Search PubMed⌕ Search

Biomedical subjects

George E Stelmach

Publications and source records attributed to George E Stelmach.

14 recordsLinked to original sources
PubMed2003

Altered aiming movements in Parkinson's disease patients and elderly adults as a function of delays in movement onset.

This study investigated the effect of lengthening the time the hand remains immobilized on an aiming movement performed by Parkinson's disease (PD) patients and elderly adults, and whether visual information could compensate for the effects of delay. In Experiment One, PD patients and elderly adults kept the limb in a static position for 1, 6, or 10 s prior to movement initiation, both with and without vision of the initial limb position and the movement trajectory. Compared to elderly adults, PD patients had increased movement times and jerk scores, and exhibited shorter primary submovements that erred in initial movement direction. Lengthening the time delay increased movement time, decreased mean acceleration, and decreased the distance covered in the primary submovement for both groups. Parkinsonian patients, however, exhibited reduced length of the primary submovement across delay compared to elderly adults. Occluding vision caused the movements of PD patients to deteriorate on all measures. Although the performance of both groups was enhanced when vision was available, vision was not able to fully counteract the effects of delay in either group. In Experiment Two, participants moved to a previously viewed target to examine movement accuracy. Systematic undershooting of the target as a function of delay was found for both groups. Parkinsonian patients exhibited greater undershooting of the target after the primary submovement both with and without vision. Visual feedback reduced the effects of delay for both the elderly and PD patients. It can be inferred from the results that the decay in position sense as a function of time produces impairments in incorporating the initial limb position in motor planning process.

Aged↗
PubMed2003

Memory-motor transformations are impaired in Parkinson's disease.

Parkinson's disease patients are known to suffer loss of dopaminergic input to the rostral caudate nucleus. Recent functional magnetic resonance imaging (fMRI) studies have implicated this structure in the transformation of spatial information in memory to guide action, suggesting that memory to motor transformations may be selectively impaired in Parkinson's disease. In order to investigate this possibility we tested a group of Parkinson's disease patients (PDs) using a memory-guided pointing task. Of interest was whether patients showed reduced accuracy in the task as a function of memory load. Twelve PD patients and 13 elderly controls were asked to recall single or four step target sequences with 2 time delays (500 and 3,500 ms). In all memory-guided conditions PD patients showed increased variability in memory-guided movement end-points. This effect was not affected by delay, number of items, or the sequence familiarity. The results are consistent with increased variability in memory-motor transformations in early PD, due to dopamine depletion within the rostral caudate nucleus.

Aged↗
PubMed2003

Time delays prior to movement alter the drawing kinematics of elderly adults.

Position sense has been found to decay as a function of the time delay the limb remains in a static position prior to movement onset. Position sense has also been found to deteriorate as a function of aging, with increased reliance on vision by the elderly. This study investigated whether the pointing kinematics of elderly adults were differentially affected by delay compared to young adults, and whether visual information could compensate for the effects of delay. Young and elderly adults kept the limb in a static position for 1, 6, or 10 s prior to movement onset, both with and without vision of the limb, initial position, and the movement trajectory. Across groups, delay resulted in increased overall movement duration, decreased peak velocity including a shorter relative time to peak velocity, with decreased distance and duration of the primary submovement. Delay and lack of vision differentially decreased distance of the primary submovement for elderly adults. Vision was able to compensate to some degree for the effects of delay across age groups. The findings provide evidence that decays in position sense as a function of time create difficulties in incorporating the initial limb position in motor planning process in elderly adults.

Adult↗
PubMed2003

Effects of target height and width on 2D pointing movement duration and kinematics.

This study examined the impact of target geometry on the trajectories of rapid pointing movements. Participants performed a graphic point-to-point task using a pen on a digitizer tablet with targets and real time trajectories displayed on a computer screen. Circular- and elliptical-shaped targets were used in order to systematically vary the accuracy constraints along two dimensions. Consistent with Fitts Law, movement time increased as target difficulty increased. Analysis of movement kinematics revealed different patterns for targets constrained by height (H) and width (W). When W was the constraining factor, movements of greater precision were characterized by a lower peak velocity and a longer deceleration phase, with trajectories that were aimed relatively farther away from the center of the target and were more variable across trials. This indicates an emphasis on reactive, sensory-based control. When H was the constraining factor, however, movements of greater precision were characterized by a longer acceleration phase, a lower peak velocity, and a longer deceleration phase. The initial trajectory was aimed closer to the center of the target, and the trajectory path across trials was more constrained. This suggests a greater reliance on both predictive and reactive control.

Acceleration↗
PubMed2003

Developmental differences in children's ballistic aiming movements of the arm.

