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At least 721 records · Page 40Linked to original sources

PubMed2003

On-line trajectory modifications of planar, goal-directed arm movements.

Sometimes a goal-directed arm movement has to be modified en route due to an unforeseen perturbation such as a target displacement or a hand displacement by an external force. In this paper several aspects of that modification process are addressed. Subjects had to perform a point-to-point movement task on a computer screen using a mouse-coupled pointer as the representation of the hand position. Trajectory modifications were imposed by unexpectedly changing the position of the target or by changing the relation between mouse and screen pointer. In the first series of experiments, we examined how often a trajectory is updated. Here, trajectory modifications were imposed by unexpectedly changing the normal relation between mouse and pointer to a shear-like relation, where a percentage of the forward/backward position of the hand was added to the pointer position in the left/right direction. Withdrawal of visual feedback during the movement revealed that trajectories were updated at interval times shorter than 200 ms. From the similarity with experiments where the original relation between mouse and pointer was restored during the movements, we conclude that motor plans are updated on-line to move the hand from its current perceived position to the target. In a second series of experiments, we studied whether a continuous change in target position yields similar trajectory modifications as a continuous hand displacement. To mimic the latter perturbation, we used the above-mentioned distortion of the mouse-pointer relation. We found that the resulting hand paths did not differ for the two visual perturbations and conclude that the perturbed, goal-directed movements are modified in a consistent way, irrespective of whether the position of the target or hand was perturbed. Simulations of the experimental data with a kinematic reaching model support this conclusion.

Acceleration↗

PubMed2002

Reduced corticomotor excitability with cyclic passive movement: a study using transcranial magnetic stimulation.

Human voluntary movement involves the integration of kinaesthetic information with efferent motor activity during the planning and execution stages of movement. While much is known of the inhibitory and excitatory effects resulting from activation of specific kinaesthetic sensory receptors, in the present study we employed cyclic passive movement of the index finger in order to activate a range of kinaesthetic receptors in a manner that was intended to correspond to how these receptors might be active during a comparable voluntary movement. We intended to identify how this passive movement protocol might affect the excitability of the corticomotor pathway. During 1 Hz cyclic passive movement of the index finger there was an approximately 60% reduction in the amplitude of the motor evoked response from the first dorsal interosseous muscle. The results of the present study demonstrate that passive movement can have a profound effect on the excitability of the corticomotor pathway.

Adult↗

PubMed2003

Activation patterns in forearm muscles during archery shooting.

A contraction and relaxation strategy with regard to forearm muscles during the release of the bowstring has often been observed during archery, but has not well been described. The purpose of this study was to analyze this strategy in archers with different levels of expertise; elite, beginner and non-archers. Electromyography (EMG) activity of the M. flexor digitorum superficialis and the M. extensor digitorum were recorded at a sampling frequency of 500 Hz, together with a pulse synchronized with the clicker snap, for twelve shots by each subject. Raw EMG records, 1-s before and after the clicker pulse, were rectified, integrated and normalized. The data was then averaged for successive shots of each subject and later for each group. All subjects including non-archers developed an active contraction of the M. extensor digitorum and a gradual relaxation of the M. flexor digitorum superficialis with the fall of the clicker. In elite archers release started about 100 ms after the fall of the clicker, whereas in beginners and non-archers release started after about 200 and 300 ms, respectively. Non-archers displayed a preparation phase involving extensive extensor activity before the release of the bowstring, which was not observed in elite and beginner archers. In conclusion, archers released the bowstring by active contraction of the forearm extensors, whereas a clear relaxation of the forearm flexors affecting the release movement was not observed.

Adolescent↗

PubMed2003

Learning to coordinate redundant degrees of freedom in a dynamic balance task.

