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.     

Movement substructures change as a function of practice in children and adults

An experiment is reported in which participants at 6 (n = 20), 9 (n = 20), and 24 years (n = 20) of age either received or did not receive practice on a rapid aiming task using the arm and hand. The purpose of the experiment was to document the changes in movement substructures (in addition to movement time) as a function of practice. After receiving 10 baseline trials, subjects in the practice groups received 30 practice trials followed by 10 retention trials on each of 5 days, while subjects in the no-practice group had only baseline and retention trials. Retention-only trials were divided into primary (reflecting the ballistic controlled part of the movement) and secondary (reflecting corrective movement adjustments) submovements. In addition, jerk (the 3rd derivative of movement displacement) was calculated as an estimate of the smoothness of the movement. Participants increased the primary submovement as a function of practice; however, the increases were substantially larger in the children (25-30%) than in the adults (10%). Participants also decreased jerk as a function of practice and the decreases were greater in children than in adults. The results suggest that with practice the primary submovement is lengthened so that it ends nearer the target, especially in children. Associated with the primary submovement covering a larger percentage of the movement length and time, movements became smoother.     

Exploring how arm movement moderates the effect of task difficulty on balance performance in young and older adults

Emerging evidence highlights that arm movements exert a substantial and functionally relevant contribution on quiet standing balance control in young adults. Ageing is associated with “non-functional” compensatory postural control strategies (i.e., lower limb co-contraction), which in turn, may increase the reliance on an upper body strategy to control upright stance. Thus, the primary purpose of this study was to compare the effects of free versus restricted arm movements on balance performance in young and older adults, during tasks of different difficulty. Fifteen young (mean ± SD age; 21.3 ± 4.2 years) and fifteen older (mean ± SD age; 73.3 ± 5.0 years) adults performed bipedal, semi-tandem and tandem balance tasks under two arm position conditions: restricted arm movements and free arm movements. Centre of pressure (COP) amplitude and frequency were calculated as indices of postural performance and strategy, respectively. Especially in older adults, restriction of arm movement resulted in increased sway amplitude and frequency, which was primarily observed for the mediolateral direction. Further, increasing balance task difficulty raised the arm restriction cost (ARC; a new measure to quantify free vs. restricted arm movement differences in postural control) that was more prominent in older adults. These findings indicate the ARC provides a measure of reliance on the upper body for balance control and that arm movement is important for postural control in older adults, especially during tasks of greater difficulty.     

Control of interjoint coordination in the performance of manual circular movements can explain lateral specialization

Between-arm performance asymmetry can be seen in different arm movements requiring specific interjoint coordination to generate the desired hand trajectory. In the current investigation, we assessed between-arm asymmetry of shoulder-elbow coordination and its stability in the performance of circular movements. Participants were 16 healthy right-handed university students. The task consisted of performing cyclic circular movements with either the dominant right arm or the nondominant left arm at movement frequencies ranging from 40% of maximum to maximum frequency in steps of 15%. Kinematic analysis of shoulder and elbow motions was performed through an optoelectronic system in the three-dimensional space. Results showed that as movement frequency increased circularity of left arm movements diminished, taking an elliptical shape, becoming significantly different from the right arm at higher movement frequencies. Shoulder-elbow coordination was found to be asymmetric between the two arms across movement frequencies, with lower shoulder-elbow angle coefficients and higher relative phase for the left compared to the right arm. Results also revealed greater variability of left arm movements in all variables assessed, an outcome observed from low to high movement frequencies. From these findings, we propose that specialization of the left cerebral hemisphere for motor control resides in its higher capacity to generate appropriate and stable interjoint coordination leading to the planned hand trajectory.     

Reduced asymmetry in motor skill learning in left-handed compared to right-handed individuals

Hemispheric specialization for motor control influences how individuals perform and adapt to goal-directed movements. In contrast to adaptation, motor skill learning involves a process wherein one learns to synthesize novel movement capabilities in absence of perturbation such that they are performed with greater accuracy, consistency and efficiency. Here, we investigated manual asymmetry in acquisition and retention of a complex motor skill that requires speed and accuracy for optimal performance in right-handed and left-handed individuals. We further determined if degree of handedness influences motor skill learning. Ten right-handed (RH) and 10 left-handed (LH) adults practiced two distinct motor skills with their dominant or nondominant arms during separate sessions two–four weeks apart. Learning was quantified by changes in the speed–accuracy tradeoff function measured at baseline and one-day retention. Manual asymmetry was evident in the RH group but not the LH group. RH group demonstrated significantly greater skill improvement for their dominant-right hand than their nondominant-left hand. In contrast, for the LH group, both dominant and nondominant hands demonstrated comparable learning. Less strongly-LH individuals (lower EHI scores) exhibited more learning of their dominant hand. These results suggest that while hemispheric specialization influences motor skill learning, these effects may be influenced by handedness.     

