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CONTINUING EDUCATION
Common Clinical Encounters:
Do We Really Know Them?
By Ted Venema, PhD
IHS offers a diversity of options for obtaining continuing education credit: seminars and classroom training,
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A
s those working in the hearing healthcare field, it
is our duty for the purposes of rehabilitation to
walk with the knowledge of how the ear works.
We are the ones who, during our clinical encounters, counsel and educate patients, caregivers, and sometimes physicians. Yet, can we explain the basis for many of our daily
common clinical encounters?
What Exactly is the Occlusion Effect,
and Why Do We Get It
The typical definition of the occlusion effect is that one’s
own voice sounds louder when one’s ear is plugged. After
all, this is why hearing aids have vents. But we get the occlusion effect because low-frequency, bone-conducted sounds
Occlusion Effect: Low-Frequency, Bone Conducted
Sounds are Louder When the Ear is Plugged
Figure 1. The mass of the skull is shown in gray, and the outer ear
canal is shown in beige. When occluded (red), the low-frequency
energy cannot escape, and so it is forced toward the cochlea. This
results in a louder perception of sound when the ear is plugged.
THE HEARING PROFESSIONAL
are louder for the plugged ear. Mass resonates with low
frequencies and stiffness resonates with higher frequencies.
The mass of the skull resonate with the lows of one’s own
voice. This, in turn, vibrates the cartilaginous portion of
the outer ear canal. When the ear is plugged, this added
resonance cannot escape (Figure 1). It has nowhere else to
go but through the middle ear and into the cochlea, hence
the occlusion effect.
When listening to your own voice on a recording, you
hear yourself as others hear you through air conduction
alone. When you hear yourself talking, you hear by air and
by bone conduction, and you perceive much more lowfrequency sound. The low frequencies are by far the loudest portion of speech. These lows cause the skull to resonate. It’s these low frequencies that are heard most loudly
when we experience the occlusion effect. Say “s” while repeatedly plugging and unplugging your ear. Now try the
same thing while saying a lower frequency sound like
“mmm.” You should notice a robust effect with the
“mmm” but not with the “s.”
The Bing tuning fork test is based on the occlusion effect. It compares the sound of a low-frequency tuning fork
held against the mastoid bone while the outer ear canal is
repeatedly plugged and unplugged. The fork is normally
louder when the ear is plugged. With conductive hearing
loss, the occlusion effect is less. Plugging the ear still blocks
the low-frequency bone conducted sound from escaping,
but the middle ear pathology prevents the blocked sound
from passing through the middle ear and going on to the
Ted Venema, PhD, is a professor of the Hearing Instrument
Specialist Program at Conestoga College in Ontario, Canada. He
earned his bachelor’s degree at Calvin College and his master’s
degree in audiology at Western Washington University, and his
PhD at the University of Oklahoma. Venema also served as a volunteer on IHS’s education committee, the International Institute
for Hearing Instruments Studies.
5
CONTINUING EDUCATION
cochlea. The Bing test can also be done simply by using
one’s own voice, as indicated above.
What Does Ear Canal Resonance
Offer to the Understanding of Speech
Look at the combined resonances offered by the outer ear
canal and the concha (Figure 2).
Figure 3. The middle ear increases the pressure of incoming sound,
mainly due to the larger size of the eardrum relative to that of the
stapes. Another pressure increase is due to the leverage action of the
ossicular chain. The manubrium of the malleus (green) is slightly
longer than the long process of the incus (blue). The fulcrum is the
straight line running through the head of the malleus and the short
process of the incus.
Figure 2. Note how the open adult ear canal has a resonance between
1500 and 4000 Hz. The peak occurs at about 2700 Hz. These
frequencies are most important for discerning what word is spoken.
The odd shape of the outer ear causes these resonances.
