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Biomedical subjects

R C Schmidt

Publications and source records attributed to R C Schmidt.

At least 37 records · Page 2Linked to original sources
PubMed1993

Coupling dynamics in interlimb coordination.

In 1:1 frequency locking, the interlimb phase difference phi is an order parameter quantifying the spatial-temporal organization of 2 rhythmic subsystems. Dynamical modeling and experimental analyses indicate that an intentional parameter phi psi (intended coordination mode, phi = 0 degrees or phi = 180 degrees) and 2 control parameters omega c (coupled frequency) and delta omega (difference between uncoupled eigen-frequencies) affect phi. An experiment was conducted on 1:1 frequency locking in which phi psi, omega c, and delta omega were manipulated using a paradigm in which a person swings hand-held pendulums. As delta omega deviated from 0, the observed phi deviated from the phi psi, indicating a displacement in the phi attractor point. The displacements were exaggerated by increasing omega c. The displacements were coordinated with a decrease in the stability of phi and with higher harmonics in power spectrum of phi. Implications of the results for modeling interlimb coordination are discussed.

Adult↗
PubMed1992

Average phase difference theory and 1:1 phase entrainment in interlimb coordination.

The dynamics of coupled biological oscillators can be modeled by averaging the effects of coupling over each oscillatory cycle so that the coupling depends on the phase difference phi between the two oscillators and not on their specific states. Average phase difference theory claims that mode locking phenomena can be predicted by the average effects of the coupling influences. As a starting point for both empirical and theoretical investigations, Rand et al. (1988) have proposed d phi/dt = delta omega--K sin phi, with phase-locked solutions phi = arcsin(delta omega/K), where delta omega is the difference between the uncoupled frequencies and K is the coupling strength. Phase-locking was evaluated in three experiments using an interlimb coordination paradigm in which a person oscillates hand-held pendulums. Delta omega was controlled through length differences in the left and right pendulums. The coupled frequency omega c was varied by a metronome, and scaled to the eigenfrequency omega v of the coupled system; K was assumed to vary inversely with omega c. The results indicate that: (1) delta omega and K contribute multiplicatively to phi; (2) phi = 0 or phi = pi regardless of K when delta omega = 0; (3) phi approximately 0 or phi approximately pi regardless of delta omega when K is large (relative to delta omega); (4) results (1) to (3) hold identically for both in phase and antiphase coordination. The results also indicate that the relevant frequency is omega c/omega v rather than omega c.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Dynamical aspects of learning an interlimb rhythmic movement pattern.

Learning a bimanual rhythmic task is explored from the perspective that motor skill acquisition involves the successive reparameterization of a dynamical control structure in the direction of increasing stability, where the intentional process of reparameterization is itself dynamical. Subjects learned to oscillate pendulums held in the right and left hands such that the right hand frequency was twice that of the left (2:1 frequency lock). Over 12 learning sessions of 20 trials each, we interpreted the decreasing fluctuations in the frequency locking to be an index of the increasing concavity of the underlying potential, a measure of stability; the time required to achieve the 2: 1 pattern was interpreted as indexing the relaxation time of an intentional dynamic. Power spectral analyses of the phase velocity ratio exhibited two strategies for acquiring the interlimb movement pattern: (a) adding spectral peaks at integer multiples of the left hand frequency or (b) distributing power across many frequencies in a l/f-like manner. Results are discussed in terms of the promise of a dynamical approach to learning coordinated movements.

Journal Article↗
PubMed1991

Task dynamics and resource dynamics in the assembly of a coordinated rhythmic activity.

Task dynamics corresponding to rhythmic movements emerge from interactions among dynamical resources composed of the musculature, the link segments, and the nervous and circulatory systems. This article investigated whether perturbations of interlimb coordination might be effect over circulatory and nervous elements. Stiffness of wrist-pendulums oscillated at a common tempo and at 180 degrees relative phase was perturbed through the use of tonic activity about an ankle. Left and right stiffnesses, the common period, and the phase relation all changed. Stiffnesses increased with ankle torque in proportion to the wrist's inertial load. Despite different changes in stiffness at the two wrists, isochrony was preserved. The stability was shown to be consistent with the proportionality of changes in stiffness to the inertial loads. The phase departed from antiphase in proportion to the asymmetry of inertial loads. The size of departures decreased with increasing ankle torque. An account was developed in terms of muscular, circulatory, and nervous functions.

Adult↗
PubMed1991

Dynamical substructure of coordinated rhythmic movements.