Rapid aimed limb movements: differential effects of practice on component submovements

Three experiments are reported in which subjects practiced rapid aimed limb movements (arm pointing and wrist rotation) toward a visible target region. Subjects were required to minimize their movement durations while still landing in the target. The movement trajectories were examined to assess the effects of practice on separate component submovements of the limb movements. The results revealed that practice improved primarily temporal, not spatial, aspects of performance. Practice reduced the overall movement durations, but had different effects on the individual submovements. Practice allowed subjects to reduce the amount of time spent performing final corrective submovements, but actually increased slightly the time needed to produce the initial ballistic submovement. The results suggest that practice in the present task primarily enhanced the ability to use feedback information, but there was also some evidence of changes in the ballistic, preprogrammed portion of the movements. The results demonstrate that analysis of submovements can reveal important details of the underlying motor control processes.     

Rapid Aimed Limb Movements: Differential Effects of Practice on Component Submovements

Three experiments are reported in which subjects practiced rapid aimed limb movements (arm pointing and wrist rotation) toward a visible target region. Subjects were required to minimize their movement durations while still landing in the target. The movement trajectories were examined to assess the effects of practice on separate component submovements of the limb movements. The results revealed that practice improved primarily temporal, not spatial, aspects of performance. Practice reduced the overall movement durations, but had different effects on the individual submovements: Practice allowed subjects to reduce the amount of time spent performing final corrective submovements, but actually increased slightly the time needed to produce the initial ballistic submovement. The results suggest that practice in the present task primarily enhanced the ability to use feedback information, but there was also some evidence of changes in the ballistic, preprogrammed portion of the movements. The results demonstrate that analysis of submovements can reveal important details of the underlying motor control processes.     

Developmental Features of Rapid Aiming Arm Movements Across the Lifespan

Using a lifespan approach, the authors investigated developmental features of the control of ballistic aiming arm movements by manipulating movement complexity, response uncertainty, and the use of precues. Four different age groups of participants (6- and 9-year-old boys and girls and 24- and 73-year- old men and women, 20 participants in each age group) performed 7 types of rapid aiming arm movements on the surface of a digitizer. Their movement characteristics such as movement velocity, normalized jerk, relative timing, movement linearity, and intersegment intervals were profiled. Analyses of variance with repeated measures were conducted on age and task effects in varying movement complexity (Study 1), response uncertainty (Study 2), and precue use (Study 3) conditions. Young children and senior adults had slower, more variant, less smooth, and less linear arm movements than older children and young adults. Increasing the number of movement segments resulted in slower and more variant responses. Movement accuracy demands or response uncertainty interacted with age so that the 6- and 74-year-old participants had poorer performances but responded similarly to the varying treatments. Even though older children and young adults had better performances than young children and senior adults, their arm movement performance declined when response uncertainty increased. The analyses suggested that young children's and senior adults' performances are poorer because less of their movement is under central control, and they therefore use on-line adjustments. In addition, older children and young adults use a valid precue more effectively to prepare for subsequent movements than do young children and senior adults, suggesting that older children and young adults are more capable of organizing motor responses than arc young children and senior adults.     

Three-dimensional kinematics of upper limb anatomical movements in asymptomatic adults: Dominant vs. non-dominant

The effect of dominance on upper limb (UL) kinematics has only been studied on scapular movements. Moreover, when an anatomical UL movement is performed in a specific plane, secondary movements in the remaining planes involuntarily occur. These secondary movements have not been previously evaluated. The aim of this study was to compare the kinematics of primary and secondary angles of dominant and non-dominant UL during anatomical movements in asymptomatic adults.25 asymptomatic adults performed 6 anatomical movements bilaterally: shoulder flexion-extension, abduction-adduction, horizontal abduction-adduction, internal-external rotation, elbow flexion-extension and wrist pronation-supination. Kinematics of the dominant and non-dominant UL were compared by their ranges of motion (ROM) and their angular waveforms (Coefficient of Multiple Correlations, CMC).The comparison between dominant and non-dominant UL kinematics showed different strategies of movement, most notably during elbow flexion-extension (CMC = 0.29): the dominant UL exhibited more pronation at maximal elbow flexion. Significant secondary angles were found on most of the UL anatomical movements; e.g. a secondary ROM of shoulder (humero-thoracic) external-internal rotation (69° ± 16°) was found when the subject intended to perform maximal shoulder abduction-adduction (119° ± 21°).Bias of dominance should be considered when comparing pathological limb to the controlateral one. Normative values of primary and secondary angles during anatomical movements could be used as a reference for future studies on UL of subjects with neurological or orthopedic pathologies.     