The most important frequencies for understanding speech
lie roughly between 1000–4000Hz. As Figure 2 shows,
the outer ear creates an added 15–20 dB gain for these allimportant speech sounds. The connection between speech
and hearing here is unmistakable. The shape of this resonance also has a lot to do with the shape of noise-induced
hearing loss (NIHL).
The three middle ear ossicles are strangely twisted because in this way, they can provide the leverage action that
further increases sound pressure by 1.3:1. The length of
the manubrium of the malleus is about 1.3 times the length
of the long process of the incus.
Lastly, the buckling action of the TM increases the pressure of airborne sound by 2:1 (Figure 4). The movement of
the TM surface varies between the annulus (outer ring) and
umbo (center where the manubrium of the malleus ends),
and the areas in between. This is the buckling action.
Why Do Mammals
Have Middle Ears
The cochlea is filled with perilymph fluid in the scala vestibule, and the footplate of the stapes sits inside the oval
window. Most of the pressure of sound waves carried
through air bounces off fluids. Imagine your head under
water in a swimming pool. If one were standing on the
edge of the pool talking to you, you wouldn’t hear a word.
Almost all of the sound will bounce off the surface of the
water. Something has to help airborne sound puncture or
penetrate the fluid-filled cochlea, and that is purpose of the
middle ear.
The middle ear increases the pressure of airborne sound
in three ways: the size of the eardrum relative to that of the
stapes, the leverage action of the ossicular chain, and the
buckling action of the eardrum or tympanic membrane
(TM). The TM has 17 times the useful surface area as the
footplate of the stapes (Figure 3). Pressure is force over an
area; when sound pressure upon the relatively large area of
the TM is converged upon the much smaller stapes footplate, the pressure is increased by 17:1.
6
Figure 4. The TM is held fast by its outer ring, the annulus, and so it
cannot be displaced there. TM movement is greatest between the umbo
and annulus. Less displacement at the umbo means more force at the
umbo. This buckling action increases pressure by 2:1.
The impact of all these sound pressure increases can be
seen by multiplying the factors together: 17 @ 1.3 @ 2 =
about 44:1. A 10:1 sound pressure increase corresponds to
a 20 dB increase. A 100:1 pressure increase is a 40 dB increase, etc. A 44:1 pressure increase is somewhere between
a 20 and a 40 dB increase. Actually, the middle ear offers
an increase of close to 30–33 dB.
OCTOBER • NOVEMBER • DECEMBER 2010
CONTINUING EDUCATION
If the Middle Ear Makes Up 33 dB,
Why Can a Conductive
Hearing Loss be More Than That
We have all seen flat conductive hearing losses of 50–60
dB HL. When the oval window is pushed inward, the
round window bulges. Cochlear fluid does not compress so
easily, so if the round window could not bulge outward,
the oval window could not push inward. Otitis media
might result in this, because complete fluid buildup in the
middle ear space would prevent the round window from
bulging outward. Otosclerosis might also prevent the oval
window from being pushed inward. Without oval/round
window actions, conductive hearing loss can well surpass
the 33 dB that the middle ear adds to incoming sounds.
The Rinne tuning fork test is based upon the dB increase
offered by the middle ear. When the tuning fork is held
first against the mastoid bone and then held near the outer
ear, the sound of the tuning fork held near the outer ear is
normally heard loudest. This is because air conduction involves the outer, middle, and inner ears. It is a much more
efficient way to hear than hearing by simple bone conduction. Louder hearing by air conduction should occur for
both normal hearing and with SNHL. A healthy middle
ear makes up 33 dB, and the Rinne test is a simple and eloquent demonstration of this increase.
Why Are Hearing Thresholds
in dB Sound Pressure Level
Shaped as a Curve
The dB increases offered by the middle ear are different for
different frequencies. The resonances of the outer and middle ears combined together form the curve of human hearing threshold, as shown in Figure 5. At quiet inputs, the
ear is most sensitive to frequencies between 500 to 4000
Hz. Thresholds of 0 dB HL, across the seven audiometric
octave frequencies, therefore represent very different SPLs.