A coordinated rhythmic movement pattern is a dynamical activity involving many hidden layers of rhythmic subtasks. To investigate this dynamical substructure, spectroscopic concepts and methods were applied to an interlimb rhythmic movement task requiring 1:1 frequency locking of two hand-held pendulums in 180 degrees phase relation. The pendulums could be of identical or very different dimensions, thereby providing different values of the ratio omega of uncoupled frequencies. Analyses focused on the power spectrum of continuous relative phase as a function of variation in omega. Predictions were derived from the theories of mode locking and fractal time. Experimental results were in agreement with theoretical expectations and were discussed in terms of the possible recruiting of rhythmic subtasks in the assembling of interlimb absolute coordination, the interdependence of these subtasks, and the general dynamical principles that relate coordinative processes occurring at different length and time scales.

Adult↗
PubMed1990

Phase transitions and critical fluctuations in the visual coordination of rhythmic movements between people.

By watching each other's lower oscillating leg, 2 seated Ss kept a common tempo and a particular phase relation of either 0 degrees (symmetric mode) or 180 degrees (alternate mode). This study investigated the differential stability of the 2 phase modes. In Experiment 1, in which Ss were instructed to remain in the initial phase mode, the alternate phase mode was found to be less stable as the frequency of oscillation increased. In addition, analysis of the nonsteady state cycles revealed evidence of a switching to the symmetric phase mode for the initial alternate phase mode trials. In Experiments 2 and 3, Ss were instructed to remain at a noninitial phase angle if it was found to be more comfortable. The transition observed between the 2 phase modes satisfies the criteria of a physical bifurcation--hysteresis, critical fluctuations, and divergence--and is consonant with previous findings on transitions in limb coordination within a person.

Adult↗
PubMed1989

Aimed movements to visual targets in hemiplegic and normal children: is the "good" hand of children with infantile hemiplegia also normal?

The accuracy, reaction and movement time of pointing movements to visual targets were examined in children aged 3-13 yr with infantile hemiplegia and compared to those of comparably aged normal children. Hemiplegic children pointed with the "good" hand (i.e. ipsilateral to the lesion). Half the normal children used the preferred hand, half the non-preferred hand. Movements were made with unrestricted/restricted visual feedback, when movement distance was short/medium/long, and when number of target alternatives were 2/4/8. Normal children using the preferred hand were more accurate but reacted more slowly than children using the non-preferred hand. The performance of most of the hemiplegic children with bilateral and/or unilateral lesions was impaired; degree of accuracy was related to the extent of the brain lesion; and reaction time was related to the level of intelligence. It was concluded that unilateral lesions in children can result in bilateral visuomotor impairment.

Adolescent↗
PubMed1989

'Clock' and 'motor' components in absolute coordination of rhythmic movements.

Human subjects swung, through motions at the two wrists, hand-held pendulums of variable mass and length. Within a pair, the two pendulums could be of the same or different magnitude. The subjects were required to produce a coordinated state in which the two rhythmic units oscillated at a single common period. Fifty-four conditions of absolute coordination, that is, 54 different pairs of wrist-pendulum systems, were investigated for each of three subjects in the course of six sessions. Each condition of absolute coordination was conducted in the out of phase mode and at the single most comfortable period. The period variances of the right and left systems in the 162 instances of absolute coordination were analysed according to a method that assumes that a timekeeper function and a motor implementation function contribute independently to the variance in the periodic timing of a rhythmic movement. The major findings were that in absolute coordination: (a) a system's 'motor' variance, but not its 'clock' variance, depended on the deviation of the period of absolute coordination tau from the system's characteristic period; (b) right and left 'clock' variances were related and (c) neither the 'motor' variances nor the 'clock' variances were affected by deviations in the mean phase relation from 180 degrees. The results were discussed in terms of their implications for interpreting von Holst's notions of maintenance tendency and magnetic effect and, more generally, the neural and dynamical basis of absolute coordination.

Adult↗
PubMed1989

Hefting for a maximum distance throw: a smart perceptual mechanism.

Objects for throwing to a maximum distance were selected by hefting objects varying in size and weight. Preferred weights increased with size reproducing size-weight illusion scaling between weight and volume. In maximum distance throws, preferred objects were thrown the farthest. Throwing was related to hefting as a smart perceptual mechanism. Two strategies for conveying high kinetic energy to projectiles were investigated by studying the kinematics of hefting light, preferred, and heavy objects. Changes in tendon lengths occurring when objects of varying size were grasped corresponded to changes in stiffness at the wrist. Hefting with preferred objects produced an invariant phase between the wrist and elbow. This result corresponded to an optimal relation at peak kinetic energy for the hefting. A paradigm for the study of perceptual properties was compared to size-weight illusion methodology.

Adult↗
PubMed1988

On the time allometry of co-ordinated rhythmic movements.