The present study investigated Bernstein's [The co-ordination and regulation of movements, 1967] proposal regarding the three stages of learning in the changing coordination and control of redundant joint-space degrees of freedom. Six participants practiced maintaining balance on a moving platform that was sinusoidally translated in the anterior-posterior direction for 30 trials on day 1 and 10 trials on day 2. At the beginning of practice, the motion of the torso and limb segments was less coherent in the attempt to compensate for the movement of the support surface in retaining a balanced posture. However, with practice, the organization of a compensatory postural coordination mode became highly coherent and also progressively utilized the passive, inertial forces generated by the movement of the support surface. The findings support the propositions that: (a) the pathway of change over time in the coordination pattern of the torso and joint motions depends on the task goal and constraints to action and (b) the changes in limb and torso motion are in support of the learning of a global body center of mass/platform dynamic.

Adult↗

PubMed2002

Evidence for internal representation of a static nonlinearity in a visual tracking task.

A group of 24 participants was given over 3 h practice at a visual pursuit tracking task with a pronounced static nonlinearity between movement of the joystick and the resulting deflection of the response cursor. The aim was twofold: (1) to determine whether or not participants compensated for the nonlinearity and (2) to show that any such compensation involved the formation of an internal representation of the nonlinear relationship between movement of the joystick as sensed kinaesthetically and/or visually and movement of the response cursor as sensed visually. Results show that participants introduce partial compensation for the static nonlinearity. Furthermore, partial compensation was present even during open-loop tracking when participants were deprived of visual feedback of the position of the response cursor. This implies that participants are able to form an internal representation of the nonlinear relationship between movement of the joystick and the resulting movement of the response cursor.

Adult↗

PubMedDate not supplied

Persistent mal de debarquement syndrome: a motion-induced subjective disorder of balance.

Six patients with a distinct syndrome of persistent sensations of imbalance are presented. Common features included onset following a period of motion exposure, symptoms lasting months to years, mild unsteadiness and anxiety, minimal relief from antivertiginous medication, and normal neurologic and quantitative vestibulo-ocular examinations. One patient experienced recurrent episodes. Mal de debarquement refers to sensations of motion experienced on return to stable land after adaptation to motion lasting from hours to days in normal individuals. The presented patients exemplify a syndrome of persistent mal de debarquement. The entity is found in a relatively small number of dizzy patients. Persistent mal de debarquement is discussed in the context of what is known about long-term vestibulo-ocular adaptation to alterations of visual or vestibular environments.

Adult↗

PubMed1982

Computer-assisted handwriting instruction and visual/kinaesthetic feedback processes.

An evaluation of computer-assisted handwriting exercises which offer significant advantages over more conventional teaching techniques is described. Handwriting is considered as a skill that must be regulated by processes which at first are externally controlled but which become internalized as the learner becomes more proficient at the skill. Handwriting samples of lower-case alphanumeric characters were obtained from nine mentally retarded school children. After a training program spread over a period of four weeks (approximately 5 hours in total), the greatest improvement in handwriting ability occurred where the constraints of the computer-assisted handwriting exercises encouraged students to gradually transfer control of letter formation from computer-mediated cues to more internal ones. These results are discussed in terms of control functions and the acquisition of skilled behavior.

Adolescent↗

PubMedDate not supplied

Memory for kinesthetically defined target location: evidence for manual asymmetries.

Sixteen right-handed male adults performed a pointing task without vision. The participant's arm was moved passively to one of four targets which was subsequently pointed to following a delay of 1, 2, or 10 s. Our previous research on visual memory for target location showed a rapid decay which was comparable for both hands. The present study of memory for kinesthetic target location found decay for the left hand only. These findings suggest two memory stores for target location information, one visual which decays over time but is accessible to both hands and another based on kinesthetic information which is more stable and limb specific.

Adult↗

PubMedDate not supplied

Left-side infant holding: a test of the hemispheric arousal-attentional hypothesis.

