Ocular Counterrolling Research Articles

Vertical (Z-axis) acceleration alters the ocular response to linear acceleration in the rabbit

Whether ocular orientation to gravity is produced solely by linear acceleration in the horizontal plane of the head or depends on both horizontal and vertical components of the acceleration of gravity is controversial. Here, we compared orienting eye movements of rabbits during head tilt to those produced by centrifugation that generated centripetal acceleration along the naso-occipital (X-), bitemporal (Y-) and vertical (Z-) axes in a constant gravitational field. Sensitivities of ocular counter-pitch and vergence during pitch tilts were approximately 25 degrees /g and approximately 26 degrees /g, respectively, and of ocular counter-roll during roll tilts was approximately 20 degrees /g. During X-axis centripetal acceleration with 1 g of gravity along the Z-axis, pitch and vergence sensitivities were reduced to approximately 13 degrees /g and approximately 16 degrees /g. Similarly, Y-axis acceleration with 1g along the Z-axis reduced the roll sensitivity to approximately 16 degrees /g. Modulation of Z-axis centripetal acceleration caused sensitivities to drop by approximately 6 degrees /g in pitch, approximately 2 degrees /g in vergence, and approximately 5 degrees /g in roll. Thus, the constant 1g acceleration along the Z-axis reduced the sensitivity of ocular orientation to linear accelerations in the horizontal plane. Orienting responses were also modulated by varying the head Z-axis acceleration; the sensitivity of response to Z-axis acceleration was linearly related to the response to static tilt. Although the sign of the Z-axis modulation is opposite in the lateral-eyed rabbit from that in frontal-eyed species, these data provide evidence that the brain uses both the horizontal and the vertical components of acceleration from the otolith organs to determine the magnitude of ocular orientation in response to linear acceleration.

Insights into the Control of Torsional Eye Position: Dissociated Hysteresis of Static Ocular Counterroll in Humans, by A Palla, CJ Bockisch, O Bergamin, and D Straumann. J Neurophysiol 95:2222–32, 2006

Insights into the Control of Torsional Eye Position: Dissociated Hysteresis of Static Ocular Counterroll in Humans, by A Palla, CJ Bockisch, O Bergamin, and D Straumann. J Neurophysiol 95:2222–32, 2006

The effect of alcohol ingestion on ocular counterrolling

Nineteen normal subjects underwent two naso-occipital rotations to 90 degrees right and left ear down in our standard ocular counterrolling (OCR) protocol. Both eyes were videotaped. Following two rotations, subjects drank 90 ml vodka in 180 ml orange juice; and in about 20 min, when blood alcohol levels reached 0.04-0.09%, the protocol was repeated. An SMI videooculography system provided measurements. Results showed that amplitude of OCR was significantly decreased after alcohol ingestion; smoothness was significantly increased after alcohol, similar to alcohol's effect on essential tremor. Although disconjugacy was not significantly different in the two conditions when the entire trials were examined, the latter portions of the post-alcohol trials did show significant disconjugacy, similar to earlier findings in vestibular-defective patients whose OCR deficits were apparent only in the final segments of the rotation trials. We postulate the results are due to alcohol's action on cerebellar GABAergic Purkinje cells projecting to vestibular nuclei.

Three-Dimensional Eye–Head Coordination After Injection of Muscimol Into the Interstitial Nucleus of Cajal (INC)

The interstitial nucleus of Cajal (INC) is thought to be the "neural integrator" for torsional/vertical eye position and head posture. Here, we investigated the coordination of eye and head movements after reversible INC inactivation. Three-dimensional (3-D) eye-head movements were recorded in three head-unrestrained monkeys using search coils. INC sites were identified by unit recording/electrical stimulation and then reversibly inactivated by 0.3 mul of 0.05% muscimol injection into 26 INC sites. After muscimol injection, the eye and head 1) began to drift (an inability to maintain stable fixation) torsionally: clockwise (CW)/counterclockwise (CCW) after left/right INC inactivation respectively. 2) The eye and head tilted torsionally CW/CCW after left/right INC inactivation, respectively. Horizontal gaze/head drifts were inconsistently present and did not result in considerable position offsets. Vertical eye drift was dependent on both vertical eye position and the magnitude of the previous vertical saccade, as in head-fixed condition. This correlation was smaller for gaze and head drift, suggesting that the gaze and head deficits could not be explained by a first-order integrator model. Ocular counterroll (OC) was completely disrupted. The gain of torsional vestibuloocular reflex (VOR) during spontaneous eye and head movements was reduced by 22% in both CW/CCW directions after either left or right INC inactivation. Our results suggest a complex interdependence of eye and head deficits after INC inactivation during fixation, gaze shifts, and VOR. Some of our results resemble the symptoms of spasmodic torticollis (ST).

