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At least 271 records · Page 15Linked to original sources
PubMed1996

Basic features of phasic activation for reaching in vertical planes.

The purpose of this study was to fully characterize the timing and intensity of the phasic portion of the electromyographic (EMG) waveform for reaching movements in vertical planes. Electromyographic activity was simultaneously recorded from nine superficial elbow and/or shoulder muscles while human subjects made rapid arm movements. Hand paths comprised 20 directions in a sagittal plane and 20 directions in a frontal plane. In order to focus on the more phasic aspects of muscle activation, estimates of postural EMG activity were subtracted from the EMG traces recorded during rapid reaches. These postural estimates were obtained from activity recorded during very slow reaches to the same targets. After subtraction of this postural activity, agonist or antagonist burst patterns were often observed in the phasic EMG traces. For nearly all muscles and all subjects, the relation between phasic EMG intensity and movement direction was a function with multiple peaks. For all muscles, the timing of phasic EMG bursts varied as a function of movement direction: the data from each muscle exhibited a gradual temporal shift of activity over a certain range of directions. This gradual temporal shift has no obvious correspondence to the mechanical requirements of the task and might represent a neuromuscular control strategy in which burst timing contributes to the specification of movement direction.

Adult↗
PubMed1982

Afferent and efferent components of joint position sense; interpretation of kinaesthetic illusion.

The present model of joint angle perception is based on the following hypotheses: the perception and control of joint angle are closely interrelated processes; central motor commands are adequately expressed by shifts of an equilibrium point resulting from the interaction of antagonistic muscles and a load; two fundamental commands--reciprocal (r) and coactivative (c) provide for changes in activity of the antagonistic muscle pair. The dependence of joint angle on static muscle torque and r and c commands is derived (Eq. 5). The following principles of joint position sense are formulated: 1) the r component of the efferent copy plays the role of a reference point which shifts during voluntary regulation of muscle state, but remains unchanged during any passive alterations of joint position; 2) muscle afferent signals deliver not absolute but relative information (i.e. measured relatively to the central reference point). These signals turn out to be related to active muscle torque; 3) the nervous system evaluates muscle afferent signals on the basis of a scale determined by the level of coactivation of the antagonistic muscles. Kinaesthetic illusions appear to be due to disruptions in perception of afferent and/or efferent components of position sense. The present model is consistent with all the variety of kinaesthetic illusions observed experimentally. A qualitative neurophysiological schema for joint angle perception is proposed involving efferent copy and information concerning muscle torque delivered by the tendon organ, muscle spindle, and, perhaps, articular receptors. It is known that the cerebellum incorporates both afferent and efferent information concerning movements. One may presume that it plays an essential role in position sense.

Afferent Pathways↗
PubMed1981

The threshold of perception of angular acceleration as a function of duration.

The threshold for rotation about the yaw axis was determined for constant acceleration stimuli as a function of their duration in the range from 3 to 25 s. From the torsion-swing model the following theoretical equation can be derived: alpha thr = C/[1--exp(-ts/tau 1)], where alpha thr = acceleration amplitude at threshold, ts = duration of the acceleration, tau 1 = time constant, C = threshold for very long stimuli. According to this formula the Mulder product (i.e. the product of the threshold acceleration amplitude and the duration of the stimulus) is constant for durations up to 0.3 tau 1. The best fit of this theoretical function to the somatosensory data is found for tau 1 = 14.5 s, and C = 0.220/s2. The time within the Mulder product is constant (about 5 s) is doubtless due to the mechanics of the semicircular canals. For the oculogyral data a lower value of tau 1 is found. We do not have any explanation for this lower value.

Acceleration↗
PubMed1993

Perceptual-motor development and prevention of clumsiness.

This longitudinal study, following children's development over three years, examines the developmental trends in the processes underlying perceptual-motor behaviour. Entry into the study was at first year of primary school, at age 6. The study has three aims: (1) to obtain developmental trends in kinaesthesis and motor-programming processes; (2) to examine the relationship between slow kinaesthetic and motor development; (3) to establish the effect of accelerated kinaesthetic development and prevention of perceptual-motor dysfunction (clumsiness). The results to date show that over 60% of children entering primary school have not developed the kinaesthetic ability necessary for the acquisition and learning of educationally demanded motor skills. Kinaesthetic development is accelerated spontaneously in some children as a response to educational demands; in others a single exposure to kinaesthetic input triggers significant improvement. In the remaining 17% kinaesthetic training can alleviate the kinaesthetic dysfunction. At age 5-6 years only 25 children (8.1%) performed the Perceptual-Motor Abilities Test at levels indicative of perceptual-motor dysfunction. Of these, 13 children (4.2%) were identified as having motor difficulties. These low incidence rates indicate that a low level of kinaesthetic ability has no effect on general motor function at the beginning of schooling, and that only when competence in complex motor skills is expected, from the third year of schooling, does perceptual-motor dysfunction (PMD) become manifest.

