Visual-manual tracking during a five-day dry immersion

The effect of low proprioceptive, tactile, and support afferentation on visual-manual tracking was determined using a five-day horizontal dry immersion, which provided support deprivation, as well as minimization of muscle activity and proprioceptive afferentation, simulating the physiological effects of microgravity. Hand-eye motor coordination was studied in the 13 subjects participating in the experiment with five-day dry immersion who tracked the jumpy and smooth movements of a point visual stimulus (linear and pendulum-like; horizontal and vertical; circular, clockwise and counterclockwise). Ocular movements were recorded using binocular electrooculography; and manual motions were recorded using a joystick with a biological visual feedback, when one of the two stimuli on the screen showed the current joystick tilt. Computerized stimulation was provided using virtual reality goggles. The following parameters were evaluated: the latent and total reaction time; the amplitudes and velocities of the eye and hand movements; and the coefficients of effectiveness (amplitude ratio) and the gain (velocity ratio). The examinations were performed before immersion, after 3 h of immersion, on days 3 and 5 of immersion, during the first hours after the termination of immersion, and three days after the immersion (in all subjects); and on days 5–7 after the immersion (in four subjects). It was shown that support deprivation and minimization of proprioceptive afferentation affected ocular tracking to a larger extent than the accuracy of manual movements following the visual stimulus. It was found that, in all subjects, manual tracking, which did not significantly change during the test sessions, was more accurate than visual tracking; in contrast, the accuracy of visual tracking changed noticeably both in the course of dry immersion and after its termination.     

The effects of support-proprioceptive deprivation on visual-manual tracking and vestibular function

In order to determine the effects of support and proprioceptive afferentation on the characteristics of visual-manual tracking (VMT), we used a model of weightlessness—horizontal dry immersion. Altogether 30 subjects who stayed in the immersion bath from 5 to 7 days were examined to evaluate the accuracy of the VMT in tasks to pursue the jerky (saccadically) and smooth (linear, pendular and circular) movement of a point visual stimulus. Examinations were performed before, during and after immersion using electrooculography (to record eye movements) and a joystick (to record hand movements) with a biological visual feedback—one of the two visible stimuli on the screen matched the current angle of the joystick handle. Computerized visual stimulation programs were presented to subjects using virtual-reality glasses. We analyzed the time, amplitude and velocity characteristics of the visual and manual tracking (VT and MT respectively), including the efficiency ratio (eVT and eMT) and the gain (gVT and gMT) as the respective ratios of the amplitudes and velocities of the eyes/hand movements to the stimulus movement. eVT was significantly reduced in comparison to the baseline all the time, while the subject lay in the immersion bath and until R+4 day after immersion. eMT decreased significantly only on I-1 and I-3 days of immersion. gVT significantly differed from the baseline only on I-3 and I-6 days of immersion and R+1 day after immersion. We found no significant changes in gMT. Evaluations of the vestibular function (VF) were performed before and after immersion using videooculography. We analyzed the static torsional otolith-cervical-ocular reflex (OCOR), the dynamical vestibular-cervical-ocular reactions (VCOR), spontaneous eye movements (SpEM), and the accuracy of the perception of the subjective visual vertical (SVV). After immersion, 47% of all subjects had a significant reduction of OCOR with a simultaneous significant increase of VCOR on 37% of subjects, as well as significant changes in the accuracy of the perception of the SVV, which correlated with changes in OCOR. We found a correlation between characteristics of the VT and MT and between the characteristics of the VF and VT, but we found no correlation between VF and MT. We discovered that removal of the support and minimization of the proprioceptive afferentation has a greater impact upon the accuracy of the VT than the accuracy of the MT.     

Effect of optokinetic stimulation on visual–manual tracking under the conditions of support-proprioceptive deprivation

