Journal of Vestibular Research - Volume 2, issue 1

Authors: Schnabolk, Charles | Raphan, Theodore

Article Type: Research Article

Abstract: Off-vertical-axis rotation (OVAR) in darkness generates continuous compensatory eye velocity. No model has yet been presented that defines the signal processing necessary to estimate head velocity in three dimensions for arbitrary rotations during OVAR. The present study develops a model capable of estimating all 3 components of head velocity in space accurately. It shows that processing of two patterns of otolith activation, one delayed with respect to the other, for each plane of eye movement is not sufficient. (A pattern in this context is an array of signals emanating from the otoliths. Each component of the array is a signal …corresponding to a class of otolith hair cells with a given polarization vector as described by Tou and Gonzalez in 1974.) The key result is that estimation of head velocity in space can be achieved by processing three temporally displaced patterns, each representing a sampling of gravity as the head rotates. A vector cross product of differences between pairs of the sampled gravity vectors implements the estimation. An interesting property of this model is that the component of velocity about the axis of rotation reduces to that derived previously using the pattern estimator model described by Raphan and Schnabolk in 1988 and Fanelli et al in 1990. This study suggests that the central nervous system (CNS) maintains a current as well as 2 delayed representations of gravity at every head orientation during rotation. It also suggests that computing vector cross products and implementing delays may be fundamental operations in the CNS for generating orientation information associated with motion. Show more

Keywords: otolith, OVAR, modeling, nystagmus

DOI: 10.3233/VES-1992-2101

Citation: Journal of Vestibular Research, vol. 2, no. 1, pp. 1-14, 1992

Authors: de Graaf, Bernd | Bekkering, Harold | Erasmus, Corrie | Bles, Willem

Article Type: Research Article

Abstract: By combining a tilting chair and a tilting room we investigated the subjective horizontal (SH) and ocular counterrotation (OCR) as a function of body tilt, trunk tilt, and tilt of a visual frame. Significant influences of (isolated or combined) vestibular and visual information were found, but no influence of neck proprioception. A second and similar experiment, however, now conducted with subjects devoid of labyrinthine function, suggested a contribution of the neck as well as of somatosensory origin. This made a reinter-pretation of our data for normal subjects possible.

Keywords: multisensory tilt information, subjective horizontal, ocular counterrotation

DOI: 10.3233/VES-1992-2102

Citation: Journal of Vestibular Research, vol. 2, no. 1, pp. 15-30, 1992

Authors: Prigioni, I. | Masetto, S. | Russo, G. | Taglietti, V.

Article Type: Research Article

Abstract: Some properties of Ca2+ currents in hair cells isolated from frog semicircular canals by enzymatic or mechanical treatment were studied by using the whole-cell configuration of the patch-clamp technique. After blocking the large outward K+ currents by substituting Cs+ for K+ and adding tetraethylammonium to the pipette filling solution, voltage- and time-dependent inward currents were clearly detectable in the presence of 4 mM Ca2+ in the extracellular solution. Ca2+ current was recruited at test potentials more positive than -60 mV, showed a rapid activation, and exhibited no inactivation during 150-ms depolarizing pulses. The maximal …amplitude was attained at about -20 mV, with an average value of about 80 pA. When Ca2+ in the extracellular solution was replaced with Ba2+ , the magnitude of inward currents increased about twofold. Ba2+ currents were blocked more effectively by Cd2+ than by Ni2+ , were suppressed by 0.5 μ M ω -conotoxin, and were virtually unaffected by amiloride. The dihydropyridine Bay K 8644 caused a marked voltage-dependent increase in inward currents. The present data suggest that hair cells from frog crista ampullaris are endowed with a homogeneous population of Ca2+ channels having several properties similar to those described for neuronal L channels. Since these channels are recruited in a range of potentials close to the resting level, it is suggested that they subserve the control of both resting and evoked transmitter release from the basal pole of the hair cells. Show more

Keywords: frog, semicircular canals, isolated hair cells, patch-damp, calcium currents

DOI: 10.3233/VES-1992-2103

Citation: Journal of Vestibular Research, vol. 2, no. 1, pp. 31-39, 1992

Authors: Huygen, P.L.M. | Nicolasen, M.G.M.

Article Type: Research Article

Abstract: A method is described to obtain suitable parameter values for an adaptation model that can be used to simulate velocity step (VS) responses. The input parameters are the dominant time constant fitted to the first part of the VS response and the time of reversal in nystagmus direction. This method allows a particular solution for the model previously defined by others with a vestibulo-ocular reflex (VOR) time constant, a time constant of adaptation, and a fixed (unitary) gain of the adaptation element. However, because it might be arbitrary to assume a unitary gain, we also studied a more general model …with a variable gain element. It appeared that patients showing short responses had a short VOR time constant and less adaptation than normal. Patients exhibiting prolonged responses appeared to have an excessively long VOR time constant and more adaptation than normal, presumably to compensate for the long time constant. Show more

Keywords: VOR, gain, time constant, phase reversal

DOI: 10.3233/VES-1992-2104

Citation: Journal of Vestibular Research, vol. 2, no. 1, pp. 41-57, 1992

Authors: Peterka, Robert J. | Benolken, Martha S.