30
30
Total Ear Canal
&
Concha
20
Middle Ear
20
+
10
10
0
250
500
1000 2000 4000 8000
500
1000 2000 4000 8000
Our hearing sensitivity
40
=
0
250
Note how important speech Hz’s
emphasized
dB 25
SPL
10
0
125
250
500
1000
Hz
2000
4000
8000
Figure 5. The outer ear (top left) and middle ear (top right) together
contribute to the equal loudness curve (bottom). This curve actually
represents the sensitivity of one ear under a headphone; 0 dB HL on
the audiogram.
THE HEARING PROFESSIONAL
Why Does Carhart’s Notch
Appear with Otosclerosis
The term sclerosis means “hardening.” Otosclerosis is actually a growth of soft porous bone tissue around the oval
window and stapes. Therefore, some have called the pathology otospongiosis. A decrease in bone conduction
thresholds, mostly at 2000 Hz (Carhart’s notch), is commonly noted as a trademark for otosclerosis (Figure 6).
Figure 6. Carhart’s notch is not an indication of cochlear hair cell
damage. It is an artifact of the way we test bone conduction. The drop
in bone scores is most pronounced at 2000 Hz, which is also the
resonance of the middle ear ossicles.
Carhart’s notch does not, however, truly represent a drop
in cochlear sensitivity at 2000 Hz. Otosclerosis simply
changes the contributions of the ossicular chain to normal
bone conduction testing. There are actually three elements
that contribute to normal 0 dB HL bone conduction thresholds: 1) distortional bone conduction—hair cell stimulation
caused by vibration of the skull with the bone oscillator;
2) inertial bone conduction—the tiny lag in ossicular chain
movement when the skull is vibrating; and 3) osseotympanic bone conduction—the tiny vibration of the air column in the outer ear canal which can move the TM. With
otosclerosis, the stapes is fixated in the oval window and so
both inertial and osseotympanic bone conduction are compromised. The most obvious result is at 2000 Hz, the resonant frequency of the middle ear ossicles.
Acoustic Reflexes:
Why Do We Have Them
Acoustic reflex (AR) testing used to be performed more
frequently, and it should still be routinely performed today.
Here’s why.
The brain-going parts of the AR are the outer and middle ears, the cochlea, the VIII nerve, and the low brain
stem. The ear-going parts of the AR are the low brain
stem, and the VII and V nerves. These connect to the stapedius and tensor tympani muscles of the middle ear, respectively. We often think of ARs as nature’s protection
device against loud sounds because loud sounds “set them
7
CONTINUING EDUCATION
off.” Note, however, that ARs are most robust for low frequencies (500 and 1000 Hz). They reduce the intensity of
low-frequency sounds by about 15 dB. Recall that vowels
are loudest and lowest in frequency. Therefore, they stimulate the AR when we speak. The AR allows us to hear important high-frequency sounds by reducing the lowfrequency sounds that would otherwise easily mask them.
ARs occur while we talk; in fact, they occur about 1/20th
of a second before we begin to speak. It appears that the
AR enables us to better hear high-frequency sounds while
we speak.
ARs can also be thought of as a non-behavioral test of
inner hair cells (IHCs). Normal IHCs and OHCs are shown
in Figure 7.
Normal
Inner
&
Outer
Hair Cells
Picture by
R. Harrison (1988)
Charles C.Thomas,
Publisher
Springfield IL
Figure 7. An electron microscope photograph shows normal healthy
human IHCs and OHCs.
Damaged hair cells, especially OHCs, are shown in Figure 8. OHC damage often precedes IHC damage. OHC
damage often results in moderate sensorineural hearing
loss (SNHL), while severe-profound SNHL is associated
with both OHC and IHC damage. All things being equal,
IHCs are known to be responsible for poor speech discrimination. OHCs help IHCs to sense soft incoming
Damaged
sounds, but their damage will not normally result in as
poor speech discrimination. Two people who have a similar 50 dB flat SNHL may have very different speech discrimination. Chances are, the person with good speech
discrimination will have ARs present (at reduced sensation
levels); the person with poor speech discrimination will
most likely have absent ARs.
