Richard A. Schmidt

Premotor and Motor Reaction Time as a Function of Preliminary Muscular Tension

Ss squeezed a hand grip device to 1 of 3 submaximal tensions, and reacted to either a light (Exp. I, N = 30) or to a buzzer (Exp. II, N = 24) by squeezing as quickly and forcefully as possible. Total RT was the time from stimulus to the change in tension, and this was divided into Premotor RT (stimulus to change in EMG) and Motor RT (change in EMG to change in tension) to determine the locus of changes in Total RT found by Clarke (1968). Whereas Total RT was unaffected by increased pre-tension, Premotor RT shortened and Motor RT lengthened. Partial programming or activation hypotheses were tenable for the Premotor RT changes, whereas changes in the contractile component, but not in the series elastic component, were tenable for the Motor RT changes.

Proactive Interference in Short-Term Motor Retention

Proactive inhibition (PI) in motor short-term memory (STM) was investigated to determine if the PI effects commonly found in verbal STM are also present in motor STM. A simple linear positioning task was used in which a criterion position was presented to the blind-folded S (N = 72), with recall of the criterion after either 10 or 120 sec. The variable of greatest interest was the number (either 0, 2, or 4) of similar positions presented prior to the criterion, the previous positions and the criterion being recalled in reverse order following the retention interval. With 4 previous positions, Ss displayed greater absolute error and greater undershooting with algebraic error than with either 0 or 2 previous positions, indicating that PI effects were present in motor STM and that verbal and motor STM may be governed by the same set of laws.

Performance and Learning a Gross Motor Skill under Conditions of Artificially-Induced Fatigue

Abstract The status of physical fatigue as a variable affecting performance and/or learning of a gross motor skill was investigated. Three groups practiced ten 30-second trials on the Bachman ladder with a 90-second intertrial interval (Day 1). Two fatigue groups rode a bicycle ergometer for two minutes prior to Trial 1, and thereafter, for 75 seconds between each subsequential ladder trial at work loads of 750 (N = 13) and 1200 (N = 14) kgm/min., respectively. A control group (N = 20) cancelled vowels between trials. All groups returned two days later (Day 2) for four trials with intertrial rest, the mean of which was the criterion of amount learned. Fatiguing activity caused decrements in Day 1 performance (F = 3.32), but failed to affect Day 2 performance (F = .47), indicating that fatigue was a performance variable rather than a learning variable.

Attention demand during storage of traces in motor short-term memory

Abstract The proactive inhibition (PI) found in earlier work on motor short-term memory may have been confounded with attentional demands during storage of the traces, and 2 experiments determined the role of attention demands on recall. Attention demand was manipulated by having Ss rehearse consonant trigrams (exp. 1) or by counting forward by ‘ls’ or backward by ‘3s’ (exp. 2) during storage of traces from a positioning task. Although rehearsing trigrams failed to influence accuracy of recall, counting backward resulted in nearly twice the error as counting forward, indicating that not all of the PI found in the earlier work could be attributable to motor interference.

Consistency of Response Components as a Function of Selected Motor Variables

Abstract The consistency of separate components of a timing response were measured, and the relationship of these consistencies to the changes in distance, speed, and resistance of the movement were determined. The inconsistency of the total response was less than the sum of the inconsistencies of the response components. Factors which increase the movement time (e.g., greater distance or slower speed) tend to decrease the consistency of both movement time and time of initiation of the response, tending to make the total response more inconsistent. There was a tendency for load to have a stabilizing effect on slower movements and to decrease the consistency of faster movements.

Postural set as a factor in short-term motor memory

The present study attempted to differentiate between a set vs an interference explanation of the decrements in recall when activities are included in the retention interval. Using a lever-positioning task with three retention intervals (12, 22, and 37 sec) and two types of activity during the retention interval, it was found that movement caused a significant overestimation of the target position using algebraic error, and that a movement by retention interval interaction was not significant. Since the decrements in recall were independent of the retention interval length, the results indicated that the effect of movement was to reduce S’s postural set. No differences were found when using absolute errors.

Effects of positional tensioning and stretch on reaction latency and contraction speed of muscle.

Abstract High school boys (N = 58) were carefully positioned on their right sides in a special apparatus. Positional tensioning (temporary, passive elongation) of right hamstrings was varied by means of four levels of hip flexion with a constant knee angle. Reaction and movement times for a maximal-speed knee flexion were measured. Before one testing period a stretching exercise was given. It was found that the flexibility of the hip joint was significantly increased by this exercise. The exercise had no effect on reaction time or on movement time. Increases in positional tensioning decreased reaction time significantly but had no effect on movement time.