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Figure 16–17. Effect of amplitude correction on cVEMP interaural amplitude
asymmetry with varying degrees of E
amplitude correction, mean group amplitude asymmetry data for all conditions did not exceed 18%. From McCaslin, D. L., Fowler, A., and Jacobson, G.
P. (2014). Amplitude normalization reduces cervical vestibular evoked myogenic potential (cVEMP) amplitude asymmetries in normal subjects: Proof
of concept. Journal of the American Academy of Audiology, 25(3), 268–277.
doi:10.3766/jaaa.25.3.6. Used with permission.
amplitude is important to know when amplitude normalization techniques are being applied to responses.
The underlying assumption that is used when employing amplitude normalization is that EMG level and
peak-to-peak amplitude of the cVEMP are linearly correlated. However, McCaslin et al. (2014) reported that
when increasing the EMG target level from 300 µV to
400 µV, there continue to be significant differences in
tonic SCM EMG amplitude with no observable differences in cVEMP peak-to-peak amplitude. Although
amplitude normalization techniques have been shown
to be highly effective at controlling for moderate levels
of EMG, collecting cVEMP responses at supramaximal
levels and then using amplitude correction may produce invalid responses and lead to misinterpretation.
We suggested that it is safe to use an EMG target that
is between 50 µV and 300 µV RMS (McCaslin, Fowler,
& Jacobson, 2014). A summary of cVEMP recording
parameters is presented in Table 16–3.
MG amplitude asymmetry. Following
Effect of Age on cVEMP
Measurement Parameters
Beginning early on in the life span, there are significant maturational changes that occur in the peripheral
and central vestibular systems. Therefore, it is critically
important to account for these age-related differences in
laboratory normative data when judgments are being
made as to whether a response is normal or abnormal. Numerous studies have been published describing the age-related changes in cVEMP measurement
parameters. To date, the majority of cVEMP studies
have focused on describing the degenerative changes
that occur as patients grow older. A few of the findings
that are consistently reported are an overall decrease
in peak-to-peak cVEMP amplitude, decreased EMG
amplitude, and higher thresholds (Akin et al., 2011;
Lee, Cha, et al., 2008; McCaslin et al., 2013; Su, Huang,
Young, & Cheng, 2004; Welgampola & Colebatch,
16. VESTIBULAR-EVOKED MYOGENIC POTENTIALS (VEMPS) 415
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table 16–3. cVEMP Recording Protocol
Inverting electrode (reference) Sternoclavicular junction
Noninverting electrode (active) Midpoint or upper third of
SCM mastoid muscle
Ground (Earth) Forehead (chest if using
skull taps)
Electrode impedances <10,000 ohms
Channels
Amplification (gain) 5,000
Artifact rejection Disabled
Filter bandpass 10 to 1000 Hz
Epoch 100 ms
Number of accepted samples 100 to 200
Number of completed
averages
Two channels (left and right
SCM)
Two minimum to ensure
repeatability
2001b; Zapala & Brey, 2004). An additional finding that
has been reported is the high percentage of bilaterally
absent cVEMP responses in some patient populations.
In fact, it has been reported that up to 40% of neurologically and otologically intact people between 60 and 75
years of age do not generate a cVEMP (Su et al., 2004).
This inability to record cVEMPs has also been reported
in very young subjects. For example, Chen, Wang,
Wang, Hsieh, and Young (2007) reported that cVEMPs
recorded from newborns were absent in 33% of the ears
evaluated. This most likely occurred because unlike
adults, infants are unable to follow the commands that
are necessary to activate the SCM. Even though both of
these studies highlight findings from the extreme ends
of the aging continuum, it is important to remember
that an absent cVEMP response may not simply be due
to pathology affecting the peripheral components of the
system (i.e., saccule and/or inferior vestibular nerve).
Rather, the absence of recordable cVEMP responses
may represent impairment occurring anywhere along
the cVEMP pathway.