Why Do High Frequencies Stimulate
the Base of the Cochlea and
Low Frequencies Stimulate the Apex
The cochlea is an incredibly complex organ that changes
fluid motion into electricity. High frequencies stimulate the
basilar membrane near the base of the cochlea, and that
low frequencies stimulate the basilar membrane near the
apex of the cochlea. Why does this occur? Some mistakenly think it is because high frequencies have relatively
short sound waves, and so their traveling waves are also
short; low frequencies have relatively long sound waves,
and so their traveling waves are also longer. This concept is
fundamentally false because sound waves in air have little
in common with cochlear traveling waves. The basilar
membrane is the “floor” upon which the hair cells sit. It is
sandwiched between the scala tympani and the scala
media. All cochlear traveling waves involve the basilar
membrane. Consider that a 250 Hz tone has a wave about
4.5 feet in length. The entire length of the basilar membrane, however, is just over an inch! There is no way these
lengths of airborne sound waves can enter the cochlea.
The real reason is that the basilar membrane is narrow
at the base and wide at the apex of the cochlea. We actually have three rows of OHCs at the base of the cochlea,
and five rows of OHCs at the apex. High frequencies stimulate the base of the cochlea because the basilar membrane
has less mass and more stiffness near the base. Low frequencies stimulate the apex because the basilar membrane
there has more mass there, and it is more flaccid (Figure 9).
Because
Basilar Membrane (hair cell “floor”)
฀
Hair
Cells
฀
฀
฀
฀ ฀
฀
฀
฀
฀ ฀
฀ ฀
฀
฀
Helicotrema
Scala Vestibuli Oval Window
Reissner’s Membrane
(mostly
outer)
Scala Media
Promotory
Basilar Membrane
Picture by
Engstrom (1988)
Copyright by
Widex
Figure 8. An electron microscope photograph shows damaged hair
cells. Note that most damage is confined to the OHCs, as is typically
the case.
8
Scala Tympani
Round Window
From: Compression for Clinicians, 2ed,Venema, T., Thomson Delmar, 2006
Figure 9. At the narrow apex (left), the basilar membrane widens.
At the wide base (right), the basilar membrane narrows. These physical
mass and stiffness qualities of the basilar membrane determine the
peak of the cochlear traveling wave.
OCTOBER • NOVEMBER • DECEMBER 2010
CONTINUING EDUCATION
We also know the traveling wave has an “active” component (Figure 10). Here, the traveling wave is amplified
and also sharpened. These are the contributions of the
OHCs. Their natural cochlear amplification of the wave
enables us to hear soft sounds below the levels of conversational speech. The sharpening of the wave also enables us
to distinguish among frequencies that are close together.
Outer Hair Cells Sharpen the Peak!
They are the “muscles” of the cochlea
They usually get damaged first
Apex
Lows
Base
Basilar Membrane
Highs
Figure 10. A dull, rounded traveling wave occurs with OHC damage.
First, soft sounds are no longer audible; second, the resolution required
to separate or distinguish among frequencies close together is
diminished. OHCs tend to die first, resulting in a moderate degree of
SNHL. This degree is consistent with presbycusis.
