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Biomedical subjects

Charles H Shea

Publications and source records attributed to Charles H Shea.

At least 19 recordsLinked to original sources
PubMed2006

Target width scaling in a repetitive aiming task: switching between cyclical and discrete units of action.

An aiming task was used to identify the processes whereby the motor system adapted a repetitive aiming action to systematic changes in ID (ID = log(2 )(2A/W), Fitts in J Exp Psychol 47:381-391, 1954) within a single trial. Task ID was scaled in a trial by moving the outside edge of two stationary targets to produce nine different target IDs in a trail. The ID within a trial was scaled in one of two directions: (1) an increasing ID condition, starting with an ID = 3.07 and ending with an ID = 5.91; and (2) a decreasing ID condition, starting with an ID = 5.91 and ending with an ID = 3.07. An index of movement harmonicity (Guiard in Acta Psychol 82:139-159, 1993) revealed that the repetitive aiming action was harmonic in nature when task ID was 3.07, and consisted of a series of discrete segments when task ID was 5.91. This finding provides evidence for the existence of discrete and cyclical units of action that are irreducible and that may be employed independently to assemble longer continuous actions. The scaling of ID within a trial promoted a transition in repetitive aiming motions assembled from discrete and cyclical units of action. A variety of kinematic measures (e.g., movement harmonicity, time spent accelerating the limb) revealed a critical ID (ID(c)) region (4.01-4.91) separating aiming motions governed by the different units of action. Enhancement of fluctuations before the transition were found in the movement harmonicity data and in the distance traveled to peak velocity data, with variability in these measures highest in the ID(c) region. The enhancement of fluctuations indicates that loss of stability in the limb's motion acted as a key mechanism underlying the transition between units of action. The loss of stability was associated with the transition from cyclical to discrete actions and with the transition from discrete to cyclical actions. The transition between units of action may be conceptualized as a transition from a limit cycle attractor (cyclical unit of action) to a shift between two fixed-point attractors (discrete unit of action) when ID was increased, with the transition occurring in the opposite direction when ID was decreased.

Adaptation, Physiological↗
PubMed2006

The intention superiority effect in motor skill learning.

Three experiments were conducted to determine if the intention to perform motor sequences in the future results in similar patterns of activation and inhibition as observed for verbal scripts. In Experiments 1 and 2, intention was induced by informing one group that they would be tested on the tasks following acquisition; the other group was not informed of the retention test. Recognition tests administered prior to and after the retention test indicated a strong intention superiority effect. However, intention instructions provided either at the end of acquisition (Experiment 1) or before acquisition (Experiment 2) failed to impact acquisition or retention performance of the motor sequences, but did influence the latency of responding on the retention test. Experiment 3 was designed to replicate the results of Experiments 1 and 2 using a within-subjects design and extend these findings to observation. The results indicated that intention instructions resulted in a strong intention superiority effect for both the physical and observational practice participants, but the performance on the intentional tasks was enhanced only for the observational practice group.

Adult↗
PubMed2006

Error detection processes during observational learning.

The purpose of this experiment was to determine whether a faded knowledge of results (KR) frequency during observation of a model's performance enhanced error detection capabilities. During the observation phase, participants observed a model performing a timing task and received KR about the model's performance on each trial or on one of two trials. Delayed retention and transfer tests were used to assess the observer's ability to detect error in the model's performance and in the participant's performance while physically practicing the task. Results indicated a beneficial effect of a reduced KR frequency for performance stability and the ability to detect errors in both the model and the participant's own performance. The results suggest that aspects of the processing mechanism(s) developed in observational learning and related to KR are probably similar to those developed through physical practice.

Adolescent↗
PubMed2006

Intention in motor learning through observation.

The purpose of this experiment was to assess whether learning an action through observation is enhanced by the intention to reproduce the observed behaviour. Two groups of participants observed a model practise a timing task and performed a 24-hour delayed retention test. Participants in the first group of observers were explicitly instructed that they would be required to execute the timing task that they had observed as accurately as possible during the delayed retention test. Observers in the second group were instructed that they would be required to describe as accurately as possible the behaviour that they had observed. A control group of participants, who did not observe the model, was also administered the delayed retention test. The results of the retention test indicated that absolute timing (parameterization) was learned by the observers to the same extent with or without intention to reproduce the task. Indeed, on the retention test absolute timing for the two groups of observers was as effective as that for the models. However, observing with an intention to reproduce the task was beneficial for learning the movement's relative timing structure. Results are discussed with respect to a potential mechanism by which intention enhances observation.

Adolescent↗
PubMed2006

Proportional and nonproportional transfer of movement sequences.