When asked to hold a young infant in their arms, most adults hold on the left side (Harris, 1997). In a prior study, we found the same bias when we asked adults merely to imagine holding an infant in their arms (Harris, Almerigi, & Kirsch, 1999). It has been hypothesized that the left-side bias is the product of right-hemisphere arousal accompanying certain aspects of the act, causing attention to be driven to the contralateral, or left, side of personal space. Left-side holding, whether actual or imagined, thus would be consistent with the direction to which the holder's attention has been endogenously directed. We tested this hypothesis by giving 250 college students the "imagine-holding" task and then, as an independent measure of lateralized hemispheric arousal, a 34-item Chimeric Faces Test (CFT). On the "imagine" test, a significant majority reported a left-side hold, and, on the CFT, left-side holders had a significantly stronger left-hemispace bias than right-side holders, although both left- and right side holders had left-hemispace CFT biases. The results thus support the attentional-arousal hypothesis but indicate that other factors are contributing as well.

Adult↗

PubMed2000

On the fractal properties of natural human standing.

We analyzed the temporal evolution of the displacement of the center of pressure (COP) during prolonged unconstrained standing (30 min) in non-impaired human subjects. The COP represents the collective outcome of the postural control system and the force of gravity and is the main parameter used in studies on postural control. Our analysis showed that the COP displacement during human standing displays fractal properties that were quantified by the Hurst exponent obtained from the classical rescaled adjusted range analysis. The average fractal or Hurst exponent (H) was 0.35+/-0.06. The presence of long-range correlations from a few seconds to several minutes due to the fractal characteristics of the postural control system has several important implications for the analysis of human balance.

Adult↗

PubMed2000

Muscular exercise improves knee position sense in humans.

To determine how position sense depends on the functional state of the receptors involved, we assessed the accuracy of knee position sense before and after a moderate exercise on a cycle ergometer. Measurements were done on 32 healthy subjects with four protocols combining two tasks (intramodal: using the contralateral leg, and crossmodal: using a scheme of a leg on a screen) and two ways of positioning (active and passive). Results showed an improved position sense after exercise with the intramodal protocol combined with active positioning of the reference leg. Whatever the mechanisms involved, enhanced motor performances after exercise can be due not only to improved mechanical properties of the muscles but also to better kinesthetic sensibility.

Adult↗

PubMed2002

Informational constraints in human precision aiming.

Twelve human subjects performed a reciprocal precision aiming task of varying difficulty (index of difficulty=4, 5, or 6) while vision of the ongoing movement was available either continuously or intermittently. In the intermittent conditions, vision of the moving end-effector was available at regular intervals (equal to 100%, 125%, or 150% of the movement durations measured under continuous visibility conditions) for varying amounts of time (75%, 50%, or 25% of the duration of the interval). Movement time (MT) increased with both increasing task difficulty and decreasing availability of visual information. Increases in MT were brought about by the same systematic changes in the kinematic characteristics of movement, whether task difficulty increased or availability of visual information decreased. At higher levels of task difficulty, subjects organized their movements so as to make visual information available at particular instances (at the start and at the end of the aiming movement).

Adult↗

PubMed2003

Dynamics of the learning of a morphokinetic movement sequence in humans.

We studied the dynamics of the process through which subjects build a visuomotor representation in memory as they learn a morphokinetic movement sequence presented on videotape. It was hypothesized that recall accuracy is closely tied to the dynamics of the movement-representation process. When analyzed in the form of time series, recall performance should exhibit a deterministic inter-trial relationship reflecting the memorization activity. Twelve subjects divided into two groups recalled a sequence of arm movements 60 times. The model was presented to Group 1 (G1) on all 60 trials, whereas Group 2 only saw the model on the first 30 trials. During these first 30 trials, the analysis of accuracy time series pointed out the short-term historicity of the deterministic inter-trials relationship. For the last 30 trials, this deterministic relationship disappeared in both experimental conditions, except for two subjects of G1, and was replaced by a white-noise process suggesting that a stable representation of the sequence has been built in long-term memory.

Analysis of Variance↗

PubMed2003

Contribution of action to perception of self-orientation in humans.