Activity of pursuit neurons in the caudal part of the frontal eye fields during static roll-tilt

The smooth-pursuit system and vestibular system interact to keep the retinal target image on the fovea during head and/or whole body movements. The caudal part of the frontal eye fields (FEF) in the fundus of arcuate sulcus contains pursuit neurons and the majority of them respond to vestibular stimulation induced by whole-body rotation, that activates primarily semi-circular canals, and by whole-body translation, that activates otoliths. To examine whether coordinate frames representing FEF pursuit signals are orbital or earth-vertical, we compared preferred directions during upright and static, whole-body roll-tilt in head- and trunk-restrained monkeys. Preferred directions (re monkeys' head/trunk axis) of virtually all pursuit neurons tested (n = 21) were similar during upright and static whole-body roll-tilt. The slight shift of preferred directions of the majority of neurons could be accounted for by ocular counter-rolling. The mean (+/-SD) differences in preferred directions between upright and 40 degrees right ear down and between upright and 40 degrees left ear down were 6 degrees (+/-6 degrees) and 5 degrees (+/-5 degrees), respectively. Visual motion preferred directions were also similar in five pursuit neurons tested. To examine whether FEF pursuit neurons could signal static whole-body roll-tilt, we compared mean discharge rates of 29 neurons during fixation of a stationary spot while upright and during static, whole-body roll-tilt. Virtually all neurons tested (28/29) did not exhibit a significant difference in mean discharge rates between the two conditions. These results suggest that FEF pursuit neurons do not signal static roll-tilt and that they code pursuit signals in head/trunk-centered coordinates.

A clinical test of otolith function: static ocular counterroll with passive head tilt

When roll-tilted around the naso-occipital axis, humans exhibit compensatory torsional rotation of the eyes in the opposite direction owing to the torsional vestibulo-ocular reflex. In the static condition (sustained head roll), the utricles act as responsible sensors for 'static ocular counterroll'. Contributions of cervico-ocular reflexes remain unknown. To find an easy, clinically useful test of utricular function, we induced ocular counterroll in 10 healthy study participants (two men, mean age 27+/-2 years) under three stimulation conditions (active/passive head tilt and passive whole body tilt in roll plane), used three-dimensional video-oculography to measure it, and compared values. Active head-tilt-induced ocular counterroll varied most and was thus less reliable than passive head and body tilt-induced ocular counterroll. Utricular function can thus be tested simply by measuring passive head tilt with video-oculography.

外来で行える簡易眼球反対回旋検査（健常成人）―赤外線ＣＣＤ付きＦｒｅｎｚｅｌ眼鏡を使用して―

The dolls' eyes manoeuvre in head tilt in roll (DM), recognised as one of the otolith function tests from Barany's era in 1906 and treated as a classic test in the roll plane which yields ocular counter-rolling (OCR), was investigated in normal subjects. The DM is a simple, safe, and sound test but has not yet become quantitative. Recently, we devised a new three-dimensional eye movement image analysis technique using a commercialised infrared CCD camera, a personal computer, and public domain software. Image analysis was performed automatically using the public domain software NIH Image.As the result of the DM, OCRs in particular torsional components of eye movements, of which analysis was performed by NIH Image, were performed by seven healthy normal subjects sampled among fifty normal subjects.Six subjects were able to perform smooth OCRs under our critical instruction, except one subject wearing soft contact lens. They all reported no perception disorder and experienced had no sickness during the DM.In a future study, we would like to apply the DM to patients with Meniere's disease (MD). The histopathological feature of MD is defined as endolymphatic hydrops (EH) and EH initially involves the whole inner ear system. If possible, to detect EH in the inner ear organs, we would like to investigate whether or not there is any abnormality of OCRs in MD patients. The DM can be useful to detect such abnormalities, non-invasively.