Two experiments were designed to determine participants' ability to transfer a learned movement sequence to new spatial locations. A 16-element dynamic arm movement sequence was used in both experiments. The task required participants to move a horizontal lever to sequentially projected targets. Experiment 1 included 2 groups. One group practised a pattern in which targets were located at 20, 40, 60, and 80 degrees from the start position (long sequence). The other group practised a pattern with targets at 20, 26.67, 60, and 80 degrees (mixed sequence). Both groups were tested 24 hours later on the long, mixed, and short sequence. The short sequence was considered a proportional transfer for the long acquisition group because all the amplitudes between targets were reduced by the same proportion. Nonproportional transfer occurred when the amplitudes between targets did not have the same proportions as those for their practice sequence (e.g., long sequence to mixed sequence or vice versa). The results indicated that participants could effectively transfer to new target configurations regardless of whether the transfer required proportional or nonproportional spatial changes to the movement pattern. Experiment 2 assessed the effects of extended practice on proportional and nonproportional spatial transfer. The data indicated that while participants can effectively transfer to both proportional and nonproportional spatial transfer conditions after 1 day of practice, they are only effective at transferring to proportional transfer conditions after 4 days of practice. The results are discussed in terms of the mechanism by which response sequences become increasingly specific over extended practice in an attempt to optimize movement production.

Analysis of Variance↗
PubMed2006

Learning of similar complex movement sequences: proactive and retroactive effects on learning.

The authors used an interference paradigm to determine the extent to which the learning of 2 similar movement sequences influences the learning of each other. Participants (N=30) produced the sequences by moving a lever with their right arm and hand to sequentially presented target locations. They practiced 2 similar 16-element movement sequences (S1 and S2), 1 sequence on each of 2 consecutive days of practice. Control groups received only 1 day of practice on 1 of the sequences. Early in S2 practice, the experimental group demonstrated a relatively strong level of proactive facilitation arising from previous practice with S1. The advantage was not evident at the end of S2 practice or on the S2 retention test. No advantage of practicing the 1st sequence on the learning of the 2nd sequence (proactive effect) was found in the analysis of element duration in the retention and transfer tests, even though 14 of the 16 elements were common to both sequences. A strong retroactive interference on the switched elements was detected, however. Thus, the memories underpinning S1 seemed to be "overwritten" or adapted in response to the learning of S2.

Humans↗
PubMed2006

Age-related effects in sequential motor learning.

BACKGROUND AND PURPOSE: When learning multi-element movement sequences, participants organize individual elements into subsequences. Imposing this type of structure on the elements leads to the efficient production of sequences because the processing of all but the first elements in a subsequence can be completed prior to their execution. The primary purpose of this study was to determine whether older adults organize lengthy movement sequences with the same efficiency as young adults. SUBJECTS AND METHODS: Participants were young adults (N=8, 19-23 years of age) and older adults (N=8, 65-68 years of age). The task required participants to move a lever as quickly as possible to targets sequentially projected on a tabletop. At various stages during practice, random practice blocks were inserted between the repeated sequence blocks. Repeated and random sequence retention tests were administered after 24 hours. RESULTS: The results indicated that the young adults performed the repeated sequences substantially faster than the older adults and that this difference increased over practice. On the retention tests, there were no differences in response time for the random sequence blocks, but the young performers were substantially faster than the older performers when repeated sequences were used. No differences were detected in the interview or on the recognition (chi square=1.22, P>.05) and completion (chi square=0.89, P>.05) tests designed to determine explicit or implicit knowledge of the sequences. DISCUSSION AND CONCLUSION: Analysis of the sequence structure indicated that the older adults did not organize their responses into subsequences as effectively as the young adults. The failure of older adults to optimally organize movement sequences may contribute to the overall slowing of sequential movement production.

Adult↗
PubMed2005

Random and blocked practice of movement sequences: differential effects on response structure and movement speed.

Three similar six-element key press sequences were practiced under blocked or random practice schedules with acquisition conducted on one day and retention and transfer on the next day. The task required participants to type, as quickly as possible, one of three 6-element sequences as observed on a computer monitor. In blocked practice, participants completed all practice in one repeated sequence before the next repeated sequence was introduced. In random acquisition practice, the three repeated sequences were randomly presented to the participants. The data suggest that random practice results in participants adopting a uniform response structure, while blocked practice allows participants to exploit unique sequential aspects of the individual tasks. This finding suggests that random practice may not be as effective as blocked practice when one of the tasks being practiced together can be optimized through the development of a unique response structure.

Humans↗
PubMed2005

Sequence learning: response structure and effector transfer.

