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"IN VIGOROUS DEFENSE OF VOLUME CONTROL"
By Max Stanley Chartrand
If normal ears came equipped with a volume control (VC)
and, for the sake of example, it was turned up slightly
louder than one's most comfortable loudness (MCL), one
would undoubtedly complain that their own voice sounds
"bright, hollow, in a well." If it was turned slightly
downward from MCL, one would complain that their voice
sounds, "as if I have a cold, plugged up, occluded." Why
is that?
For starters, normal ears are endowed with an elaborate
own-voice monitoring system comprised of interneural
connections from the facial nerve (cranial nerve IX) in
the forehead sinuses all the way into the larynx and
pharynx region along the vagus (cranial nerve X).
Interspersed here and there are involved myriad neuronal
junctures as well, the trigeminal (cranial nerve V), a
branch of the fourth cervical, tympanic plexus and
stampedes, to name a few participants in this elaborate
network.
Why, then, would it not be a vital imperative in
auditory rehabilitation to work toward restoration of
one's ability to monitor their own voice when fitting
hearing aids? Alas, we have hour-to-hour, day-to-day
variables with which to contend in the impaired ear:
eustachian tube dysfunction, auditory fatigue and a host
of amplitude-affected cochlear anomalies, such as
diplacusis, loudness growth abnormalities and loudness
intolerance.
Since the advent of AGC, ASP, TILL, WDRC, multiple mic
array and expansion technology, there seems to be
arising chorus of consensus that the end is near...of
the hearing aid volume control, that is. But, how do we
accommodate the above-mentioned auditory brick walls if
not with the lowly user volume control? Indeed, it is
arguable that pervasive disregard of the above concerns
has cost our industry unfathomable financial loss in the
form of unsustainable credit return rates, even more
shell remakes and unnecessary and circuit/model changes.
Thus, some continue to ignore these realities at their
peril, to the disappointment of those entrusted in their
professional care.
Typically, we as a profession approach own-voice
complaints as a simple venting problem. However, it is
generally agreed that this theory has been carried to
the extreme of often eliminating or destroying real ear
acoustical advantages of modern amplification. Venting
should be carefully integrated into the
acoustic/resonance schemata, not in response to "own
voice" complaints.
In this article, we will review when a user VC may be
contraindicated and when its utilization is not only
indicated, but necessary. Furthermore, we will outline
the rationale for training our patients on how to
utilize their VC to successfully overcome "own voice"
and other communicative complaints that no current
technology can otherwise resolve.
CONTRAINDICATIONS FOR A USER VC
All hearing instruments feature a volume control. The
issue is whether the VC should be user-adjusted or
reserved only for manipulation by a professional
practitioner.
When is a user-controlled VC contraindicated? Certainly,
deep-fitting CICs cannot accommodate a user VC. In
addition, those with severe dexterity limitations and
those with cognitive challenges contraindicate
utilization of a user VC, irrespective of other
considerations. But a word of caution, loudness
perception changes are so dramatic with directional
technology that such is never recommended without a user
VC. If the patient does not have the dexterity to
manipulate a user VC, would they not also have the same
difficulty adjusting mic array settings?
In an of the above cases the specialist and the patient
must prioritize the various aspects of the fitting. Is
optimum intelligibility or cosmetics more important than
user convenience? Are own-voice and non-acoustic
occlusion complaints more important than loudness growth
and signal-to-noise issues? Do patient limitations
override other amplification considerations?
FIVE REASONS USER VC ARE REQUIRED
It is this author's finding in both research and
hands-on work with thousands of hearing instrument users
that most moderate and severe cases require a user VC
for better control of their listening environment.
Especially included in this group are those who have
precipitous patterns, where lows are near normal and
highs fall steeply after-ward. This latter group has
been credited with contributing to the largest number of
repeated shell modifications and returns for credit.
However, incidence of credit returns and remakes
plummet.
Following are five reasons, often undetectable in the
initial evaluation, that may indicate need for and
training with a user VC.
1. Auditory fatigue: Even normal hearing subjects
experience some degree of lessened auditory sensitivity
as the day wears on, albeit only about one difference
limen (DL or jnd), or 3ó4dB. That same 3-4dB in, say, a
precipitous loss of 55dB PTA could translate into 2-5
DLs, or a sensation loss of what is perceived as a
8-20dB jump for every decibel of increase in the high
frequencies by the end of a long, noisy (and
over-amplified) day. Hence, a programmed or screw-set VC
set in the morning may evoke complaints of "fuzzy, dull
hearing" by
evening (along with an increased sensation of
occlusion). Conversely, VCs set in the late afternoon or
evening may rudely awaken ears as "too sharp, too loud"
by morning after a good night's sleep (and recuperation
of the fatigued ear). Patients with extreme recruitment
are particularly at risk when auditory fatigue is not
considered in choice and use of the VC.
