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Biomedical subjects

J J Summers

Publications and source records attributed to J J Summers.

31 records · Page 2Linked to original sources
PubMed1994

Current status of the motor program.

Motor program theory has provided physical therapists with one approach to understanding how the brain controls movement. Analogous with computer programs that specify the operations of computer hardware, motor programs are thought to contain commands for muscles that allow movements to occur without the need for continuous peripheral feedback. A review of the physical therapy literature reveals many instances in which motor program theory has been used as a theoretical framework for clinical practice. Yet despite the contribution programming theory has made to the advancement of movement science, the motor program construct is currently under considerable threat. Keele's (1968) original definition no longer seems tenable, given the problems of program storage, motor equivalence, movement flexibility, and context-conditioned variability. The finding that researchers from different disciplines define the motor program in a variety of ways adds difficulty to the task of evaluating the efficacy of the model. A critical appraisal of programming theory and its use in physical therapy suggests that clinicians need to reconsider the usefulness of the motor program model as a basis for movement rehabilitation following brain damage and musculoskeletal disorders.

Humans↗
PubMed1994

Ability to modulate walking cadence remains intact in Parkinson's disease.

Gait hypokinesia (slowness) is a characteristic feature of Parkinson's disease. It is not clear, however, whether the slowness is due to a problem in regulation of the timing of consecutive steps or the control of stride size. Examination of cadence control for slow to medium walking speeds has shown an increase in step frequency that was a compensation for reduced stride length. In this investigation the ability of Parkinsonian patients to modulate their cadence (steps per minute) at the fast walking speeds exhibited by age and height matched controls was examined. The findings indicated that cadence control remains unaffected throughout its entire range in Parkinson's disease and that gait hypokinesia is directly attributable to an inability to internally generate sufficiently large steps.

Adaptation, Physiological↗
PubMed1993

The influence of perceptual and motor factors on bimanual coordination in a polyrhythmic tapping task.

In this study the role of perceptual and motor factors on the motor organization (integrated versus parallel) adopted by musically skilled and unskilled subjects in a polyrhythmic tapping task was investigated. Subjects tapped a 3:2 polyrhythm to match the timing of two isochronous tone trains, one tone train for each hand. Perceptual factors were examined by the manipulation of the frequency difference between the tone trains to produce either an integrated or a streamed percept. Motor factors were examined by comparison of performance on two versions of the 3:2 polyrhythm. In one (simultaneous) version, each cycle of the polyrhythm began with a simultaneous left- and right-hand tap. In the other (shifted) version a 100-ms interval was introduced between the initial left and right taps in each cycle. Examination of the pattern of variances and covariances among intertap intervals suggested that most of the subjects in this study adopted an integrated motor organization that involved interleaving the timing of the two hands. Further analysis revealed that a serial chained model described the pattern of covariances best for the simultaneous pattern, whereas a hierarchical organization described the pattern of covariances for the shifted pattern best. The finding that performance was more accurate with integrated tones than with streamed tones provides some support for a perceptual-motor facilitation hypothesis.

Adult↗
PubMed1993

Production of polyrhythms.

Previous research has shown that there are strong constraints on the concurrent performance of nonharmonically related motor sequences such as polyrhythms. A model of polyrhythm production is proposed that involves a hierarchical timing system. The model assumes a single mechanism (a counter) for the timing and serial ordering of responses. Predictions derived from the model were tested in an experiment in which skilled (musically trained) and unskilled Ss attempted to reproduce polyrhythms of varying complexity. The results agreed with the model's predictions and showed that Ss adopted a hierarchical form of integrated motor organization in which movements of the slow hand were subordinate to movements of the fast hand. This strategy was consistent across S groups, polyrhythms, and hand arrangements.

Attention↗
PubMed1992

Performance on trials without knowledge results (KR) in reduced relative frequency presentations of KR.

Following Salmoni, Schmidt, & Walter's (1984) discussion of knowledge of results (KR) as a variable influencing learning, the effect of varying relative frequency of KR while holding absolute number of trials constant was examined. In two experiments, the same treatment groups were compared in acquisition, retention (after 2 min and 24 hr), and on their pattern of responses on the sequence of no-KR trials following a KR trial. In Experiment 1, differences between groups in acquisition were consistent with the number of KR trials received, and there were no differences between groups in either of the retention conditions. Experiment 2 replicated Experiment 1 with a more difficult task. There were no between-group differences in acquisition. In Retention 1, the 100% and 33% relative frequency groups outperformed the less frequent KR groups, whereas in Retention 2, this trend was reversed. The findings from Experiment 2 provide qualified support for the hypothesis that reduced relative frequency of KR in acquisition facilitates performance in retention. The pattern of responses on the sequence of no-KR trials following a KR trial were consistent with Adams' (1971) perceptual-trace decay hypothesis.

Journal Article↗
PubMed1989

Perceptual and motor factors in the imitation of simple temporal patterns.

This study investigated the relative importance of perceptual and motor factors in the imitation of simple temporal patterns. Previous research in which subjects tap out interval sequences using one finger has suggested that perceptual factors play an important role in response timing. Studies of bimanual tapping, in contrast, stress the importance of motor interactions between the two hands. In this experiment we compared the ability of subjects to tap out two-interval sequences using one finger, two fingers on one hand, and two fingers on opposite hands. The results showed almost identical performance under the three response conditions. It is suggested that the perceptual relations between intervals in a pattern were the main determinant of performance in this experiment.

Adult↗
PubMed1986

Acute intestinal ischemia studies by phosphorus nuclear magnetic resonance spectroscopy.

31P nuclear magnetic resonance (NMR) spectroscopy has been used to follow the metabolism of acutely ischemic rat small intestine and its recovery after reversal of ischemia. Loops of small intestine were subjected to occlusive external pressure for up to 60 minutes, followed by a recovery period. The depletion of PCr and ATP is rapid and complete within 20 minutes. Recovery from ischemia is also rapid but with recovery ATP levels lower than initial values after prolonged ischemic periods. Intestinal shock was avoided. Clinical recovery correlated with shorter ischemic periods. 31P NMR spectroscopy thus appears to be a suitable technique for studying the effects of pharmacological agents and other treatments for amelioration of ischemic effects on the bowel.

Adenine Nucleotides↗
PubMed1981

The role of playing and efference in the recall location and distance cues in short-term motor memory.

Previous studies have suggested that the superior accuracy of preselected (subject-defined) over constrained (experimenter-defined) movements is due to both the availability of a movement plan and efferent-command information. The present experiment examined the contribution of the planning and efferent components to the preselection effect in a location and a distance task. The availability of a movement plan was manipulated by providing preselected and constrained groups of subjects with a rehearsal movement. Furthermore, the amount of efferent information available was varied by requiring both active and passive rehearsal movements. The results suggested that while strategy alone is responsible for the superiority of preselected location, both strategy and efferent information underlie the superiority of preselected distance reproduction.

Journal Article↗