Two experiments are reported that investigate the response structure and effector transfer of repeated movement sequences. Participants moved a lever to targets sequentially presented on the computer monitor. In Experiment 1 the learning of 10- and 16-element sequences (identical movement pattern) was contrasted. After 1 day of practice the 10-element sequence was organized into fewer subsequences and, thus, performed more rapidly than the 16-element sequence. The imposed organization appeared to be coded in a relatively abstract way, as evidenced by effector transfer that was as good as that on the retention test. In Experiment 2 the 16-element sequence was studied after more extensive practice. By the end of 4 days of practice the participants produced relatively seamless responses void of obvious transitions between subsequences, but the control of the movement was less effector independent than observed earlier in practice. The results suggest that the process of consolidating the sequence, which led to more fluent response production, also resulted in the utilization of effector specific information.

Computers↗
PubMed2005

Schema theory: a critical appraisal and reevaluation.

The authors critically review a number of the constructs and associated predictions proposed in schema theory (R. A. Schmidt, 1975). The authors propose that new control and learning theories should include a reformulated (a) notion of a generalized motor program that is not based on motor program but still accounts for the strong tendency for responses to maintain their relative characteristics; (b) mechanism or processes whereby an abstract movement structure based on proportional principles (e.g., relative timing, relative force) is developed through practice; and (c) explanation for parameter learning that accounts for the benefits of parameter variability but also considers how variability is scheduled. Furthermore, they also propose that new theories of motor learning must be able to account for the consistent findings spawned as a result of the schema theory proposal and must not be simply discounted because of some disfavor with the motor program notion, in general, or schema theory, more specifically.

Empirical Research↗
PubMed2004

Systematic scaling of target width: dynamics, planning, and feedback.

The target width of a single target in a two-target reciprocal aiming task was scaled from small (ID = 5.85) to large (ID = 2.85) and large-to-small within individual trials with movement amplitude fixed. Scaling target width produced a transition in the end-effector's dynamics and based on a measure of movement harmonicity, the transition was sensitive to the initial conditions but not to the direction of target width scaling. Hysteresis emerged in a variety of kinematic measures suggesting that the interdependency of planning and feedback control processes was sensitive to initial conditions as well as the direction of target width scaling. Practice increased the efficiency of the reciprocal movements and produced changes in movement time and the measure of harmonic motion that revealed a tuning of the end-effector's dynamics to cyclical motion over as large of range of IDs as possible. The tuning occurred through the modulation of time spent accelerating and decelerating the end-effector for IDs outside the range of 3.85-4.26. The results are discussed with reference to a critical ID boundary that separates regions of parameter space wherein the end-effector's dynamics are more cyclical (limit-cycle) or discrete (fixed-point) in nature.

Acceleration↗
PubMed2004

Part-whole practice of movement sequences.

A 16-element movement sequence was taught under part-whole and whole-practice conditions. Participants (N = 18) produced a right-arm lever movement to sequentially presented target locations. The authors constructed part-whole practice by providing practice on only the 1st 8 elements on the 1st day of practice (100 repetitions of the 8-element sequence) and on all 16 elements on the 2nd day of practice (100 repetitions of the 16-element sequence). The whole-practice group practiced all 16 elements on both days (100 repetitions of the 16-element sequence per day). No differences in sequence structure or in movement duration of the 16-element sequence were noted on the retention test (Day 3). On transfer tests in which the 1st and last 8 elements were tested separately, however, the participants in the part-whole practice group performed more quickly than the participants in the whole-practice group, especially on the last 8 elements. Participants in the whole-practice group appeared to code the sequence so that it was relatively difficult to fully partition it into separate movements. Thus, on the transfer tests, there continued to be residual effects of the 8 elements that did not have to be produced but slowed down the rate of responding for the whole-practice group. That finding was not observed for the part-whole practice group.

Adult↗
PubMed2003

Discrete and cyclical units of action in a mixed target pair aiming task.

Two experiments addressed the issue of discrete and cyclical units as possible basic units of action that might be used to construct complex actions based on task constraints. The experiments examined the influence of low and high accuracy constraints on the end-effector's motion in rhythmical aiming movements. Both experiments utilized a Fitts-type task under three accuracy constraints: (1) big target pairing-low index of movement difficulty (ID), (2) small target pairing-high ID, and (3) mixed target pairing-one target high ID and the other target low ID. Experiment I was a 1-degree-of-freedom ( df) task that required subjects to crossover the inside edge of targets in a target pair using elbow flexion-extension motions. Experiment II used a 2- df task that required subjects to tap back and forth between targets in a target pair using a hand-held stylus. In both experiments, end-effector motion in the low ID condition was cyclical with the end-effector's motion consistent with a limit-cycle attractor description, while in the high ID condition end-effector motion was discrete and consistent with a fixed-point attractor description. The mixed target pairing produced both discrete and cyclical features in the end-effector's dynamics that suggested a functional linking of discrete and cyclical units of action as the optimal movement solution. Evidence supporting the above statements was found in the kinematic measures of movement time (MT), dwell time, proportion of MT accelerating and decelerating, and in a measure of harmonicity (Guiard 1993, Acta Psychol 82:139-159; Guiard 1997, Hum Mov Sci 16:97-131). Extended practice in the mixed target condition revealed a bias towards cyclical motion with practice. The results demonstrate that discrete and cyclical motion, represented as limit-cycle and fixed-point attractors, are basic units of action that the motor system uses in constructing more complex action sequences. The results are discussed with reference to coordinative structures and the generalized motor program as basic units of action. Issues pertaining to visual feedback processing and movement braking in rapid aiming tasks are also discussed.

