together with the small hemodynamic perturbation, could be a possible mechanism for generating the postural sway. 相似文献
8.
There is controversy as to whether dyslexic children present systematic postural deficiency. Clinicians use a combination of ophthalmic prisms and proprioceptive soles to improve postural performances. This study examines the effects of convergent prisms and spherical lenses on posture. Fourteen dyslexics (13–17 years-old) and 11 non dyslexics (13–16 years-old) participated in the study. Quiet stance posturography was performed with the TechnoConcept device while subjects fixated a target at eye-level from a distance of 1_m. Four conditions were run: normal viewing; viewing the target with spherical lenses of −1 diopter (ACCOM1) over each eye; viewing with −3 diopters over each eye (ACCOM3); viewing with a convergent prism of 8 diopters per eye. Relative to normal viewing, the −1 lenses increased the surface of body sway significantly whereas the −3 diopter lenses only resulted in a significant increase of antero-posterior body sway. Thus, adolescents would appear to cope more effectively with stronger conflicts rather than subtle ones. The prism condition resulted in a significant increase in both the surface and the antero-posterior body sway. Importantly, all of these effects were similar for the two groups. Wavelet analysis (time frequency domain) revealed high spectral power of antero-posterior sway for the prism condition in both groups. In the ACCOM3 condition, the spectral power of antero-posterior sway decreased for non dyslexics but increased for dyslexics suggesting that dyslexics encounter more difficulty with accommodation. The cancelling time for medium range frequency (believed to be controlled by the cerebellum), was shorter in dyslexics, suggesting fewer instances of optimal control. We conclude that dyslexics achieve similar postural performances albeit less efficiently. Prisms and lenses destabilize posture for all teenagers. Thus, contrary to adults, adolescents do not seem to use efferent, proprioceptive ocular motor signals to improve their posture, at least not immediately when confronted to convergence accommodation conflict. 相似文献
9.
G. Gomez R. Voigt J. Atema 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,185(5):427-436
To understand how chemoreceptor organs may extract temporal information from odor plumes, we investigated the frequency filter
properties of lobster chemoreceptor cells. We used rapid stimulation and high-resolution stimulus measurement for accurate
stimulus control and recorded extracellular responses from chemoreceptors in the lobster lateral antennule in situ. We tested
16 hydroxyproline-sensitive cells with a series of ten 100-ms pulses at 10, 100 and 1000 μmol l−1 at stimulation frequencies from 0.5 Hz to 4 Hz. Receptor cell responses could accurately encode 10 μmol l−1, but not 100 or 1000 μmol l−1 pulses, delivered at rates of 4 Hz. Flicker-fusion frequency and synchronization with the stimulus pulse train were concentration
dependent: performance rates above 1 Hz became poorer both with increasing pulse amplitude and frequency. Flicker fusion frequency
was 3 Hz for 100 μmol l−1 pulses and 2 Hz for 1000 μmol l−1 pulses. Individual cells showed differences in their stimulus pulse following capabilities, as measured by the synchronization
coefficient. These individual differences may form a basis for coding temporal features of an odor plume in an across-fiber
pattern.
Accepted: 7 July 1999 相似文献
10.
The purpose of the study was to investigate the effects of sleep deprivation (SD) in adaptation of the coupling between visual information and body sway in young adults’ postural control due to changes in optic flow characteristics. Fifteen young adults were kept awake for approximately 25 hours and formed the SD group, while fifteen adults who slept normally the night before the experiment participated as part of the control group. All participants stood as still as possible in a moving room before and after being exposed to one trial with higher amplitude and velocity of room movement. Postural performance and the coupling between visual information, provided by a moving room, and body sway were examined. Results showed that after an abrupt change in visual cues, larger amplitude, and higher velocity of the room, the influence of room motion on body sway was decreased in both groups. However, such a decrease was less pronounced in sleep deprived as compared to control subjects. Sleep deprived adults were able to adapt motor responses to the environmental change provided by the increase in room motion amplitude. Nevertheless, they were not as efficient as control subjects in doing so, which demonstrates that SD impairs the ability to adapt sensorimotor coupling while controlling posture when a perturbation occurs. 相似文献
11.
Ewa Bie? Joanna Zima Dorota Wójtowicz Bo?ena Wojciechowska-Maszkowska Krzysztof Kr?cisz Micha? Kuczyński 《PloS one》2014,9(4)
To evaluate postural control and performance in subjects with Down syndrome (SwDS), we measured postural sway (COP) in quiet stance in four 20-second tests: with eyes open or closed and on hard or foam surface. Ten SwDS and eleven healthy subjects participated, aged 29.8 (4.8) and 28.4 (3.9), respectively. The time-series recorded with the sampling rate of 100 Hz were used to evaluate postural performance (COP amplitude and mean velocity) and strategies (COP frequency, fractal dimension and entropy). There were no intergroup differences in the amplitude except the stance on foam pad with eyes open when SwDS had larger sway. The COP velocity and frequency were larger in SwDS than controls in all trials on foam pad. During stances on the foam pad SwDS increased fractal dimension showing higher complexity of their equilibrium system, while controls decreased sample entropy exhibiting more conscious control of posture in comparison to the stances on hard support surface. This indicated that each group used entirely different adjustments of postural strategies to the somatosensory challenge. It is proposed that the inferior postural control of SwDS results mainly from insufficient experience in dealing with unpredictable postural stimuli and deficit in motor learning. 相似文献
12.