In an attempt to describe the effects of age on
cVEMP response metrics, McCaslin et al. (2013) compared cVEMP findings in three different groups of neurologically and otologically healthy participants (i.e.,
5 to 17 years of age, 18 to 40 years of age, and 41 to 70
years of age). The authors compared P1 latency, peakto-peak amplitude, RMS EMG, and EMG variability
in the various groups. The authors reported that there
were significant increases in p13 latency associated
with increased age. The finding that P1 occurs earlier
in younger subjects has been reported by other investigators (Kelsch, Schaefer, & Esquivel, 2006; Phillips &
Backous, 2002; Sheykholeslami, Megerian, Arnold, &
Kaga, 2005). It has been suggested that the finding of
shorter latencies in younger individuals may be a result
of structural differences. In this regard, P1 latencies in
children have been significantly correlated with the
length of the participant’s neck (Chang, Yang, Wang,
& Young, 2007). Additionally, N23 latency has been
shown to occur at longer latencies as age increases (Lee,
Cha, et al., 2008; Su, Huang, Young, & Cheng, 2004).
The latencies of P1 and N1 represent central nervous
system transmission through the afferent and efferent
limbs of the reflex. Thus, these prolonged latencies may
represent age-related slowing in the conduction velocity of the response through the cVEMP pathway (e.g.,
age-related degenerative changes in sensory and motor
neural conduction).
In addition to the finding of significantly longer latencies with increasing age, the investigators
reported significantly different cVEMP peak-to-peak
amplitudes between all three groups (McCaslin et al.,
2013). The amplitudes were largest for the pediatric
group and smallest for the oldest group (Figure 16–18).
The authors hypothesized that one contributor to the
larger amplitudes in the younger populations could be
related to the decreased amount of tissue interposed
between the muscle and the recording electrode.
Chang et al. (2007) showed that cVEMP amplitudes
416 BALANCE FUNCTION ASSESSMENT AND MANAGEMENT
P1–N1Amplitude
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(µV)
ErrorBars:+/–1StandardDeviaon
figure 16–18. Grouped P1–N1 amplitudes as a function of age. Cervical vestibular evoked myogenic potential amplitude decreased
with increases in subject age when similar EMG targets were
employed. From
P., and
and E
and Hearing, 34(4), 482–490.
DeLong, A. P. (2013). The effects of amplitude normalization
MG targets on cVEMP interaural amplitude asymmetry. Ear
McCaslin, D. L., Jacobson, G. P., Hatton, K., Fowler, A.
Age
Used with permission.
in adults were negatively correlated with the thickness of the subcutaneous tissue. The authors also suggested that other anatomical factors such as head size
could potentially contribute to the finding of larger
amplitudes in younger individuals. Others have also
documented decreased cVEMP amplitude with aging
(Akin, Murnane, Tampas, & Clinard, 2011; Basta, Todt,
& Ernst, 2007; Su et al., 2004; Welgampola & Colebatch,
2001b). Akin et al. (2011) reported that when cVEMP
responses were obtained from a younger and an older
group using similar EMG targets, the younger group
generated significantly larger amplitudes. The authors
suggested that the reduced amplitudes observed in
the older group were a result of the degenerative effects
on the vestibular system and not the muscle tonus,
since similar EMG targets were employed (i.e., 30 and
50 µV).
One of the key questions regarding reported agerelated decrements in cVEMP amplitude is whether the
observed changes are caused by degeneration of structures that are part of the afferent limb, efferent limb, or
both limbs of the reflex. One approach that has been
used to answer this question is use of a standard EMG
target and then measurement of both the tonic activity
of the SCM EMG and P1–N1 amplitude in subjects of
different ages (Akin et al., 2011; McCaslin et al., 2013).
Using this methodology, McCaslin and colleagues
(2013) reported decreased SCM EMG amplitude with
increasing age across the three age groups when a
similar EMG target level was used. The investigators
designed the study to determine whether the significantly increased peak-to-peak amplitudes observed
in the younger groups were a direct effect of the tonic
EMG that was recorded during the cVEMP recording.
The results, in fact, showed that there were significant
differences in the RMS value of the tonic EMG activity
recorded from the SCM when pediatric and older adult
groups and young adult and older adult groups were
compared. That is, even when the visual target (i.e.,
µV) was provided to the patient, the level of EMG
50
varied with age. Interestingly, there was no difference
in EMG activity recorded from the pediatric and young
adults, suggesting that the SCM tonic activity is largely
equivalent in the two groups. The finding that there
is a difference in the SCM EMG between younger and
older populations using the same target has also been
16. vEstiBulAr-EvoKEd myogEniC PotEntiAls (vEmPs) 417
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reported by Akin et al. (2011). The authors reported
that when older and younger groups were compared
using a similar EMG target, EMG amplitude was significantly smaller for the older group. The results of
these two studies support the idea that the smaller
cVEMP amplitudes noted throughout the literature
most likely represent the accumulated effects of age on
the SCM and the afferent and efferent limbs of the VCR.
