J Neurol Neurosurg Psychiatry 2001;71:53–57
53
Vestibular function in severe bilateral
vestibulopathy
G Wiest, J L Demer, J Tian, B T Crane, R W Baloh
Reed Neurological
Research Center,
Department of
Neurology, UCLA
School of Medicine,
Los Angeles, USA
G Wiest
J L Demer
J Tian
B T Crane
Jules Stein Eye
Institute, 100 Stein
Plaza, UCLA, Los
Angeles, CA
90095–7002, USA
J L Demer
R W Baloh
Correspondence to:
Dr J L Demer
jld@ucla.edu
Received 26 September 2000
and in revised form
10 January 2001
Accepted 24 January 2001
Abstract
Objectives—To assess residual vestibular
function in patients with severe bilateral
vestibulopathy comparing low frequency
sinusoidal rotation with the novel technique of random, high acceleration rotation of the whole body.
Methods—Eye movements were recorded
by electro-oculography in darkness during passive, whole body sinusoidal yaw
rotations at frequencies between 0.05 and
1.6 Hz in four patients who had absent
caloric vestibular responses. These were
compared with recordings using magnetic
search coils during the first 100 ms after
onset of whole body yaw rotation at peak
accelerations of 2800°/s2. OV centre rotations added novel information about otolithic function.
Results—Sinusoidal yaw rotations at 0.05
Hz, peak veocity 240°/s yielded minimal
responses, with gain (eye velocity/head
velocity)<0.02, but gain increased and
phase decreased at frequencies between
0.2 and 1.6 Hz in a manner resembling the
vestibulo-ocular reflex. By contrast, the
patients had profoundly attenuated responses to both centred and eccentric high
acceleration transients, representing virtually absent responses to this powerful
vestibular stimulus.
Conclusion—The analysis of the early
ocular response to random, high acceleration rotation of the whole body disclosed a
profound deficit of semicircular canal and
otolith function in patients for whom
higher frequency sinusoidal testing was
only modestly abnormal. This suggests
that the high frequency responses during
sinusoidal rotation were of extravestibular
origin. Contributions from the somatosensory or central predictor mechanisms,
might account for the generation of these
responses. Random, transient rotation is
better suited than steady state rotation for
quantifying vestibular function in vestibulopathic patients.
(J Neurol Neurosurg Psychiatry 2001;71:53–57)
Keywords: bilateral vestibulopathy; vestibulo-ocular
reflex; high acceleration rotation
Patients with absent caloric vestibular responses often have robust compensatory eye
movements in darkness at higher frequencies of
sinusoidal rotation.1 2 It is unclear whether
these eye movements arise from the vestibular
labyrinths, or some other sensory system. The
predictability of sinusoidal head motion might
www.jnnp.com
allow subjects to generate responses synchronised to non-vestibular sensory cues. Experimental studies in animals showed that bilaterally labyrinthectomised monkeys develop
preprogrammed compensatory eye movements
in anticipation of a head movement.3
A powerful method to quantify reliably the
vestibulo-ocular reflex (VOR) without contamination by non-vestibular mechanisms involves testing during random transient rotations at high acceleration. Although the direct
response of labyrinthine aVerents is vital to
generation of the short latency VOR, considerable central processing aVects the late and
steady state VOR. As central processing takes
time, the basic labyrinthine response can be
isolated by examining the earliest response to
transient head rotation. When visually salient
targets are presented within a few 10s of milliseconds before (or even during) transient rotation, VOR responses during the first 100 ms are
highly repeatable within individual subjects
and yet attributable only to labyrinthine input.
Previous rotational studies in normal human
subjects used whole body accelerations only in
the range of 300°/s2 to 1000°/s2.4 5 In the
present experiments, patients were exposed to
whole body peak accelerations of 2800°/s2, as
previous studies showed that the initial VOR
depends qualitatively and quantitatively on the
magnitude of head acceleration.6 To our
knowledge, this technique has not yet been
used to examine residual vestibular function in
patients with bilateral vestibulopathy. We compared ocular responses to standard sinusoidal
stimulation over a wide frequency range with
responses to random, high acceleration transients of the whole body in four patients who
lacked caloric responses. We investigated
whether the dynamics of the sinusoidal compensatory eye movements were similar to those
of the VOR, and whether they correlated with
the magnitude of the responses evoked by
unpredictable, high acceleration transients.