Interlimb differences in visuomotor and dynamic adaptation during targeted reaching in children

While a number of studies have focused on movement (a)symmetries between the arms in adults, less is known about movement asymmetries in typically developing children. The goal of this study was to examine interlimb differences in children when adapting to novel visuomotor and dynamic conditions while performing a center-out reaching task. We tested 13 right-handed children aged 9–11 years old. Prior to movement, one of eight targets arranged radially around the start position was randomly displayed. Movements were made either with the right (dominant) arm or the left (nondominant) arm. The children participated in two experiments separated by at least one week. In one experiment, subjects were exposed to a rotated visual display (30° about the start circle); and in the other, a 1 kg mass (attached eccentrically to the forearm axis). Each experiment consisted of three blocks: pre-exposure, exposure and post-exposure. Three measures of task performance were calculated from hand trajectory data: hand-path deviation from the straight target line, direction error at peak velocity and final position error. Results showed that during visuomotor adaptation, no interlimb differences were observed for any of the three measures. During dynamic adaptation, however, a significant difference between the arms was observed at the first cycle during dynamic adaptation. With regard to the aftereffects observed during the post-exposure block, direction error data indicate considerably large aftereffects for both arms during visuomotor adaptation; and there was a significant difference between the arms, resulting in substantially larger aftereffects for the right arm. Similarly, dynamic adaptation results also showed a significant difference between the arms; and post hoc analyses indicated that aftereffects were present only for the right arm. Collectively, these findings indicate that the dominant arm advantage for developing an internal model associated with a novel visuomotor or dynamic transform, as previously shown in young adults, may already be apparent at 9 to 11-year old children.     

Interlimb coordination following stroke

Studies investigating whether simultaneous bilateral movements can facilitate performance of the impaired limb(s) of stroke patients have returned mixed results. In the present study we compared unilateral limb performance (amplitude, cycle duration) with performance during an interlimb coordination task involving both homologous (both arms, both legs) and non-homologous (one arm, one leg) limbs in stroke participants (n=7) and healthy age-matched controls (n=7). In addition, the effect of on-line augmented visual feedback on interlimb coordination was investigated. Participants performed cyclical flexion-extension movements of the arms and legs in the sagittal plane paced by an auditory metronome (1 Hz). Movement amplitudes were larger and cycle durations shorter during homologous limb coordination than non-homologous coordination. Compared with unilateral movements both groups had reduced movement amplitudes and the stroke group increased cycle duration when interlimb coordination tasks were performed. These effects were most evident during non-homologous (arm and leg) coordination. No evidence of facilitation of the impaired limb(s) was found in any of the interlimb coordination conditions. Augmented visual feedback had minimal effect on the movements of control participants but lead to an increase of cycle duration for stroke participants.     

Kinematics of Goal-Directed Arm Movements in Neglect: Control of Hand Velocity

Do patients with unilateral neglect exhibit direction-specific deficits in the control of movement velocity when performing goal-directed arm movements? Five patients with left-sided neglect performed unrestrained three-dimensional pointing movements to visual targets presented at body midline, the left and right hemispace. A group of healthy adults and a group of patients with right-hemispheric brain damage but no neglect served as controls. Pointing was performed under normal room light or in darkness. Time-position data of the hand were recorded with an opto-electronic camera system. We found that compared to healthy controls, movement times were longer in both patient groups due to prolonged acceleration and deceleration phases. Tangential peak hand velocity was lower in both patient groups, but not significantly different from controls. Single peak, bell-shaped velocity profiles of the hand were preserved in all right hemispheric patients and in three out of five neglect patients. Most important, the velocity profiles of neglect patients to leftward targets did not differ significantly from those to targets in the right hemispace. In summary, we found evidence for general bradykinesia in neglect patients, but not for a direction-specific deficit in the control of hand velocity. We conclude that visual neglect induces characteristic changes in exploratory behavior, but not in the kinematics of goal-directed movements to objects in peripersonal space.     