The effects of additional dynamic visual stimuli (retinal optokinetic stimulation (ROKS)) on the visual–manual tracking (VMT) indicators in the absence of support afferentation and with a reduced level of proprioceptive afferentation were determined using a model of horizontal “dry” immersion. The accuracy of the VMT of jerky and smooth (linear, pendular, and circular) movements represented by visual dot stimuli was evaluated in all 18 participants aged 19–31 before, during and after their exposure to a five- to seven-day immersion bath. The eye movements were recorded by electrooculography, while the hand movements were recorded by a joystick with a biological visual feedback (the current angle of the joystick handle was imaged on the screen). Computerized visual stimulation tests were presented, through virtual reality glasses, to subjects in the absence and against the background ROKS. We analyzed the temporal and the amplitude- and velocity-related visual and manual tracking (VT and MT) characteristics, including the efficiency (e) and gain (g) coefficients as the ratios between the amplitudes and velocities of eye/hand movements and the amplitude of stimulus movements. The efficiency and gain coefficients of both VT and MT without ROKS were significantly decreased against the baseline during the entire period including three days of immersion and 3 post-immersion days. The most pronounced worsening was observed in the VT parameters. Whereas the VT and MT parameters remained unchanged against the threshold ROKS before the immersion, they were improved during and after the immersion (the improvement was significant on the fifth to seventh day of immersion and on the thirdthird post-immersion day, compared to the test indicators on the clean screen). The most pronounced impact of ROKS was observed in the VT parameters. The vestibular function (VF) was evaluated by videooculography before and after immersion. We analyzed the static torsional otolith-cervicalocular reflex (OCOR), dynamic vestibular-cervical-ocular reactions (VCOR), vestibular reactivity (VR), and spontaneous eye movements (SpEM). A significant decrease in OCOR (gOCOR was 0.1, compared to the background gOCOR value of 0.25) was detected alongside a simultaneous significant increase in the VCOR/VR parameters in 28% of subjects on day R + 1 after immersion. Correlational has been found between the parameters of VT and MT, as well as between those of VF and VT, but no correlation has been found between the VF and MT characteristics. The results have shown that the removal of support afferentation and the minimization of proprioceptive afferentation more affected the accuracy of VT rather than that of MT. The correlational links between the studied parameters against the background of ROKS were not only preserved, but also intensified. The obtained results confirm the development of sensory deprivation (and afferent deficit) under the exposure to an immersion bath and indicate the approach to correcting the sensory deprivation through additional ROKS.     

Visual–manual tracking after long spaceflights

This study presents the results of the pre- and postflight clinical and physiological examination (CPE) and scientific experiment “Sensory Adaptation-2” at the Gagarin Research and Test Cosmonaut Training Center, which involved 14 Russian cosmonauts, crewmembers of long-term international spaceflights ISS-28/29 to ISS 36/37, who were in microgravity from 159 to 195 days. The cosmonauts were aged 35–50 years. The studies were conducted twice before the spaceflight (the background), as well as on days R+1(2), R+4(5), and R+8(9) after landing. In the study of visual–manual tracking (VMT), eye movements were recorded by the electrooculography method (EOG), and hand movements were recorded by a joystick (the screen represented the current tilt angle of a joystick handle). The examinations were conducted using stimulation computer programs, were presented to an examined subject on the screen of the Sensomotor hardware–software complex. The examinations took place in the dialog mode and included the EOG calibration; VMT within ±10° on the screen with blank background (the smooth linear and sinusoidal movement of a point target with a frequency of 0.16 Hz in the vertical and horizontal directions). The study estimated the time, amplitude, and velocity characteristics of visual and manual tracking (VT and MT), including the effectiveness (ec) and gain (gc) coefficients as the ratios of the amplitude and velocity of eye/hand movements to the amplitude and velocity of the visual stimulus. The study of the vestibular function (VF) was performed before and after the spaceflight using videooculography. The static torsion otolith–cervical–ocular reflex (OCOR), dynamic vestibular–cervical–ocular reactions (VCOR), vestibular reactivity, and spontaneous eye movements were assessed. The study of VF in the first postflight days has shown a sharp decrease (up to its complete absence) of static vestibular excitability accompanied by the increased dynamic reactivity of the vestibular system. The study of VTM in the first postflight days has shown a significant decrease in the ec and gc of VT as well as correlations between the parameters of VT and MT and between the parameters of VF and VT and has not found a correlation between the parameters of VF and MT. The conditions of the spaceflight have been revealed to affect the accuracy of VT more strongly than the accuracy of MT. A complete return of the characteristics of VMT and VF to the baseline was observed on R+8(9) days after the spaceflight.     