In this study, a model for the estimation of the dynamics of the lower extremities in standing sway from force plate data
only is presented. A three-dimensional, five-segment, four-joint model of the human body was used to describe postural standing
sway dynamics. Force-plate data of the reactive forces and centers of pressure were measured bilaterally. By applying the
equations of motion to these data, the transversal trajectory of the center of gravity (CG) of the body was resolved in the
sagittal and coronal planes. An inverse kinematics algorithm was used to evaluate the kinematics of the body segments. The
dynamics of the segments was then resolved by using the Newton-Euler equations, and the model's estimated dynamic quantities
of the distal segments were compared with those actually measured. Differences between model and measured dynamics were calculated
and minimized, using an iterative algorithm to re-estimate joint positioning and anthropometric properties. The above method
was tested with a group of 11 able-bodied subjects, and the results indicated that the relative errors obtained in the final
iteration were of the same order of magnitude as those reported for closed loop problems involved in direct kinematics measurements
of human gait.
Received: 22 July 1997 / Accepted in revised form: 29 January 1998 相似文献
13.
Purpose of the studyThe influence of the stomatognathic apparatus on body posture is a continuously discussed topic with contrasting results. The aim of this study is to analyze differences in postural stability between subjects with and without myogenous TMD.Methods25 subjects affected by myogenous TMD according with DC/TMD (6 males, 19 females; mean age 31.75 ± 6.68 years) and a healthy control group of 19 subjects (4 Males, 15 Females; mean age 27.26 ± 3.85 years) were enrolled in the study.Both groups underwent a posturo-stabilometric force platform exam under different mandibular and visual conditions. Sway area and sway velocity of the COP (Center Of foot Pressure) posturo-stabilometric parameters were evaluated and compared applying Mann-U-Whitney statistical test.ResultsThe sway area and sway velocity parameters resulted statistically significantly higher in the TMD group (sway area p < 0.01; sway velocity p < 0.05) in mandibular maximum intercuspation and rest positions with eyes open.ConclusionsThis study demonstrates a significant difference in body postural stability between subjects with myogenous TMD and healthy controls. In particular, sway area and sway velocity postural parameters are increased in these subjects. 相似文献
14.
We studied the effect of sinusoidal stimulation of the labyrinths on postural reflexes in man, using a 0.3 Hz current of alternating polarity and +/- 1 mA intensity for stimulation. The test subjects were tested binaurally by the bipolar method (BB), with two electrodes on the mastoid processes, and binaurally by the monopolar method (BM), with electrodes localized bilaterally on the mastoid process and the hand. Stabilographic postural parameters were measured in 22 subjects in five experimental situations. Each situation lasted 60 s. Body sway, detected by astabilometer, was recorded on a Philips FM tape-recorder and then analysed off-line on a PDP-11/34 computer. On BB stimulation of the labyrinths, the variance of body sway in the left-right (LR) direction increased more than in the anteroposterior (AP) direction. In BM stimulation, only the variance of LR sway increased. Other posturographic parameters displayed a similar effect. From the aspect of body sway frequency, BB stimulation produced a peak in the course of the power spectral density of the lateral stabilogram at 0.3 Hz. In this experimental situation, a habituation effect was manifested, depending on the subject. It can be stated that binaural bipolar (BB) stimulation of the labyrinths selectively influences lateral body sway, while the increase in AP body sway in this situation is merely a concomitant phenomenon. 相似文献
15.
The frequency sensitivity of weak periodic signal detection has been studied via numerical simulations for both a single
neuron and a neuronal network. The dependence of the critical amplitude of the signal upon its frequency and a resonance between
the intrinsic oscillations of a neuron and the signal could account for the frequency sensitivity. In the presence of both
a subthreshold periodic signal and noise, the signal-to-noise ratio (SNR) of the output of either a single neuron or a neuronal
network present the typical characteristics of stochastic resonance. In particular, there exists a frequency-sensitive range
of 30–100 Hz, and for signals with frequencies within this range the SNRs have large values. This implies that the system
under consideration (a single neuron or a neuronal network) is more sensitive to the detection of periodic signals, and the
frequency sensitivity may be of a functional significance to signal processing.
Received: 26 October 1999 / Accepted in revised form: 25 July 2000 相似文献
16.