Methods
PATIENTS
Four patients with bilateral vestibulopathy and
absent caloric responses were selected. All
patients had dysequilibrium, worse in the dark,
and prominent oscillopsia. As none had associated hearing loss, history of ophthalmological
disorders, exposure to known ototoxins, or a
positive family history, the patients were
diagnosed as having idiopathic bilateral vestibulopathy.7 None had spontaneous or gaze
evoked nystagmus while fixating. Their average
age was 52 (SD 17) years, range 39–78 years.
The interval between onset of symptoms and
time of testing varied from 2 months to 2 years.
Wiest, Demer, Tian, et al
54
Table 1 Gain values for high acceleration transients and sinusoidal rotation in patients
and normal controls
Mean transient gain
Patient 1
Patient 2
Patient 3
Patient 4
Normal subjects*
Centred rotations 25–100
ms
Eccentric rotations
25–100 ms
Sinusoidal gain 0.8
Hz
0.05 (0.006)
0.27 (0.004)
0.04 (0.007)
0.03 (0.005)
0.88 (0.002)‡
0.12 (0.007)
0.29 (0.005)
0.08 (0.006)
0.03 (0.005)
0.95 (0.002)‡
0.58
0.72
0.30
0.42
0.71 (0.18)†
Transient gain values are mean (CW+CCW)/2 SEM).
*Normal controls (n=11).
†Normal mean (SD) (Baloh et al, Ann Neurol 1988;23:32–7).
‡ Normal mean (SEM)6
TEST PROCEDURES
Patients were rotated sinusoidally in the
horizontal plane in darkness with their eyes
open, using a servomotor driven rotational
chair. They performed mental arithmetic
throughout the testing to maintain a constant
state of alertness. All patients were rotated for
4–8 cycles at 0.05 Hz (peak velocity 60, 120,
and 240°/s), 0.2 Hz (60°/s), 0.4 Hz (30 °/s), 0.8
Hz (30°/s), and 1.2 Hz (30°/s); two patients
were additionally rotated at 1.6 Hz (30°/s).
During sinusoidal rotation, eye movements
were recorded with electro-oculography digitally sampled at 200 Hz. Calibration by fixation
of targets at known eccentricities was performed before rotation at each test frequency.
Recordings were simultaneously displayed on
polygraph paper and analyzed on line by a digital computer.
High acceleration, transient, whole body yaw
rotations were administered by a 500 N-m,
high resolution stepper motor (Compumotor,
Rohnert Park, CA, USA) with a dedicated
driver and position feedback digital controller.
A detailed description of the equipment has
been published.6
Briefly, subjects sat in a wooden chair that
was fitted with dense foam cushions, and their
bodies were secured by lap and chest belts
while their knees and feet were firmly held by
padded braces. Subjects’ heads were tightly
secured within a non-metallic, conforming
head holder. Directionally and temporally
unpredictable transient yaw rotations were
delivered about an axis centred between the
otoliths to examine pure canal responses, and
oV centre 20 cm posterior to the eyes.
Eccentric rotation provides simultaneous angular and linear motion and thus enables
assessment of combined otolith and canal
responses. Ten rotations were performed in
random sequence in each direction. Subjects
were instructed to fixate a target located 500
cm in front of them, consisting of a 14 cm black
cross on a 102×81 cm white background. Fifty
to 70 ms before onset of each rotation, room
lights were extinguished and subjects were
instructed to maintain gaze on the remembered
target. Peak acceleration was 2800°/s2 to a
maximum velocity of 190°/s, which rotated the
head 40° in 250 ms. Eccentric rotation yielded
peak otolith tangential acceleration of 0.6 g.
