Journal of Vestibular Research - Volume 14, issue 4

Authors: Keshner, Emily A. | Kenyon, Robert V. | Langston, Jessica

Article Type: Research Article

Abstract: The purpose of this study was to identify how the postural system weights coincident yet discordant disturbances of the visual and proprioceptive/vestibular systems. Eleven healthy subjects (25–38 yrs) received either fore-aft translations of an immersive, wide field-of-view visual environment (0.1 Hz, ± 3.7 m/sec), or anterior-posterior translations of the support surface (0.25 Hz, ± 15 cm/sec), or both concurrently. Kinematics of the head, trunk, and shank were collected with an Optotrak system and angular motion of each segment plotted across time. With only support surface translation, segmental responses were small (1°–2°) and mostly opposed the direction of sled translation. When …only the visual scene was moving, segmental responses increased as the trial progressed. When the inputs were presented coincidentally, response amplitudes were large even at the onset of the trial. Mean RMS values across subjects were significantly greater with combined stimuli than for either stimulus presented alone and areas under the power curve across subjects were significantly increased at the frequency of the visual input when both inputs were presented. Thus, intra-modality dependencies were observed, such that responses to the visual inputs significantly increased and responses to the somatosensory signals reflected the stimulus amplitude only when the two inputs were combined. We believe it unlikely that the role of any single pathway contributing to postural control can be accurately characterized in a static environment if the function of that pathway is context dependent. Show more

Keywords: virtual reality, vestibular, postural control, motion analysis, sensory re-weighting

DOI: 10.3233/VES-2004-14401

Citation: Journal of Vestibular Research, vol. 14, no. 4, pp. 307-319, 2004

Authors: Sarès, Frédéric | Bourdin, Christophe | Prieur, Jean-Michel | Vercher, Jean-Louis | Menu, Jean-Pierre | Gauthier, Gabriel M.

Article Type: Research Article

Abstract: The way in which the head is controlled in roll was investigated by dissociating the body axis and the gravito-inertial force orientation. Seated subjects (N = 8) were requested to align their head with their trunk, 30° to the left, 30° to the right or with the gravito-inertial vector, before, during (Per Rotation), after off-center rotation and on a tilted chair without rotation (Tilted). The gravito-inertial vector angle during rotation and the chair tilt angle were identical (17°). The subjects were either in total darkness or facing a visual frame that was fixed to the trunk. Both final error …and within-subject variability of head positioning increased when the body axis and the gravito-inertial vector were dissociated (Per Rotation and Tilted). However, the behavior was different depending on whether the subjects were in the Tilted or Per Rotation conditions. The presentation of the visual frame reduced the within-subject variability and modified the perception of the gravito-inertial vector's orientation on the tilted chair. As head positioning with respect to the body and sensing of the gravito-inertial vector are modified when body axis and gravito-inertial vector orientation are dissociated, the observed decrease in performance while executing motor tasks in a gravito-inertial field may be at least in part attributed to the inaccurate sensing of head position. Show more

DOI: 10.3233/VES-2004-14402

Citation: Journal of Vestibular Research, vol. 14, no. 4, pp. 321-333, 2004

Authors: Flanagan, Moira B. | May, James G. | Dobie, Thomas G.

Article Type: Research Article

Abstract: Motion sickness is a term that is commonly used to describe the ill effects of many provocative motion (e.g. seagoing or air travel) and apparent motion (e.g. IMAX movies and virtual reality) environments on human well-being and performance. It can be extremely debilitating and yet we do not have a precise understanding of its cause. This study evaluates the importance of three factors that are purported to be involved in the etiology of motion sickness (MS). Most provocative motion environments cause three distinct, but possibly related, responses: reflexive eye movements (EM), sensory conflict (SC), and postural instability (PS). Three current …theories, concerning the etiology of motion sickness, emphasize one of these responses, but deny the importance of the others. Such theoretical approaches preclude the possibility of a synergistic interaction of these factors. This experiment employed a three-factor experimental design wherein each factor was manipulated alone or in combination with the others. The independent variables involved two levels of: PS (induced by having the subject stand on a stationary platform or on a posturally challenging platform mounted atop a partially inflated rubber inner tube); SC (with or without illusory self movement elicited visually by whole field stimulation); and EM (unrestricted or controlled by a stable fixation point). Analysis of measures of PS, SC and EM confirmed the effectiveness of these manipulations. Analysis of MS measures (questionnaires, magnitude ratings, tolerance times) revealed a main effect of SC (p < 0.01), increased MS found with illusory self motion conditions. In addition, measures of MS symptomatology revealed a significant three-way interaction between SC, PS and EM (p < 0.05), greater amounts of MS found with conditions of illusory self motion, postural challenge, and unrestricted EM. This suggests support for a multi-factorial approach to the study of MS etiology. These findings suggest a major role of SC in the elicitation of MS, but also suggest important contributions from the EM and PS mechanisms. Show more

Keywords: motion sickness, sensory conflict, posture, eye movement

DOI: 10.3233/VES-2004-14403

Citation: Journal of Vestibular Research, vol. 14, no. 4, pp. 335-346, 2004

Authors: Brantberg, Krister | Mathiesen, Tiit

Article Type: Research Article

Abstract: Sound and skull-tap induced vestibular evoked myogenic potentials (VEMP) were studied in a 43-year-old man following inferior vestibular neurectomy. Surgery was performed because of a small acoustic neuroma. Postoperative caloric testing suggested sparing of superior vestibular nerve function on the operated side. In response to sound stimulation there were no VEMP on the operated side, irrespective of whether sounds were presented by air- or bone-conduction. This suggests sound-induced VEMP to be critically dependent on inferior vestibular nerve function and this is in agreement with present knowledge. However, VEMP were obtained in response to forehead skull taps, i.e. positive-negative VEMP not …only on the healthy side but also on the operated side. This suggests remnant vestibular function on the operated side of importance for forehead skull tap VEMP, because with complete unilateral vestibular loss there are no (positive-negative) VEMP on the lesioned side. Thus, forehead skull-tap VEMP depend, at least partly, on the superior vestibular nerve function. Show more

Keywords: VEMP, vestibulocollic, skull tap, vestibular nerve, acoustic neuroma

DOI: 10.3233/VES-2004-14404

Citation: Journal of Vestibular Research, vol. 14, no. 4, pp. 347-351, 2004

Authors: Schmid-Priscoveanu, A. | Kori, A.A. | Straumann, D.

Article Type: Research Article

Abstract: In a recent study we demonstrated that otolith input modifies the torsional angular vestibulo-ocular reflex (torVOR) of healthy human subjects: Compared to turntable oscillations in supine position, oscillations in upright position increased the gain of torVOR by 0.1 and cancelled the phase lead originating from low-frequency semicircular canal signals. We asked whether these otolith-related changes of torVOR are still present in patients after vestibular neuritis (VN). Eight patients were sinusoidally oscillated about their naso-occipital axis in supine (canal-only stimulation) and upright (canal-and-otolith stimulation) position. Three-dimensional eye movements were recorded with dual search coils. The patients showed similar otolith-related gain and …phase changes of the torVOR as healthy subjects: the gain increased by about 0.1 (p < 0.05) and the low-frequency phase lead from semicircular canal signals was abolished. These results indicate that otolith function after VN is still sufficient to interact with semicircular canal signals to optimize torsional gaze stabilization when the head is upright. Show more

DOI: 10.3233/VES-2004-14405

Citation: Journal of Vestibular Research, vol. 14, no. 4, pp. 353-359, 2004