Biomedical subjects

Andrew M Gordon

Publications and source records attributed to Andrew M Gordon.

10 recordsLinked to original sources

PubMed2003

Influence of fingertip contact on illusory arm movements.

Recent evidence suggests that reaching movements are more accurate when end point contact occurs, suggesting that fingertip contact contributes to a final estimation of arm position. In the present study we tested two hypotheses: 1). that fingertip contact influences illusions of arm movement produced by muscle vibration and 2). that this influence depends on the a priori context of the stability of the contact surface. Subjects sat with their elbows on a table and eyes closed. They demonstrated the perceived orientation of the left (cue) arm by mirroring the location with the right (report) arm. We manipulated deep proprioceptive cues by vibrating the left biceps brachia, causing illusions of elbow extension, and tested whether these illusions were altered when the fingertip remained in contact with a stable external surface. The context at this point represents a prior assumption that the external contact surface is stable. Midway through the experiment, the context was changed by challenging the prior assumption that the contact surface was stable by demonstrating that it could move. Unbeknownst to the subject, the external contact surface remained stable during data collection throughout the experiment. As expected, without tactile cues, biceps vibration caused illusory elbow extension. Conditions with fingertip contact and biceps vibration in the stable context demonstrated that contact largely eliminated the overestimation of cue arm elbow angle. However, in the context of a possibly unstable (movable) contact surface, the reports of elbow extension returned. Thus a priori notions about the stability context of an external contact surface influence how this tactile cue is integrated with proprioceptive sensory modalities to generate an estimate of arm location in space. These findings support the notion that tactile cues are used to calibrate proprioception against external spatial frameworks.

Adult↗

PubMed2003

Tactile feedback contributes to consistency of finger movements during typing.

Touch typing movements are typically too brief to use on-line feedback. Yet, previous studies have shown that blocking tactile feedback of the fingertip of typists leads to an increase in typing errors. To determine the contribution of tactile information to rapid fine motor skills, we analyzed kinematics of the right index finger during typing with and without tactile feedback. Twelve expert touch typists copy-typed sentences on a computer keyboard without vision of their hands or the computer screen. Following control trials, their right index fingertip was anesthetized, and sentences were typed again. The movements of the finger were recorded with an instrumented glove and electromagnetic position sensor. During anesthesia, typing errors of that finger increased sevenfold. While the inter-keypress timing and average kinematics were unaffected, there was an increase in variability of all measures. Regression analysis showed that endpoint variability was largely accounted for by start location variability. The results suggest that tactile cues provide information about the start location of the finger, which is necessary to perform typing movements accurately.

Adult↗

PubMed2003

Internal representations underlying respiration during object manipulation.

We examined the presence of anticipatory control and the resulting interactions of the respiratory and motor systems during discrete object manipulation. In response to an auditory signal, subjects reached forward, grasped, and lifted an instrumented object weighing 150 or 1000 g while the breathing pattern, fingertip forces, and movements were measured. Following every block of five lifts, the object was removed from sight and replaced with the same or an alternate mass. Thus, the object's weight was predictable during the last lift of each block and unpredictable during the first lift after the transition. When the object's weight was predictable, the force application was faster and inspiratory duration and the tidal volume were reduced for the breath associated with the lift for 1000-g compared to 150-g lifts. Following the transition, when the object's weight was unpredictable, the force application reflected the weight of the object during the previous lift while the respiratory output, regardless of the preceding weight, resembled that used for 1000-g lifts. Additionally, inspiratory duration was significantly correlated with the reach duration in three of the four unpredictable lifting conditions. We conclude that these system-specific anticipatory alterations may arise from a common internal representation that was formed through past manipulatory weight experience.

Adult↗

PubMed2003

Selective use of visual information signaling objects' center of mass for anticipatory control of manipulative fingertip forces.