Eye and head positions were measured with
magnetic search coils (Skalar Medical, Delft,
The Netherlands), placed on the right eye
www.jnnp.com
under topical anaesthesia, and on a bite bar
moulded to the upper teeth, respectively.
Search coil data (horizontal and vertical gaze
and head position) were low pass filtered over a
bandwidth of 300 Hz before simultaneous digital sampling at 1.2 kHz, 16 bit resolution.
DATA ANALYSIS
A detailed description of the on line digital
computer analysis technique for the sinusoidal
rotational responses has been published elsewhere.1 Eye position was diVerentiated to yield
instantaneous eye velocity. Fast components
were identified by their characteristic velocity
profile and removed from the data. The gaps in
the remaining slow phase eye velocity record
were filled by interpolation with a quadratic
regression line. A fast Fourier transform was
executed giving the magnitude and phase of
the fundamental and first five harmonics. As
the responses were roughly symmetric, the gain
and phase were calculated by comparing the
fundamental with the stimulus velocity trace.
Only responses with coherence>0.95 were
accepted for evaluation. Time constants were
calculated from sinusoidal rotational responses. Calculation of the time constant from
constant velocity rotational testing was not
possible due to absence of postrotatory nystagmus in all patients, consistent with the
ultrashort time constants found in the sinusoidal responses.
A detailed description of the methods for
analyzing high acceleration responses appears
elsewhere.6 Data were analyzed using the
MacEyeball custom software package running
under LabView (National Instruments, Austin,
TX,USA). For each subject, rotations were
grouped based on direction and rotation axis.
Events in which eye position varied by>0.2° in
the 80 ms preceding head rotation were
discarded as failures of fixation. After digital
diVerentiation, eye and head velocity data were
filtered using a third order low pass Butterworth filter (0–50 Hz). Gain was determined
by dividing instantaneous eye velocity by head
velocity. Right eye position was defined as zero
before the chair began moving because the target was directly in front of the right eye.
Normative data have been reported for both
types of rotational stimuli.6 8
Results
RESPONSES TO SINUSOIDAL ROTATION
Sinusoidal rotation of vestibulopathic subjects
at 0.05 Hz yielded minimal responses
(gain<0.02) even at peak velocities of 240°/s.
The VOR gain increased with increasing
frequency in all patients, ranging from 0.03–
0.15 at 0.2 Hz and from 0.43–0.70 at 1.6 Hz.
By contrast, phase lead decreased with higher
frequencies. At 0.2 Hz phase lead ranged from
41°-59° in all patients, decreasing to a range of
21°-34° at 0.8 Hz. Figure 1 shows electrooculographic recordings of all patients at 0.2
and 0.8 Hz. Mean gain at 0.8 Hz was 0.50 (SD
0.18) (table 1) and mean phase lead was 30.9
(SD 10)°, yielding a mean time constant of
0.36 (SD 0.13) s (range 0.21–0.51 s) at 0.8 Hz.
Gain and phase values at higher frequencies
Vestibular function in severe bilateral vestibulopathy
55
CW rotations
(a)
8
6
(b)
Head
Position (deg)
4
(c)
(d)
0
Patient 1
Patient 4
Patient 3
Patient 2
–2
Eye
–4
Stimulus
–6
10
deg
1 sec
0.2 Hz
–8
0.8 Hz
Normal
0
20
40
60
80
100
120
Time (ms)
Figure 1 Electro-oculographic recordings of eye position
during sinusoidal rotation of patient 1 (a), 2 (b), 3 (c),
and 4 (d) at 0.2 and 0.8 Hz. At 0.8 Hz mostly smooth
compensatory eye movements occurred. Responses at 0.2
Hz clearly show quick and slow phases, consistent with
reflexive eye movements.
