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V Grigorova

Publications and source records attributed to V Grigorova.

17 recordsLinked to original sources
PubMed2006

On the distribution of attention in a visuo-manual adaptation task.

We have observed in a previous study that adaptation to reversed visual feedback in a tracking task is better when subjects are instructed to look at the cursor providing feedback (group C) rather than at the target (group T). Since both groups actually looked at the target, irrespective of their instructions, we suggested that the advantage of group C is not related to their eye movements, but rather to their allocation of spatial attention. The present study scrutinized this view by combining the same adaptation task with a concurrent reaction-time task, designed to spread subjects' attention across the whole display area. Again, subjects were instructed to look at the cursor or at the target, and again, both groups actually looked at the target. Adaptation was similar to group T, and poorer than group C of the previous study. We therefore concluded that adaptation indeed depends on the subjects' allocation of attention: focussing attention mainly on the target, or spreading it across the whole display area, is not as good as distributing attention between target and cursor.

Adaptation, Physiological↗
PubMed2006

The role of eye movements in visuo-manual adaptation.

The present study evaluated the role of eye movements for manual adaptation to reversed vision. Subjects tracked a visual target using a mouse-driven cursor. In Experiment A, they were instructed to look at the target, look at the cursor, fixate straight ahead, or received no instructions regarding eye movements (Groups T, C, F, and N, respectively). Experiment B involved Groups T and C only. In accordance with literature, baseline manual tracking was more accurate when subjects were instructed to move their eyes rather than to fixate straight ahead. In contrast, no such benefit was observed for the adaptive improvement of tracking. We therefore concluded that transfer of information from the oculomotor to the hand motor system enhances the ongoing control of hand movements but not their adaptive modification; probably because the large computational demand of adaptation does not allow an additional processing of supplementary oculomotor signals. We further found adaptation to be worse in T than in any other group. In particular, adaptation was worse in T than in C although eye movements were the same: subjects in both groups moved their eyes in close relationship with the target rather than the cursor, Group C thus disobeying our instructions. The deficient performance of Group T is therefore not related to eye movements per se, but rather to our instructions. We conclude that an independently moving target strongly attracts eye movements independent of instruction (i.e. Groups T and C), but instructions may redirect spatially selective attention (i.e. Group T vs C), and thus influence adaptation.

Adaptation, Physiological↗
PubMed2004

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.

Acoustic Stimulation↗
PubMed2001

[Large uterine myoma during pregnancy and delivery - choice of management].

There are scanty of available data about the management of myoma of the uterus during pregnancy and birth. The authors describe two cases of such a pathology--big myoma of the uterus > 10 sm diameter (d.), who were treated conservatively and ended successfully, without serious complications. The pregnant women were done cesarean section and during the operation the myomas were excisiert. There were no complications intra- and postoperationem. The authors suggest that myectomy during pregnancy and cesarean section must not be don routinely.

Adult↗
PubMed2001

Nonlinear dynamics of human postural sway during upright stance.

We present a procedure for characterizing the postural sway during quiet upright stance using methods of nonlinear dynamics. The displacements of the centre of foot pressure in anterior-posterior and lateral directions were measured using a force platform. We examined the changes of the postural control mechanisms when visual or proprioceptive information are reduced. We applied four analytic procedures to test the nature of posturographic time series: Kolmogorov-Smirnov test for amplitude distribution; shapes of autocorelation functions; structure functions and log-log plots of power spectra. Nongaussian distribution and nonlinear dynamics were established by all tests. The power spectra (PS) exhibited an exponential decreasing shape, which is commonly referred to as "1/f noise". The fractal structure of the process was characterised by fractal dimension (Df) and shape of structure functions. Our results show that the maintenance of postural stability in upright stance and reduced sensory inputs is nonlinear dynamic process with fractal structure.

Adult↗
PubMed2001

Effect of sensory inputs alteration and central sensory disinteraction on postural sway and optokinetic reflex maintaining simultaneously body balance.