Developmental features of rapid aiming arm movements across the lifespan

Using a lifespan approach, the authors investigated developmental features of the control of ballistic aiming arm movements by manipulating movement complexity, response uncertainty, and the use of precues. Four different age groups of participants (6- and 9-year-old boys and girls and 24- and 73-year-old men and women, 20 participants in each age group) performed 7 types of rapid aiming arm movements on the surface of a digitizer. Their movement characteristics such as movement velocity, normalized jerk, relative timing, movement linearity, and intersegment intervals were profiled. Analyses of variance with repeated measures were conducted on age and task effects in varying movement complexity (Study 1), response uncertainty (Study 2), and precue use (Study 3) conditions. Young children and senior adults had slower, more variant, less smooth, and less linear arm movements than older children and young adults. Increasing the number of movement segments resulted in slower and more variant responses. Movement accuracy demands or response uncertainty interacted with age so that the 6- and 74-year-old participants had poorer performances but responded similarly to the varying treatments. Even though older children and young adults had better performances than young children and senior adults, their arm movement performance declined when response uncertainty increased. The analyses suggested that young children's and senior adults' performances are poorer because less of their movement is under central control, and they therefore use on-line adjustments. In addition, older children and young adults use a valid precue more effectively to prepare for subsequent movements than do young children and senior adults, suggesting that older children and young adults are more capable of organizing motor responses than are young children and senior adults.     

Concurrent verbal interference of right and left proximal and distal upper extremity tapping

The purpose of this study was to investigate crossed and uncrossed control of the proximal (upper arm and shoulder) and distal (lower arm and hand) musculature of the arms using the dual-task paradigm. Forty-one strongly right-handed men performed a tapping task using primarily the musculature of the upper or lower arms, with and without concurrent verbal processing demands. The results showed that the left distal region was distinguished from the other three effector locations by its relative insensitivity to the demands of the dual-task (verbal processing) condition. Rapid alternating movements of the left arm were functionally independent from the left index finger location in response to dual-task demands. Dual verbal and tapping demands at this effector produced greater interference on both the primary and secondary task. The results preclude the attribution of interference effects to manual dominance factors alone. The results generally support anatomical accounts of increased ipsilateral control over left side arm but not hand movements. Neither the traditional cognitive hemispheric model nor the manual dominance hypothesis were adequate in accounting for the results. An alternative generalized capacity hypothesis was required to account for performance at the LE.     

Matching of Movements Made Independently by the Two Arms in Normal Humans

Comparisons were made of voluntary movements of the right and left arms in normal human subjects. A series of movements of different amplitudes, made at the subject’s own speed, was performed with one limb. After a rest period, the same series was repeated with the contralateral limb. The relation between movement peak velocity and movement amplitude was linear and was the same for both arms. With repeated testing over periods up to two months, the slope of the peak velocity—amplitude relation decreased during the first week, thereafter remaining unchanged. In a second series of experiments, six normal subjects continuously wore a 1 lb (0.45 kg) weight strapped to their left (non-dominant) forearm for up to 1 week. This resulted in an increase in the slope of the peak-velocity/amplitude relation in this arm. A parallel change occurred in movements made independently by the right (non-loaded) arm. A similar matching of movement performance of the two limbs was seen following removal of the weight. The data is interpreted as providing support for the hypothesis that there is a single movement “command” which is applied to both limbs. The interaction of this command with the limbs which have similar second-order mechanical properties yields similar movements even when they are made independently.     

Matching of movements made independently by the two arms in normal humans

Comparisons were made of voluntary movements of the right and left arms in normal human subjects. A series of movements of different amplitudes, made at the subject' own speed, was performed with one limb. After a rest period, the same series was repeated with the contralateral limb. The relation between movement peak velocity and movement amplitude was linear and was the same for both arms. With repeated testing over periods up to two months, the slope of the peak velocity-amplitude relation decreased during the first week, thereafter remaining unchanged. In a second series of experiments, six normal subjects continuously wore a 1 lb (0.45 kg) weight strapped to their left (non-dominant) forearm for up to 1 week. This resulted in an increase in the slope of the peak-velocity/amplitude relation in this arm. A parallel change occurred in movements made independently by the right (non-loaded) arm. A similar matching of movement performance of the two limbs was seen following removal of the weight. The data is interpreted as proving support for the hypothesis that there is a single movement "command" which is applied to both limbs. The interaction of this command with the limbs which have similar second-order mechanical properties yields similar movements even when they are made independently.     