CCW rotations
8
6
Normal
4
Position (deg)
1.2
1.0
0.8
Gain
2
0.6
Eye
Patient 2
Patient 1
Patient 3
Patient 4
2
0
–2
–4
Head
0.4
–6
0.2
–8
0
0.01
0.1
10
Patient 1
Patient 2
Patient 3
Patient 4
Coherence < 0.95
80
70
60
Phase (deg)
1
50
40
30
20
10
0
–1.0
0.01
0.1
1
10
Frequency (Hz)
Figure 2 Bode plots of gain and phase for sinusoidal VOR
at 0.05, 0.2, 0.4, 0.8, 1.2 and 1.6 Hz in all patients. The
bold horizontal lines and the vertical bars indicate the
normal mean (SD). Note the increase in gain and the
decrease of phase in the patients’ responses at higher
frequencies, corresponding to a first order linear model of the
VOR. *Coherence<0.95.
were consistent with a 1st order high pass linear
system. Figure 2 plots the gain and phase of
responses to sinusoidal stimulation compared
with normal subjects. Phase lead was abnormally large at low frequencies, but at the highest frequencies phase lead approached the normal value of zero. Slow compensatory and fast
anticompensatory eye movements were present
at 0.2 Hz (fig 1).
RESPONSES TO TRANSIENT HIGH ACCELERATION
0
20
40
60
80
100
120
Time (ms)
Figure 3 Magnetic search coil recordings of eye and head
position during the initial 100 ms of transient rotation to
peak acceleration 2800°/s2. Each plot represents the average
(SEM) of 10 rotations centred at the interaural point in a
normal subject (normal) and in each patient (patients
1–4) for clockwise (CW) and counter clockwise (CCW)
directions. Patient 2 showed the highest response bilaterally,
suggesting residual vestibular function. Responses were
minimal for patients 1, 3, and 4. Error limits were typically
indistinguishable from data traces.
clockwise and counter clockwise rotations.
Each trace represents averages of 8–10 rotations under identical conditions. By comparison with normal controls, responses of vestibulopathic subjects both to centred and eccentric
rotations were almost abolished (table 1). The
VOR gain for rotations centred between the
otoliths averaged over the interval 25 ms-100
ms after rotation onset ranged from 0.02 to
0.35 for both directions. A shift in axis
eccentricity to 20 cm posterior to the eyes creates a strong otolith stimulus synergistic with
the angular VOR that normally increases gain
markedly; yet in the patients there was only a
minimal increase in gain (table 1). Gain during
eccentric rotations 25 ms-00 ms after rotation
onset ranged from 0.01 to 0.49 for both directions, with slow phase eye velocities ranging
from 2.2°/s to 46°/s. Mean gain values of each
patient are compared with normal controls in
the table 1. Patient 2 had some residual VOR
(fig 3) to transient rotation. Surprisingly, this
patient had the lowest sinusoidal gain at 0.2 Hz
and the highest gain at 0.8 Hz (fig 2).
ROTATION
Figure 3 shows responses to transient rotations
centred between the otoliths, so that net otolith
stimulation was minimal. The responses of
each patient and a normal subject (normal data
taken from Crane and Demer6) are shown for
www.jnnp.com
Discussion
The current study examined reflexive eye
movements in response to random, transient
high accelerations of the whole body about
centred and eccentric axes, demonstrating a
Wiest, Demer, Tian, et al
56
profound deficit of the VOR to both semicircular canal and otolith stimulation in patients
with bilateral loss of caloric responsiveness.
Conventional “impulse” rotational tests have
been performed using whole body rotations to
constant velocity, with eye movement recording by electro-oculography.9 These tests measure the slow component velocity of nystagmus
after step changes in angular velocity and provide assessment of gain and the time constant
of the VOR. As these tests use 20-fold lower
accelerations of about 140°/s2 and as slow
component velocities of the VOR are measured
in a time window of up to 30 seconds,10 the
responses are not comparable with the high
acceleration transients of 2800°/s2 employed in
the present study. The response in the first 100
ms after onset of high acceleration rotation is
likely to be a pure vestibular response as there
is insuYcient time for other systems (for example, vision, somatosensory) to contribute, making this stimulus an ideal tool for the
assessment of vestibular function.