Why does NIHL Drop at 4000 Hz
and Improve at 8000 Hz
The audiometric configuration of NIHL (Figure 12) is
unique. One reason this occurs is that the AR is most robust
for low frequencies, and so low frequencies tend to be most
protected. The noise presented by a gun, however, happens
faster than the reaction time of the AR, and so the damage
is done before the AR occurs. Poorer blood supply to the
4000 Hz region of hair cells is another reason why NIHL is
most pronounced at 4000 Hz. Another reason is that the
stapes footplate motion creates a particular fluid motion in
the cochlea with negative effects on the hair cells there. Another reason, however, is the complementary shape of NIHL
and the outer ear resonances (Figure 2). Noise tends to damage hair cells approximately a half-octave higher than the
frequency of the noise itself. Since the outer ear resonance
adds 15–20 dB of gain to incoming sounds, noise is constantly filtered through this resonance. The peak seen at
2700 Hz can simply be pushed upwards half an octave, and
flipped upside-down, at about 4000 Hz.
Noise Induced Hearing Loss (NIHL)
Noise tends to
–10
125
250
500
1000
2000
4000
8000
0
damage hair cells
10
20
1/2 octave higher
30
40
People with OHC damage most often have a reduced
ability to distinguish between frequencies that are close together. No wonder people who wear hearing aids commonly report difficulty when listening to speech in background noise (Figure 11).
50
60
70
80
90
100
110
120
It’s the “sharpening” thing that’s the main challenge
This is why hearing aids for ears aren’t like glasses for eyes
Natural shape of fluid wave:
2 peaks from 2 tones close in Hz
Hair cell damage results in:
smaller rounded peaks
Hearing aids make wave bigger:
but cannot sharpen it
Figure 11. OHC damage removes the “active” component of the normal
traveling waves that might occur with two stimuli close together in
frequency (top panel). The middle panel shows traveling waves with
reduced amplification and sharpness. The bottom panel shows what
happens to the middle wave with amplification. The amplitude is
restored, but not the sharpness.
THE HEARING PROFESSIONAL
Figure 12. NIHL has a shape that looks like the typical REUR flipped
upside-down, and shifted to the right about half an octave.
Why Does Ménière’s Disease
Typically Present with
a Rising Audiogram
Ménière’s is associated with an excess of endolymph fluid
inside the scala media of the cochlea. The membranous
boundaries or walls of the scala media are the basilar
membrane and Reissner’s membrane. These separate the
scala media from the scala vestibuli and the scala tympani.
Recall the unique shape of the basilar membrane. An excess of fluid buildup inside the scala media will tend to
bulge its membranous walls where they are largest and
most flaccid. Excess pressure of endolymph will thus become most evident at the apex of the cochlea, and will
mostly affect the low-frequency hair cells. This results in
Ménière’s disease having a rising reverse audiogram (Figure 13).
9
CONTINUING EDUCATION
Meniere’s Disease: Why A Rising, Reverse SNHL?
Apical basilar membrane
฀
฀
฀
250
500
1000
Basal basilar membrane
฀
฀
฀
2000
4000
8000 Hz
Endolymphatic hydrops 0
10
(too much fluid
20
in scala media)
30
40
Causes less stiff
50
apical BM to
60
be affected more
70
by excess pressure 80
90
100
110
Figure 13. An excess of endolymph fluid pressure will bulge the basilar
membrane mostly at the apex. This mechanically compromises
traveling wave motion and hair cell excitation mostly at the apex,
causing a low-frequency SNHL. Figure created by the author.
How Does the Asymmetrical
Traveling Wave Shape Show Itself
With Cochlear Dead Spots
The traveling wave shown in Figure 10 has an asymmetrical shape. Its peak is closer to the steep front of the wave
than to the more shallow “tail.” The steep peak always
faces the apex (low frequencies). The asymmetrical traveling wave shape is also seen in Figure 14. This creates what
is known as the “upward spread of masking.” A loud rumbling of a truck will easily mask the soft chirping of a canary, but a loud chirping of a canary will not mask the soft
rumbling of a truck. Loud, low-frequency stimulation creates a traveling wave with a large peak near the apex, and
a shallow tail sloping toward the base. The soft chirp of a
canary makes a small traveling wave with a peak confined
near the base. The tail of the traveling wave produced by
the loud truck will easily cover the wave produced by the
soft chirping of a canary. Low-frequency background noise
thus easily masks soft high-frequency consonants of speech.