The focus is the power formulae relating periodic time in terrestrial locomotion and flight to mass and length. The periodic timing of limbs and wings oscillating comfortably in absolute co-ordination is viewed as the characteristic period tau 0 of a system in which the free, undamped oscillatory motion of a point mass m at a distance l from a fixed axis does work against two conservative forces. These forces are in the form of gravity g acting on the point mass and a spring of stiffness k acting at a distance b from the axis. The system's characteristic period can be expressed most simply as: tau 0 = 2 pi [ml2/(mlg + kb2)]1/2. In the biological instantiation of this hybrid mass-spring/simple pendulum system, muscular and other tissues function as the spring that elastically stores and releases mechanical energy. Regular oscillations are brought about and sustained by a muscular driving force that ordinarily is close to resonance. The resultant dynamical regime--basically, raising and lowering a mass at regular intervals with respect to gravity--is referred to as the pendular clocking mode of movement organization. The mode is investigated comfortably at a common period and a fixed phase. In absolute co-ordination, two wrist-pendulum systems can be interpreted physically as a virtual single system. The evidence suggests that the scalings of the periodic times of such systems to mass and to length follow directly from the dynamical properties inherent in the resonance equation of the pendular clocking mode. Recourse to biological constants to rationalize the time scale is unnecessary. Experiments on human wrist-pendular activity and detailed analyses of the mass and length dependencies of the locomotory cycle times of quadrupeds, large birds, small passerines, hummingbirds, and insects are performed with respect to the dynamical properties predicted for systems in the pendular clocking mode. The major conclusion is that all the time scales of terrestrial in locomotory time allometries follow systematically from differences in the length scale and differences in the relation of mass to length.

Animals↗
PubMed1986

Fluctuations and phase symmetry in coordinated rhythmic movements.

Pendular, clocking movements typify mammalian terrestrial locomotion. They can be investigated with a procedure in which people swing hand-held pendulums at the wrists, comfortably and rhythmically. Pendular, clocking behavior was examined for in-phase and out-of-phase coordinations. The periodic timing and powering of rhythmic movements in the comfort state follow from different laws (Kugler & Turvey, 1986). One law guides the assembling of the reference frame for "clocking." Another law guides the assembling of the muscular, escapement processes determining the cycle energy. Wing and Kristofferson's (1973) method for parsing periodic-timing variance into independent "clock" and "motor" sources was applied. Mean periodicity was unaffected by phase. "Clock" fluctuations, however, were larger out of phase than in phase. "Motor" fluctuations were indifferent to phase but reflected the departures of individual wrist-pendulum systems from their preferred periods. It appears that an intended phase relation is realized as a constraint on "clock" states. These states are more stable under the in-phase constraint than under the out-of-phase constraint.

Biophysical Phenomena↗
PubMed1985

Cognitive development in epilepsy. The relative influence of epileptic activity and of brain damage.

A total of 37 children, aged between 12 and 18 years and resident in an epileptic colony, were assessed in several ways for the frequency of their epileptic discharging activity and for the extent of underlying brain pathology. In addition, the children were evaluated for their level of performance on various tests of cognitive and visuo-motor functions. The influence on test performance of the discharging activity and of the extent of pathology was then compared, taking other factors such as age at onset of the seizures, duration of the epileptic illness and level of medication into account as far as possible. Only two factors, namely certain indices of discharging activity and level of medication, were found to have significantly influenced particular aspects of cognitive performance; it was impossible to document an influence of brain pathology statistically.

Adolescent↗
PubMed1982

[Stereo magnification angiography--its application in neuroradiology (author's transl)].

The article discusses the stereo magnification technique using the Stereolix system and explains its clinical application in neuroradiology. The special advantage of the Stereolix tube is that it can be used in routine procedure, since it is suitable both for normal serial angiography and--by pressing a button--for stereo magnification angiography. The emphasis of trials was on the applicability for spinal angiography and in the diagnosis of cerebral aneurysms and arteriovenous angiomas.

Angiography↗
PubMed1981

[The diameters of the cervical spinal cord shown by amipaque-myelography (author's transl)].

The sagittal and cross diameters of the cervical spinal cord were measured in 53 patients with cervical nerve root compression and with no evidence of spinal cord involvement, as well as in 45 patients with spastic tetraparesis and no localised space occupying lesion, and 29 patients with myelographically proven cervical myelography. The true diameters were calculated by the known magnification factor (1:1,4). Patients with spastic tetraparesis showed diameters in normal ranges, as well as widened or diminished sizes of the cord. Some of the patients with cervical myelopathy showed diminished diameters in the caudal parts. This may be a hint for a poor outcome after decompression operation.

Adolescent↗