Previous studies have achieved high head
accelerations using manually delivered thrusts
of the head on the trunk to evaluate deficits of
unilateral vestibular lesions.11 12 Such rotations
are inherently more variable across time,
experimenters, and subjects. Tabak et al
induced passive step displacements of the head
by a reactive torque helmet in patients with
absent caloric responses.13 These authors
found that the magnitude of the gain reduction
correlated well with the degree of disability.
However, transient head velocities in these
patients only reached 55°/s, by comparison
with 190°/s in our experiments, and the
relatively high average gain of about 0.48 for
transient head rotation was attributed by the
authors to inhomogeneity and partial lesions in
their patient population.
High acceleration transient rotations of the
whole body at 3000°/s2 have been recently used
to examine the response dynamics of the VOR
both in normal monkeys and in monkeys after
unilateral plugging of the semicircular canals.14 15 Residual vestibular function in vestibulopathic patients has not to our knowledge
been evaluated with this method. By contrast
with passive head on trunk rotation, transient
whole body acceleration is not confounded by
additional neck receptor stimulation and provides a direct comparison with the sinusoidal
responses in standard rotational testing. The
VOR gain in our patients 25–100 ms after
onset of the high acceleration transients ranged
from 0.05 to 0.27, being minimally aVected by
shifting the rotational axis oV centre. This
examination confirmed essentially absent
semicircular canal and otolithic function in
patients 1, 3, and 4, calling into question the
origin of the sinusoidal rotational responses.
Sinusoidal rotational testing in our patients
with bilateral vestibulopathy showed a markedly decreased sensitivity to low frequency
stimulation, consistent with previous studies.1 2
The responses at higher frequencies showed
VOR-like dynamics of increasing gain and
decreasing phase lead with increasing frequency, but had remarkably short time con-
www.jnnp.com
stants. Shortening of the VOR time constant
has previously been reported only in patients
with CNS lesions.8 16 If the sinusoidal rotational responses (which probe the VOR in the
frequency domain) are of vestibular origin,
they should correlate with the responses to the
high acceleration impulses, which probe the
VOR in the time domain.11 17 18
Compensatory slow eye movements have
also been reported in a patient with bilateral
vestibular nerve section.19 Passive, unpredictable transient head movements in this patient
evoked smooth compensatory eye movements
of low gain (about 0.3), which were thought to
be generated by cervical sources. During whole
body rotation, this patient was instructed to
maintain gaze on the location of an earth fixed
light after it had been extinguished. The
authors concluded that the compensatory eye
movements in this test were produced by pursuit of the imaginary fixation light. Maintaining
gaze on an imagined earth fixed target during
sinusoidal rotation in darkness requires a
central percept of head velocity to generate
appropriate compensatory eye movements, and
some sensory information about self motion.
Although none of our patients was instructed
to fixate or imagine the location of an earth
fixed target during sinusoidal rotation, it is
conceivable that they might have used extravestibular cues and predictor mechanisms.
Experimental studies confirmed that normal
subjects could generate smooth pursuit of predictable, imaginary, or invisible stimuli in
darkness.20 21 Smooth eye movements can
occur in anticipation of a target motion even
when the stimulus does not appear and a
period as long as 4 seconds has elapsed from
the previous visual stimulus.22 Smooth pursuit
and fixation of an imagined earth fixed target
during sinusoidal rotation are achieved by the
same neural mechanisms.23
Even if we assume the eYciency of predictor
mechanisms in generating compensatory eye
movements in our patients, there must still be
another mechanism indicating the temporal
characteristics of the stimulus. In the absence
of vestibular cues, a likely source for this information might be the somatosensory system.