Stabilization of the gaze in chameleons: visual and vestibular reflexes

Some visual, vestibular and proprioceptive reflexes which contribute to gaze (head + eye) stabilization were quantified in the chameleon. All the reflexes were analysed in the horizontal plane, and the visual reflexes were also studied in the vertical plane. In restrained-head animals, both the optokinetic nystagmus (OKN) and the vestibulo-ocular reflex (VOR) had low gains. In free-head animals, the head (opto-collic or vestibulo-collic reflex) and eye (OKN or VOR) responses added their effects, thus improving gaze stabilization, especially during vestibular stimulation. Cervical stimulation provoked both a cervico-ocular reflex (COR) in the compensatory direction and a large number of saccades. The saccadic response was especially marked in the presence of patterned visual surroundings.     

Effect of real and simulated weightlessness on the characteristics of the static otolith reflex

To determine the role of the support-proprioceptive factor in functioning of the vestibular system, in particular, the role of static torsional otolith-cervical-ocular reflex (OCOR), the latter was studied in 16 subjects after a seven-day “dry” horizontal immersion and in 14 cosmonauts after a prolonged exposure to weightlessness (for 126–195 days). OCOR was studied by the videooculography method during alternately tilting the head towards the right or left shoulder by an angle of 30° in the frontal plane before the flight and before immersion, as well as on days 1, 3, and 7 after the completion of the immersion experiment and on days 1 (2), 4 (5), and 8 (9) after the spaceflight. For the first time it was demonstrated that elimination of the support and minimizing the proprioceptive afferentation may lead to the absence or inversion of the static torsional OCOR, as well as to a positional nystagmus against the background of the inverted reflex. Comparison of OCOR in cosmonauts after prolonged exposure to weightlessness and in the subjects examined after immersion revealed similarity in this reaction. However, changes in OCOR after immersion were encountered only in 60% of the subjects, whereas after the spaceflight, in 90% of the cosmonauts examined. The post-flight changes in OCOR were more pronounced and long-lasting.     

Time constants of vestibular nuclei neurons in the goldfish: A model with ocular proprioception

A simple model of the vestibular-ocular reflex with a proprioceptive eye velocity feedback loop is used to simulate recent data on the vestibular responses of neurons in the vestibular nuclei of spinal goldfish. The data support the hypothesis that a proprioceptive feedback loop elongates the vestibular nucleus time constant to equal that of the slow phase eye movements of vestibular nystagmus.     

Dynamic Reweighting of Three Modalities for Sensor Fusion

We simultaneously perturbed visual, vestibular and proprioceptive modalities to understand how sensory feedback is re-weighted so that overall feedback remains suited to stabilizing upright stance. Ten healthy young subjects received an 80 Hz vibratory stimulus to their bilateral Achilles tendons (stimulus turns on-off at 0.28 Hz), a ±1 mA binaural monopolar galvanic vestibular stimulus at 0.36 Hz, and a visual stimulus at 0.2 Hz during standing. The visual stimulus was presented at different amplitudes (0.2, 0.8 deg rotation about ankle axis) to measure: the change in gain (weighting) to vision, an intramodal effect; and a change in gain to vibration and galvanic vestibular stimulation, both intermodal effects. The results showed a clear intramodal visual effect, indicating a de-emphasis on vision when the amplitude of visual stimulus increased. At the same time, an intermodal visual-proprioceptive reweighting effect was observed with the addition of vibration, which is thought to change proprioceptive inputs at the ankles, forcing the nervous system to rely more on vision and vestibular modalities. Similar intermodal effects for visual-vestibular reweighting were observed, suggesting that vestibular information is not a “fixed” reference, but is dynamically adjusted in the sensor fusion process. This is the first time, to our knowledge, that the interplay between the three primary modalities for postural control has been clearly delineated, illustrating a central process that fuses these modalities for accurate estimates of self-motion.     

Effects of vestibular and support afferentation upon visual pursuit in microgravity

Evaluation of the accuracy of eye turns (saccades) to fix a jerky pointed stimulus, and smooth pursuit of slow linear and sinusoidal movements of both pointed and optokinetic stimuli was performed in 31 cosmonauts on flight days 2-3, 5-8, 30, and once in one or two months of mission. An additional investigation of the eye pursuit function involved 10 cosmonauts, who, after testing during free floating, fulfilled stimulus tracking following a cycle of active head rotation, and 14 cosmonauts who received support afferentation. It was found that at the beginning of adaptation and periodically in the course of long mission, the systems of slow pursuit tracking adopted the strategy of saccadic approximation whereby gaze fixation was achieved through a sequence of macro- or microsaccadic movements. It was demonstrated that these disturbances, practically in all investigated cosmonauts, were consequent to the vestibular deprivation developing in microgravity. Vestibular afferentation produced by active head rotation improved characteristics of visual pursuit. Support deprivation also affects pursuit tracking by cosmonauts who form the concept of space orientation based on perception of their head and leg position. With support afferentation, these cosmonauts demonstrated improved visual pursuit characteristics.     

