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Biomedical subjects

W Bles

Publications and source records attributed to W Bles.

At least 37 records · Page 2Linked to original sources
PubMed1991

The Aubert-Fleischl paradox does appear in visually induced self-motion.

An experiment was set up to investigate the possible influence of oculomotor activity on experienced speed of circular vection. With the standard lined inner wall of an optokinetic drum as stimulus, we found that subjects, sequentially exposed to periods with or without fixation point, experienced an increment in speed of circular vection when the eyes were kept stationary as compared to when optokinetic nystagmus occurred. In a control condition, however, where the influence of optokinetic nystagmus vs fixed gaze on the speed of circular vection was measured separately, the effect was not significant. These findings might explain a discrepancy found in the literature.

Adult↗
PubMed1991

Ocular rotation and perception of the horizontal under static tilt conditions in patients without labyrinthine function.

In a previous study (1) it was found that in healthy subjects Ocular (Counter) Rotation is mainly due to otolith stimulation and only to a minor extent induced by slanted visual structures. Stimulation of the neck by tilting the trunk laterally upwards did not result in a systematic rotation of the eyes. In the present study it was found that subjects with bilateral loss of vestibular function showed a higher visually induced ocular rotation. Tilting the head (cervical stimulation) or the whole body (somatosensory stimulation) also led to a considerable OCR, demonstrating substitution of other sensory modalities for the loss of vestibular function. Estimates of the subjective horizontal were noisy, demonstrating the lack of an adequate gravitational reference signal.

Ear, Inner↗
PubMed1991

The tilting room and posturography.

The tilting room examination technique is detailed. The advantages of posturography with the tilting room as an additional tool in the clinical vestibular examination are described for patients with uni- and bilateral loss of vestibular function, for patients with an acoustic neurinoma and for patients suffering from cervical ataxia. Some illustrations are also given of other applications of the tilting room.

Ataxia↗
PubMed1990

Angular velocity, not temporal frequency determines circular vection.

This paper shows that the experienced speed of circular vection depends on stimulus speed, not on stimulus temporal frequency. But why would anyone think the contrary? The point is that many modelers in the field of motion perception believe that perceived speed is determined by temporal frequency. Moreover, the optokinetic behaviour of the fly is said to be dependent on the temporal frequency, not the speed, of the stimulus pattern (Reichardt, 1987). It was the aim of the present experiment to test the notion that the experienced speed of circular vection is proportional to stimulus velocity information, which is carried by the temporal and the spatial characteristics of light.

Adult↗
PubMed1989

Influence of gravitoinertial force on vestibular nystagmus in man observed in a centrifuge.

The influence of gravity load on the vestibular system in man was investigated in a centrifuge operating on the free swing principle. The vertical vestibular nystagmus induced by acceleration to 3G was analyzed and compared with reference measurements during 1G. Our data indicate that the effects of increased gravity load include a prolonged decay time constant of upbeat nystagmus and a subject-dependent persisting upbeat nystagmus. In an attempt to explain these findings, an extension of the velocity storage model is proposed, with gravity as a second stimulus function in addition to angular acceleration.

Acceleration↗
PubMed1989

Performance and well-being under tilting conditions: the effects of visual reference and artificial horizon.

It is generally agreed that the incidence of motion sickness in sailors working below deck is higher than in sailors who have the horizon as a visual reference on the bridge. This study investigated the possible beneficial effect of a projected artificial horizon as a means to prevent seasickness. Twelve subjects were exposed to angular motion in a tilting room under three experimental conditions: a) With the windows covered, allowing no visual reference from the outside world; b) With the windows uncovered, thus allowing a partial view of the environment; and c) With the windows covered and a horizon projected on the walls by a rotating laser beam. Subjects were exposed for 35 min in each condition while performing different computerised tasks. There was a reduction in well-being and performance as a function of exposure time. These effects were clearly shown in the "closed cabin" condition. There were less motion sickness symptoms in the "artificial horizon" and "window" conditions. The presence of a visual reference prevented the decrement in performance found in the "closed cabin" condition. The results of this study suggest that a projected horizon might alleviate motion sickness aboard naval vessels, and thus improve the performance of sailors at sea.

Female↗
PubMed1985

Differential effects of ambivalent visual-vestibular-somatosensory stimulation on the perception of self-motion.

