[The dependence of motor response time in discrimination task on the type of available visual information].

The interaction of proprioceptive and visual afferentation was studied in motor task for discrimination of weights of falling objects. The availability of visual information decreased the time of motor response but to different extent depending on the kind of this information. The shortening of response time was significantly greater when subject have seen the beginning of real fall that when he simply seen the control LED signaling the release of object by electromagnet. So, subject accomplishes the task of discrimination of light and heavy object more efficiently if he sees the real falling object. This may be due to the capacity of CNS to predict the time of the impact more accurately when subject observe the initial part of real trajectory and not just an abstract visual signal.

Load detection and discrimination in a catching task: role of haptic and auditory information.

The aim of this study was to verify the contribution of haptic and auditory cues in the quick discrimination of an object mass. Ten subjects had to brake with the right hand the movement of a cup due to the falling impact of an object that could be of two different masses. They were asked to perform a quick left hand movement if the object was of the prescribed mass according to the proprioceptive and auditory cues they received from object contact with the cup and did not react to the other object. Three conditions were established: with both proprioceptive and auditory cues, only with proprioceptive cue or only with an auditory cue. When proprioceptive information was available subjects advanced responses time to the impact of the heavy object as compared with that of the light object. The addition of an auditory cue did not improve the advancement for the heavy object. We conclude that when a motor response has to be chosen according to different combinations of auditory and proprioceptive load-related information, subjects used mainly haptic information to fast respond and that auditory cues do not add relevant information that could ameliorate the quickness of a correct response.

[Participation of the primary motor cortex in programming of muscle activity during catching of falling object].

Object fell into the cup that sitting subject held between thumb and index fingers. Transcranial magnetic stimulation (TMS) of the primary motor cortex was performed early before and during anticipatory grip force increasing. Comparison of current EMG activity of adductor pollicis brevis and first dorsal interosseous muscles and responses of these muscles on TMS showed that responses were increased before the raising of muscle activity. From the other side only slight augmentation of responses was observed during subsequent strong muscle activation. It is assumed that the increasing of the TMS responses that occurred before the initiation of muscle activity reflects the enhancement ofthe motor cortex excitability associated to specific processes related to the motor cortex participation in programming of the muscles activities.

[Internal reference frame for representation and storage of visual information during standing].

The participation of different afferent systems in organization of internal reference frame was studied. For this was chosen the task of visual comparison that executed in different experimental conditions: in upright standing, with inclined body or head in frontal plane and availability or non-availability visual information about external environment. Results showed that dominant orientation of referent stimulus (minimal value of mean error and minimal variability of responses) was connected with body position, mainly head position but not with gravity and visual vertical even when visual environment was available. It means that for creating the internal representing of vertical CNS mainly uses proprioceptive information about longitudinal axis of body.

[Dependence of anticipatory grip force in catching task on previous trial].

Heavy or light object fell into the cup that sitting subject held between thumb and index fingers. A grip force applied to the cup was measured at the moment of impact. The grip force was stronger in trials following the trial with heavy object than after the trial with light object independently of object weight in the current trial. It means that the anticipatory grip force was planned accounting the result of previous trial.

[Influence of preliminary information about mass on anticipatory muscle activity during catching of falling object].

Heavy or light object fell into the cup held between thumb and index fingers of sitting subject. The anticipatory muscle activity and the grip force applied to cup depended on the mass of object while the temporal parameters (time of beginning of muscle activity, duration of the activity, the time of grip force maximum) were constant. The preliminary verbal information about mass of the falling object was enough for predictive force programming. Without such information, i.e. during fall the object of unknown mass the anticipatory activity was planned in expectation of heavy weight.

[Errors in targeted movements of the hand under the conditions of orbital space flight]. / Oshibki tselevykh dvizhenii ruki v usloviiakh orbila'nogo poleta.

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.

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.

[Study of the microgravity effect on the inertia of mental tracking of moving objects]. / Issledovanie vliianiia nevesomosti na inertsiiu myslennogo proslezhivaniia dvizhushchikhsia ob"ektov.

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.

[The effect of weightlessness on sensorimotor interaction during operator activity: visual feedback. Motor response latency time]. / Vliianie nevesomosti na sensomotornoe vzaimodeistvie pri operatorskoi deiatel'nosti: zritel'naia obratnaia sviaz'. Latentnoe vremia dvigatel'nogo otveta.

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.

[Effects of weightlessness on sensorimotor interaction in the operator'work: proprioceptive feedbacks]. / Vliianie nevesomosti na sensomotornoe vzaimodeistvie pri operatorskoi deiatelnosti:propriotseptivnye obratnye sviazi.

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.

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.

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.