Experimental study of static ocular counterrolling under altered gravity environment

Experimental study of static ocular counterrolling under altered gravity environment

Dissociated Hysteresis of Static Ocular Counterroll in Humans

In stationary head roll positions, the eyes are cyclodivergent. We asked whether this phenomenon can be explained by a static hysteresis that differs between the eyes contra- (CE) and ipsilateral (IE) to head roll. Using a motorized turntable, healthy human subjects (n = 8) were continuously rotated about the earth-horizontal naso-occipital axis. Starting from the upright position, a total of three full rotations at a constant velocity (2 degrees/s) were completed (acceleration = 0.05 degrees/s2, velocity plateau reached after 40 s). Subjects directed their gaze on a flashing laser dot straight ahead (switched on 20 ms every 2 s). Binocular three-dimensional eye movements were recorded with dual search coils that were modified (wires exiting inferiorly) to minimize torsional artifacts by the eyelids. A sinusoidal function with a first and second harmonic was fitted to torsional eye position as a function of torsional whole body position at constant turntable velocity. The amplitude and phase of the first harmonic differed significantly between the two eyes (paired t-test: P < 0.05): on average, counterroll amplitude of IE was larger [CE: 6.6 +/- 1.6 degrees (SD); IE: 8.1 +/- 1.7 degrees), whereas CE showed more position lag relative to the turntable (CE: 12.5 +/- 10.7 degrees; IE: 5.1 +/- 8.7 degrees). We conclude that cyclodivergence observed during static ocular counterroll is mainly a result of hysteresis that depends on whether eyes are contra- or ipsilateral to head roll. Static hysteresis also explains the phenomenon of residual torsion, i.e., an incomplete torsional return of the eyes when the first 360 degrees whole body rotation was completed and subjects were back in upright position (extorsion of CE: 2.0 +/- 0.10 degrees; intorsion of IE: 1.4 +/- 0.10 degrees). A computer model that includes asymmetric backlash for each eye can explain dissociated torsional hysteresis during quasi-static binocular counterroll. We hypothesize that ocular torsional hysteresis is introduced at the level of the otolith pathways because the direction-dependent torsional position lag of the eyes is related to the head roll position and not the eye position.

Static Ocular Counterroll: Video-based Analysis After Minimizing the False-Torsion Factors

To determine the validity and usefulness of a newly developed measurement method of static ocular counterrolling (s-OCR) that eliminates false-torsion factors and to test the Jampel hypothesis that s-OCR does not exist. A lightweight measurement device, consisting of a video camera, a coaxial light source, and a laser pointer projecting a fixation target on the wall, was fixed to a subject's head by means of a mouthpiece. In 11 healthy adults (mean age: 30 +/- 15 years), digital images of the right eye were captured while the subject kept his head tilted at a randomly selected angle ranging from 0 degrees to 50 degrees . By a frame-by-frame analysis of movements of the corneal light reflex and the iris patterns, OCR was evaluated. Torsional eye movement in the opposite direction to head tilt was found in all subjects. The amount of torsion continuously increased until the head-tilt angle reached 40 degrees. The average (+/- SD) amplitude of a fitted sine curve was 7.6 +/- 3.2 degrees (range: 4.3 degrees-10.3 degrees), and the individual amplitude was significantly larger than the test-retest repeatability of the measurement (+/-1.7 degrees). The measurement method used in this study provided good test-retest repeatability and ease of application. The characteristics of torsional eye movements that we observed after minimizing the false-torsion factors agree with previous reports supporting the existence of s-OCR.

Comparison of static ocular counter-roll induced by active and passive head tilt and whole body roll

Background: When humans are roll-tilted around the naso-occipital axis, a compensatory torsional rotation of the eyes in the opposite direction occurs known as ocular counterroll (OCR). This is thought to be mainly a vestibular (otolithic) response. The contributions of cervico-ocular reflexes to OCR are still unknown. Moreover, mainly for technical reasons there are still no standardized OCR tests. Therefore, the aim of this study was (1) to compare OCR in response to active and passive lateral head tilts and whole body roll and (2) to develop a test for the evaluation of otolith function which can be used in the daily clinical routine.