Recent experiments provide evidence that the
timing and the velocity storage of anticipatory
smooth pursuit eye movements can be independently controlled through diVerent sensory
channels.24 Although anatomical and physiological findings strongly suggest a somatosensory input to the vestibular nuclei,25–28 the functional relevance of these aVerents has not yet
been established. A recent study confirmed
modulation of vestibular nucleus activity during dynamic tilt in decerebrate cats lacking
vestibular and neck somatosensory inputs.29
The authors suggested that modulation of vestibular nucleus neuronal activity in these
animals was due to activation of receptors in
the viscera, trunk, or limbs.
So far, there are only a few studies dealing
with the functional role of the somatosensory
system in patients with bilateral vestibulopathy.
Assessing purely somatosensory responses in
normal subjects is impossible with conven
Vestibular function in severe bilateral vestibulopathy
57
cctional rotational stimuli. Apparent stepping
around on a moving platform (that is, if a stationary subject steps on a rotating platform)
stimulates exclusively the somatosensory system without activating the labyrinths, producing circular vection and somatosensory nystagmus. In this paradigm, patients with defective
labyrinths exhibit a stronger somatosensory
induced nystagmus than normal subjects.30
The existence of so-called arthrokinetic nystagmus is further evidence for a functionally
significant somatosensory-vestibular convergence.31 Our findings suggest that high acceleration rotations of the whole body may be
superior to sinusoidal rotational testing in the
assessment of residual vestibular function. The
severe degradation of the VOR to transient
high whole body acceleration suggests that the
responses to high frequency sinusoidal rotations in our patients were of extravestibular
origin in at least three of four patients. It is
likely that the responses to sinusoidal rotation
were due to somatosensory or other extravestibular sensory origins, probably enhanced by
central predictor mechanisms.
We thank N DeSalles, L Fleischman, and F Henriquez for technical assistance. The work was supported by NIH grant P01
DC02952 and the Austrian Science Fund. JLD was the recipient of a Lew R Wasserman Merit Award from Research to Prevent Blindness, and is the Laraine and David Gerber Professor
of Ophthalmology.
1 Baloh RW, Honrubia V, Yee RD, et al. Changes in the human
vestibulo-ocular reflex after loss of peripheral sensitivity.
Ann Neurol 1984;16:222–8.
2 Honrubia V, Marco J, Andrews J, et al. Vestibulo-ocular
reflex in peripheral labyrinthine lesions: bilateral dysfunction. Am J Otolaryngol 1985;6:342–52.
3 Dichgans J, Bizzi E, Morasso P, et al. Mechanisms underlying recovery of eye-head coordination after bilateral
labyrinthectomy in monkeys. Exp Brain Res 1973;18:548–
62.
4 Anastasopoulos D, Gianna CC, Bronstein AM, et al.
Interaction of linear and angular vestibulo-ocular reflexes
of human subjects in response to transient motion. Exp
Brain Res 1996;110:465–72.
5 Crane BT, Viirre ES, Demer JL. The human horizontal
vestbulo-ocular reflex during combined linear and angular
acceleration. Exp Brain Res1997;114:304–20.
6 Crane BT, Demer JL. Human horizontal vestibulo-ocular
reflex initiation: eVects of acceleration, target distance, and
unilateral deaVerentation. J Neurophysiol 1998;80:1151–
66.
7 Baloh RW, Jacobson K, Honrubia V. Idiopathic bilateral
vestibulopathy. Neurology 1989;39:272–5.
8 Baloh RW, Beykirch K, Tauchi P, et al. Ultralow vestibuloocular reflex time constants. Ann Neurol 1988;23:32–7.
9 Baloh RW, Honrubia V. Clinical neurophysiology of the
vestibular system. 2nd ed. Philadelphia: FA Davis, 1990.
www.jnnp.com
10 Baloh RW, Sakala SM, Yee RD, et al. Quantitative vestibular
testing. Otolaryngol Head Neck Surg 1984;92:145–50.
11 Halmagyi GM, Curthoys IS, Cremer PD, et al. The human
horizontal vestibulo-ocular reflex in response to high acceleration stimulation before and after unilateral vestibular
neurectomy. Exp Brain Res 1990;81:479–90.