Age Effects of cVEMP Tuning
The frequency “tuning” of the otolith system has been
the subject of a number of recent investigations. In
healthy subjects, when VEMP responses are elicited
with different frequency acoustic signals, some stimuli
elicit larger amplitude VEMPs than others (Chihara
et al., 2009; McCue & Guinan, 1995; Piker et al., 2013;
Rauch, Zhou, Kujawa, Guinan, & Herrmann, 2004;
Todd, Rosengren, Govender, & Colebatch, 2009; Welgampola & Colebatch, 2001a). In the majority of studies,
it is a stimulus frequency close to 500 Hz that produces
the largest VEMP amplitude and lowest VEMP threshold (Akin et al., 2003; Murofushi et al., 1999; Timmer
et al., 2006). It is precisely for this reason that a 500 Hz
tone burst has been selected as the stimulus of choice
in most clinics. However, there is speculation that agerelated changes in the vestibular system may change
the “best” frequency. As such, studies have been conducted evaluating how the tuning of the vestibular
system changes as we age. In 2009, Janky and Shepard
described the age-related changes in the tuning of the
vestibular system using cVEMPs. Subjects enrolled in
the study consisted of five age categories spanning 20
to 60+ years. The investigators used clicks and 250, 500,
750, and 1000 Hz tone bursts and reported on changes
in cVEMP response amplitude, threshold, and latency.
There were no differences detected between ears for
any of the metrics tested, but significant differences
were identified for latency and threshold. Cervical
VEMP threshold was reported to be positively correlated with age (i.e., thresholds increased with increasing age). However, peak-to-peak amplitude was shown
to be negatively correlated with age (i.e., p13 amplitude
decreased with increasing age). The lowest threshold
responses were obtained using the 500 Hz stimuli, and
as mentioned previously, the presence of measurable
responses was found to decrease with increasing age.
These findings prompted the authors to conclude that
age should always be considered when interpreting
cVEMP thresholds. This has important implications
for the identification of disorders that manifest them-
selves with abnormally reduced cVEMP thresholds
(e.g., superior canal dehiscence [SCD]).
In a similar study, Piker, Jacobson, Burkard,
McCaslin, and Hood (2013) characterized the effects of
age on the optimal frequency, or frequencies, used to
record the cVEMP. Thirty-nine study participants were
divided into three groups based on age (18–39 years,
40–59 years, >60 years). As had been shown in previous
studies, the vestibular system in all three age groups
showed broad tuning, unlike the auditory system,
which is finely tuned. The investigators reported that
stimulus frequencies 500, 750, and 1000 Hz produced
significantly larger amplitudes than 125, 250, 1500,
and 2000 Hz stimulus frequencies. However, no significant differences in mean amplitude were observed
between 500, 750, and 1000 Hz. In the youngest group
of subjects, the “best” frequency was 750 Hz (i.e., the
tip of the tuning curve), while in the oldest group the
“best” frequency was 1000 Hz (Figure 16–19). It was
the author’s contention that these findings represented
evidence of age-related tuning shifts in the vestibular
system. That is, the “best” frequency shifted to a higher
frequency for the oldest group. The clinical utility of
this finding is that 500 Hz may not always be the ideal
frequency to elicit a cVEMP, especially when age is considered. When assessing patients who are older, 750 or
1000 Hz tone-burst stimuli may yield better responses.
CVEMP ANALYSIS AND NORMATIVE DATA
Amplitude
Traditionally, the analysis of cVEMP responses consists
of four key measures: interaural latency difference,
peak latency, response threshold, and the amplitude
asymmetry ratio (AR). The data presented in this
chapter represent normative data from several different laboratories. Each clinical site should have its own
age- and sex-adjusted normative data with upper and
lower limits (e.g., 2.5 SD). It has been recently recommended that normative data should be collected using
recordings from at least 10 healthy subjects from each
decade of life (Papathanasiou et al., 2014).
Investigators have evaluated the use of absolute
amplitude of P1–N1 response, but the large degree of
interindividual variability has limited the clinical utility of absolute amplitude measures (Li, Houlden, &
Tomlinson, 1999). In order to control for the intersubject variability in the amplitude of cVEMP responses,
side-to-side differences can be expressed as percent
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Figure 16–19. The peak-to-peak amplitude of the cVEMP as a function of stimulus frequency for different age groups. From Piker, E.