Magnetic Resonance Imaging of Human Extraocular Muscles During Static Ocular Counter-Rolling

The rectus extraocular muscle (EOM) pulleys constrain EOM paths. During visual fixation with head immobile, actively controlled pulleys are known to maintain positions causing EOM pulling directions to change by one-half the change in eye position. This pulley behavior is consistent with Listing's law (LL) of ocular torsion as observed during fixation, saccades, and pursuit. However, pulley behavior during the vestibulo-ocular reflex (VOR) has been unstudied. This experiment studied ocular counter-rolling (OCR), a static torsional VOR that violates LL but can be evoked during MRI. Tri-planar MRI was performed in 10 adult humans during central target fixation while positioned in right and left side down positions known to evoke static OCR. EOM cross-sections and paths were determined from area centroids. Paths were used to locate pulleys in three dimensions. Significant (P < 0.025) counter-rotational repositioning of the rectus pulley arrays of both orbits was observed in the coronal plane averaging 4.1 degrees (maximum, 8.7 degrees ) from right to left side down positions for the inferior, medial, and superior rectus pulleys. There was a trend for the lateral rectus averaging 1.4 degrees . Torsional shift of the rectus pulley array was associated with significant contractile cross-section changes in the superior and inferior oblique muscles. Torsional rectus pulley shift during OCR, which changes pulling directions of the rectus EOMs, correlates with known insertions of the oblique EOM orbital layers on rectus pulleys. The amount of pulley reconfiguration is roughly one-half of published values of ocular torsion during static OCR, an arrangement that would cause rectus pulling directions to change by less than one-half the amount of ocular torsion.

Thresholds for perception of direction of linear acceleration as a possible evaluation of the otolith function

BackgroundPrevious attempts to measure otolith function using ocular counter-rolling have shown poor sensitivity and specificity, thereby hindering a useful clinical application. We have conducted a study to investigate whether thresholds for the perception of the direction of linear acceleration might be an alternative for the clinical evaluation of otolith or statolith function.MethodsPerception of the direction of motion was evaluated in 28 healthy subjects while all external auditory and visual cues were eliminated. Whole body motion stimulus was generated by a motor driven linear sled at a stimulus frequency of 1 Hz at a linear acceleration ranging from 0 to maximum 40 cm/ s2. Subjects were required to correctly indicate the direction of motion (anterior-posterior or lateral) or whether they were stationary. Both velocity and acceleration thresholds were measured.ResultsThe median acceleration thresholds for the perception of direction of linear movement for anterior-posterior movement was 8.5 cm/s2 and for lateral movement 6.5 cm/s2. According to the literature, acceleration thresholds depend on the stimulus profile whereas velocity thresholds do not. The median velocity thresholds for the perception of direction of linear movement for anterior-posterior movement was 13.5 cm/s and for lateral movement was 10.4 cm/s. The median velocity thresholds for the perception of direction of linear movement for anterior-posterior movement increased linearly with age, whereas the median velocity threshold for lateral movement was not correlated with age.ConclusionThe thresholds found in this study are lower than reported in the literature before which may be due to the repetative predictive sinusoidal stimulus which makes it relatively easy to lower the threshold by learning already within one test prophile.The variablity is large in line with the previous literature, but our experiments indicate that variability decreases after a training session. We interprete the literature and our current results that linear velocity thresholds after some training might reflect the sensitivity of the otolith system per se.

Residual Torsion Following Ocular Counterroll

A recent study on static ocular counterroll suggested the existence of residual torsion (RT): when healthy subjects repositioned their head to the upright position after sustained static tilt, eye position differed from the original ocular torsion measured prior to the static head tilt. Our experiments aimed at further characterizing this phenomenon. Using a three-dimensional motorized turntable, healthy human subjects (n = 8) were rotated quasi-statically (0.05 deg/s2, 2 deg/s velocity plateau reached after 40 s) from the upright position about the naso-occipital axis. Three full whole-body rotations were completed while subjects fixed upon a blinking laser dot straight ahead in otherwise complete darkness. Three-dimensional eye movements were recorded with modified dual search coils (wires exiting inferiorly). Torsional position of the right eye at consecutive upright body positions was analyzed. The torsional eye position before the beginning of the chair rotation was defined as zero torsion. On average, the right eye was intorted by 1.3 degrees or extorted by 2.0 degrees after the first full chair rotation in the clockwise or counterclockwise direction, respectively. These torsional offset values of the right eye did not significantly change after the two subsequent full chair rotations. We conclude that RT observed after static ocular counterroll is the result of static hysteresis, that is, a position lag of the eye, which depends on the direction of head roll. The fact that residual torsion did not further increase after the first rotation cycle emphasizes that RT is a static rather than a dynamic phenomenon.