Aptitude↗
PubMed1993

Motor functions of the basal ganglia.

A study of movement disorders such as Parkinson's disease and Huntington's disease can provide an indication of the motor functions of the basal ganglia. Basal-ganglia diseases affect voluntary movement and can cause involuntary movement. Deficits are often manifested during the coordination of fine multi-joint movements (e.g., handwriting). The disturbances of motor control (e.g. akinesia, bradykinesia) caused by basal-ganglia disorders are illustrated. Data suggest that the basal ganglia play an important role in the automatic execution of serially ordered complex movements.

Basal Ganglia↗
PubMed1993

A neural-network model enabling sensorimotor learning: application to the control of arm movements and some implications for speech-motor control and stuttering.

Low-level motor control is defined as adapting an organism to the unique physical properties of its own limbs. The two-jointed arm serves to exemplify that effective low-level motor control demands a neurally medicated inversion of the dynamics, as well as of the kinematics, of a limb system. Reflex-like processing--that is, feedforword of either actual or predicted proprioceptive signals--is thereby assumed to be the principle of the dynamics control. As regards speech-motor control, the overall tool transformation is assumed to transform the force pattern of the articulatory muscles into speech sounds. Like the arm model, the vocal-tract transformation thus defined is also divided into two parts, namely the transformation relating the muscle forces to the mechanospatial states of the vocal tract (which is analogous to the forward dynamics including natural interarticulatory couplings), and the transformation relating the mechanospatial states to the speech sounds. Low-level speech-motor control, then, needs to invert both transformations, each of which can be learned by means of the self-imitation algorithm. Erroneous learning can fail to decouple interarticulatory coupling and therefore lead to abnormal feedback loops through the reflex-like operating neural network, which in turn can cause stuttering if audiophonatoric coupling is involved in learning.

Algorithms↗
PubMed1996

Adaptation of a reaching model to handwriting: how different effectors can produce the same written output, and other results.

This report shows how a model initially developed for the control of reaching can be adapted for the control of handwriting. The main problem addressed by the model is how people can produce essentially the same written output with different effectors (e.g., the preferred or nonpreferred hand, the foot, or even the mouth). The model is based on the assumption that writers strive for invariant graphic outputs when they write with different effectors, when they write on surfaces with different orientations, or when they write large or small script; such output invariance is an essential requirement for later recognition of the written result. Given this assumption, the question is how the motor system enables the relevant effectors to generate the necessary pen strokes. The adapted model provides one possible answer to this question. It is first fully working model of multijoint activity underlying writing and related graphic tasks. We describe how the model differs from other models developed in the past, and we review the model's strengths and weaknesses.

Female↗
PubMed1996

The effect of enactment on memory for order.

The effect of enactment on memory for serial order was investigated in two experiments. In both experiments a reconstruction task was used to separate order from item information. In Experiment 1 enactment and test information was manipulated between groups. For subjects who had not been informed about the reconstruction test, performance of verbal and motor groups was similar with regard to both serial-position curves and overall performance. For subjects who knew beforehand that they would be tested for memory of the order of the action events, performance in the verbal condition was significantly better than in the motor condition. In Experiment 2, the reversed enactment effect for test-informed subjects was replicated with a within-subjects design. The results agree with Engelkamp and Zimmer's (1984, 1994) position that enactment serves exclusively to enhance item information, and indicate that subjects have less control over the encoding processes when they are enacting than during verbal encoding (cf. Cohen, 1981).

Adult↗
PubMed1981

Factors affecting the perception of low-level vibration.

The level at which vibration becomes a nuisance is low, well below the vibration intensity discussed with regard to the health of industrial workers in the International Standard ISO-2631 draft. The relationships between the various factors and the human response to low-level vibration generated by vehicular traffic, are discussed from the results obtained from questionnaires. A female may respond to a lower level than male. There is no difference in response to low-level vibration between standing and sitting postures. Accompanying noise distracts the perception of low-level vibration, however at high levels, the effect of distraction is reduced.

Adolescent↗