12 Halmagyi GM, Curthoys IS, Todd MJ, et al. Unilateral vestibular neurectomy in man causes a severe permanent horizontal vestibulo-ocular reflex deficit in response to
high-acceleration ampullofugal stimulation. Acta Otolaryngol Suppl 1991;481:411–14.
13 Tabak S, Collewijn H, Boumans LJJM, et al. Gain and delay
of human vestibulo-ocular reflexes to oscillation and steps
of the head by a reactive torque helmet. II Vestibulardeficient subjects. Acta Otolaryngol 1997;117:796–809.
14 Minor LB, Lasker DM, Backous DD, et al. Horizontal vestibuloocular reflex evoked by high acceleration rotations in
the squirrel monkey. I. Normal responses. J Neurophysiol
1999;82:1254–70.
15 Lasker DM, Backous DD, Lysakowski A, et al. Horizontal
vestibuloocular reflex evoked by high acceleration rotations
in the squirrel monkey. II. Responses after canal plugging.
J Neurophysiol 1999;82:1271–85.
16 Demer JL, Zee DS. Vestibulo-ocular and optokinetic deficits
in albinos with congenital nystagmus. Invest Ophthalmol Vis
Sci 1984;25:739–45.
17 Foster CA, Demer JL, Morrow MJ, et al. Deficits of gaze
stability in multiple axes following unilateral vestibular
lesions. Exp Brain Res 1997;116:501–9.
18 Gilchrist DPD, Curthoys IS, Cartwright AD, et al. High
acceleration impulsive rotations reveal severe long term
deficits of the horizontal vestibulo-ocular reflex in the
guinea pig. Exp Brain Res 1998;123:242–54.
19 Halmagyi GM, Curthoys IS. Human compensatory slow
eye movements in the absence of vestibular function. In:
Graham MD, Kemink JL, eds. The vestibular system: neurophysiologic and clinical research. New York: Raven Press,
1987.
20 Gauthier GM, HoVerer JM. Eye tracking of self moved targets in the absence of vision. Exp Brain Res 1976;26:121–
39.
21 Whittaker SG, Eaholtz G. Learning patterns of eye motion
for foveal pursuit. Invest Ophthalmol Visual Sci 1982;23:
393–7.
22 Barnes GR, Asselman PT. The mechanism of prediction in
human smooth pursuit eye movements. J Physiol 1991;439:
439–61.
23 Barnes GR, Eason RD. EVects of visual and non-visual
mechanisms on the vestibulo-ocular reflex during pseudorandom head movements in man. J Physiol 1988;395:383–
400.
24 Barnes GR, Donelan SF. The remembered pursuit task: evidence for segregation of timing and velocity storage in predictive oculomotor control. Exp Brain Res 1999;129:57–67.
25 Wilson VJ, Kato M, Thomas RS, et al. Excitation of lateral
vestibular neurons by peripheral aVerent fibers. J Neurophysiol 1966;29:508–29.
26 Wilson VJ, Wylie RM, Marco LA. Synaptic inputs to cells in
the medial vestibular nucleus. J Neurophysiol 1968;31:176–
85.
27 Pompeiano O. Spinovestibular relations: anatomical and
physiological aspects. Prog Brain Res 1972;37:263–96.
28 Rubin AM, Liedgren SR, Odkvist LM, et al. Limb input to
the cat vestibular nuclei. Acta Otolaryngol 1979;87:113–22.
29 Yates BJ, Jian BJ, Cotter LA, et al. Responses of vestibular
nucleus neurons to tilt following chronic bilateral removal
of vestibular inputs. Exp Brain Res 2000;130:151–8.
30 Bles W, Vianney de Jong JMB, de Wit G. Somatosensory
compensation for loss of labyrinthine function. Acta
Otolaryngol 1984;97:213–21.
31 Brandt Th, Buechele W, Arnold F. Arthrokinetic nystagmus
and ego-motion sensation. Exp Brain Res 1977;30:331–8.