Drift in Ocular Counterrolling during Static Head Tilt

A decreasing drift of the counter-rolled eye position (OCR) during head tilt was recently described. The underlying mechanism is not known. OCR in eleven healthy subjects was recorded (Search coil, Skalar) during a head tilt paradigm in two test conditions. The head was tilted with a velocity below (test 1) and above (test 2) detection threshold for the semicircular canals (SC) and held static for eight minutes. A significant drift of OCR was revealed in test 2 (P = .0006, ANOVA) and close to significant in test 1 (P = .07). No statistical difference was found between the two test conditions. The results suggest that the OCR drift was not caused by the SC complex merely.

Das Kopfneigephänomen bei einseitigen und beidseitig symmetrischen Trochlearisparesen

The head-tilt phenomenon (difference between the vertical deviations with an ipsilateral and contralateral head-tilt by 45 deg. each) occurring in patients with a superior oblique palsy has traditionally been explained by the lacking contraction of the superior oblique muscle within the synkinetic movement of ocular counterrolling. However, using a computer model, Robinson showed that the superior oblique palsy itself causes only a relatively small head-tilt phenomenon. Adaptive mechanisms amplifying the otolith reflex were suggested to explain the increase of the head-tilt phenomenon in the course of time. In order to reduce the abnormal head posture required for binocular vision, the otolith reflex would be amplified, accepting the greater vertical deviation when the head is tilted to the paretic side . If the head-tilt phenomenon were solely caused by the lacking contraction of the superior oblique muscle, it should be greater in bilateral than in unilateral superior oblique palsies. If an adaptive mechanism were acting to reduce the abnormal head posture, the head-tilt phenomenon should not be greater, and could even be smaller in bilateral than in unilateral superior oblique palsy, because in bilateral (symmetric) trochlear nerve palsies the vertical deviation at straight gaze is already small or absent without adaptation. We have carried out a retrospective comparison of 10 patients with bilateral symmetric superior oblique palsies and 10 patients with unilateral superior oblique palsy. In all cases, the palsy was acquired and had been present for at least 1 year. The patients with bilateral superior oblique palsy had a head-tilt phenomenon ranging from 0 to 7 degrees (median, 2 deg.). The patients with unilateral superior oblique palsy had a head-tilt phenomenon between 2 and 13 degrees (median, 8 deg.). The difference was significant (p = 0.0117). The head-tilt phenomenon is smaller in long-standing bilateral symmetric superior oblique palsies than in long-standing unilateral superior oblique palsy. This finding supports the hypothesis that in unilateral superior oblique palsy, an adaptive mechanism augments the head-tilt phenomenon by an amplification of the otolith reflex. However, we presume that the amplification of the otolith reflex is only a side effect of the adaptive change of the vertical fusional vergence tonus and thus the price of the improved vertical fusion, rather than a compensatory mechanism.

Drift in Ocular Torsion during Sustained Head Tilt

Purpose: A head tilt towards the shoulder (roll) induces an ocular counter-roll (OCR), i.e. torsion in the opposite direction to the head. How this counter-rolled position is maintained during a static head tilt is in debate. In a previous study, we reported an OCR-increasing drift subsequent to the head tilt. This finding is in contrast to other reports where no such response was found. The primary aim of this study was to repeat the experiment during a prolonged head-tilt test and to describe the OCR characteristics. A secondary aim was to investigate the influence of spatial visual cues on OCR. Methods: Five male subjects performed a head tilt (30°) towards the right shoulder while the eye position was recorded during a 10-minute interval. In test 1, the subjects viewed a target with no cues for spatial orientation. The same head-tilt paradigm was repeated in test 2 with a visual target with spatial cues. Two samples of data were extracted from the start and the end of the recordings for statistical analysis. Results: Subsequent to the head tilt, a slow OCR-increasing drift in the opposite direction to the head roll was found in all subjects. On average, this drift lasted for 30 sec (± 5) in test 1 and for 55 sec (± 18) in test 2. The drift was then found to change its direction, i.e. the eyes were rotated in the same direction as the head roll. When measured after 10 minutes, the OCR was significantly decreased. Conclusions: The OCR during static head tilt is not constant. During the first minute there is a gradually increasing OCR. Thereafter, the amplitude of the OCR decreases gradually. These changes are influenced to some extent by spatial visual cues. Possible mechanisms are adaptive responses in otolithic afferents as well as central nervous memory functions related to the semicircular canal system.

