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HEARING EVALUATION IN THE DISPENSING PRACTICE, Part II
By Max Stanley Chartrand
(Note: Illustrations were lost during the transfer of
material to this site.)
Figure 5.4 Above is an example of the aided responses of
a client with a slight to moderate hearing loss as shown
in Fig. 5.6.
For our purposes here we will go on to describe some
other essential factors relative to speech
discrimination testing, keeping in mind that, again, we
are taking primarily the rehabilitative focal point:
1. Because of the prevalence of phonemic regression in
many sensorineural and presbycusis cases, it is dubious
at best to expect to obtain true potential aided discrim
scores before adaptation to amplification. Indeed, it is
widely accepted that an average of 60-90 days (or more)
is required for most sufferers of this central auditory
condition to overcome its effects. What has been
long-forgotten must be relearned and, upon receiving the
lost sounds anew, does not clearly exhibit the
rehabilitative potential for improved speech
discrimination at the beginning of that process. See
figure 5.5 for a better illustration of a “time-based
adaptation curve as shown in one recent study (Gatehouse
and Killion, 1993).
2. Unless a specific pattern in the defective speech
sounds is detected during discrim testing the
information obtained will have little relevant
information pertaining to the prescribed amplification
parameters. The Duffy method is frequency-specific and
is based on recognition of patterns of missed
consonants, vowels, and semi-vowels.
3. For speech discrim testing to hold any validation
capability it must be scientifically applicable in
soundfield testing which is the only complete validation
technique available to the hearing health professional.
Furthermore, it must be repeatable from one evaluator to
another.
4. With the introduction of noise competition such as
provided in speech-in-noise (SiN) or signal-to-noise
(S/N) testing, it is important for the evaluator to
detect which specific speech sounds are abnormally
affected.
Along with the above observations, the author recommends
that the student study the phoneme recognition quick
test (Duffy, 1987) and its application as a validation
protocol in their hearing aid fittings. The literature
is now replete with explanations, critiques, and reports
to guide the specialist in the mastery of this advanced
concept. For that reason we'll not provide a dialogue
for the speech tests or a procedural description, with
the hope that the conscientious specialist will initiate
further study on the topic individually. Speech discrim
testing is a most vital part of the hearing evaluation
that requires the utmost skill and attention of the
specialist. Furthermore, as the basis for evaluation,
validation, and counseling, it will serve as an
indispensable tool in the modern hearing aid practice.
Figure 5.5 Time-based speech-in-noise (SiN) score
comparisons from Gatehouse (1992) in patients fitted
with flat and shaped response curves. Note the
significant improvements in the shaped-response patients
from delivery of hearing instruments (day 1) to end of
12-week rehabilitation period. Used by permission of
Gatehouse & Killion from an article on HABRAT.
Delivery and Verification
Most problems that arise from hearing aid fittings
result not so much from the evaluation process, but more
from (lack of) delivery protocol. It is imperative for
the specialist to develop a uniform protocol for
delivery and verification to assure that every point is
covered, and that expectations from amplification are
realistic. The more important aspects of counseling
occur from this stage and beyond. Therefore, we will
recommend, in the following pages, a delivery pattern
for consideration, keeping in mind that this is a basic
pattern that may be reproduced by all dispensers, new
and experienced alike. Some of the particulars are left
to the individual dispenser to utilize with their own
knowledge and skills relative to the needs of their
patients.
Before getting into the suggested delivery method, it
must be explained that several goals are to be
accomplished to make this a viable procedure:
1. Preliminary programming and quality assurance
procedures are to be performed BEFORE the patient
arrives.
2. By the end of the delivery, the patient should be
able to:
-Insert and remove the instruments properly
-Adjust volume controls to their own voice utilizing
biofeedback methodology
-Learn how to cope with wind, background, large area
listening, etc.
-Know how to use on the telephone
-Insert & remove the battery
-Know how to care and maintain the instruments
-Understand all federal and state disclosures
3. Be given a long-range aural rehabilitation program
overview, including instructions on a wearing schedule
4. The third party and patient BOTH should receive
counseling in communication coping strategies, and any
other assistance necessary to meet their specific needs
5. Have a post-fitting adjustment appointment date and
time in hand
Explanation of the biofeedback volume control method.
Since 1978, the author has utilized the “own voice
first” approach to setting hearing aid controls with
consistent success. At the time little research
information was available to explain the neurological
“markers” of the ear canal that were incited by
insertion of a hearing instrument. Even to this day,
with a virtual explosion in knowledge about the
neuroanatomy of the ear, it seems we are still learning
as an industry to respect those reflexes that nature set
in place to protect the ear from “foreign objects”.
Indeed, the hearing aid is a foreign object of the first
order. The trigeminal nerve (Cranial V), vagus nerve
(Cranial X), facial nerve (Cranial VII),
glossopharyngeal nerve (Cranial IX), and a host of
other, more intermediary branches of nerves course
through and around the external meatus, the tympanic
plexus at the TM, and around the middle ear and
Eustachian tube. Non-acoustic occlusion complaints can
occur in disregard of these reflexes when fitting
hearing aids or earmolds (Hickock et al, 1993)(McSpaden
et al, 1993).