Figure 3. Five good reasons a user VC maybe advisable.
2. Abnormal loudness growth: Many patients with
sensorineural losses exhibiting thresholds greater than
60dB PTA often go from SRT to MCL in a mere 5-lOdB span,
creating a loudness growth sensation up to five times as
fast as their normal hearing counterpart. In other
cases, the UCL can be a mere 5-lOdB above MCL. In either
case, current compression technologyó without risking
loss of clarityócannot adequately accommodate either the
recruitment or dynamic range limitations. This is
further compounded when accompanied by critical
bandwidth distortions in the faster-growing high
frequencies. A user VC allows the patient one more level
of control over untenable variations in sound pressures
within their listening environment.
3. Own-voice complaints: Arguably, own-voice complaints
comprise one of the most common reasons given for credit
returns. First of all, a VC should be set to the user's
own voice first before anyone else's. In most cases, the
PB Max most practical performance level is achieved when
gain is set to the user's voiceónot to some external
source or arbitrarily derived gain curve. As it has been
stated again and again in the literature, people listen
at MCL, not at SRT. Granted, during delivery of the
hearing instruments and the rehabilitative process, some
patients may need to learn to speak at a more normal
level. Perhaps monitoring the conversational voice at
60-65dB SL with an SPL meter will help during auditory
rehab training. In a subsequent issue of The Hearing
Professional, the author will de- scribe an effective
method aimed at training users to manipulate their VC to
accommodate occlusion and own-voice complaints. Suffice
it to say here that an estimated 90 percent or more of
own voice complaints may be resolved by the patient's
learning to properly manipulate the VC.
4. Better function in noise: Something often overlooked
in explaining the new technologies is how users may
utilize the VC to improve their signal-to-noise
function. No longer are these VCs simply volume
controls, changing only the gain of an instrument. They
often, depending upon the technology used,
simultaneously alter gain, output and input sensitivity
(depending upon TK and expansion levels). Hence,
rotating the user VC forward often increases sensitivity
for distance hearing with a slight lessening of
sensitivity for sounds up close. Conversely,
rotating the VC backward increases sensitivity to sounds
close with a slight lessening of sensitivity for sounds
at a distance (primarily because output has been lowered
slightly). Two extreme listening situations can then be
improved by advantageous manipulation of the VC for
hyper-recruiting patients: conversation in a noisy
restaurant where sensitivity is important for voices
close by or in a quiet meeting where sensitivity should
reach out to the softest spoken voice at the other end
of the table without over-amplifying voices closest to
the listener.
5. Limitations caused by cochlear distortion artifacts:
Severely hearing impaired users nearly always exhibit
considerable manifestations of the above four problems.
Additionally, we often find diplacusis, cochlear
summation (abnormal expansion of critical bandwidth) and
octave confusion. These, in combination or singly, may
be more effectively ameliorated- all other factors being
equal- the patient can manipulate a VC when the
listening environment or critical listening situation
becomes challenging.
DISCUSSION
A note is in order over why CICs may be considered
exempt from requiring a user VC. True, CIC users may
also be subject to the above anomalies; indeed, some may
experience any of these problems to a greater degree
than many non-CIC users. However, because of the very
close proximity of the CIC receiver tube to the TM
(ideally less than 1/4 inch), we are talking
(physically) of much smaller decibels. Since decibel
intervals are algorithmic sound pressure ratios rather
than equal steps of intensity, the higher the intensity,
the larger the physical size of each succeeding
interval. Thus, auditory fatigue fluctuations are much
smaller, as is the growth of loudness, with CIC
instruments.
Proximity of the CIC microphone to the TM also enhances
the high frequencies better, which tends to improve
signal-to-noise ratio. However, many if not most
individuals may not be candidates for the CIC due to
severity of hearing loss and attendant idiosyncrasies,
epithelial hyper-sensitivity and/or dexterity
limitations.
CONCLUSION
The question of whether a patient requires or would be
helped with a user VC should be handled on an individual
basis. However, it is the author's belief that most
patients will benefit by having a user VC. Such control
allows them to better accommodate a whole host of
conditions, most of which may be undetectable during the
initial evaluation battery.
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