Cross-Modal Calibration of Vestibular Afference for Human Balance

To determine how the vestibular sense controls balance, we used instantaneous head angular velocity to drive a galvanic vestibular stimulus so that afference would signal that head movement was faster or slower than actual. In effect, this changed vestibular afferent gain. This increased sway 4-fold when subjects (N = 8) stood without vision. However, after a 240 s conditioning period with stable balance achieved through reliable visual or somatosensory cues, sway returned to normal. An equivalent galvanic stimulus unrelated to sway (not driven by head motion) was equally destabilising but in this situation the conditioning period of stable balance did not reduce sway. Reflex muscle responses evoked by an independent, higher bandwidth vestibular stimulus were initially reduced in amplitude by the galvanic stimulus but returned to normal levels after the conditioning period, contrary to predictions that they would decrease after adaptation to increased sensory gain and increase after adaptation to decreased sensory gain. We conclude that an erroneous vestibular signal of head motion during standing has profound effects on balance control. If it is unrelated to current head motion, the CNS has no immediate mechanism of ignoring the vestibular signal to reduce its influence on destabilising balance. This result is inconsistent with sensory reweighting based on disturbances. The increase in sway with increased sensory gain is also inconsistent with a simple feedback model of vestibular reflex action. Thus, we propose that recalibration of a forward sensory model best explains the reinterpretation of an altered reafferent signal of head motion during stable balance.     

The effect of a long stay under microgravity on the vestibular function and tracking eye movements

Pre-and postflight examinations of cosmonauts participating in missions ISS-3 to ISS-9 on the International Space Station were performed using a computer-aided method of integrated assessment of the oculomotor system. The role and significance of the vestibular system in the eye tracking were determined; the individual and general characteristics of spontaneous oculomotor reactions and oculomotor reactions induced by visual and vestibular stimuli after a long-term stay at zero gravity (126–195 days) were determined; and the changes in the indices of oculomotor reactions were monitored. Studies of the vestibular function, intersensory interactions, and the tracking function of the eyes in the crew members were performed on the second, fifth (sixth), and ninth (tenth) days of the readaptation period. The results of the postflight examinations showed a significant change in the accuracy, velocity, and temporal characteristics of eye tracking and an increase in the vestibular reactivity. It was shown that the structure of visual tracking (the accuracy of fixational eye rotations and smooth tracking) was disturbed (the appearance of correcting saccades, the transition of smooth tracking to saccadic tracking) only in those cosmonauts who, in parallel to an increased reactivity of the vestibular input, also had central changes in the oculomotor system (spontaneous nystagmus, gaze nystagmus). With one exception, recovery of the indices of the accuracy of tracking eye movements in cosmonauts to the background level in the selected period of examination was not observed, although a positive trend was recorded.     

Effect of a real and simulated weightlessness on characteristics of the static torsional otolith-cervical-ocular reflex

To determine the role of the support-proprioceptive factor in the functioning of the vestibular system, in particular the static torsional otolith-cervical-ocular reflex (OCOR), comparative OCOR studies with videooculography recording were performed after a 7-day "dry" horizontal immersion (16 immersion subjects) and after a prolonged (126 to 195 days) exposure to weightlessness (14 ISS cosmonauts). For the first time it was demonstrated that minimization of the support and propripceptive afferentation may results in an inversion or absence of the static torsional OCOR and the development of a positional nystagmus with an inverted reflex. A comparative OCOR data analysis of cosmonauts and immersion subjects has revealed similarity of responses. However, changes in OCOR after immersion were noted in only 60% of subjects, while after space fight, 90% of cosmonauts showed them. Post-flight changes were more frequent, marked and long-lasting.     

