Journal of Vestibular Research - Volume 10, issue 4-5

Authors: Holly, Jan E.

Article Type: Research Article

Abstract: The laws of physics explain many human misperceptions of whole-body passive self-motion. One classic misperception occurs in a rotating chair in the dark: If the chair is decelerated to a stop after a period of counterclockwise rotation, then a subject will typically perceive clockwise rotation. The laws of physics show that, indeed, a clockwise rotation would be perceived even by a perfect processor of angular acceleration information, assuming that the processor is initialized (prior to the deceleration) with a typical subject's initial perception – of no rotation in this case. The motion perceived by a perfect acceleration processor serves as …a baseline by which to judge human self-motion perception; this baseline makes a rough prediction and also forms a basis for comparison, with uniquely physiological properties of perception showing up as deviations from the baseline. These same principles, using the motion perceived by a perfect acceleration processor as a baseline, are used in the present paper to investigate complex motions that involve simultaneous linear and angular accelerations with a changing axis of rotation. Baselines – motions that would be perceived by a perfect acceleration processor, given the same initial perception (prior to the motion of interest) as that of a typical subject – are computed for the acceleration and deceleration stages of centrifuge runs in which the human carriage tilts along with the vector resultant of the centripetal and gravity vectors. The computations generate a three-dimensional picture of the motion perceived by a perfect acceleration processor, by simultaneously using all six interacting degrees of freedom (three angular and three linear) and taking into account the non-commutativity of rotations in three dimensions. The resulting three-dimensional baselines predict stronger perceptual effects during deceleration than during acceleration, despite the equal magnitudes (with opposite direction) of forces on the subject during acceleration and deceleration. For a centrifuge run with the subject facing tangentially in the direction of motion, the deceleration baseline shows a perception of forward tumble (pitch rotation) beginning with ascent from the earth, while the acceleration baseline does not have analogous pitch and vertical motion. These results give a three-dimensional explanation for certain puzzling acceleration-deceleration perceptual differences observed experimentally by Guedry, Rupert, McGrath, and Oman (Journal of Vestibular Research, 1992 (2 ).). The present analysis is consistent with, and expands upon, previous analyses of individual components of motion. Show more

Keywords: vestibular system, spatial orientation, centrifuge, models

DOI: 10.3233/VES-2000-104-501

Citation: Journal of Vestibular Research, vol. 10, no. 4-5, pp. 163-178, 2000

Authors: Tilikete, C. | Ventre-Dominey, J. | Denise, P. | Nighoghossian, N. | Vighetto, A.

Article Type: Research Article

Abstract: We investigated the horizontal and the vertical otolith-ocular reflex induced by off-vertical-axis rotation and subjective visual vertical in 14 patients with skew deviation due to brain stem lesion. Patients were divided into two groups: the group C (N = 7 ) with caudal brain stem lesions and the group R (N = 7 ) with rostral brain stem lesions as defined by the midpons level. The patient group was compared to a control group of 20 healthy subjects. The otolith-ocular reflex was evoked by constant velocity rotation in yaw plane around an axis tilted at 15 …deg with respect to gravity. In group C, the horizontal off-vertical-axis nystagmus bias was negative i.e. anticompensatory to chair rotation, when directed toward the lesioned side. Furthermore, patients of group C were presenting with a significant tilt of subjective visual vertical. In group R, a vertical downward offset was induced predominantly in the hypotropic eye and in the direction of rotation away from the lesion. Finally, in patients of group R, horizontal and vertical modulation was increased for rotation away from the lesion. These results are discussed in terms of 1) asymmetrical horizontal and vertical dynamic otolith signals feeding the velocity storage network after brain stem lesion, 2) possible involvement of cerebellar function in OVAN modulation. Show more

Keywords: otolith-ocular reflex, subjective visual vertical, velocity storage mechanism, human

DOI: 10.3233/VES-2000-104-502

Citation: Journal of Vestibular Research, vol. 10, no. 4-5, pp. 179-192, 2000

Authors: Grunfeld, E.A. | Okada, T. | Jáuregui-Renaud, K. | Bronstein, A.M.