In this study, we evaluated the effect of action on the perception of an egocentric illusion. Eighteen participants were asked to indicate the perceived morphological horizon under two backward body tilts from upright in the median plane (i.e. pitch) using five different response modes. The response modes varied in the degree of motor and cognitive involvement. Differences in perception of the morphological horizon between the two body tilts were significant only when proximal limb control was not involved. These results suggest that motor involvement and frame of reference may both be important in visual-vestibular illusions.

Adult↗

PubMed2002

Perceptual changes in illusory wrist flexion angles resulting from motor imagery of the same wrist movements.

Recent neuroimaging studies have suggested that similar cortical motor areas are recruited both by kinesthetic sensations elicited by tendon vibration and by voluntarily imaging one's own movements of the same joints. Little is known, however, as to whether kinesthetic motor imagery interacts with kinesthetic illusion. We examined such interaction by behavioral analysis in which 19 subjects imagined wrist flexion or extension, with or without illusory flexion induced by tendon vibration. Electromyograms were also recorded to monitor the peripheral modulations caused by the interaction. The kinesthetic motor imagery had a psychophysical effect on kinesthetic illusion in the absence of overt movement. It was confirmed that the subjects could imagine wrist movements without facilitating muscle activities in the absence of vibration stimuli. The electromyogram activity of the vibrated extensor muscles was significantly higher than that of non-vibrated flexor muscles. Motor imagery of wrist extension, when illusory flexion was experienced, reduced the angle of illusory flexion while enhancing extensor muscle activities in comparison with the control. On the other hand, flexion motor imagery increased the angle of illusory flexion with or without enhancement of flexor muscle activities. Our results indicate that motor imagery interacts with kinesthetic illusion with or without enhancement of activities of the related muscles. This suggests (1) that common neural substrates shared by imagery and by illusion exist and (2) that different physiological mechanisms contribute to the enhancement of muscle activities of vibrated muscles and their antagonists.

Adolescent↗

PubMed2003

Adaptive plasticity in the otolith-ocular reflex.

This review focuses on the plasticity in the vestibulo-ocular reflex (VOR), especially in the otolith-ocular reflex (OOR). The VOR is a mechanism for the production of rapid compensatory eye movements during head movements. The VOR is under adaptive control which corrects VOR performance when visual-vestibular mismatch arises during head movements. It has been demonstrated that chronic exposure to certain visual environments, those generated by magnifying lenses and reversing prisms, alter the gain and phase of VOR in the dark in numerous species. Most experiments concerning such modification of the VOR have used semicircular canal stimulation. The VOR consists of the semicircular-ocular reflex (ScOR) and the OOR. There are few results regarding the relationship between the gain of the ScOR and the OOR. This review summarizes the studies on plasticity in the OOR. In addition, the difficulty in evaluating the OOR using current conventional methods including earth horizontal axis (EHA) rotation, off-vertical axis rotation (OVAR) and linear sled, is discussed. We believe that the ScOR and the OOR share common neural pathways in such a way that a change in the synaptic efficacy of one pathway is accompanied by a change in the other.

Animals↗

PubMed2003

Flexibility of vestibulo-ocular reflex adaptation to modified visual input in human.