The present study examines whether visual information indicating the center of mass (CM) of an object can be used for the appropriate scaling of fingertip forces at each digit during precision grip. In separate experiments subjects lifted an object with various types of visual cues concerning the CM location several times and then rotated and lifted it again to determine whether the visual cues signaling the new location of the CM could be used to appropriately scale the fingertip forces. Specifically, subjects had either no visual cues, visual instructional cues (i.e., an indicator) or visual geometric cues where the longer axis of the object indicated the CM. When no visual cues were provided, subjects were unable to appropriately scale the load forces at each digit following rotation despite their knowledge of the new weight distribution. When visual cues regarding the CM location were provided, the nature of the visual cues determined their effectiveness in retrieval of internal representations underlying the anticipatory scaling of fingertip forces. Specifically, when subjects were provided with visual instructional information, they were unable to appropriately scale the forces. More appropriate scaling of the load forces occurred when the visual cues were ecologically meaningful, i.e., when the shape of the object indicated the CM location. We suggest that visual instructional cues do not have access to the implicit processes underlying dynamic force control, whereas visual geometric cues can be used for the retrieval of the internal representation related to CM for appropriate partitioning of the forces in each digit.

Adolescent↗

PubMed2003

Coordination of fingertip forces in object transport during locomotion.

Walking while carrying a hand-held object requires the generation of appropriate grip forces to offset the inertial forces produced during locomotion. The present study examined the interaction between grip forces and locomotion-induced inertial forces across the gait cycle. Eight subjects transported a container under three conditions: self-paced transport with and without accuracy constraints and a velocity-constrained condition. The results showed that the trunk and transported container moved in a synchronized, sinusoidal pattern during all conditions. Grip and inertial forces of the transporting hand were highly coupled in an anticipatory fashion, regardless of task demands. The inertial forces were higher and the coupling was greater in the faster, unconstrained condition. However, grip force modulation was observed even when the inertial forces acting on the container were small and applied indirectly to the container through the locomotor effects originating in the legs and trunk. We suggest that continuous grip force adjustment is used as a generalized strategy to maximize efficiency during object transport regardless of the size or origin of the inertial forces.

Adult↗

PubMed2003

Coordination of fingertip forces during precision grasping in multiple system atrophy.

While the pathology and autonomic nervous system components of multiple system atrophy (MSA) have been well described, little is known about the associated motor dysfunction. One prominent feature of MSA is parkinsonism, although ataxias and pyramidal tract signs are frequently present. To investigate the nature of motor deficits in MSA, a natural grip-lift movement requiring a precision grasp was used to examine force coordination. Subjects were asked to grasp an instrumented object using the fingertips of the thumb and index finger and lift it 10 cm above the table surface. Subjects with MSA demonstrated a prolonged duration between object contact and initiation of the lifting drive that increased with the weight of the object. During this period these subjects produced large grasping forces generating a significant portion of the eventual grip force employed to hold the object. In contrast, control subjects generated grip and load forces in parallel after establishing contact with the object. Therefore, subjects with MSA showed a disrupted performance on both the sequential (grasp, then lift) and simultaneous (grip and load force development) portions of this task. Only after initiation of the vertical lifting drive did subjects with MSA generate forces in a similar manner to control subjects. These findings demonstrate that subjects with MSA exhibit a disrupted coordination of grasp and could suggest a general deficit in motor control resulting from multi-focal neural degeneration.

Adaptation, Physiological↗

PubMed2003

Object release under varying task constraints in children with hemiplegic cerebral palsy.

Considerable attention has been given in recent years to fingertip force coordination during grasping and lifting small objects in children with cerebral palsy (CP). However, little is known about the children's ability to replace and release an object from grasp. The present study examined the coordination of fingertip forces during replacement and release of an object from grasp under varying task constraints in the involved hand of 15 children (10 males, five females, age range 7 to 14 years) with hemiplegic CP and in the non-dominant hand of 15 age-matched, typically-developing children (seven males, eight females). Participants released an object, instrumented with force transducers and held with a precision grip, onto a stable surface and onto an unstable surface (requiring higher accuracy) at self-paced and fast-as-possible speeds. Temporal and force measures were recorded and the dependent measures were tested using analyses of variance. Results showed that force coordination was impaired in children with hemiplegia, resulting in prolonged and uncoordinated replacement and release of the object (p<0.05). Differences between controls and children with hemiplegia were greater when speed and accuracy constraints were imposed (i.e. task performance was affected by these constraints to a greater extent in the children with CP, p<0.05). Impairments in temporal coordination of object release were also observed in the non-involved hand under all conditions (p<0.05). These results provide additional information about impaired hand function in children with hemiplegic CP. Clinical implications of these findings are discussed.