An experiment was conducted to examine the change in the relation between programming and "on-line" correction as a developmental explanation of children's arm movement performance. Each of 54 children in three age groups (5, 8, and 10 yr.) completed two types of rapid aiming arm movements in the longitudinal plane on the surface of a digitizer. Percent primary submovements and timing variability were dependent variables. Analysis suggested that the 5-yr.-olds used "on-line" monitoring during the arm movement and did not perform the movement sequence as a functional unit. Compared with 8- and 10-yr.-olds, the 5-yr.-olds planned a smaller portion of movements, executed the arm movements with more variability in time to peak velocity. The 8- and 10-yr.-olds appeared to plan their movements and execute the sequence as a unit. The developmental implications were discussed.

Age Factors↗
PubMed2002

Alterations in transport path differentially affect temporal and spatial movement parameters.

Many studies have examined the coordination of reach-to-grasp movements. However, there is debate regarding the mechanism of coordination between the transport and grasp components. The current study investigated the stability of temporal and spatial measures for reaches in which transport path was altered early or late in the reaching action. Transport alteration was accomplished by placing an obstacle either 10 cm (near) or 20 cm (far) from the hand starting position. Obstacle location affected the formation of transport path such that maximum wrist elevation coincided with the location of the obstacle. Kinematic analyses revealed that reaches over the near obstacle significantly prolonged transport time and time to maximum velocity compared with reaches over the far obstacle. A similar pattern of results was observed for the grasp component; reaches over the near obstacle resulted in a prolongation of grip duration, time to maximum aperture, and time to maximum opening and closing velocity. Grip closing velocity was decreased in the obstacle conditions. These results confirm findings from earlier studies that have shown that changes in the transport component affect grasp formation. A spatial and temporal analysis of grasp opening and closing was also performed. Grasp closing time varied significantly between conditions, while closing distance or the distance traveled by the wrist after maximum aperture remained essentially constant across conditions. These results suggest that the central nervous system may be using a spatial controller to coordinate prehensile components.

Adult↗
PubMed2002

Segment difficulty in two-stroke movements in patients with Parkinson's disease.

In the horizontal plane on a digitizer tablet, subjects made an elbow-extension, two-stroke movement away from the trunk to a first target and then on to a second target. If the two segments of the movement were executed in an integrative manner, the accuracy constraint on the first segment should have produced changes in kinematic features not only of that segment but also of the second segment. Two-stroke movements of ten Parkinson's disease (PD) patients and ten controls were studied to examine whether a high-accuracy constraint on the first segment influences the performance of the second, when the second target has either a high- or low-accuracy requirement. When the accuracy requirement of the second segment was low, both PD patients and controls showed that changing the first target size from large to small influenced the performance of not only the first segment but also the second segment. For the first segment, movement time, acceleration time, and deceleration time increased when moving to the small first target as compared to the large first target. The peak velocity and peak acceleration also decreased as the first target size decreased. For the second segment, similar patterns of kinematic changes in relation to the first segment were observed in all of these parameters. When the accuracy requirement of the second segment was high, the controls showed similar changes in the first and second segments in relation to the change of first target sizes. In contrast, the PD patients showed that the target size that defined the first movement mainly influenced the performance of that segment. Among kinematic parameters tested for the second segment, only acceleration time increased as the first target size decreased. Other parameters in general did not change, regardless of whether movement of the first segment was made to the small or large target. These results indicate that the two-stroke movements of PD patients showed little evidence that they were planned and organized in an integrative manner when there was a high-accuracy constraint imposed on the second segment. On the other hand, control subjects performed two-stroke movements in a manner that suggested the two segments were planned and organized together regardless of an accuracy constraint imposed.

Aged↗
PubMed2002

Coordination and control of forces during multifingered grasping in Parkinson's disease.

In this study, we focused on how subjects with Parkinson's disease (PD) grasp and lift with five-digits of the hand. This task provided the opportunity to simultaneously examine (a) the coordination of multiple segments (i.e., digits), (b) the sequencing of multiple tasks (i.e., force development, object lift, and hold), and (c) the control of force output. We found that PD patients coordinated and controlled five-digit forces comparable to that of age-matched controls. Specifically, these groups developed and maintained similar force amplitudes and force sharing patterns across all grasping phases. In addition, PD patients demonstrated similar levels of variability both within and across trials. In the frequency domain, however, some differences were observed across groups, especially in PD patients exhibiting obvious action tremor (AT) at a single modal frequency. In these subjects (four of nine PD patients), there was a systematic disruption, i.e., a phase-shifting away from approximately 0 degrees, in-phase force synchronization patterns normally observed between digits. This disruption typically occurred at and around the AT frequency, while at many other frequencies synchronization patterns were maintained. The composite of these findings implies that although global features observed in five-digit grasping in PD patients are preserved, more subtle aspects of the coordination between digits, as revealed by frequency domain analysis, are not. These results are discussed in relation to the neural mechanisms that might underlie physiological synchronization of forces and its pathological disruption.