Jacobson,
Effects of age on the tuning of the c
34(6), e65–73.
G. P., Burkard, R. F., McCaslin, D. L., and Hood, L. J. (2013).
Used with permission.
G.,
VEMP and oVEMP. Ear and Hearing,
asymmetry (Welgampola & Colebatch, 2001a). This is
a similar approach to how caloric responses are analyzed using the Jongkees formula (Jongkees, 1964). The
VEMP asymmetry ratio is determined by the following
equation:
(Amplitude right cVEMP − Amplitude left cVEMP)
(Amplitude right cVEMP + Amplitude left cVEMP)
× 100
Table 16–4 shows our laboratory upper limits of
percent cVEMP asymmetry (mean + 2 SD) by age in
healthy subjects. When the cVEMP asymmetry exceeds
the upper limit for the appropriate age group, we consider the examination to be abnormal. The weaker side
(i.e., side with the smaller response) is typically considered the impaired side but not in all cases (e.g., SCD).
Interaural asymmetry measures can also be calculated
following a correction for the EMG level (McCaslin et al.,
2014; Miyamoto, Seo, Node, Hashimoto, & Sakagami,
2006; Welgampola & Colebatch, 2001a). Side-to-side
amplitude differences in healthy subjects have typically been reported to be in the range of ~20% to ~45%
depending on the technique used (e.g., monoaural or
binaural stimulation) and whether or not EMG amplitude correction was used (Brantberg & Fransson, 2001;
Li et al., 1999; McCaslin et al., 2013; Welgampola &
Colebatch, 2001a; Zapala & Brey, 2004).
Table 16–4. cVEMP Interaural Amplitude Asymmetry
(
Vanderbilt Normative Data)
Age Group (years) Asymmetry % Mean + 2 SD
5 to 17 12.87 33.75
18 to 40 16.72 42.84
>41 20.72 47.86
Latency
Peak latency has also been used to identify pathology
in the cVEMP pathway. Investigators have reported on
the diagnostic usefulness of significantly prolonged
cVEMP responses (Murofushi, Shimizu, Takegoshi,
& Cheng, 2001; Shimizu, Murofushi, Sakurai, & Halmagyi, 2000). In a retrospective study, cVEMP latencies were measured in 134 patients (61 men and 73
women) with a variety of disorders. The diagnoses
included vestibular neuritis, Ménière’s disease, vestibular schwannoma, and multiple sclerosis. The results
of latency were varied depending on the disorder.
Specifically, there was very little change in latency for
patients suffering from Ménière’s disease or vestibular neuritis. Only four patients with acoustic neuromas
showed a significantly prolonged P1. Interestingly, all
16. VESTIBULAR-EVOKED MYOGENIC POTENTIALS (VEMPS) 419
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of the patients with diagnoses of multiple sclerosis
demonstrated significantly late P1 responses. It was
the contention of the authors based on these findings
that prolonged cVEMP latencies are suggestive of retrolabyrinthine impairments localized to the vestibulospinal tract. Findings from studies such as these have
led to the recommendation that the latency of P1 and
N1 should be reported. Prolonged latencies may be
suggestive of retrolabyrinthine impairments.
threshold
Cervical VEMP thresholds are also an important measurement parameter when interpreting the response,
and can add greatly to the differential diagnosis. The
cVEMP threshold is the lowest intensity level at which
a cVEMP response can be measured and reproduced.
In our clinic, the practice is to reduce the intensity of
the stimulus in 10-dB steps until there is no longer a
reproducible response and then increase intensity by
5 dB until the response is identified. This effectively
becomes the threshold. In normal subjects, cVEMPs
are not measurable below 75 to 80 dB nHL (Streubel,
Cremer, Carey, Weg, & Minor, 2001). The presence of a
cVEMP below these intensity levels is often suggestive
of pathology such as SCD. The cVEMP is now known
to be highly sensitive to the presence of SCD (Aw et al.,
2010; Brantberg, Bergenius, & Tribukait, 1999; Cremer,
Minor, Carey, & Della Santina, 2000; Zuniga, Janky,
Nguyen, Welgampola, & Carey, 2013). In patients with
SCD and other “third window” pathologies (e.g., fistulas or lateral canal dehiscence), VEMPs recorded
from the affected side are often measurable at a significantly softer sound pressure level than would normally be expected (Figure 16–20). Additionally, when
stimulus intensity remains constant, VEMP recordings
from SCD ears will often yield significantly larger P1
and N1 amplitudes than ears without SCD (Brantberg
et al., 1999). It is noteworthy that thresholds should
always be obtained when performing cVEMP testing. In cases where a patient may have a unilateral
SCD, the presence of a larger amplitude response on
the impaired side could be interpreted as impairment
on the intact side (i.e., the smaller response from the
normal ear). Tables 16–5 and 16–6 show cVEMP and
oVEMP sensitivity and specificity for patients diagnosed with SCD.
