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Biomedical subjects

D E Sherwood

Publications and source records attributed to D E Sherwood.

17 recordsLinked to original sources
PubMed2001

Divided attention in bimanual aiming movements: effects on movement accuracy.

The role of focusing attention on one limb or both limbs in a bimanual aiming task was investigated in two experiments. Participants were prompted to focus attention on either limb (Experiment 1) or were free to choose their attentional strategy (Experiment 2). Fifty-two college-aged participants made quick, bimanual lever reversals in the sagittal plane over 20 degrees and 60 degrees in 210 ms to the reversal point. In both experiments, spatial accuracy was better when participants focused their attention on a single limb compared to the nonattended limb and when they paid attention to both limbs. However, no differences were shown on a no-knowledge of results (KR) retention test when participants paid attention to both limbs. In the second experiment, differences were maintained on a no-KR retention test when participants continued to select their own attentional strategy, although the statistical effect was smaller than in the first experiment. The findings suggested that the movement parameter selection process benefited from attentional focus.

Adolescent↗
PubMed1999

Spatial assimilation effects and error detection in rapid overlapping and sequential bimanual movements.

This study verified earlier anecdotal evidence indicating that spatial assimilations could be reduced by offsetting movements in time. In Experiment 1, 40 right-handed participants (ages 18-23 years) made single and dual quick lever reversals of 20 degrees and 60 degrees with the left and right limbs, respectively. Participants were assigned to either the Overlapping (O) group, in which one limb began when the other limb reached the reversal point, or to the Sequential (S) group in which one limb followed the other with a delay of 114 ms, on average. The shorter-distance limb of the O group overshot relative to the S group. Short-distance spatial assimilations were also shown in the S group in Experiment 2, when the delay was increased to 250, 500, or 1,500 ms (N = 30), suggesting that assimilation effects can be caused by command interactions at both the planning and the execution levels.

Adolescent↗
PubMed1996

The benefits of random variable practice for spatial accuracy and error detection in a rapid aiming task.

The role of blocked and random variable practice in the development of a spatial error detection mechanism in 2 experiments was investigated in the present study. Twenty-four (Experiment 1) and 40 (Experiment 2) college-aged participants made either 20, 40, 60 degrees quick lever reversal movements in the sagittal plane. During acquisition in both experiments, blocked practice resulted in less spatial absolute constant error (ICEI) relative to the random group. The blocked practice group showed a smaller mean absolute objective-subjective difference than the random practice group during acquisition (Experiment 1). On no-knowledge of results retention tests in both studies, the random practice group showed a smaller spatial ICEI and a smaller mean absolute objective-subjective difference than the blocked practice group, even on a novel amplitude (Experiment 2). The study demonstrated the advantage of random variable practice over blocked variable practice on retention tests for spatial performance and in developing a spatial error detection capability.

Adult↗
PubMed1994

Hand preference, practice order, and spatial assimilations in rapid bimanual movement.

When subjects make rapid bimanual aiming movements over different distances, spatial assimilations are shown; the shorter distance limb overshoots when paired with a longer distance limb. Recent research has also shown spatial assimilations to be greater in the nonpreferred left limb of right-handed subjects, but it is not known whether the increased spatial assimilations represent a handedness effect or one of hemispheric lateralization of motor control. To determine the nature of the asymmetric effect, left- (n = 32) and right- (n = 60) handed subjects part practiced, then whole practiced, short (20 degrees ) and long 60 degrees ) reversal movements. During whole practice, both groups showed spatial assimilations in the shorter distance limb, particularly when the left limb performed the short movement. This asymmetry was greatest for right-handed subjects, but left-handed subjects showed smaller, but systematic effects, providing moderate support for the hypothesis that the asymmetric effect is due to hemispheric lateralization of motor control. All interlimb differences in spatial accuracy for the short and long movements were eliminated with practice, however, suggesting the asymmetric effect was temporary as well. In addition, subjects who part practiced the long movement just prior to whole practice showed greater overshooting in the short distance limb compared with subjects who followed the other practice order throughout whole practice and the no-KR retention trials. Such findings suggest that the part-practice order of bimanual tasks can directionally bias whole-task performance.

Journal Article↗
PubMed1994

A comparison of knowledge of results scheduling methods for promoting motor skill acquisition and retention.

Providing knowledge of results (KR) to a learner about each trial in a series of trials only after the series is completed is termed summary KR. A variation of summary KR is average KR, in which KR is presented as an average value about the series of trials. This study compared groups receiving either average KR, summary KR, or KR following every attempt in acquisition of a force production task. Following acquisition, groups performed no-KR immediate and long-term retention tests. Analysis of variable error revealed group main effects and group by block interactions in acquisition and long-term retention. Post hoc tests indicated that differences were due primarily to inconsistent performance of the group receiving KR following each acquisition attempt. Post hoc tests did not, however, indicate differences between the average KR and summary KR groups in acquisition or retention. It was concluded that average and summary KR promote consistency in performance in acquisition, with this stability in responding carried over to retention performance.