Movement trajectory smoothness is not associated with the endpoint accuracy of rapid multi-joint arm movements in young and older adults

The minimum variance theory proposes that motor commands are corrupted by signal-dependent noise and smooth trajectories with low noise levels are selected to minimize endpoint error and endpoint variability. The purpose of the study was to determine the contribution of trajectory smoothness to the endpoint accuracy and endpoint variability of rapid multi-joint arm movements. Young and older adults performed arm movements (4 blocks of 25 trials) as fast and as accurately as possible to a target with the right (dominant) arm. Endpoint accuracy and endpoint variability along with trajectory smoothness and error were quantified for each block of trials. Endpoint error and endpoint variance were greater in older adults compared with young adults, but decreased at a similar rate with practice for the two age groups. The greater endpoint error and endpoint variance exhibited by older adults were primarily due to impairments in movement extent control and not movement direction control. The normalized jerk was similar for the two age groups, but was not strongly associated with endpoint error or endpoint variance for either group. However, endpoint variance was strongly associated with endpoint error for both the young and older adults. Finally, trajectory error was similar for both groups and was weakly associated with endpoint error for the older adults. The findings are not consistent with the predictions of the minimum variance theory, but support and extend previous observations that movement trajectories and endpoints are planned independently.     

Infant and adult perceptions of possible and impossible body movements: An eye-tracking study

This study investigated how infants perceive and interpret human body movement. We recorded the eye movements and pupil sizes of 9- and 12-month-old infants and of adults (N=14 per group) as they observed animation clips of biomechanically possible and impossible arm movements performed by a human and by a humanoid robot. Both 12-month-old infants and adults spent more time looking at the elbows during impossible compared with possible arm movements, irrespective of the appearance of the actor. These results suggest that by 12months of age, infants recognize biomechanical constraints on how arms move, and they extend this knowledge to humanoid robots. Adults exhibited more pupil dilation in response to the human's impossible arm movements compared with the possible ones, but 9- and 12-month-old infants showed no differential pupil dilation to the same actions. This finding suggests that the processing of human body movements might still be immature in 12-month-olds, as they did not show an emotional response to biomechanically impossible body movements. We discuss these findings in relation to the hypothesis that perception of others' body movements relies upon the infant's own sensorimotor experience.     

Practice effects on motor control in healthy seniors and patients with mild cognitive impairment and Alzheimer's disease

This research was designed to test the hypothesis that motor practice can enhance the capabilities of motor control in healthy controls (NC) and patients with a diagnosis of probable Alzheimer's disease (AD) and mild cognitive impairment (MCI), and consequently results in better motor performance. Approximately half of the subjects in the NC (n = 31), AD (n = 28), and MCI (n = 29) either received or did not receive practice on a task of fast and accurate arm movement with a digitizer. Changes in movement time (MT), movement smoothness (jerk), and percentage of primary submovement (PPS) were recorded and compared among the three groups across six blocks of trials (baseline and five training sessions). For all subjects, practice improved motor functions as reflected by faster and smoother motor execution, as well as a greater proportion of programming control. Compared to unaffected matched controls, AD and MCI subjects exhibited a greater reduction in movement jerk due to practice. Movement time and PPS data revealed that motor practice appeared to reduce the use of "on-line" correction adopted by the AD or MCI patients while performing the aiming movements. Evidently, their arm movements were quicker, smoother, and temporally more consistent than their untrained peers. The findings of this study shed light on how MCI and AD may affect motor control mechanisms, and suggest possible therapeutic interventions aimed at improving motor functioning in these impaired individuals.     

Does hand dominance affect the use of motor abundance when reaching to uncertain targets?

This study investigated hemispheric differences in utilizing motor abundance to achieve flexible patterns of joint coordination when reaching to uncertain target locations. Right-handed participants reached with each arm to the same central target when its final location was certain or when there was a 66% probability that its location could change after movement initiation. Use of greater motor abundance was observed when participants reached to the central target under target location uncertainty regardless of the arm used to reach. Joint variance associated with variability of movement direction was larger when reaching with the left, non-dominant arm. This arm also exhibited higher hand path variability compared to the dominant arm. These arm differences were not found when the final (central) target location was known in advance. The results provide preliminary evidence for a greater ability of the dominant (right) arm/left hemisphere to decouple directions in joint space. That is, to increase the use of motor abundance without simultaneously inducing unwanted hand path variability requires that joint variations be restricted to a limited subspace of joint space. Hemispheric differences in motor planning did not appear to account for arm differences related to the use of motor abundance.