Article Type: Research Article

Abstract: Subjects seated in a vertical axis rotation chair controlled their rotational velocity by adjusting a potentiometer. Their goal was to null out pseudorandom rotational perturbations in order to remain perceptually stationary. Most subjects showed a slow linear drift of velocity (a constant acceleration) to one side when they were deprived of an earth-fixed visual reference. The amplitude and direction of this drift can be considered a measure of a static bias in a subject’s perception of rotation. The presence of a perceptual bias is consistent with a small, constant imbalance of vestibular function that could be of either central or …peripheral origin. Deviations from perfect vestibulo-ocular reflex (VOR) symmetry are also assumed to be related to imbalances in either peripheral or central vestibular function. We looked for correlations between perceptual bias and various measures of vestibular reflex symmetry that might suggest a common source for both reflexive and perceptual imbalances. No correlations were found. Measurement errors could not account for these results since repeated tests in the same subjects of both perceptual bias and VOR symmetry were well correlated. Show more

Keywords: vestibular, vestibulo-ocular reflex, motion perception, manual control

DOI: 10.3233/VES-1992-2105

Citation: Journal of Vestibular Research, vol. 2, no. 1, pp. 59-69, 1992

Authors: Waterston, John A. | Barnes, Graham R.

Article Type: Research Article

Abstract: Recordings of head and eye movement were made during pursuit of mixed-frequency, pseudorandom target motion to study the mechanism of vestibulo-ocular reflex (VOR) suppression during head-free pursuit. When high velocity stimuli were used, slow-phase gaze velocity gains decreased significantly with increases in both absolute target velocity and the velocity ratio between the frequency components. These changes occurred independently of changes in the head displacement gain, which remained relatively constant at the lower frequency and were directly attributable to impaired suppression of the VOR. Similar effects were seen when visual feedback was degraded by tachistoscopic illumination of the target. The results …indicate that visual feedback, rather than an efference copy of the head velocity signal, is essential for suppression of slow-phase vestibular eye movement during head-free pursuit. When head-free and head-fixed pursuit were compared, striking similarities were seen for both slow phase gaze velocity gain and phase, indicating that gaze control during smooth pursuit is largely independent of the degree of associated head movement. This suggests that the VOR is not switched off during head-free pursuit. An estimate of the underlying VOR gain was obtained by recording the vestibular response produced by active head movements in darkness. The rather higher estimates of VOR gain obtained using an imaginary earth-fixed target paradigm were found to predict head-free gains more closely than the gains obtained during imaginary pursuit of a moving target, suggesting that such measures may be more representative of the underlying VOR gain. Show more

Keywords: eye movements, smooth pursuit, head movements, VOR suppression

DOI: 10.3233/VES-1992-2106

Citation: Journal of Vestibular Research, vol. 2, no. 1, pp. 71-88, 1992

Authors: Shelhamer, M. | Robinson, D.A. | Tan, H.S.

Article Type: Research Article

Abstract: Previous experiments show that altered visual feedback can change VOR gain. Such changes also presumably occur when eyeglasses are donned and doffed, or when bifocals are worn. In these cases, a nonvisual cue accompanies the required gain adjustment (frames on/off for eyeglasses, looking up/down for bifocals). We set out to show that a subject can establish two VOR gains, and to determine if one of the associated nonvisual cues alone is sufficient to subsequently determine which gain to employ. Each of three subjects sat in a rotating chair inside an OKN drum during 2 hours of sinusoidal rotation at 0.2 …Hz, 30∘ /s peak. For 10 minutes the chair and drum counterrotated, driving VOR gain toward 1.7, while subjects looked up 20∘ . Chair and drum were then coupled for 10 minutes, driving gain toward zero, during which subjects looked down 20∘ . This sequence was repeated for 2 hours. Immediately thereafter, VOR gains were measured while subjects looked alternately up and down, using 20∘ to 40∘ step rotations. A fixation target, presented before and after each step, provided accurate gain determination by measuring the size of the re-fixation saccade. Results show a consistent reduced VOR gain looking downward (average 6%) and increased gain looking upward (average 8%). We conclude that humans carn adjust their VOR gain dependent on a situational context; we speculate that this context can take many forms. Show more

Keywords: oculomotor, VOR, adaptation, context specificity

DOI: 10.3233/VES-1992-2107

Citation: Journal of Vestibular Research, vol. 2, no. 1, pp. 89-96, 1992

Authors: Johnston, Janine L.

Article Type: Book Review

DOI: 10.3233/VES-1992-2108

Citation: Journal of Vestibular Research, vol. 2, no. 1, pp. 97-97, 1992