Aged↗
PubMed2002

The relationship between knowledge of results and motor learning in Parkinsonian patients.

A simple timing movement was used to investigate augmented feedback on motor learning in Parkinson's disease (PD) patients and controls. During acquisition, participants received knowledge of results (KR) about their errors after every trial (100%) or every fifth trial (20%). Participants then performed a retention test without KR. Controls performed better on the retention test after having had 20% KR during acquisition. PDs showed superior retention with 100% KR. This suggests that the PD patients are more reliant on KR for learning motor skills; a difference that may be attributable to reduced proprioceptive acuity in PD patients.

Aged↗
PubMed2002

Adaptation to changes in vertical display gain during handwriting in Parkinson's disease patients, elderly and young controls.

Parkinson's disease (PD) patients, matched elderly controls, and normal young subjects were tested using a visuo-motor adaptation paradigm in which the gain of the vertical component of the visual feedback of handwriting was manipulated in real-time. Handwriting was performed on a digitizer tablet and displayed in real-time on a computer screen in front of the participant. Vision of the hand and pen was occluded. Feedback could be normal (pre- and post-exposure conditions), smaller, or larger than the actual handwriting (exposure conditions). All groups showed a gradual adaptation that compensated for the distorted visual feedback during the exposure conditions. Moreover, all the groups showed significant after-effects during the post-exposure conditions suggesting that all the participants learned to compensate for the novel display gains. Taken together, these data suggest that the mechanisms for visuo-motor adaptation to changes in vertical display gain during handwriting are robust to aging and early stage of PD. These results may have implications for the treatment of micrographia in Parkinsonism.

Adaptation, Psychological↗
PubMed2002

Age-related kinematic differences as influenced by task difficulty, target size, and movement amplitude.

Fifteen older adults (M = 68 years old) and 15 young adults (M = 23 years old) participated in a speed-accuracy task in which aiming movements were performed on a digitizing tablet to assess movement slowing and variability in older adults. Target-size and movement amplitude influences were analyzed separately to determine if they affected the performance of the young and older adults differently. When target size was increased, older adults did not increase the relative distance traveled in the primary submovement. When movement amplitude was increased, older adults did not scale movement velocities to the same magnitude as young adults did. Both the inability to scale velocity and the inability to increase the relative distance traveled in the primary submovement contribute to slower, more variable movements observed in older adults depending on task parameters. Thus, these data reveal that manipulation of target size and movement amplitude yield two distinct factors that contribute to slowness of movement in older adults.

Adult↗
PubMed2002

Changes in multi-joint performance with age.

The purpose of this study was to determine whether elderly adults exhibit deficits in the performance of multi-joint movements. Two groups of subjects (mean ages, 68.9 and 30.1 years, respectively) participated in this experiment. Subjects performed planar arm pointing movements to various targets. One target could be achieved via elbow extension only, while the remaining 3 required both elbow extension and horizontal shoulder flexion, thus requiring coordination at the 2 joints. In contrast to the young adults, the elderly adults produced movements that became less smooth and less accurate with increasing shoulder joint contribution. The results imply a selective coordination deficit for the elderly adults. In addition, the elderly adults coactivated opposing muscles more than the young adults for the single-joint movement. However, the elderly adults reduced coactivation at both joints for the 2-joint actions, while the young adults did not. These data suggest a relationship between high coactivation levels and good performance for elderly adults. It may be more difficult for the elderly to implement high coactivation levels for multi-joint movements because of the increased energy costs and complexity of planning required in comparison to the single joint actions. Thus, to achieve motor performance, elderly persons appear to use coactivation in a manner that is fundamentally different than young adults.

Adult↗
PubMed2002

Influence of biomechanical constraints on horizontal arm movements.

Influence of mechanical interactions between the shoulder and elbow on production of different coordination patterns during horizontal arm movements is investigated in the present study. Subjects performed cyclical movements along a circle and along lines of 4 different orientations. Cycling frequency was manipulated to highlight control features responsible for interactive torque regulation. When the shoulder was involved in motion, torque analysis revealed that this joint was controlled similarly during all movement types. At the elbow, however, each movement type required a specific pattern of regulation of interactive torque with muscle torque. When interactive torque acted in the direction of the required elbow rotation, the demands for active control were lower than when the interactive torque resisted elbow motion and had to be actively suppressed. Kinematic analysis demonstrated that increases in cycling frequency systematically deformed the fingertip path. The amount of these deformations differed across movement types, being more pronounced for movements where the interactive torque resisted joint motion. It appears that interactive torque can assist or resist movement at the joints, making control of some movement types more difficult than others.

Adolescent↗