Biomedical subjects

S Jaric

Publications and source records attributed to S Jaric.

5 recordsLinked to original sources

PubMed1994

The effects of practice on movement distance and final position reproduction: implications for the equilibrium-point control of movements.

Predictions of two views on single-joint motor control, namely programming of muscle force patterns and equilibrium-point control, were compared with the results of experiments with reproduction of movement distance and final location during fast unidirectional elbow flexions. Two groups of subjects were tested. The first group practiced movements over a fixed distance (36 degrees), starting from seven different initial positions (distance group, DG). The second group practiced movements from the same seven initial positions to a fixed final location (location group, LG). Later, all the subjects were tested at the practiced task with their eyes closed, and then, unexpectedly for the subjects, they were tested at the other, unpracticed task. In both groups, the task to reproduce final position had lower indices of final position variability than the task to reproduce movement distance. Analysis of the linear regression lines between initial position and final position (or movement distance) also demonstrated a better (more accurate) performance during final position reproduction than during distance reproduction. The data are in a good correspondence with the predictions of the equilibrium-point hypothesis, but not with the predictions of the force-pattern control approach.

Adult↗

PubMed1993

Principles for learning single-joint movements. I. Enhanced performance by practice.

This study investigated changes in myoelectric and mechanical variables for movements made "as fast as possible" as a function of practice in the context of the dual-strategy hypothesis of motor control (Gottlieb et al. 1989b). Five male subjects made 1400 rapid elbow flexion movements in ten blocks of 20 trials over seven experimental sessions. Improved performance was defined as increased peak movement velocity, decreased peak velocity variability, increased acceleration and deceleration, a proportionately greater increase in peak deceleration than peak acceleration, and greater consistency in terminal location. The changes observed over experimental sessions were very similar to (but larger and more consistent than) those seen for the first experimental session, with the partial exception of the timing of the antagonist electromyogram (EMG). In general, the increases in the values of the measured mechanical variables covary with myoelectric measures in the same way as when subjects are asked to intentionally change speed in accordance with the rules of the speed-sensitive strategy (Corcos et al. 1989). However, there are differences between subjects in the extent to which speed changes can be attributable to the agonist muscle, the antagonist muscle, or in the timing between the muscles. In one of the five subjects, the latency of the antagonist EMG decreased over blocks on the 1st day but increased over experimental sessions and was consequently activated proportionately later in the movement. This suggests that extended practice can give at least some subjects flexibility in modifying the motor programs that underlie movement.

Adult↗

PubMed1993

Principles for learning single-joint movements. II. Generalizing a learned behavior.

The previous paper in this series showed that changes both within and between experimental sessions can be understood in the framework of the dual-strategy hypothesis of motor control, with a modification sometimes required for the timing of the antagonist muscle. The present paper extends these findings by determining how practicing movements at one distance generalizes to changes in performance at other distances. Five subjects made elbow flexion movements over five different distances (pretest). They then performed 1400 movements (seven sessions of ten blocks of 20 trials) at only one of those distances. The subjects then repeated the flexion movements over the five different distances (posttest). On the posttest, subjects decreased their average movement time by 20 ms. In addition, their movements became less variable. The electromyographic pattern of the faster movements was characterized by a more rapidly rising electromyogram, for three of the subjects, and an antagonist latency that decreased.

Adult↗

PubMed1992

Effects of practice on final position reproduction.

Three subjects practiced fast, accurate 36 degrees elbow flexion movements to a 2.5 degrees target for 14 sessions of 100 trials (total, 1400 trials). Subjects then returned for a 15th experimental session in which they were asked to perform 15 movements under identical conditions to the practice condition. They were then tested under three experimental conditions without visual feedback: (1) identical to the practice conditions, (2) with small shifts in starting position (+/- 3 degrees of the practiced starting position), that were insufficient for subjective discrimination and, therefore, subjects were instructed to repeat the practiced movements; and (3) with a large shift in starting position (range, +/- 15 degrees of the practiced starting position), under the instruction to move to the same target. Experimental conditions 2 and 3 demonstrated that shifts in starting position were partially correlated with shifts in final position. These results are interpreted from the point of view of the equilibrium-point hypothesis of motor control.

Adult↗

PubMed1988

Practice improves even the simplest movements.

Three subjects practiced accurate, fast elbow flexions of 54 degrees to a 3 degrees wide target. Movements of 36 degrees, 54 degrees and 72 degrees were then tested. Comparison over the three distances showed that the normally monotonic relationship between movement distance and movement time is alterable by specific training. Subjects learn to go faster over the practiced distance by refining their neural commands to the muscles. The benefits of practice only partially transfer to other distances. We conclude that many of the relationships seen among movement variables in simple tasks are plastic in nature and affected by prior experience.

Adult↗