figure 16–20. Example of a patient with reduced cVEMP thresholds and a confirmed
superior canal dehiscence.
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table 16–5. Cervical Vestibular-Evoked Myogenic Potential Sensitivity and Specificity for Patients
Superior Canal Dehiscence
with
Cutoff Value Sensitivity (%) Specificity (%)
Tone-burst-oVEMP Peak-to-peak
amplitudes
Tone-burst-oVEMP N1 amplitudes >7.5
Click-o
VEMP Peak-to-peak
>11.7
>17.1
>20.3
100
100
97
100
>9.3
>9.9
100
93
>9.9 100 100
88
98
100
94
100
100
amplitudes
Click-oVEMP N1 amplitudes >2.5
>6.6
Source: Data from Zuniga, M. G., Janky, K. L., Nguyen, K. D., Welgampola, M. S., and Carey, J. P. (2013). Ocular
versus cervical VEMPs in the diagnosis of superior semicircular canal dehiscence syndrome. Otology and
Neurotology, 34, 121–126.
100
94
68
100
table 16–6. Ocular Vestibular-Evoked Myogenic Potential Sensitivity and
Specificity for Patients with Superior Canal Dehiscence
Cutoff Value
Age Decade
30s <75
(µv) (threshold) Sensitivity (%) Specificity (%)
<85
<90
80
80
100
100
73
46
Source: Data from Zuniga, M. G., Janky, K. L., Nguyen, K. D., Welgampola, M. S., and
Carey, J. P. (2013). Ocular versus cervical VEMPs in the diagnosis of superior semicircular canal dehiscence syndrome. Otology and Neurotology, 34, 121–126.
40s <75
<85
<90
50s <75
<85
<90
60s <75
<85
<90
45
73
90
45
73
90
50
100
100
100
87
54
100
100
60
100
100
75
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OCULAR VESTIBULAR-EVOKED
MYOGENIC POTENTIAL
Description of the Response
The oVEMP is dominated by a negative peak that is
followed by a positive peak. The negative peak in
response to click stimuli has a mean latency of ~11 ms
and is referred to as N1 or n11. The following positivity
shows a mean peak latency of ~15 ms and is referred to
as either P1 or p15. The direction of the initial deflection suggests that the oVEMP is an onset response (i.e.,
moving from a state where there is no EMG activity
to a state where there is an onset of stimulus-synchronized EMG activity). An ipsilateral response also can
be recorded; however, it is inconsistently present. The
mean latencies of N1 and P1 are significantly longer,
and the peak-to-peak amplitude is significantly smaller,
recorded ipsilaterally compared with contralaterally.
Data culled from oVEMP waveforms include the
peak latencies of n11 and p15, the n11 threshold (in dB
nHL or peak SPL), the interaural N1/n11 latency difference, and the percent interaural peak-to-peak amplitude asymmetry.
oVEMP Pathway
Like the cVEMP, the oVEMP is recorded from extraocular muscles with skin surface electrodes. The predominant peripheral generator of the oVEMP is now
known to be the ipsilateral utricular macula (Curthoys,
2010; Iwasaki et al., 2009). The first-order neurons are
activated by shearing of the kinocilia that occurs when
a low-frequency, high-intensity acoustical transient is
routed through the oval window into the vestibule.
In this way the acoustical energy is transformed into
hydromechanical energy. Transduction also can occur
when the skull is vibrated with a calibrated vibratory device (e.g., a Bruel & Kjaer 4810 Mini-Shaker)
or tapped in the forehead with a reflex hammer that
has been modified so that a trigger pulse is produced
each time the hammer strikes the skin. The activity from
the utricle is routed through the utricular branch of the
superior vestibular nerve. The superior vestibular nerve
becomes part of the VIIIth cranial nerve, which terminates at its root entry zone at the junction of the pons
and the medulla (Curthoys et al., 2011). The signal is
then routed to the vestibular nuclei, and that is the end
of the afferent limb of the vestibulo-ocular reflex (VOR).
