Biomedical subjects

J F Soechting

Publications and source records attributed to J F Soechting.

At least 55 records · Page 3Linked to original sources

PubMed1989

Sensorimotor representations for pointing to targets in three-dimensional space.

1. The accuracy with which subjects pointed to targets in extrapersonal space was assessed under a variety of experimental conditions. 2. When subjects pointed in the dark to remembered target locations, they made substantial errors. Errors in distance, measured from the shoulder to the target, were sometimes as much as 15 cm. Errors in direction, also measured from the shoulder, were smaller. 3. An analysis of the information transmitted by the location of the subject's finger about the location of the target showed that the information about the target's distance was consistently lower than the information about its direction. 4. The errors in distance persisted when subjects had their arm in view and pointed in the light to remembered target locations. 5. The errors were much smaller when subjects used a pointer to point to the target or when they were asked to reproduce the position of their finger after it had been passively moved to the target. 6. From these findings we conclude that subjects have a reasonably accurate visual representation of target location and are able to effectively use kinesthetically derived information about target location. We therefore suggest that errors in pointing result from errors in the sensorimotor transformation from the visual representation of the target location to the kinematic representation of the arm movement.

Darkness↗

PubMed1989

Errors in pointing are due to approximations in sensorimotor transformations.

1. We define an extrinsic frame of reference to represent the location of a point in extrapersonal space relative to a human subject's shoulder, and we define an intrinsic frame of reference to represent the orientation of the arm and forearm. 2. We examined the relations between coordinates in the extrinsic and intrinsic frames of reference under two experimental conditions: when subjects made inaccurate movements by pointing to virtual targets in the dark and when they made accurate movements by pointing to actual targets in the light. 3. When subjects made inaccurate movements, there was a close-to-linear relationship between the orientation angles of the arm (intrinsic coordinates) at its final position and the extrinsic coordinates of the target. When they made accurate movements, these relationships were more nonlinear. 4. Specifically, arm and forearm elevations depended principally on target distance and elevation, whereas the two yaw angles depended mainly on the target's azimuth. 5. We propose that errors in pointing occur because subjects implement a linear approximation to the transformation from extrinsic to intrinsic coordinates and that this transformation is one step in the process of transforming a visually derived representation of target location into an appropriate pattern of muscle activity.

Darkness↗

PubMed1988

Effect of load perturbations on EMG activity and trajectories of pointing movements.

Force perturbations were applied to the upper arm during pointing movements to a target. Following the perturbation, the trajectories of shoulder and elbow angular velocities converged on those obtained during trials in which no perturbation was imposed, but with a temporal offset. Changes in EMG activity in shoulder and elbow flexors evoked by the perturbation were similar to those observed previously under quasi-static conditions, the change in a given muscle depending on shoulder and elbow motion.

Arm↗

PubMed1988

Sensorimotor transformations underlying the organization of arm movements in three-dimensional space.

Coordinated movements in three-dimensional space involve sensorimotor transformations between extrinsic and intrinsic coordinates. It is hypothesized that a key aspect underlying the organization of such movements is the need to simplify these transformations by means of suitable approximations and the imposition of constraints. Motor tasks involving the drawing of circles and ellipses in different planes were analyzed from this perspective, and some rules are presented whereby the plane of motion and the slant of an ellipse can be specified in a simple way in terms of intrinsic parameters. It is shown that these rules can be generalized to hold for more complicated wrist motions if one assumes that they consist of segments of elliptical arcs.

Arm↗

PubMed1988

Quantitative evaluation of the electromyographic responses to multidirectional load perturbations of the human arm.