The direction of perceived self-motion was determined as a function of combined visual-vestibular and vestibulo-somatosensory stimulations about the earth's vertical z-axis by means of a rotary chair and drum system. The predominant influence of concurrent antagonistic vestibular stimulation on circular vection (CV) even at small accelerations has been demonstrated by several studies in the past. The results of the present paper do not confirm the generally assumed influence of the vestibular system on exocentric motion perception, but instead produce evidence of the dominance of the visual channel even at high acceleration levels. Using a joystick to indicate perceived self-motion, we found the following: Constant CV (visual stimulus velocity: 40 degrees/s) could only be cancelled by vestibular stimulations at oppositely directed mean angular accelerations of 26.9 +/- 9.1 degrees/s2. Smaller accelerations led merely to an acceleration level-related decrease in the perceived velocity of CV. Despite a clear decision with respect to the direction of the perceived motion, subjects (Ss) reported dizziness or even strong motion sickness symptoms. Similar results were obtained with vestibulo-somatosensory interactions. The results are interpreted in terms of an intensive visual support in the processing of visual-vestibular signals, particularly at cortical level, assuming a cortical velocity generator (CVG).

Adolescent↗
PubMed1985

Patients with an acoustic neurinoma examined with a tilting room.

Patients with acoustic neurinomas do not usually show vertigo or spontaneous nystagmus, suggesting a gradual decrease of vestibular function with adequate compensation. Seventeen patients with acoustic neurinoma were examined to test their postural control. Examination in the tilting room showed a visual dominance in postural control with these patients irrespective of involvement of the central vestibular system. The subjective horizon was determined in addition to routine audiovestibular examination, to be informed about the compensation process. When routine audiovestibular examination points to an acoustic neurinoma, a pathological subjective horizon favours the diagnosis, although this is not mandatory. The combination of tilting room and stabilometry is superior in detecting visual dominance to the standard Romberg test.

Humans↗
PubMed1984

Postural and oculomotor signs in labyrinthine-defective subjects.

Bilabyrinthless subjects, i.e. subjects clinically devoid of labyrinthine responses, show a greater than normal decrease in postural stability following eye closure. Because changes in head position, which affect posture in healthy subjects, do not do so in bilabyrinthless patients, static afferent information from healthy neck receptors does not contribute to postural stabilization. Somatosensory nystagmus and dynamic cervico-ocular responses are equally greater in bilabyrinthless than normal subjects, which indicates that both categories of eye movements are mediated by the same mechanism. Optokinetic nystagmus is slightly diminished in bilabyrinthless patients and optokinetic after-nystagmus was mostly absent. In terms of the Raphan-Cohen model our findings confirm that destruction of the labyrinthine function abolishes the vestibulo-ocular integrator function.

Ear, Inner↗
PubMed1984

[Somatosensory-visual-vestibular interaction in a case of vermis agenesis].

It is well known that the somatosensory input is important for keep a balance as well as the visual and the vestibular inputs. However the knowledge of somatosensory-visual-vestibular interaction is incomplete at now. We have already made a mathematical model of these interactions by extension of the Raphan-Cohen model (Raphan et al, 1979) for visual-vestibular interaction with a direct and an indirect somatosensory pathway. This indirect somatosensory pathway has access to the common visual-vestibular velocity storage integrative mechanism. So the purpose of the present experiment was to verify whether such an extended model (Fig. 4) can be used to describe the nystagmus due to stimulation of the sensory system apart or in combination in case of vermis agenesis with Dandy-Walker's cyst. It was checked, on the other hand, where the lesion are extended. And moreover it was suspected that each parts of the mathematical model are compared with any central neural regions. As a result, the indirect pathways of visual, vestibular and somatosensory inputs and the direct pathways of visual and somatosensory inputs were disturbed completely. The disturbance of the indirect pathways was caused by lesion in the velocity storage integrator which was though to be included in the vestibular nuclei in monkey. The lesion in epsilon 3-h2 was suspected to explain a blockage of the direct visual pathway, and a disturbance of the direct somatosensory pathway was suspected the lesion in gs. We could explain this cause by a mathematical model for somatosensory-visual-vestibular interaction, so we could conclude that this model was useful for human beings as well as monkey.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebellum↗
PubMed1981

Nystagmus, gaze shift, and self-motion perception during sinusoidal head and neck rotation.

Report on eye movements and perceived horizontal head rotation in 26 healthy students during sinusoidal vestibular, visual, cervical, congruent vestibular-plus-visual, or vestibular-plus-cervical stimulation. Circularvection occurred more often during neck afferent than during full-field optokinetic stimuli. In contrast, the cervico-ocular response had a low average velocity. As first noted by Frenzel (1928), a greater gaze shift distinguished the normal cervical from the normal labyrinthine response. The cervico-ocular and vestibulo-ocular responses were found to add up. Clinically, the results imply that ocular movements may be a poor measure of dizziness in cervical syndromes.

Adult↗
PubMed1979

Height vertigo and human posture.

A theory is presented supporting a geometrical explanation for physiological height vertigo being a distance vertigo through visual destabilization of postural balance when the distance between the eyes and visible stationary contrasts becomes critically large. Physiological and posturographic data obtained under natural height vertigo conditions are consistent with this hypothesis.

Humans↗