ABSTRACT: To decrease the influence of postural sway during spinal measurements, an instrumented fixation posture (called G) was proposed and tested in comparison with the free standing posture (A) using the DTP-3 system in a group of 70 healthy volunteers. The measurement was performed 5 times on each subject and each position was tested by a newly developed device for non-invasive spinal measurements called DTP-3 system. Changes in postural stability of the spinous processes for each subject/the whole group were evaluated by employing standard statistical tools. Posture G, when compared to posture A, reduced postural sway significantly in all spinous processes from C3 to L5 in both the mediolateral and anterioposterior directions. Posture G also significantly reduced postural sway in the vertical direction in 18 out of 22 spinous processes. Importantly, posture G did not significantly influence the spinal curvature. 相似文献
17.
Tests of a linear model of visual-vestibular interaction using the technique of parameter estimation
Vallabh E. Das Alfred O. DiScenna Andrew Feltz Stacy Yaniglos R. John Leigh 《Biological cybernetics》1998,78(3):183-195
The goal of this study was to test whether a superposition model of smooth-pursuit and vestibulo-ocular reflex (VOR) eye
movements could account for the stability of gaze that subjects show as they view a stationary target, during head rotations
at frequencies that correspond to natural movements. Horizontal smooth-pursuit and the VOR were tested using sinusoidal stimuli
with frequencies in the range 1.0–3.5 Hz. During head rotation, subjects viewed a stationary target either directly or through
an optical device that required eye movements to be approximately twice the amplitude of head movements in order to maintain
foveal vision of the target. The gain of compensatory eye movements during viewing through the optical device was generally
greater than during direct viewing or during attempted fixation of the remembered target location in darkness. This suggests
that visual factors influence the response, even at high frequencies of head rotation. During viewing through the optical
device, the gain of compensatory eye movements declined as a function of the frequency of head rotation (P < 0.001) but, at any particular frequency, there was no correlation with peak head velocity (P > 0.23), peak head acceleration (P > 0.22) or retinal slip speed (P > 0.22). The optimal values of parameters of smooth-pursuit and VOR components of a simple superposition model were estimated
in the frequency domain, using the measured responses during head rotation, as each subject viewed the stationary target through
the optical device. We then compared the model's prediction of smooth-pursuit gain and phase, at each frequency, with values
obtained experimentally. Each subject's pursuit showed lower gain and greater phase lag than the model predicted. Smooth-pursuit
performance did not improve significantly if the moving target was a 10 deg × 10 deg Amsler grid, or if sinusoidal oscillation
of the target was superimposed on ramp motion. Further, subjects were still able to modulate the gain of compensatory eye
movements during pseudo-random head perturbations, making improved predictor performance during visual-vestibular interactions
unlikely. We conclude that the increase in gain of eye movements that compensate for head rotations when subjects view, rather
than imagine, a stationary target cannot be adequately explained by superposition of VOR and smooth-pursuit signals. Instead,
vision may affect VOR performance by determining the context of the behavior.
Received: 16 June 1997 / Accepted: 5 December 1997 相似文献
18.
To investigate what sampling frequency is adequate for gait, the correlation of spatiotemporal parameters and the kinematic differences, between normal and CP spastic gait, for three sampling frequencies (100 Hz, 50 Hz, 25 Hz) were assessed. Spatiotemporal, angular, and linear displacement variables in the sagittal plane along with their 1st and 2nd derivatives were analyzed. Spatiotemporal stride parameters were highly correlated among the three sampling frequencies. The statistical model (2 × 3 ANOVA) gave no interactions between the factors group and frequency, indicating that group differences were invariant of sampling frequency. Lower frequencies led to smoother curves for all the variables, with a loss of information though, especially for the 2nd derivatives, having a homologous effect as the one of oversmoothing. It is proposed that in the circumstance that only spatiotemporal stride parameters, as well as angular and linear displacements are to be used, in gait reports, then commercial video camera speeds (25/30 Hz, 50/60 Hz when deinterlaced) can be considered as a low-cost solution to produce acceptable results. 相似文献
19.
20.
T. C. Tricas J. G. New 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,182(1):89-101
Elasmobranch fishes localize weak electric sources at field intensities of <5 ηV cm−1, but the response dynamics of electrosensory primary afferent neurons to near threshold stimuli in situ are not well characterized.
Electrosensory primary afferents in the round stingray, Urolophus halleri, have a relatively high discharge rate, a regular discharge pattern and entrain to 1-Hz sinusoidal peak electric field gradients
of ≤20 ηV cm−1. Peak neural discharge for units increases as a non-linear function of stimulus intensity, and unit sensitivity (gain) decreases
as stimulus intensity increases. Average peak rate-intensity encoding is commonly lost when peak spike rate approximately
doubles that of resting, and for many units occurs at intensities <1 μV cm−1. Best neural sensitivity for nearly all units is at 1–2 Hz with a low-frequency slope of 8 dB/decade and a high-frequency
slope of −23 dB/decade. The response characteristics of stingray electrosensory primary afferents indicate sensory adaptations
for detection of extremely weak phasic fields near 1–2 Hz. We argue that these properties reflect evolutionary adaptations
in elasmobranch fishes to enhance detection of prey, communication and social interactions, and possibly electric-mediated
geomagnetic orientation.
Accepted: 20 June 1997 相似文献