Article Type: Research Article

Abstract: A technique was applied to assess vestibular sensation without reference to external spatial, position cues. The stimuli were stopping responses to velocity-steps of 90 deg/s in the dark. Subjects indicated their perceived angular velocity by turning a flywheel connected to a tachogenerator. Two separate experiments were conducted. In one, subjects were rotated in yaw about an earth-vertical axis before and after prolonged rotational or visual (optokinetic) stimuli. In the second experiment, subjects were rotated in roll supine, with either the head (`roll centred') or the feet (`roll eccentric') on the axis of rotation. The two aims of the paper were …to (i) examine the effect of repetitive vestibular and optokinetic stimulation on the time constant of decay of vestibular sensation in yaw; (ii) to compare vestibular sensation responses to rotation in roll both with and without the addition of a Z-axis centrifugal force. The pre-habituation sensation response in yaw decayed exponentially with a median time constant of 12.8 s. The duration of the sensation responses were significantly reduced following both prolonged vestibular and optokinetic stimulation. The reduction in vestibular responses following prolonged visual and vestibular stimuli, 1) is likely to occur in velocity storage mechanisms mediating ocular and perceptual responses, 2) may represent a mechanism for reducing the disorientating consequences of visual-vestibular conflict and 3) supports the use of optokinetic stimuli as a treatment for vestibular patients. The time constant of the sensation responses in roll was shorter and not significantly influenced by head position: 5.7 s in the head-centred position compared to 4.7 s in the eccentric head position. Therefore, perceptual as well as ocular responses to rotation in roll are determined primarily by cupula dynamics and not influenced by velocity storage. Show more

Keywords: velocity storage, optokinetic, roll, yaw

DOI: 10.3233/VES-2000-104-503

Citation: Journal of Vestibular Research, vol. 10, no. 4-5, pp. 193-200, 2000

Authors: Savino, Gustavo | Dickmann, Anna | Ottaviani, Fabrizio | Di Nardo, Walter | Scullica, Luigi | Di Girolamo, Stefano

Article Type: Research Article

Abstract: Visually dependent postural stabilization decreases as a consequence of a long-standing reduction of visual cues in patients affected by congenital nystagmus. The aim of the present study was to verify whether the changes in postural control in this group of patients are due to ocular oscillations or to reduced visual acuity. Therefore, postural control was evaluated when the nystagmus was blocked by the blocking position or by prisms and compared with the postural score observed in a group of normal controls whose visual acuity had been artificially reduced to the same level as that of the patients using Bangerter's filters. …The results show a statistically significant improvement of visually dependent postural stabilization when ocular oscillations are inhibited either by the gaze blocking position or by prisms. They also show that postural control in normal subjects with Bangerter's filters is reduced, but is still significantly better than that observed when ocular oscillations are inhibited in patients affected by congenital nystagmus. Our data strongly support the role of ocular oscillations in visually dependent postural control, since postural impairment recovered under any condition in which ocular oscillations were abolished, despite differences in visual acuity. Our data also show that reduced visual acuity decreases visually dependent postural control to a lesser degree than ocular oscillations. This could be due to the fact that ocular oscillations are a disturbing input, usually inhibited centrally, in order to avoid oscillopsia. This mechanism is probably responsible for the reduced role of visual cues in the postural control in this group of patients. The reduction of visual acuity, by comparison, merely causes a decrease in visual cues, depending on the degree of visual loss. It can be concluded that the impaired postural control in patients affected by congenital nystagmus is mainly due to ocular oscillations, with reduced visual acuity creating a secondary effect. Show more

Keywords: congenital nystagmus, position of gaze, ocular oscillations, visually dependent postural stabilization

DOI: 10.3233/VES-2000-104-504

Citation: Journal of Vestibular Research, vol. 10, no. 4-5, pp. 201-206, 2000

Authors: Keshner, E.A. | Kenyon, R.V.

Article Type: Research Article

Abstract: We examined the effect of a 3-dimensional stereoscopic scene on segmental stabilization. Eight subjects participated in static sway and locomotion experiments with a visual scene that moved sinusoidally or at constant velocity about the pitch or roll axes. Segmental displacements, Fast Fourier Transforms, and Root Mean Square values were calculated. In both pitch and roll, subjects exhibited greater magnitudes of motion in head and trunk than ankle. Smaller amplitudes and frequent phase reversals suggested control of the ankle by segmental proprioceptive inputs and ground reaction forces rather than by the visual-vestibular signals. Postural controllers may set limits of motion at …each body segment rather than be governed solely by a perception of the visual vertical. Two locomotor strategies were also exhibited, implying that some subjects could override the effect of the roll axis optic flow field. Our results demonstrate task dependent differences that argue against using static postural responses to moving visual fields when assessing more dynamic tasks. Show more