The effects of simulated microgravity on characteristics of slow presaccadic potentials

The parameters of saccades and presaccadic slow potentials were studied in seven right-handed male volunteers with a dominant right eye before and after exposure to 6-day dry immersion. Visual stimuli were presented using three light diodes, which were located in the center of the visual field (the central fixation stimulus) and 10° to the right and left of it (peripheral stimuli (PSs)). The subjects performed a test with simple saccades to a PS and a test with antisaccades to the point located symmetrically in the opposite visual field. The EEG (19 monopolar leads) and electrooculogram were recorded. To isolate slow potentials, backward EEG averaging was performed, with the moment of switching on the PS serving as a trigger for the averaging. It was found that the characteristics of saccadic eye movements did not substantially change after exposure to immersion. However, both tests revealed a change in topography and a decrease in the amplitude of presaccadic slow negative potentials (PSNPs) during immersion. Characteristically, the focus of presaccadic negativity shifted to the right hemisphere so that the PSNP amplitude sharply decreased in the left and increased in the right hemisphere. A significant decrease in the PSNP amplitude on day 6 of immersion was found in the midline and left-hemispheric frontal and parietal leads. It may be suggested that, because of support unloading and a decrease in proprioceptive input, exposure to microgravity causes a decrease in the activity of the left hemisphere and prefrontal and parietal cortices, initially involved in preparation and realization of motor responses. The activation of the right hemisphere could be of compensatory character.     

Normal gait is differentially influenced by the otoliths

Postural control depends on the integration of vestibular, somatosensory and visual orientation signals. The otolith contribution to postural control is achieved by the integration of otolith inputs and peripheral afferent inputs involved in crossed reflex pathways. This study shows that a functional linkage between otolith signals and activity in lower limb muscles is detectable in normal human gait. The otolith input appears to dominate particularly the neck proprioceptive and gaze motor influences during normal gait. This is demonstrated by an increase of tibialis anterior muscle activity during retroflexion of the head/neck, leading to an increased stability and counteracting possible perturbations. It is also shown by decrease of coordination during the movement caused by larger displacement of the centre of gravity demonstrated in vector diagrams.     

The influence of support withdrawal on presaccadic EEG potentials in subjects with different asymmetry profiles

Characteristics of saccades and parameters of slow presaccadic potentials were studied in 12 volunteers, including seven subjects with a leading right eye (the RE group) and five subjects with a leading left eye (the LE group) before and on the sixth day of dry immersion. For visual stimulation, three light-emitting diodes were used; one of them was located in the center of the visual field, and two other, 10° away from the horizontal axis to the right and left of the first one. The subjects performed an anti-saccade test, which included making saccades at the spot that was symmetrically located in the visual field opposite to the stimulus. The EEG (19 standard unipolar derivations) and electrooculogram were recorded. To obtain slow presaccadic potentials (PSPs), backward averaging triggered by switching on a peripheral stimulus was performed. Before the immersion, there were no significant differences in the characteristics of saccades in both groups of subjects. At the same time, the amplitude of presaccadic negativity (PSN) in the LE group was decreased, especially in the frontal region, and had considerable asymmetry during the analysis. During the immersion, the latent periods of the saccades and the percentage of incorrect reactions did not change in RE subjects and were increased in LE subjects. Both groups demonstrated a decrease in the PSN amplitude and its shift to the right hemisphere; intergroup differences decreased in immersion conditions. The characteristic feature of the RE group was a significant decrease in PSN in frontal leas at immersion, apparently caused by sensory disintegration and a decrease in the tonic afferent input. In the LE group, the maximal amplitude of PSN was observed in the central region.     

Intrinsic and synaptic plasticity in the vestibular system

The vestibular system provides an attractive model for understanding how changes in cellular and synaptic activity influence learning and memory in a quantifiable behavior, the vestibulo-ocular reflex. The vestibulo-ocular reflex produces eye movements that compensate for head motion; simple yet powerful forms of motor learning calibrate the circuit throughout life. Learning in the vestibulo-ocular reflex depends initially on the activity of Purkinje cells in the cerebellar flocculus, but consolidated memories appear to be stored downstream of Purkinje cells, probably in the vestibular nuclei. Recent studies have demonstrated that the neurons of the vestibular nucleus possess the capacity for both synaptic and intrinsic plasticity. Mechanistic analyses of a novel form of firing rate potentiation in neurons of the vestibular nucleus have revealed new rules of plasticity that could apply to spontaneously firing neurons in other parts of the brain.     