We aimed at estimating the effect of central sensory disinteraction on postural sway (PS) and optokinetic reflex (OKR) maintaining concurrently body balance. Healthy humans (N) and patients (P) with multiple sclerosis, and undergone infarct in the middle cerebral artery were examined. They stood on stable platform and foam rubber under three conditions: eyes open; eyes closed; during horizontal central optokinetic stimulation (COKS). On stable platform, a difference between PS of N and P was not found, while on foam rubber, PS of P was significantly greater than PS of N. During COKS on stable platform, PS increased only in P, while on foam rubber it increased in both N and P. OKR gain of N was circa 1 on stable and unstable supports, while that of P was 0.5. We concluded that artificial sensory disinteraction causes strong postural instability, but does not affect OKR.

Adult↗
PubMed2001

Sensory inputs contribution to vestibulo-ocular reflex and postural response maintaining simultaneously body balance.

We investigated which sensor had dominant contribution to vestibulo-ocular reflex (VOR) and postural sway (PS) for the optimal body balance maintenance under conditions of visual or/and somatosensory input reduction. Healthy subjects were examined in upright stance on stable platform and foam rubber, under following conditions: in quiet stance with eyes open (EO) and closed (EC); during voluntary head movements in horizontal plane at frequency 0.2 - 0.3 Hz with EO (HO) and EC (HC). The results showed that PS increased smaller during HC than during HO on both supports stable and unstable, but particularly on the foam rubber. Mean gain of VOR induced by HO was 1.2 and this one evoked by HC was 0.9 on the two supports. Therefore, when in upright stance the vestibular input is stimulated, the reduction of either or both inputs visual and proprioceptive influences postural stability positively while VOR is affected negligibly. Hence, the vestibular contribution to both VOR and PS is dominant.

Adult↗
PubMed2000

[Medicines and thermal treatment in Pautalia, Thrace].

The city of Pautalia (Kyustendil in Bulgaria) is located near thermal springs in the Strymon valley (Strouma), on a site occupied from the Iron Age onward by the Thracian tribe of Dentheletes. The temple of Asclepios and the walls of Pautalia, located on the hill of Hissarlaka, as well as the roman thermae in the center of modern Kyustendil are among the more important archaeological vestiges in the area. In 1990, near the village of Dragodan, district of Kyustendil, different surgical instruments in bronze were unearthed in a tumulus attributed to the roman period (IInd century A.D.). During the excavation of another tumulus in 1992, a truly exceptional discovery was made near the town of Kotcherinovo, district of Kyustendil: A variety of medicines were discovered in a small bronze case, dating from the roman period (IInd century A.D.). The complete results of the analysis of these substances and few hypotheses about their possible use are presented in this publication.

Balneology↗
PubMed1997

Is central optokinetic nystagmus gravity-dependent?

Up-down asymmetry of vertical optokinetic nystagmus (OKN) has been attributed to a potential effect of gravity. This suggestion has been supported by some investigations in microgravity where a reverse of up-down asymmetry (downward OKN greater than upward OKN) was found. In joint Bulgarian-Russian space experiment "Labyrinth", the part "Optokinez" was devoted to central OKN and its gravity dependence. We aimed at answering questions: 1) Was central optokinetic nystagmus gravity dependent, in particular vertical OKN? If it was: 2) What happened with up-down asymmetry in adaptation period to weightlessness and re-adaptation period to gravity. Furthermore, in our recent study (3) on upright standing humans we found a consistent downward prevalence in central vertical OKN. Thus, a new question arises: What determines the direction of up-down OKN asymmetry?

Eye Movements↗
PubMed1995

[Neurophysiological patterns of vestibular adaptation to microgravity].