1. Force perturbations consisting of a random train of pulses were applied to the forearms of human subjects, the direction of the force being varied +/- 60 degrees from vertical in the sagittal plane in different trials. 2. Both forearm and upper arm were free to move, and the perturbations resulted in angular motion and torque at both joints. By varying the direction of the force, different combinations of these variables could be obtained. 3. Average angular motion and net torque at the shoulder and elbow joints and electromyographic activity of shoulder and elbow muscles due to a single pulse of force were computed by cross-correlation methods. 4. The pattern of responses in biceps, brachio-radialis, and anterior deltoid was not related uniquely to angular motion at the shoulder or elbow joints. Furthermore, the responses appeared to consist of two distinct components, an "early" one with a latency less than 40 ms and a "late" one with a latency of approximately 80 ms. 5. The average amplitude of the early response was best correlated with the average change in angular velocities, whereas that of the late one was best correlated with average changes in torque resulting from the perturbation. The data are consistent with the hypothesis that the two components have different anatomical substrates and that they have different functional implications for the stabilization of the limb in the face of perturbations.

Arm↗

PubMed1987

Organization of arm movements. Motion is segmented.

A kinematic analysis of human arm trajectories which underlie the production of learned, continuous movements (such as drawing of 'figure 8s' and stars) in free space is presented. The objective of this investigation was to see if a set of rules, which had been identified previously and which are appropriate for generating circular or elliptical motion of the wrist in an arbitrary plane, also hold true for arbitrary, learned trajectories provided one additional assumption is made: that apparently continuous complex movements are composed of unit segments. The results presented in this paper are consistent with this hypothesis. Furthermore, as predicted by the hypothesis, the wrist trajectory deviates little from planar motion in each segment while the plane of motion can change abruptly from one segment to the next.

Arm↗

PubMed1987

Organization of arm movements in three-dimensional space. Wrist motion is piecewise planar.

It is shown that human subjects are incapable of producing with the arm, in free space, planned or extemporaneously drawn trajectories in which the plane of wrist motion changes smoothly or continuously. The three-dimensional nature of these movements results from the fact that the plane of motion changes abruptly from one segment of the trajectory to the next, being confined to one plane during each segment (i.e. piecewise planar).

Arm↗

PubMed1987

A note on the kinematcis of drawing movements in children.

The relationship between instantaneous tangential velocity and radius of curvature (power 1/3) that is characteristic of adult subjects was found to be already present in children 3 to 11 years old. The correlation coefficient between these two parameters increases gradually with age without apparent discontinuities. However, even at the upper limit of the age range examined, the values are still lower than in the adults.

Journal Article↗

PubMed1987

Changes in spatial scale in drawing and handwriting: kinematic contributions by proximal and distal joints.

The coordination of arm and hand motions was studied in tasks involving drawing and handwriting movements of different amplitudes. To this end, pen motion was recorded by means of a digitizing table, while the positions of different markers on the limb were monitored by the ELITE system. It was found that the amplitude of shoulder and elbow angular motions scales roughly with the size of the figure drawn or of the script, whereas the amplitude of wrist and finger motions is small, independent of size. Consequently, the larger the limb movement, the smaller the magnitude of the contributions by motions at distal joints relative to that at proximal joints. Furthermore, while shoulder and elbow motions are tightly coupled (constant phase relation), motions at distal joints are loosely coupled to those at the proximal joints (variable phase relation). On the other hand, motion at distal joints increases the accuracy of the movement, as indicated by the smaller variability of pen trajectories compared to that of wrist trajectories.

Art↗

PubMed1986

EMG responses to load perturbations of the upper limb: effect of dynamic coupling between shoulder and elbow motion.