The use of matrices in analyzing the three-dimensional behavior of the vestibulo-ocular reflex

The vestibulo-ocular reflex rotates the eye about the axis of a head rotation at the same speed but in the opposite direction to make the visual axes in space independent of head motion. This reflex works in all three degrees of freedom: roll, pitch, and yaw. The rotations may be described by vectors and the reflex by a transformation in the form of a matrix. The reflex consists of three parts: sensory, central, and motor. The transduction of head rotation into three neural signals, which may also be described by a vector, is described by a canal matrix. The neural, motorcommand vector is transformed to an eye rotation by a muscle matrix. Since these two matrices are known, one can solve for the central matrix which gives the strength of the connections between all the vestibular neurons and all the eye-muscle motoneurons. The role of the metric tensor in these transformations is described. This method of analysis is used in three applications. A lesion may be simulated by altering the elements in any or all of the three component matrices. By matrix multiplication, the resulting abnormal behavior of the reflex can be described quantitatively in all degrees of freedom. The method is also used to directly compare the differences in brain-stem connections between humans and rabbits that accommodate the altered actions of the muscles of the two species. Finally the method allows a quantitative assessment of the changes that take place in the brainstem connections when plastic changes are induced by artificially dissociating head movements from apparent motion of the visual environment.     

Effect of seven-day dry immersion on the mechanisms of ocular saccadic movement generation

In order to evaluate the impact of prolonged support deprivation on the mechanisms of ocular saccadic movement generation, four volunteers were tested immediately before seven-day dry immersion and on the day of its completion. The task consisted of tapping random light stimuli emerging on the periphery of a sensory screen. During testing, the subject??s head was kept in a fixed position. The subjects could suppress the stimuli in two ways: (1) by touching an appropriate area on the screen with their fingers with gaze shifting and fixation accompanying coordinated hand movement or (2) by clicking the computer mouse button after gaze fixation on the stimulus. The movement pattern of each eye was recorded and analyzed in the infrared frequency of 200 Hz. It is assumed that the identical effects of immersion on the dependence of the peak saccade velocity on its amplitude in tests where the two methods of stimulus tapping were used suggest saccade acceleration after immersion as a direct effect of prolonged support deprivation.     

Mathematical requirements of visual–vestibular integration

This article addresses the intersection between perceptual estimates of head motion based on purely vestibular and purely visual sensation, by considering how nonvisual (e.g. vestibular and proprioceptive) sensory signals for head and eye motion can be combined with visual signals available from a single landmark to generate a complete perception of self-motion. In order to do this, mathematical dimensions of sensory signals and perceptual parameterizations of self-motion are evaluated, and equations for the sensory-to-perceptual transition are derived. With constant velocity translation and vision of a single point, it is shown that visual sensation allows only for the externalization, to the frame of reference given by the landmark, of an inertial self-motion estimate from nonvisual signals. However, it is also shown that, with nonzero translational acceleration, use of simple visual signals provides a biologically plausible strategy for integration of inertial acceleration sensation, to recover translational velocity. A dimension argument proves similar results for horizontal flow of any number of discrete visible points. The results provide insight into the convergence of visual and vestibular sensory signals for self-motion and indicate perceptual algorithms by which primitive visual and vestibular signals may be integrated for self-motion perception.     

Motor reactions and vestibular reflexes in cats and monkey in weightlessness

Close morpho-functional relationships of the cerebellum and vestibular system at all stages of phylogenesis of vertebrates suggest that cerebellum can be regarded as an important center of gravireceptive function. Direct examination of electrical activity of the labyrinth in cats during transient (1-2 sec) state of weightlessness produced by free fall has shown that there was an almost two fold increase in both the rate and amplitude of electrical activity in the vestibular ganglion. It is commonly accepted at present time that the conditions of orbital flight around Earth closely connect with weightlessness that usually manifests itself as undesirable factor of flight. It is known, that vestibular, proprioceptive, visual and other sensory modalities are converted on the cerebellum, which would indicate that this information is used for motor coordination and spatial orientation. Undoubtedly, origin of many vestibulo-motor disturbances during flight and in postflight period to a considerable degree depends on weightlessness. On the whole the visual illusions, motor discoordination, and space sickness, including vomiting are referred to the "space adaptation syndrome." But nature of these disturbances still is not well understood. This investigation was dedicated to study of vestibular and motor reactions of cats and monkey in short-term microgravity.