Biomedical subjects

Jin-Hoon Park

Publications and source records attributed to Jin-Hoon Park.

8 recordsLinked to original sources

PubMed2006

Force development during target-directed isometric force production in Parkinson's disease.

Performing various daily activities requires precise application and control of forces, which has been well addressed in neurologically healthy individuals. Recent experiments have demonstrated that in young, normal subjects generating rapid force pulses over various force amplitudes was accomplished by linearly increasing the rate of force development while keeping time to peak force approximately constant (i.e., a pulse-height control strategy). Using Parkinson's disease (PD) patients the present study examined whether PD patients use a pulse-height control strategy during rapid and accurate isometric force production. Subjects were instructed to produce force pulses to three different target amplitudes (15, 35, and 55% of their maximal voluntary contractions) at their preferred speed and as fast as possible. When the task was performed as fast as possible, PD patients differed from controls by producing reduced rates of force development and prolonged times to peak force as a function of force amplitude. During performance of the task at preferred speed, which leaves the rate of force production unconstrained, PD patients did not show improved regulation of time to peak force in scaling different force amplitudes compared to controls. These results suggest that PD patients have a difficulty in utilizing a pulse-height control strategy and that such impairments are not dependent on speed.

Adaptation, Physiological↗

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

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

Effect of combined variation of force amplitude and rate of force development on the modulation characteristics of muscle activation during rapid isometric aiming force production.

Studies of rapid target-directed limb movements have suggested that various control schemes can be defined by the modulation pattern of the muscle activity. The present study was aimed to address the question regarding the extent to which a simultaneous control of force amplitude, and rate of force development influences the modulation characteristics of muscle activation associated with producing rapid isometric aiming forces at the elbow joint. The subjects were instructed to produce rapid isometric force pulses to three different force amplitudes (15, 35, and 55% of their maximal voluntary contractions) under systematically varied force-rate conditions ranging from a fast and accurate force-rate to the fastest force-rate possible. The results showed that larger force amplitudes were achieved by increasing the rate of force development (d F/d t) while the time to peak force remained relatively constant. The magnitude of the electromyographic (EMG) burst systematically increased as a function of force amplitude at all force-rate conditions. The primary finding was that the characteristic of the EMG burst duration associated with different force amplitudes showed a significant difference among force-rate conditions. Under a fast and accurate force-rate condition, the duration of the agonist burst increased linearly with force amplitude. A gradual transition into a fixed duration of the agonist burst then was observed over the remaining three force-rate requirements. With increasingly faster force-rates, there were no changes in the agonist burst duration over three force amplitudes. These results indicate that the combined variations in force amplitude and force-rate examined relative to the most rapid force-rate influence the control patterns for the muscle activation during the fast isometric force production. Changes in the EMG modulation patterns observed are likely due to the constraints imposed by muscle contractile properties.

Adult↗

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↗

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

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↗