Load perturbations were applied to the arm of human subjects under conditions where both limb segments (upper arm and forearm) were free to move. The perturbations consisted of pulses of torque 50 ms in duration and of pseudo-random sequences of such pulses. They were applied to either the forearm or the upper arm. Under all conditions, the perturbations resulted in angular motion at the shoulder and elbow joints and evoked consistent responses in muscles acting about these joints (biceps, triceps, anterior and posterior deltoid). Activity in biceps and triceps was not related simply to angular motion at the elbow joint. For example, activation of biceps could be evoked during elbow flexion (by applying a torque perturbation at the shoulder) as well as during elbow extension (by applying a torque perturbation at the elbow). The effect of varying degrees of dynamic coupling between upper arm and forearm on EMG responses was investigated by applying torque perturbations to the upper arm over a wide range of elbow angles. When the forearm is extended, such a perturbation induces a greater amount of elbow flexion than when the forearm is in a flexed position. The results of these experiments showed that the larger was the amount of flexion of the forearm induced by the perturbation, the larger was the activation of biceps. The results are incompatible with the notion of a negative feedback of total muscle length as being responsible for the EMG activity following the load perturbations. It is suggested that the EMG responses can best be interpreted functionally in terms of parameters more global than muscle length. Among such global parameters, changes in net torque at a joint resulting from the perturbation gave the best correlation with the pattern of EMG activities observed.

Arm↗

PubMed1986

Responses of mono- and bi-articular muscles to load perturbations of the human arm.

We studied the behavior of muscles acting synergistically in elbow flexion in response to load perturbations. The perturbations were applied either proximally or distally to the elbow joint and consisted of single pulses or steps of torque and of pseudo-random sequences of torque pulses. They produced changes in angular position and torque at both the shoulder and elbow joints. The electromyographic (EMG) responses evoked in biceps, brachio-radialis and brachialis muscles were different when elbow and shoulder motion was in the same direction and when the two angular motions were oppositely directed. For example, elbow extension resulted both when a downward force perturbation was applied to the forearm as well as when a posteriorly directed force applied to the upper arm was released. Elbow flexors were activated at a short latency only in the former case and not in the latter. The modulation of EMG activity in elbow flexors evoked by the perturbations was related to the global motion of the limb, including the angular motions at both the shoulder and elbow joints. The time course of the EMG responses in biceps, which acts on both joints, differed from that of brachio-radialis and brachialis muscles, which act only at the elbow. The results are discussed in the context of the possible mechanisms responsible for the muscle responses to the perturbations.

Arm↗

PubMed1986

Simulation studies on the control of posture and movement in a multi-jointed limb.

Simulation studies were performed to evaluate the effectiveness of different control schemes in stabilizing a multi-jointed limb (human arm) in response to force perturbations. The mechanical properties of the arm were modeled as a linear visco-elastic system and the effectiveness of negative feedback of angular position and torque was evaluated. The effectiveness of a given amount of position feedback depended strongly on the initial position of the arm and on the perturbation, while torque feedback was much more consistently effective in damping the motion of the limb.

Animals↗

PubMed1986

An algorithm for the generation of curvilinear wrist motion in an arbitrary plane in three-dimensional space.

The elements of an algorithm are presented which predicts for some simple forms (circles and ellipses) the kinematic and figural aspects of the trajectories of the human wrist when these are drawn in any arbitrary plane of free, three-dimensional space. The algorithm is based on theoretical considerations and experimental data and specifies in a unique way the angular motion at the shoulder and elbow joints by utilizing a coordinate transformation, which is only approximate, between the chosen extrinsic (trajectory) and intrinsic (joint angles) parameters. A way to extend the use of this algorithm to generate any arbitrary complex movement in all possible planes of space is also suggested.

Algorithms↗

PubMed1986

Coordination of arm movements in three-dimensional space. Sensorimotor mapping during drawing movement.