Adolescent↗

PubMed2003

Learning of grasp control in children with hemiplegic cerebral palsy.

This study examined whether children with hemiplegic cerebral palsy (CP) have anticipatory control of fingertip forces during lifts of familiar objects, and what type of practice (blocked or random) best enhances the retention of anticipatory control during lifts of novel objects. Eighteen children with hemiplegic CP (7 females, 11 males; 7 to 14 years of age, mean age 10 years, SD 1.8) and 18 age-matched typically developing children (8 males, 10 females; mean age 10.4 years, SD 1.7) participated in the study. In the first experiment the children lifted familiar objects of various weights and sizes five times each, while the vertical lifting (load) force was measured. Most participants demonstrated higher rates of load force increase for heavier (and larger) objects already during the first lift, indicating anticipatory control. Furthermore, the load force rates generally were similar across the five lifts for each object, suggesting that they had stable representations of the objects' properties. In the second experiment children lifted three novel objects varying in weight (but identical in volume) 27 times each, in either a blocked or a random order, followed by nine immediate and nine delayed (24 hours) retention trials. Blocked practice resulted in greater differentiation of the force rates between objects during acquisition than did random practice. Both practice schedules resulted in similar retention. These findings suggest that children with hemiplegic CP have a priori internal representations used for anticipatory force scaling with familiar objects. Furthermore, the results indicate that these children can form and retain internal representations of novel objects for anticipatory control, irrespective of the type of practice schedule employed. Thus, clinically based practice sessions that incorporate lifts with novel objects may enhance anticipatory force scaling and related prehensile function in children with hemiplegic CP.

Adolescent↗

PubMedDate not supplied

Manual asymmetry during object release under varying task constraints.

OBJECTIVE: This study examined differences between the dominant and nondominant hands of children during an object release task under various accuracy and speed constraints. METHOD: Fifteen children 7 to 14 years of age who were typically developing released an instrumented object held with a precision grip onto a stable or unstable surface at a self-paced or quick speed while temporal and force measures were recorded. RESULTS: Few differences were found between the two hands under stable, self-paced conditions. However, given accuracy constraints, object replacement with the nondominant hand took longer than the dominant hand. The nondominant hand exhibited different force coordination patterns than the dominant hand when both accuracy and speed constraints were imposed. CONCLUSION: Task constraints differentially affected the performance of the dominant and nondominant hands during this object release task. The results suggest that clinicians should incorporate various task constraints into hand preference evaluations and during "dominance retraining".

Adolescent↗

PubMedDate not supplied

The effect of body orientation on a point-to-point movement in healthy elderly persons.

OBJECTIVE: Upper limb retraining during the early phases of neurological rehabilitation often involves having individuals practice reaching in body orientations that reduce the effect of gravity on various joint motions (e.g., shoulder flexion, elbow extension). However, the efficacy of these training techniques has not been determined. The purpose of this study was to determine the effects of reducing gravity through a change in body orientation from sitting to side-lying on the kinematics of a point-to-point movement in healthy elderly persons. METHOD: Nine healthy, right-hand-dominant women 62 to 66 years of age pointed to a target in two different body orientations-sitting and side-lying. A 2-dimensional kinematic analysis of the movement was performed to compare the trajectory of the hand and the interjoint coordination under the two conditions. RESULTS: Regardless of body orientation relative to gravity, participants produced straight hand paths and smooth, bell-shaped velocity profiles. However, they moved slower in side-lying, and the pattern of interjoint coordination varied. The shoulder and elbow moved less, whereas the scapula made a greater contribution to the overall movement. Furthermore, the temporal coordination of the joints was modified as a consequence of body position. CONCLUSION: The results indicate that point-to-point arm movements made against gravity differ from those made in a gravity-reduced plane, particularly at the joint level, illustrating that movement organization is sensitive to this contextual difference. The effect of minimizing gravity on upper limb movement needs to be explored in patient populations to determine whether training patients in gravity-reduced orientations is efficacious.

Aged↗