The efferent limb begins when the activity from
the vestibular nuclei is routed ipsilaterally and con-
tralaterally through the medial longitudinal fasciculus
(MLF) to the motor nuclei of cranial nerves III and VI.
The cranial nerves emanating from those cranial nerve
nuclei terminate on the extraocular muscles. For the
contralateral oVEMP the cranial nerves terminate on
the inferior oblique muscle. For the ipsilateral oVEMP
the cranial nerve terminates on the superior rectus
muscle (see Figure 16–4 for schematic diagram of the
oVEMP pathway).
The VOR is a crossed and bilateral pathway. This
means that in response to vibration, or a high-intensity
and low-frequency acoustical transient, a response can
be recorded from beneath both the ipsilateral and contralateral eyes (Figure 16–21).
Stimulus Variables
Type of Stimuli
The oVEMP can be evoked by any stimulus that will
produce translation of the otoliths. The stimuli include
high-intensity sound or direct vibration of the skull.
Lastly, the oVEMP can be recorded following anodal
electrical stimulation (e.g., galvanic stimulus of ~5 mA)
of the mastoid and vestibular nerves.
The acoustical stimulus is the one most commonly
used partially because it is most easily obtained. It is
interesting that in at least one report (Cheng, Chen,
Wang, & Young, 2009) the response rates were reported
to be superior for bone-conducted sound and galvanic stimulation (i.e., 100% presence) and good in
response to air-conducted stimuli (i.e., 80% presence).
Not surprising was the shorter latency of the oVEMP
in response to galvanic stimulation because the driving signal was delivered directly to the VIIIth nerve,
bypassing the peripheral generator.
The patient need not have hearing for sound to
be used as the evoking stimulus. However, the soundconducting system must be intact if acoustical stimuli are used. When a conductive impairment exists,
acoustical stimulation may not produce a VEMP (i.e.,
since the magnitude of the stimulus is attenuated by
the conductive impairment). In that situation the preferred stimulus is vibration. For vibratory stimulation
the waveform routed to the stimulator is identical to
that routed to an earphone for acoustical stimulation.
Most clinicians evoke oVEMPs using tone burst
stimuli. In this situation the high-intensity tone burst
acts as a hydromechanical force to translate the otoliths
that rest on the otolith membrane. The best acoustical
stimulus to evoke the oVEMP is a low-frequency tone
burst (e.g., 500 Hz) that is presented at supramaximal
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figure 16–21. Left and right ocular-evoked myogenic potential waveform evoked
using a 95 dB nH
mately 11 ms and the following negativity at 15 ms.
L 500 Hz tone burst. The initial positive waveform occurs at approxi-
stimulation levels (e.g., 95 dB nHL). A vibratory
stimulus is indiscriminate in the manner it activates
the vestibular end organs. That is, a vibratory stimulus applied to the skull activates both vestibular end
organs in much the same way that a bone vibrator activates both cochlea. The skull tap acts as a short-duration, high-amplitude vibratory stimulus. As a general
rule, the vibratory and mechanical stimuli yield the
largest amplitude oVEMPs.
Stimulus Frequency
When stimulus intensity is held constant, the oVEMP is
larger in response to some acoustical tone burst frequencies and is smaller in response to others. In this way the
oVEMP can be described with respect to its “tuning.”
Several investigators have attempted to define the optimal stimulus frequency to evoke the oVEMP.
The determination of what is the best frequency
for evoking the oVEMP is based on what frequency
produces the largest oVEMP at the maximal stimulus
intensity and persists at the lowest stimulus intensity.
What constitutes the best frequency is determined, in
part, by the physical characteristics of the end organ,
including its mass and stiffness. For example, the utricle is larger than the saccule and is less rigidly attached
to the temporal bone (i.e., the utricle is “floppier” and
more compliant). Because of this, the utricle responds
preferentially to lower frequencies than the saccule
(Todd et al., 2009).
Several attempts have been made to measure the
tuning properties of the oVEMP. These studies have
varied in the level of precision by which the best frequency was determined, how the stimuli were delivered (by air or bone conduction), and what age groups
were examined.