In this paper data are presented concerning the motion of limb segments during drawing movements executed in different planes in free space. The technique used allows the determination of the wrist and elbow positions in space as well as the measurement of the elbow angle of extension. Other kinematic variables are determined trigonometrically. Elbow and shoulder torque is also calculated. For circles and ellipses, it was found that the motion at the wrist is sinusoidal in two orthogonal directions in the plane of motion. Angular motion, when described by a set of angles previously identified psychophysically as constituting an appropriate coordinate system, is also sinusoidal. Although the number of degrees of freedom of the arm affords many possible ways of performing the task, there is a fixed phase relation between the angles of elevation of the upper arm and forearm for naturally executed movements in all planes of space. Also, the phase of the yaw angles of the upper arm and forearm relative to the angles of elevation are related to the plane of motion and to the slant of ellipses in a fixed manner. There is a simple mapping between angular motion and intended wrist trajectory. Because this mapping is not valid for all planes of space, the actual trajectory can deviate from the intended one. However, the subject has no cognizance of the distortion. The calculated torque deviates substantially from sinusoidal and does change significantly when the same movement is executed in different planes. Results of simulations and mathematical analysis indicate that the fixed phase relationship between angles of elevation leads to a minimal distortion from sinusoidal motion at the wrist in an average sense and that the characteristic distortions observed in the sagittal plane result inevitably from this constraint on the phase relations. The results support the assumption that the topology of the sensorimotor map used for the production of the movement and for its perception is the same. The problem of invariant relationships between kinematic parameters is discussed and the suggestion is made that they represent a general constraint, leading through learning and practice to an optimal solution in an average sense.

Arm↗

PubMed1986

Path constraints on point-to-point arm movements in three-dimensional space.

In this paper data are presented concerning the kinematic and dynamic characteristics of point-to-point arm movements which are inwardly or outwardly directed in three-dimensional space. Elbow and wrist position as well as elbow angle of extension were measured. From these data, other angles were computed trigonometrically and elbow and shoulder torques were calculated. Some of the angles describing arm and forearm motion were found to be linearly related for any given movement. Changes in shoulder and elbow torque were found to be similar to those described for movements restricted to one degree of freedom. Shoulder and elbow motions were not affected when it was required that the orientation of the hand in space remain constant. These observations were taken to indicate that shoulder and elbow motions are tightly coupled for movements in three-dimensional space and that wrist motion has no influence on this coupling. Linear relations between angles express such coupling. They are taken to result from functional constraints and may facilitate the mapping between extrinsic and intrinsic coordinate systems. Some of the observations pertaining to the torque lead to the hypothesis of a further constraint limiting the number of possible trajectories in a point-to-point movement.

Arm↗

PubMed1984

Behavior of the stretch reflex in a multi-jointed limb.

When an external perturbation acts on a segment of a multi-jointed limb, angular motion results in all limb segments which are inertially linked to the one which is perturbed. In such a situation, different hypotheses on the functional role of the stretch reflex lead to different predictions on reflex responses by the stretched muscles. These predictions were examined experimentally and it was found that the EMG responses of elbow muscles evoked by forces applied to either the upper arm or the forearm were not uniquely related to changes in elbow angular position. They were instead correlated with the direction of changes in the net elbow torque resulting from the perturbation.

Arm↗

PubMed1984

Effect of target size on spatial and temporal characteristics of a pointing movement in man.

The effects of constraints related to movement accuracy on the spatial and temporal characteristics of pointing movements of the arm to a target were investigated. It was found that movement time increased, even at slow speeds, when target size decreased. Spatial variability of the trajectory of the index finger was also reduced, but only in proximity to the target, when higher accuracy was demanded while variability of motion at the wrist showed little change. The effect of varying the angular orientation of the target on the trajectories of the wrist and finger was also investigated. The data support the hypothesis that motion at the shoulder and elbow joints, which is closely linked, is determined primarily by target position while motion at the wrist joint, which is only loosely coupled to the motion at the more proximal joints, is related principally to the angular orientation of the target in space. The data also suggest that wrist motion is controlled separately from motion at the more proximal joints.

Adult↗

PubMed1984

Psychophysical determination of coordinate representation of human arm orientation.

The coordinate representation of the sense of limb orientation was investigated psychophysically by asking subjects to match the orientation of the arm or of the forearm in several different coordinate representations. Movement of all degrees of freedom of one arm was permitted while movement of the other limb was restricted to the degree of freedom investigated in that particular experiment. Performance on the tasks was assessed by calculating the standard deviation of the difference in the angles of the two limbs. According to this criterion, we suggest that limb orientation is represented by the angular elevation of the limb and by the yaw angle, referred to a spatial reference frame.

Arm↗