Adult↗
PubMed1992

EMG amplitude and spatial assimilation effects in rapid bimanual movement.

To investigate whether spatial assimilation effects are due to premovement control processes or postinitiation feedback processes, surface EMG recordings were made from two agonists and one antagonist during both single and dual movements involving the upper limb(s). In the single condition, subjects (N = 7) made 25 Short (20 degrees) and 25 Long (60 degrees) reversal movements using levers in the sagittal plane, in 195 ms to reversal. In the dual condition, both Short and Long movements were performed simultaneously for 75 trials, the last 25 of which were without knowledge of results. Subjects overshot the Short target in the dual condition, showing spatial assimilation effects. Overshooting was associated with increased peak EMG in the initial (premovement) agonist burst, supporting the notion that spatial assimilation effects are modulated via premovement control processes.

Adolescent↗
PubMed1991

Distance and location assimilation effects in rapid bimanual movement.

When subjects make simultaneous aiming movements of the upper limbs over different distances, assimilation effects are shown; the shorter distance limb overshoots when paired with a longer distance limb. However, it is not known whether assimilation effects are due to variations in distance per se or to variations in target location. To separate the possible influences of distance and location, 60 subjects made rapid bimanual aiming movements in one of four conditions. The two different-distance groups made a 20 degrees movement in the left hand and a 60 degrees movement in the right hand to either the same or different target locations. The comparison groups moved 20 degrees in each limb. Somewhat surprisingly, spatial assimilations were greater when moving different distances to the same, rather than different, target locations, which suggests interlimb differences in distance mediate assimilation effects rather than target location. Temporal assimilations were greater when distance and location were varied, but the assimilations were not related to interlimb differences in velocity, as predicted by Marteniuk and MacKenzie (1980).

Adolescent↗
PubMed1990

Practice and assimilation effects in a multilimb aiming task.

When two limbs are required to move different distances simultaneously, assimilation effects are shown: The shorter distance limb tends to overshoot the target, whereas the longer distance limb undershoots. The effect of practice on assimilation effects was studied in two experiments, using a simultaneous four-limb aiming task. When subjects were required to move their left limbs a shorter distance than the right (5 cm vs. 9 cm), the right limbs moved a lesser distance and had greater variable and overall errors relative to a group required to move all limbs the same distance (9 cm). Practice reduced assimilation effects in the lower limbs, but spatial assimilations were present throughout 125 acquisition trials with KR and 50 no-KR transfer trials, spanning 24 hours. When the upper limbs were required to move a greater distance than the lower limbs (15 cm vs. 9 cm), the lower limbs showed longer distances and increased overall errors early in practice compared to the lower limbs of a group required to move all limbs 9 cm. With practice, the between-group differences decreased, with no assimilation effects shown on the transfer trials. The results suggest that neural crosstalk is greater between left and right sides than between upper and lower limbs. Results are discussed in light of the functional cerebral space model of simultaneous actions.

Journal Article↗
PubMed1988

Rapid movements with reversals in direction. I. The control of movement time.

Modifications to the underlying motor control of rapid reversal movements (flexion-extension of the elbow) to accommodate experimentally induced changes in the movement time (MT) with constant movement amplitude were examined in man. MT was altered between conditions via instructions and feedback, resulting in seven distinct MT levels (from 100 to 250 ms to the reversal point) with essentially constant movement amplitude. As MT was decreased, the large increases in acceleration were met by two changes in motor control: (a) two- to three-fold increases in the peak accelerations and peak amplitudes of the agonist and antagonist EMGs, and (b) a systematic "compression" of the temporal structure of the entire acceleration-time and EMG-time patterns. This temporal "compression" with increased velocity caused by shifts in MT (distance constant) are considerably different from the constant-duration EMG bursts found when velocity is altered by changing movement distance (where MT is nearly constant). Our findings indicate that MT is a determiner of the temporal structure of rapid actions, and suggest that MT should be regarded as an important controlled variable, and not simply as an emergent property of variations in velocity.

Acceleration↗
PubMed1988

Rapid movements with reversals in direction. II. Control of movement amplitude and inertial load.

Transformations of the underlying movement control of rapid sequential (reversal) responses were examined as the movement amplitude (Experiment 1) and moment of inertia (Experiment 2) were altered, with constant movement time. Increases in amplitude and inertia were both met by sharply increased joint torques with a constant temporal structure, suggesting that the alterations may have been governed by a single gain parameter. The durations of various EMG bursts were essentially constant across changes in inertia, supporting a model in which the output of a fixed temporal representation is amplified to alter joint torques. The EMG amplitudes increased greatly with both amplitude and load. However, the fact that the EMG durations increased systematically with increases in distance provided difficulties for this model of amplitude control. The data suggest an economy in motor control in simple agravitational movements, whereby relatively simple transformations of an underlying representation can accommodate large changes in movement amplitude and moment of inertia.

Acceleration↗
PubMed1988

The force/force-variability relationship under controlled temporal conditions.