The discussion of tuning in the peripheral vestibular system is very different from that of the auditory system. Auditory physiologists are accustomed to
the description of tuning as a result of active processes
in the cochlea. The resulting tuning curves are quite
sharp with clear “tips.” Tuning is very different in the
vestibular system. There are no known active tuning
processes in the peripheral vestibular system. The
results of attempts to characterize the tuning properties of the utricle have indicated that the best acoustical frequency is ~500 Hz (i.e., 400–600 Hz) and the
best vibratory stimulus is ~100 Hz (Donnellan et al.,
2010; Lewis, Mustain, Xu, Eby, & Zhou, 2010; Murnane,
Akin, Kelly, & Byrd, 2011; Piker et al., 2013; Winters,
Berg, Grolman, & Klis, 2012; Zhang, Govender, & Colebatch, 2011, 2012; Figure 16–22).
16. VESTIBULAR-EVOKED MYOGENIC POTENTIALS (VEMPS) 423
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~95 dB nHL. Murnane et al. (2011) assessed the effects
of stimulus intensity on the oVEMP elicited with a 500
Hz tone burst (Figure 16–23). The authors reported
that oVEMP thresholds occurred at ~119 dB peak SPL
(± ~6.1 dB) or ~85 dB nHL. Once the response threshold was exceeded, the response grew with increases in
stimulus intensity. There were few responses at intensities of 105 dB peak SPL. For the remaining intensities
(110 dB peak SPL and greater), oVEMP amplitudes significantly differed for all post hoc comparisons. Interestingly, the latency of N1 and P1 decreased as stimulus
intensity was increased. That is, the absolute latency of
N1 occurring in response to a 120 dB peak SPL was significantly longer than that occurring at 125 dB peak SPL.
Stimulus Rate
The optimal stimulus rates (i.e., producing superior
amplitudes with no effect on latency) for bone-conducted oVEMP recordings have been reported to be
between 5 and 20 Hz (Chang, Cheng, Wang, & Young,
2010). As such, the investigators recommended a stimulus rate of 20 Hz for bone-conducted oVEMP testing.
For air conduction stimuli, the superior rate is 5 Hz,
and in fact, that is the stimulus rate used in our balance
function laboratory (Figure 16–24).
figure 16–22. The effect of age and stimulus frequency
on peak-to-peak amplitude of the o
the left represent individual runs and the recordings
on the right represent the average of responses. From
Piker, E.
and Hood,
the c
Used with permission.
G., Jacobson, G. P., Burkard, R. F., McCaslin, D. L.,
L. J. (2013). Effects of age on the tuning of
VEMP and oVEMP. Ear and Hearing, 34(6), e65–73.
VEMP. The tracings on
Stimulus Intensity
The oVEMP is not a graded response like the ABR but
instead is an “all or nothing” response. This means
that the oVEMP is absent until the threshold intensity
is reached, when the response is present but small in
amplitude. In otologically and neurologically intact
subjects the response is present at 85 to 95 dB nHL
(Piker et al., 2011). Once threshold has been exceeded,
the response grows quickly in amplitude and then saturates. The test normally is conducted using a stimulus
magnitude that is “supramaximal,” which is usually
Stimulus Gating
Stimulus gating has been studied systematically for
both air-conducted and bone-conducted stimuli (Kantner, Hapfelmeier, Drexl, & Gurkov, 2013). The effect of
stimulus rise/fall and plateau time (i.e., duration, see
below) on the oVEMP was examined by Cheng, Wu,
and Lee (2012). Ocular VEMPs were recorded in response to clicks (i.e., with an instantaneous rise/fall
time), and 500 Hz tone bursts with rise times, plateau
times, and fall times of 0.5 to 2-0.5 ms, 0.5 to 4-0.5 ms,
2-2-2 ms, and, 2-4-2 ms respectively. The authors reported that the oVEMP could be recorded to click stimuli (i.e., instantaneous onset) 66% of the time but was
recorded 100% of the time to tone bursts. Although the
latency of the N1 increased with rise/fall time, there were
no significant differences in the N1 amplitude with differences in plateau time. Burgess et al. (2013) reported
that for bone-conducted pure tones, the best stimulus
had a frequency of 250 or 500 Hz and a 0 ms rise time.
Stimulus Duration
The effects of tone burst stimulus duration on the
oVEMP were evaluated by Lim, Dennis, Govender,
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