The vestibulo-ocular reflex (VOR) serves to keep images relatively stable on the retina. To maintain appropriate performance and minimize image slip throughout life, VOR is subjected to long-term adaptive regulation by visual input. It has been reported that adaptive changes in VOR gain (eye velocity/head velocity) are evoked either by fitting subjects with magnifying, miniaturizing, or reversing spectacles during normal behavior, or by moving a large visual field in or out of phase relative to the subject's head movement. The changes in VOR gain are frequency selective. Here, we examine the extent of VOR gain flexibility by causing VORs of similar direction to undergo different behavioral gain changes. Nine healthy adults participated in the study, ranging in age from 24 to 38 years (mean: 26 years) and with no history of neurotological symptoms. All subjects were clinically normal according to a screening battery that included combined neurologic and otologic physical examinations. Horizontal and vertical eye positions were recorded by bitemporal DC-coupled electro-oculography (EOG). The subject sat in a rotating chair. The axis of rotation of the body was always earth-vertical, with the interaural axis crossing the axis of rotation of the chair. The head was pointed 20 degrees downwards in all experiments and stabilized in this position using a chin rest. The chair was surrounded by a half-cylindrical optokinetic screen (78 cm in diameter) placed in front of the subject, onto which random dot patterns were projected. Goggles were used to ensure that the subject was in complete darkness during both pre- and postadaptation periods. The chair was rotated sinusoidally at maximum amplitude of 30 degrees or 60 degrees : for 30 degrees the stimulation was at 0.1, 0.2, 0.3, and 0.4 Hz; for 60 degrees it was at 0.1, 0.2, and 0.3 Hz. VOR adaptation was obtained by inducing a retinal slip velocity by short-term alteration of the visual input of the large field; this change was produced by a combination of sinusoidal head rotation and the random dot patterns. In each adaptation session, the sinusoidal head rotation was either at 0.1 or 0.3 Hz and the amplitude was 30 degrees. The random dot pattern was synchronized with sinusoidal head rotation in the same direction (x0 experiment) to make the retinal slip zero, and in the opposite direction to make the retinal slip twofold (x2 experiment). Therefore, a total of four adaptation protocols were tested. The subjects were asked to fixate on a single dot with the eyes straight-ahead in the x0 experiment, and follow it within random dot patterns in the x2 experiment. Each adaptation session lasted for 30 min. Two adaptation experiments were performed on each subject once per day. The averages of VOR gain and phase lag were calculated using Fourier analysis. Seven of the subjects who participated in the x2 adaptation experiment at 0.3 Hz and 30 degrees amplitude showed a steady increase of VOR gain within a couple of trials. One of the remaining two subjects showed a decrease in VOR gain in all the three trials, and the other subject showed a VOR gain increase in three trials and decrease in two trials. In the x2 adaptation experiment at 0.3 Hz and 30 degrees amplitude (peak velocity: 28 degrees /s), the percentage gain change ((post-pre)/pre) was 133% at the same stimulation and 100% at 0.4 Hz (peak velocity: 37 degrees /s). The gain change was 65% at 0.1 Hz and 60 degrees amplitude (peak velocity: 18 degrees /s), and 64% at 0.2 Hz and 60 degrees amplitude (peak velocity: 37 degrees /s). In the x1 adaptation experiment (30 degrees at 0.3 Hz), the percentage gain change was -62% under the same conditions, -50% at 0.1 Hz and 60 degrees amplitude, and -30% at 0.2 Hz and 60 degrees amplitude. No change of VOR gain was observed at other frequencies, and the subject was not adapted at 0.1 Hz and 30 degrees amplitude. The larger VOR gain increase in the x2 adaptation experiment for the faster head angular acceleration leads to the conclusion that the VOR gain mechanism can set vuite similar in terms of the head acceleration.

Adult↗

PubMed2002

Significance of auditory and kinesthetic feedback to singers' pitch control.

An accurate control of fundamental frequency (F0) is required from singers. This control relies on auditory and kinesthetic feedback. However, a loud accompaniment may mask the auditory feedback, leaving the singers to rely on kinesthetic feedback. The object of the present study was to estimate the significance of auditory and kinesthetic feedback to pitch control in 28 students beginning a professional solo singing education. The singers sang an ascending and descending triad pattern covering their entire pitch range with and without masking noise in legato and staccato and in a slow and a fast tempo. F0 was measured by means of a computer program. The interval sizes between adjacent tones were determined and their departures from equally tempered tuning were calculated. The deviations from this tuning were used as a measure of the accuracy of intonation. Statistical analysis showed a significant effect of masking that amounted to a mean impairment of pitch accuracy by 14 cent across all subjects. Furthermore, significant effects were found of tempo as well as of the staccato/legato conditions. The results indicate that auditory feedback contributes significantly to singers' control of pitch.

Adult↗