Previously, an inverted U relationship between force and force variability was demonstrated in both static and dynamic responses. Recent research suggests that the inverted U function may be due to a lack of control of the temporal aspects of the response. To investigate this hypothesis, we examined the relationship between force and force variability in rapid movements under controlled temporal conditions. Subjects (N = 4) made rapid reversal responses with a horizontal lever (using elbow flexion and extension) such that the time to reversal (160 ms) and the distance to reversal (45 degrees ) were held constant in each of six load conditions (either 0,.260,.780, 1.040, or 1.560 kg added to the lever). When time to reversal and time to peak acceleration were held constant, a curvilinear relationship between force and force variability resulted, suggesting that the inverted U function is related to control of the temporal aspects of the response.

Journal Article↗
PubMed1988

Effect of bandwidth knowledge of results on movement consistency.

The effect of "bandwidth" knowledge of results (KR), given only if the subject's response is outside of a certain movement-time bandwidth, on learning and performance of a rapid elbow-flexion movement was examined. Subjects were randomly assigned to one of three feedback groups, a 5% bandwidth group (BW5), a 10% bandwidth group (BW10), or a control group (KR), who received knowledge of results on every trial. Subjects moved a light, horizontal, aluminum lever through 60 degrees in 200 msec., for 100 acquisition trials with KR given depending on group and 25 transfer trials without KR (transfer phase). Although the subjects in the BW10 group received knowledge of results fewer times during acquisition, they showed less within-subject variability than the BW5 and KR groups on the transfer test which suggests that giving KR about a relatively large bandwidth enhances movement consistency.

Adolescent↗
PubMed1986

Impulse characteristics in rapid movement: implications for impulse-variability models.

Three untested assumptions of the impulse-variability model were examined in two experiments utilizing rapid, uni-planar limb movements. Experiment 1 varied movement distance (A) and movement time (MT) in a rapid-timing paradigm where the subject moved a lever through a certain distance in a certain time. Experiment 2 varied A in a reversal response where the S made a rapid elbow flexion and extension in a given MT. Displacement recordings were made on every trial. KR (knowledge of results) about MT was given after every trial. The results can be summarized as follows: (a) As predicted by the model, variations in impulse size and velocity were directly related to the impulses size; (b) There was no correlation between the accelerative and decelerative impulse durations recorded during the reversal response supporting the notion that the impulses might be independent; (c) Negative correlations (-.20 to -.50) were demonstrated between peak acceleration and impulse duration for both experiments, counter to the predictions of the model; and (d) Counter to the predictions of the model, timing error (VEt) increased as A decreased for rapid-timing responses. When the correlational results are taken into account, the model has the capacity to account for curvilinear relationships between relative timing error and movement speed. Overall, the results suggest that the impulse variability model requires some restructuring before it can be considered a viable model for the control of rapid limb movements.

Journal Article↗
PubMed1983

Time requirements of changes in program and parameter variables in rapid ongoing movements.

Two experiments investigated the differences in processing time requirements of two types of modifications of a rapid ongoing movement. In response to a signal presented at either 0, 100, or 200 msec after initiation of a 400-msec horizontal arm movement, subjects attempted to either increase the speed of the movement or to reverse it. EMG modification latencies were shorter in the former condition than in the latter indicating a difference in processing-time requirement between modification types. The results support the generalized motor program hypothesis of Pew (1974) and Schmidt (1976) in that increasing the speed of an ongoing movement may require modification of a parameter variable while reversing movement direction requires the implementation of a new motor program.

Journal Article↗
PubMed1980

The relationship between force and force variability in minimal and near-maximal static and dynamic contractions.

The critical assumption of linearity between force and force variability for rapid movements made by Schmidt, Zelaznik, and Frank (1978) was studied in four experiments in the present study. The first three experiments extended earlier work showing linearity between force and force variability for submaximal force levels in static and dynamic contractions. However, at near-maximal force levels, when force was increased, force variability leveled off and then decreased in both static and dynamic conditions. A fourth experiment using the rapid-timing paradigm showed that increased submaximal loads on the movement produced slight decreases in VE. But when the loads were larger, where force and force variability were no longer linearly related, increased load led to larger decreases in VE. These observations led to the hypothesis that VE is linearly related to the ratio of force variability to force; data from two experiments are presented that support this idea. The motor-output variability theory seems to hold for a wide range of sub-maximal force values, but needs modification for those conditions where near-maximal forces are required.

Journal Article↗
PubMed1979

Cardiorespiratory health, reaction time and aging.

Visual simple and choice reaction time (RT) tests were administered to 64 male and female volunteers 23 to 59 years of age. One half of the subjects were runners involved in rigorous training programs averaging 42 miles per week. The other half of the subjects were sedentary adults. Eighty simple and 100 choice reaction time trials were given with a variable foreperiod ranging from 400 to 1100 msec. Five catch trials were given in both simple and choice reaction time conditions. The results indicated that there was a gradual decline in RT performance as age increased. However, this trend was not evident in the trained group. Reaction time remained constant with age within the trained group. It was concluded that a high state of cardiorespiratory training may prevent cognitive decrements in performance with age.

Adult↗