Results of the investigation of spontaneous and evoked by vestibular, ocular, and combined oculo-vestibular stimulation of the oculomotor reactions within space experiments Optokinesis and Labyrinth are presented. The experiments were carried out during the early adaptation to micro-g and repeated throughout long term mission. As was shown, the vestibular disturbances at the start of micro-g were not a lot of isolated individuals but regular reactions of the body sensory systems to the micro-g environment. Dynamic studies of the neurovestibular adaptive shifts in long-term microgravity allowed to register periodically evolving abnormal spontaneous and induced oculomotor reactions. Adaptation periods interchanged with the episodes of disadaptation. The periods of vestibular adaptation to microgravity and possible neural mechanisms of these events are presented.

Adaptation, Physiological↗
PubMed1993

[Preoperative immunoprophylaxis in wound and urinary infections in urological patients with Urostim].

In two groups of 25 urological patients each, with and free of urinary infection, Urostim is administered fifteen days before and after the operation. The prophylactic effect of the drug in terms of hospital transmitted wound and urinary infections is recorded on the basis of comparative study with control groups. As shown by the results obtained, Urostim immunoprophylaxis yields positive results in urological practice. In 80 per cent of the cases development of the complication is prevented. Vaccine administration in conjunction with an updated antibiotic broadens the therapeutic scope in patients with urinary infection.

Adult↗
PubMed1993

Vestibular function and sensory interaction in space flight.

The vestibular system and vestibulo-visual interaction were examined in 11 astronauts by the electrooculographic (EOG) method during short- and long-term flights on days 2, 3, 5, 9, 22, 50, 164, and 169 (experiments OPTOKINES and LABYRINTH). In space (flight days 2 and 3), they showed enhanced spontaneous vertical nystagmus, and disorders of tracking of vertical and diagonal movements of the stimulus which improved after active head movements. Early increasing of the reactivity of the cupulo-endolymphatic system (flight days 2-3) was replaced after 5 days of flight with a reduction of the vestibular function and an increase of the significance of the visual input in the formation of oculomotor responses to combined vestibulo-optokinetic stimulation. The type of spontaneous ocular reaction and vestibular stimulation of oculomotor activity under the conditions of weightlessness represented, on one hand, the general responses of sensory systems to weightlessness and, on the other hand, specificity of integrating and adaptive processes.

Electrooculography↗
PubMed1991

Modifications of spontaneous oculomotor activity in microgravitational conditions.

Investigations on spontaneous oculomotor activity were carried out prior to and after (five cosmonauts) and during space flight (two cosmonauts) on the 3rd, 5th and 164th days of the space flight. Recording of oculomotor activity was carried out by electrooculography on automated data acquisition and processing system "Zora" based on personal computers. During the space flight and after it all the cosmonauts with the eyes closed or open and dark-goggled showed an essential increase of the movements' amplitude when removing the eyes into the extreme positions especially in a vertical direction, occurrence of correcting saccadic movements (or nystagmus), an increase in time of fixing reactions.

Eye Movements↗
PubMedDate not supplied

[Pattern of spontaneous oculomotor activity in weightlessness and the readaptation period].

The results of one part Spontaneous Oculomotor Activity Study of Soviet-Bulgarian experiment "Labyrinth" conducted with the participation of 5 cosmonauts prior to and after 10- and 241-day flight are presented. Two cosmonauts have also been studied in-flight. The experiment was conducted with the use of automated data controlling and processing system "Zora" developed by the Bulgarian specialists on a personal computer basis. The horizontal and vertical electrooculograms were recorded in the subjects with eyes closed, open and open but shaded by opaque glasses with the gaze directed forward and in extreme left, right, up and down directions of the gaze. It is found that in the first 3 day of space flight especially when locking visual input, there is an increase in spontaneous activity of "swimming" and saccadic nature or spontaneous nystagmus mainly in the vertical direction. There have been sharp decreases in the rate of eye movement and increase of an amplitude when placing the eyes in the extreme positions (especially in up-down directions) accompanied by correcting saccades or adaptive nystagmus. The post- and inflight changes in the severity and pattern of spontaneous oculomotor responses were similar.

Adaptation, Ocular↗