Static and dynamic properties of vergence‐induced reduction of ocular counter‐roll in near vision

We have examined the characteristics of vergence-induced reduction of ocular counter-roll in near vision. Monkeys were trained to make convergent and divergent refixations with the head and body either upright or in various roll orientations. During near viewing requiring 17 degrees horizontal vergence, we found that static binocular torsion was suppressed by about 68% (averaged over both eyes, two monkeys and both near target locations). This result is in accordance with a previous study in which binocular torsion was quantified based on the displacement planes of eye positions in far and near viewing. Latency and duration of the change in torsional eye position depended (for each eye differently) on body roll and the depth plane of fixation. For instance, during convergent refixations in left-ear-down orientations, the latencies of the left eye were smaller and the durations were longer than those of the right eye. However, both eyes reached their final positions required to fixate the second visual target at roughly the same time. The different dynamics of the two eyes is explained by the fact that each eye rotated temporally when the eyes converged, a pattern named binocular extension of Listing's law. Coming from or aiming at a common torsional value (normal ocular counter-roll) in convergent or divergent refixations, the required torsion differs in the two eyes. The brain compensates for these differences by adjusting the dynamics of each eye's movement.

Convergence reduces ocular counterroll (OCR) during static roll-tilt

When humans are roll-tilted around the naso-occipital axis, both eyes roll or tort in the opposite direction to roll-tilt, a phenomenon known as ocular counterroll (OCR). While the magnitude of OCR is primarily determined by vestibular, somatosensory, and proprioceptive input, direction of gaze also plays a major role. The aim of this study was to measure the interaction between some of these factors in the control of OCR. Videooculography was used to measure 3D eye position during maintained whole body (en bloc) static roll-tilt in darkness, while subjects fixated first on a distant (at 130 cm) and then a near (at 30 cm) head-fixed target aligned with the subject’s midline. We found that while converging on the near target, human subjects displayed a significant reduction in OCR for both directions of roll-tilt––i.e. the interaction between OCR and vergence was not simple addition or subtraction of torsion induced by vergence with torsion induced by roll-tilt. To remove the possibility that the OCR reduction may be associated with the changed horizontal position of the eye in the orbit during symmetric convergence, we ran an experiment using asymmetric convergence in which the distant and near targets were aligned directly in front of one eye. We found the magnitude of OCR in this asymmetric convergence case was also reduced for near viewing by about the same amount as in the symmetric vergence condition, confirming that the convergence command rather than horizontal position of the eye underlies the OCR reduction, since there was no horizontal movement of the aligned eye in the orbit between fixation on the distant and near targets. Increasing vergence from 130 to 30 cm reduced OCR gain by around 35% on average. That reduction was equal in both eyes and occurred in both the symmetric and asymmetric convergence conditions. These results demonstrate the important role vergence plays in determining ocular counterroll during roll-tilt and may support the contention that vergence acts to reduce the conflict facing a stereopsis-generating mechanism.

Utricular sensitivity and preponderance assessed by the unilateral centrifugation test

Utricular sensitivity and preponderance of the right or left utricle can be assessed by means of the unilateral centrifugation test. In this test, subjects are rotated about an earth vertical axis at a velocity of 400 degrees per second. During the ongoing rotation, the subject is gradually translated 4 cm first to the right, and then to the left, along an interaural axis, to a position at which one utricle becomes aligned with the axis of rotation, and at this point is subjected only to gravitational forces. At this eccentric position, the contralateral utricle is exposed to the combination of gravity and a centrifugal acceleration of 0.4g, corresponding to an apparent roll-tilt of 21.7 degrees. This stimulus induces ocular counterrolling (OCR), which is measured on-line using three-dimensional video-oculography (VOG). We observed that ocular counterrolling appears as a linear function of the gravito-inertial acceleration tilt of the head centre (GIA(HC)) during the lateral translation. We present a theoretical model for this linear relationship that contains two parameters: 1) the slope of the linear regression is a measure for the utricular sensitivity and 2) the intercept of the linear regression is a measure of the preponderance of the right or left utricle. The strength of the model is supported by data obtained from 28 healthy subjects and 14 patients with unilateral vestibular deafferentiation (UVD) due to acoustic neuroma surgery.