Loud high-frequency sounds, however, may very well make
larger traveling wave peaks with higher amplitudes, but
the steep wave front of these waves still remain fairly confined to the base of the cochlea.
The asymmetrical traveling wave also has implications for
audiometry. With normal high-frequency hearing, a profound low-frequency hearing loss will look like a moderate
reverse or rising audiogram (Figure 15). Low-frequency
stimulation into a completely dead low-frequency hair cell
region along the basilar membrane produces a traveling
wave with a large amplitude peak in the dead hair cell region. The shallow tail of the same wave easily extends into
the living mid-frequency hair cell region. Mid-frequency
hair cells will thus become stimulated, and the person will
raise his/her hand indicating he/she heard the tone.
This is why low-frequency cochlear dead spots are associated with moderate reverse audiograms.
Moderate Reverse SNHL; Hearing Through Remote Hair Cells?
Apex
Base
250
500
1000
2000
4000
8000 Hz
0
10
20
30
40
50
60
70
80
90
100
110
Upward Spread of Masking Concept
Intense Low-Hz
traveling wave moves
entire Basilar Membrane
Intense High-Hz
traveling wave moves
Basilar Membrane only at base
Basilar
Membrane
Displacement
Basilar
Membrane
Envelopes
Figure 14. Traveling wave envelopes are shown for a low-frequency
tone stimulus (red) and a high-frequency tone stimulus (blue). A soft
high-frequency tone will produce a small traveling wave that will fit
inside of the low-frequency traveling wave. A soft low-frequency tone,
however, will produce a traveling wave that will not fit inside the highfrequency traveling wave.
10
Figure 15. Moderate Reverse SNHL is often a “signature” of actual
profound low-frequency hearing loss. Note how the “tail” of the
traveling wave here creeps into the mid-frequency regions.
With normal low-frequency hearing, a profound highfrequency hearing loss might look like a steep, precipitously dropping audiogram (Figure 16). The high-frequency
hearing loss, however, must be severe in degree. To appreciate why, imagine intense high-frequency stimulation into
a completely dead high-frequency hair cell region along the
basilar membrane. This produces a traveling wave with a
large amplitude peak in the dead high-frequency region. In
this case, however, only a tiny piece of the steep front of
the same wave can extend into the normal mid-frequency
region. With progressively higher frequencies, the peak of
the traveling wave occurs further and further inside the
dead hair cell region. Due to the steep shape of the front of
the traveling wave, dramatic increases of high-frequency
stimulation are required in order for the steep front to extend into the healthy mid-frequency hair cell regions. This
is why high-frequency cochlear dead spots are associated
with severe precipitous audiograms.
OCTOBER • NOVEMBER • DECEMBER 2010
CONTINUING EDUCATION
As the old saying goes, “one can help the dying, but not
the dead.”
Summary
It is the job of hearing healthcare professionals to elucidate
and explain how the ear works for purposes of rehabilitation. The specifics of the cochlea anatomy and physiology,
and how its complex inner workings translate into clinical
phenomena, are part of the professionals’ education. That
knowledge and ability to communicate that knowledge during clinical activities is the hearing aid specialists’ best marketing tool to patients, their caregivers, and physicians. THP
All figures within this article were created by the author.
Figure 16. Severe-profound precipitous high-frequency SNHL is
often a “signature” of actual profound high-frequency hearing loss.
Note how the front of the traveling wave here creeps into the midfrequency regions.
Implications for amplification: amplify moderate reverse
and severe precipitous audiograms with care. Applying a
lot of output into dead areas will not do much to rehabilitate the client. Clinicians might do well to amplify the
transitions of these audiograms, not the worst thresholds.
This article was adapted and reprinted with permission
of AudiologyOnline. View the original article, and earn
CEUs from hundreds of other text-based, live, and recorded
courses from the leading experts in audiology for $99/year
at AudiologyOnline. To register, visit www.audiology
online.com or call 1.800.753.2160.