Acceleration↗
PubMed2003

Effect of practice on effector independence.

The authors' primary purpose in the present experiment was to determine if practice changes the extent to which simple motor sequences are effector independent. Contralateral and ipsilateral effector transfers were assessed in 24 participants after 1 (200 trials) and 4 (800 trials) days of practice. The response sequence became increasingly effector dependent; the response structure and the scaling of force on the effector transfer tests were no better after 4 days of practice than after only 1 day, even though retention performance improved substantially. Those results are consistent with the notion that participants refine their movements over extended practice by exploiting the unique characteristics of the effectors. The additional practice results in a more effective movement when the same effectors are used but is of little value when different effectors are required.

Generalization, Psychological↗
PubMed2003

The independence of response structure and element production in timing sequences.

In three experiments, participants were asked to produce a prescribed temporal sequence of key presses. The number of elements in a key press sequence, the movement time of the elements, and uniformity of the timing elements comprising the sequence were manipulated. If the processing of the sequence structure was independent of the processing of elements comprising the sequence, increasing the number of the elements in the sequence should affect the production of the sequence but not the proficiency with which the individual elements are, produced. Increasing the movement time of the elements, however, should affect the production of the elements but have little, if any, effect on the integrity of the sequence. The findings indicated that increasing the number of elements negatively affected sequence production when the elements were nonuniform but had little or no effect when elements were uniform. Alternatively, element production was affected by movement time but not number of elements. The results of these experiments appear to confirm the independence of sequence and element production. However, Experiment 3, in which the uniformity of the elements was directly contrasted, found strong evidence for coarticulatory influences in the learning processes, whereby the longer and shorter than average elements in the sequence negatively affected the sequence integrity and the production of the individual elements. When faced with a nonuniformn timing pattern, participants appear to elongate or shrink individual elements of a uniform timing pattern to fit the desired sequence requirements. The result is that the longer or shorter than average elements require more practice to produce correctly, tend to regress across retention intervals, and are generally less stable than the elements nearer the average.

Adult↗
PubMed2002

Increasing the distance of an external focus of attention enhances learning.

Previous studies (e.g., Wulf, Höss, & Prinz, 1998) have shown that motor learning can be enhanced by directing performers' attention to the effects of their movements ("external focus"), rather than to the body movements producing the effect ("internal focus"). The purpose of the present study was to test the hypothesis that increasing the distance between the body and the action effects might further enhance the learning advantages associated with an external focus of attention. The distance of the external effect was manipulated by instructing three groups of participants learning to balance on a stabilometer to focus on markers attached to the platform located at different distances from their feet. Specifically, two groups were to focus on distant markers on the outside ("far-outside") or inside ("far-inside") of the platform, respectively, whereas another group was instructed to focus on markers close to their feet ("near"). In a retention test administered after two days of practice, all three external-focus groups showed generally more effective balance learning than an internal-focus control group. In addition, the far-outside and far-inside groups demonstrated similar performances, and both were more effective than the near group. Furthermore, the far-outside and far-inside groups showed higher-frequency movement adjustments than the near group. These results suggest that focusing on more distant effects results in enhanced learning by promoting the utilization of more natural control mechanisms. The findings are in line with a "constrained action" hypothesis that accounts for the relatively poorer learning associated with an attentional focus directed towards effects in close proximity to the body, or towards the body itself.

Analysis of Variance↗
PubMed2002

The role of parameter variability on retention, parameter transfer, and effector transfer.

The purpose of this study was to examine the effects of parameter variability on the learning of generalized motor programs (GMP) and movement parameterization. Participants attempted to exert a force pattern that resembled in force and time a waveform displayed on a computer monitor. The analysis suggested that relative timing (a measure of the GMP) performance remained remarkably stable across retention and transfer tests, whereby the structure of the movement remained intact, although the parameter or muscle group (effector) changed during transfer The results also indicated that variable parameter (time) practice did not enhance GMP learning but did degrade the learning parameter that was not varied (force). In addition, parameter specification was substantially less stable than the GMP, with time and force parameter performance deteriorating from the retention to transfer tests. These findings suggest that parameter specification, and not the GMP, is the primary cause of poorer performance in parameter and effector transfer.

Adolescent↗