Keywords: sway, stabilization, vision, stereoscopic

DOI: 10.3233/VES-2000-104-505

Citation: Journal of Vestibular Research, vol. 10, no. 4-5, pp. 207-219, 2000

Authors: Previc, Fred H. | Beer, Jeremy | Liotti, Mario | Blakemore, Colin | Fox, Peter

Article Type: Research Article

Abstract: Ambient vision comprises the visual functions that are associated with the maintenance of spatial orientation and that depend on peripheral, preconscious visual inputs. Although a limited number of brain areas appear to be activated by coherent wide-field-of-view (WFOV) motion in more than one axis, a diffuse pattern of lateralized brain activity occurs in response to clockwise or counterclockwise ambient visual roll motion [15]. In the present study involving positron emission tomography (PET), a similar finding was shown for rightward versus leftward yaw stimulation. A total of 18 PET scans were obtained from six subjects in response to either leftward or …rightward WFOV motion in a collimated display subtending > 100 ∘ horizontally. Rightward stimulation elicited mainly activation throughout the right hemisphere, whereas leftward stimulation elicited mainly activation throughout the left hemisphere. These findings provide further evidence that the ambient vision signal is either processed or transmitted throughout the entire brain, as befits a visual function that is fundamental to all other perceptual systems. Show more

Keywords: spatial orientation, laterality, functional imagings humans

DOI: 10.3233/VES-2000-104-506

Citation: Journal of Vestibular Research, vol. 10, no. 4-5, pp. 221-225, 2000

Authors: Gianna, Claire C. | Gresty, Michael A. | Bronstein, Adolfo M.

Article Type: Research Article

Abstract: Visual modulation of the linear vestibulo-ocular reflex (LVOR) was investigated in 4 normal subjects exposed to translational interaural transient accelerations of 0.08 g and 0.17 g. Binocular eye movements were recorded with the scleral search-coil technique. LVOR modulation with target proximity was studied using earth-fixed targets at distances of 30 and 60 cm (LVOR-E). LVOR suppression (LVOR-S) was provoked by similar targets which were head-fixed. For both conditions, linear acceleration evoked compensatory slow-phases whose velocities were, from onset, enhanced in proportion to acceleration and target proximity. At 80 ms after motion onset, i.e. before visually-guided eye movements could aid target …fixation, gains (eye velocity/ relative target velocity) during LVOR-E averaged 0.32 (S.D. 0.07) over all combinations of accelerations and target distances. At this time, eye velocities for LVOR-S were on average 33% for LVOR-E (1 . 8 ∘ /s vs. 2 . 7 ∘ /s). During LVOR-S, a marked suppression of eye movements appeared at 102 ms (S.D. 10 ms). We conclude that mechanisms other than pursuit can be used to attenuate the LVOR at < 80 ms but their effect is weak. The marked suppression observed around 100 ms might be due to an early visual effect on vestibular pathways or by some independent voluntary control mechanism. Show more

Keywords: vestibulo-ocular reflex, otolith, suppression, target distance

DOI: 10.3233/VES-2000-104-507

Citation: Journal of Vestibular Research, vol. 10, no. 4-5, pp. 227-238, 2000

Authors: Hegemann, Stefan | Shelhamer, Mark | Kramer, Phillip D. | Zee, David S.

Article Type: Research Article

Abstract: The phase of the translational linear VOR (LVOR) can be adaptively modified by exposure to a visual-vestibular mismatch. We extend here our earlier work on LVOR phase adaptation, and discuss the role of the oculomotor neural integrator. Ten subjects were oscillated laterally at 0.5 Hz, 0.3 g peak acceleration, while sitting upright on a linear sled. LVOR was assessed before and after adaptation with subjects tracking the remembered location of a target at 1 m in the dark. Phase and gain were measured by fitting sine waves to the desaccaded eye movements, and comparing sled and eye position. To adapt …LVOR phase, the subject viewed a computer-generated stereoscopic visual display, at a virtual distance of 1 m, that moved so as to require either a phase lead or a phase lag of 53 deg. Adaptation lasted 20 min, during which subjects were oscillated at 0.5 Hz/0.3 g. Four of five subjects produced an adaptive change in the lag condition (range 4–45 deg), and each of five produced a change in the lead condition (range 19–56 deg), as requested. Changes in drift on eccentric gaze suggest that the oculomotor velocity-to-position integrator may be involved in the phase changes. Show more

Keywords: VOR, otoliths, motor learning

DOI: 10.3233/VES-2000-104-508

Citation: Journal of Vestibular Research, vol. 10, no. 4-5, pp. 239-247, 2000