References
Musiek, F. E. (1983). Assessment of central auditory dysfunction: The
dichotic digit test revisited. Ear and Hearing, 4, 79–83.
Venema, T. H. (2006). Compression for Clinicians (2nd edition). NY:
Thomson Delmar Learning.
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THE HEARING PROFESSIONAL
11
IHS Continuing
Education Test:
Common Clinical Encounters:
Do We Really Know Them?
For continuing education credit, complete this test and send the answer section at the bottom
of the page to: International Hearing Society
16880 Middlebelt Rd., Ste. 4, Livonia, MI 48154
• After your test has been graded, you will receive a copy of the correct answers and a
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• Credit: IHS designates this professional development activity for one (1) continuing
education credit.
• Fees: $29.00 IHS member
$59.00 non-member (Payment in U.S. funds only.)
1. The resonance of the adult outer ear canal lies
roughly between:
a. 125–8000 Hz
b. 500–2000 Hz
c. 1500–4000 Hz
d. 2000–6000 Hz
e. 500–4000 Hz
6. The middle ear provides about a ____ dB increase
to incoming sound.
a. 17
b. 3.3
c. 44
d. 33
e. 2.1
2. Noise induced hearing loss occurs about ____octave
higher than the resonance of the outer ear canal.
a. 1/2
b. 1/3
c. 1/4
d. 2
e. none of the above
7. Carhart’s notch is a:
a. drop in air conduction thresholds at 2000Hz
b. drop in bone conduction thresholds at 2000Hz
c. improvement in air conduction thresholds at 2000Hz
d. improvement in bone conduction thresholds at 2000Hz
e. none of the above
3. In the cochlea, there are ____ rows of outer hair
cells at the base and ____ rows at the apex.
a. 5/3
b. 3/5
c. 3/4
d. 4/3
e. none of the above
4. This tuning fork test is based on the occlusion
effect.
a. Rinne
b. Weber
c. Bing
d. Schwabach
e. Venema
5. This tuning fork test demonstrates the SPL increase
provided by the middle ear.
a. Rinne
b. Weber
c. Bing
d. Schwabach
e. Venema
8. At the base of the cochlea, the floor upon which the
hair cells stand (basilar membrane) has:
a. more mass and less stiffness
b. more stiffness and less mass
c. more mass and more stiffness
d. less mass and less stiffness
e. more inner hair cells
9. The following is true about the traveling wave:
a. short steep wave front faces the apex of the cochlea
b. short steep wave front faces the base of the cochlea
c. long shallow wave front faces the apex of the cochlea
d. long shallow wave front faces the base of the cochlea
e. speed increases as it approaches the apex of the cochlea
10. Which of the following statements about acoustic
reflexes (ARs) is FALSE?
a. ARs are more robust for low frequencies
b. when they contract, ARs reduce low frequency sounds by
approximately 15 dB
c. they occur when we talk
d. they cause upward spread of masking
!
COMMON CLINICAL ENCOUNTERS: DO WE REALLY KNOW THEM?
Name
ANSWER SECTION
Address
City
(Circle the correct response from the test questions above.)
State/Province
Zip/Postal Code
1.
a
b
c
d
e
6.
a
b
c
d
e
2.
a
b
c
d
e
7.
a
b
c
d
e
Last Four Digits of SS/SI#
3.
a
b
c
d
e
8.
a
b
c
d
e
Professional and/or Academic Credentials:
4.
a
b
c
d
e
9.
a
b
c
d
e
(PHOTOCOPY THIS FORM AS NEEDED)
Please check one: M $29.00 (IHS member) M $59.00 (non-member)
5.
a
b
c
d
e
10.
a
b
c
d
Email
Office Telephone
12
OCTOBER • NOVEMBER • DECEMBER 2010