PubMed Health⌕ Search

Biomedical subjects

M I Lipshits

Publications and source records attributed to M I Lipshits.

17 recordsLinked to original sources
PubMed1999

[Errors in targeted movements of the hand under the conditions of orbital space flight].

Three crew members of the Russian-French MIR mission were tested to determine errors in pointing to memorized visual targets. In the laboratory, all test-subjects consistently used to point to the spot below the actual target presentation. The mean Y-error (the vertical error) made up -31.6 +/- 21.8 mm. In microgravity, the Y-error moved "upward" so that the mean Y-error was -16.8 +/- 37.0 mm. The data demonstrate adaptation of the central program of aiming arm movement to the microgravity conditions.

Adaptation, Physiological↗
PubMed1995

Measurements of human force control during a constrained arm motion using a force-actuated joystick.

1. When interacting with the environment, human arm movements may be prevented in certain directions (i.e., when sliding the hand along a surface) resulting in what is called a "constrained motion." In the directions that the movement is restricted, the subject is instead free to control the forces against the constraint. 2. Control strategies for constrained motion may be characterized by two extreme models. Under the active compliance model, an essentially feedback-based approach, measurements of contact force may be used in real time to modify the motor command and precisely control the forces generated against the constraint. Under the passive compliance model the motion would be executed in a feedforward manner, using an internal model of the constraint geometry. The feedforward model relies on the compliant behavior of the passive mechanical system to maintain contact while avoiding excessive contact forces. 3. Subjects performed a task in which they were required to slide the hand along a rigid surface. This task was performed in a virtual force environment in which contact forces were simulated by a two-dimensional force-actuated joystick. Unknown to the subject, the orientation of the surface constraint was varied from trial to trial, and contact force changes induced by these perturbations were measured. 4. Subjects showed variations in contact force correlated with the direction of the orientation perturbation. "Upward" tilts resulted in higher contact forces, whereas "downward" tilts resulted in lower contact forces. This result is consistent with a feedforward-based control of a passively compliant system. 5. Subject responses did not, however, correspond exactly to the predictions of a static analysis of a passive, feedforward-controlled system. A dynamic analysis reveals a much closer resemblance between a passive, feedforward model and the observed data. Numerical simulations demonstrate that a passive, dynamic system model of the movement captures many more of the salient features observed in the measured human data. 6. We conclude that human subjects execute surface-following motions in a largely feedforward manner, using an a priori model of the surface geometry. The evidence does not suggest that active, real time use of force feedback is used to guide the movement or to control limb impedance. We do not exclude, however, the possibility that the internal model of the constraint is updated at somewhat longer latencies on the basis of proprioceptive information.

Arm↗
PubMed1995

[Study of the microgravity effect on the inertia of mental tracking of moving objects].

Effect of microgravity on operator's ability to mentally track moving objects was investigated during the joint Russian-French space mission in 1992 and the subsequent 6 month Russian mission. Subject was to track a sequence of 4 frames in which 3 points were changing their locations in the manner as if they were moving linearly at a constant speed; after that the subject was to compare the last frame of the sequence with a new, 5th frame in which the points either had the same locations or slightly shifted on the preceding pattern or in opposite direction. Shifting of the points at which their locations in two last frames seemed to be identical was evaluated. The investigation infers that microgravity does not exert any significant influence on the inertia of mental tracking of moving object or there occurs rather quick, within a period of days, adaptation to a new situation.

Adaptation, Physiological↗
PubMed1988

Anticipatory neck muscle activity associated with rapid arm movements.

This study reveals the existence of a backward acceleration of the head prior to the onset of voluntary raising movements of the upper limb. This backward acceleration is produced by the displacement of the head-trunk as a whole. The anticipatory head movement is organized according to a sequence of activation and desactivation of the neck muscles, time locked with the anticipatory leg muscle activity. These findings highlight the existence of a complex postural behavior selected in advance of movement. It is proposed that the feedforward type of neural control of neck muscles should not be interpreted as a compensation to postural perturbation. This anticipatory process might play an important role in the widespread postural fixation of the cervical and dorsal spine.

Arm↗
PubMed1985

Changes of posture during transient perturbations in microgravity.

The control of goal-directed arm movement and of body stability before, during, and 3 d after a 7-d spaceflight has been investigated. The findings show that the anticipatory and compensatory activities of the postural muscles were highly reproducible during the first days of the space mission. The sequence of these activities, studied in two situations--in which the platform either was fixed or could rotate about near the rotation axis of the ankle--was similar to a ground-based situation. The trajectory of various body segments demonstrates that a 7-d exposure to microgravity did not result in major changes in posture. Furthermore, vision seemed to play an important role in the control of standing posture at the beginning of the flight. Postural perturbations, elicited by unexpected displacements of the foot support, involved leg muscle reflexes whose amplitudes were greatly reduced compared to those on earth.

Ankle Joint↗
PubMed1984

Adaptation of postural control to weightlessness.

Adaptation of motor control to weightlessness was studied during a 7-day spaceflight. The maintenance of control of upright posture was examined during a voluntary raising movement of the arm and during the voluntary raising on tiptoe. In order to evaluate the contribution of visual cues, three types of visual situations were examined: normal vision, central vision, and without vision. On the basis of cinematographic and mechanographic data, the postural perturbations consecutive to the movement of a body part in conditions of weightlessness were found to be similar to those observed on earth. However, in weightlessness, in contrast to the ground-based situation, erectness of posture was maintained primarily due to the predominant contraction of the ankle flexor muscles. The sequences of postural leg muscle activity associated with the arm or foot movement were well structured and varied slightly in the course of the flight. In addition, the initial posture, that is the erect posture before the movement was executed, changed throughout the flight from an exaggerated oblique position to a terrestrial standing position. Visual information was preponderant at the beginning of the space mission for the recalibration of other sensory cues affected by weightlessness. The findings are indicative of two types of adaptation of the central program of posture regulation to weightlessness: fast, short-term adaptation, characterized by a quasi-instantaneous redistribution of motor commands between ankle flexors and extensors (an "operative process") and slow, long-term adaptation, exemplified by the loss of anticipatory activation of certain muscles by the end of the flight (a "conservative process").

Adaptation, Physiological↗
PubMedDate not supplied

[The effect of weightlessness on sensorimotor interaction during operator activity: visual feedback. Motor response latency time].

During the second joint French-Soviet space mission efficiency of compensating tracking was investigated in operator by velocity. It was shown that in spite of considerable changes in proprioceptive feedbacks, performance quality remained essentially as preflight. This evidences that visual feedback during operational activity is apt to offset losses in proprioceptive feedbacks.

Feedback↗
PubMedDate not supplied

[Effects of weightlessness on sensorimotor interaction in the operator'work: proprioceptive feedbacks].

During the 2nd Soviet-French Space Flight an operator ability to reproduce from memory the different positions of handles was studied. It is indicated that the temporal parameters of movement and the number of distinguishable positions of handle were not significantly influenced by microgravity effect. However, the accuracy of setting the handle to a given position at the beginning of the flight was significantly lower with an error towards a decrease of handle deflection angle. It is assumed that the cause of this is the proprioceptive feedbacks changes.

Feedback↗