The late Elaine Kramer (1987) introduced the author to a
method she used, that developed from numerous patient
reports as the best way to achieve the desired volume
control level to accommodate the user’s own voice. Her
methodology provided a more organized format to the
author’s and has since been the subject of many
continuing education lectures. But it must be said here
that the concept appears to be generally regarded as
illusory by normal hearing educators in the hearing
instrument field, precisely because of lack of internal
reference in personal experience. But the phenomenon
remains for hearing impaired individuals who, in large
numbers, continue have difficulty adjusting to wearing
hearing aids. While its relevance to arbitrary
target-gain or PB-Max may be in question, we know from
experience that most users, especially men, prefer to
wear their volume control at a level where they no
longer experience occlusion, and where their voice
resonates freely without pressure the larynx or the
hollowness of the nasal area.
We know that one of the first things that must be
overcome is the conductive and interaural masking effect
experienced when an object touches the pinna. A related
problem involving some of the same neural reflexes and
conductivity arises when attempting to mask during bone
conduction testing (Sanders, 1991)(Feldman, 1961). The
resulting occlusion/conduction/masking effect can be as
high as 25-30dB in the low frequencies (Dirks and
Swindeman, 1967). Therefore, the masking stimulus must
be loud enough to overcome the
occlusion/conduction/masking effect that resulted from
placement of an object (the earphones) over the ears.
This has widely been assumed to be solely a result of
closure of the ear canal. Another view of this phenomena
has to do with self-monitoring of one’s own voice.
Normal hearing persons hear a combination of their own
voice internally, through bone conduction, and
externally through the external meatus. When they hear
their voice more internally than externally, they
associate it with “feeling plugged”. In actuality, they
are hearing a unique combination of nasality, middle ear
conduction, and sinus artifact that they come to accept
as “normal”. When a hearing aid is placed in their ear,
this state of “normality” is upset. Some of this upset
is due to high frequency information, part of it is an
increase in external hearing of one’s own voice. But,
when there is an increase of internal hearing of one’s
own voice, there is almost immediate rejection, as it is
perceived as an abnormal state. Such a condition also
tends to “push down” on the larynx and pharynx, the
mechanism of which we do not yet fully understand in the
hearing field. An increase of volume (and sometimes a
slight change in venting, externally or internally)
usually relieves the downward pressure and plugged
sensation---because external hearing of one’s own voice
has overcome internal voice conduction. If the volume is
set too loudly, complaints of hollowness, echo, and
brightness are evoked.
The following sequence covers common patient reports as
their volume controls are systematically manipulated to
find the best position for their own voice’s resonance.
In this example, the hearing aid is vented as
recommended for acoustic reasons and they are reading a
quotation or counting slowly to ten:
1. VC turned off, patient reports:
“feeling plugged up”
“like my head is in a barrel”
“as if I have a head cold”
“my voice sounds unnatural”
2. Volume control (VC) is turned up slightly and left at
a low level, patient reports:
“pushing down in my throat”
“pressure when I speak”
“my head still feels plugged”
3. Volume control turned up to the point near best
speech discrimination, they report:
“My voice sounds more natural”
“No pressure now”
“Seems to vibrate freely”
“Sounds more resonant”
4. Volume control adjusted above predicted use-gain
level, report becomes:
“My voice sounds hollow”
“Kind of an echo effect”
“Too bright and loud”
“Nasally”
5. Return of the VC to the setting at #4 evokes a return
to relative normality and acceptability.
By adjusting the volume control at the level best suited
to the patient’s own voice, the author has found:
· Very few own voice complaints
· Proportionate hearing of external voices and sounds
· VCs adjusted near the best level of speech
discrimination
· Far fewer remakes, modifications, and credit returns
It must also be kept in mind that at each programming or
frequency response change that the volume control will
need to be reset for the patient’s own voice. This is
particularly a consideration for those with screw-set
VCs or internally programmed VCs, making it particularly
daunting for the specialist to assure proper
readjustment of the hearing aid. Since this phenomena is
especially critical for losses that begin near-normal in
the lows and dropping off rapidly in the highs, careful
attention to this methodology is absolutely essential.
It can be safely assumed that a high percentage of shell
remakes and returns for credit at the factory are due
more to this one oversight/challenge than any other
encountered in the industry. And while remake and credit
return rates continue to plague the industry at a
consistent level, it is would be safe to assume that
more attention must be paid to the adjustment, and
counseling of own voice complaints at the time of
hearing aid delivery.
A review of the delivery procedure. If steps are skipped
in this procedure some very important psychological,
sociological, and physiological elements may be omitted
which could weaken the success of the fitting.
1. Quality assurance, pre-programming and factory
communication. Preparatory quality assurance steps
should be taken before the patient arrives for delivery.
In this way, there will be fewer surprises at delivery
and communication with the factory can be accomplished
without the pressure of a waiting patient.
Pre-programming of the instruments, in programmable
cases, to assure initialization and programming can be
accomplished on the new instruments.
2. Listening and insertion. With the patient present,
the specialist can perform a final listening and visual
examination of the new instrument(s) to assure them that
the instrument(s) meet the specialist's approval and
expectations. Before insertion the specialist should
apply a light coating of alcohol and lanolin (or other
antiseptic/lubricant) on the shell portion. This will
prevent gathering of the skin tissue at the entrance of
the ear canal, and will allow for easy insertion. This
will also prevent introduction of bacteria or fungi into
the ear canal, something no new user needs added to the
challenges ahead of them. Insert first, one side,
asking, "How does that feel?". Upon an affirmative
response, you are ready for step #3, setting the volume
control.
3. Setting the volume controls. The volume control
should be manipulated to the desired level in the manner
described above and below, beginning the process with
the instruction,
"Now, we are going to set your volume control at the
point where your voice sounds just right to you. I’d
like you to read the following quotation aloud, in a
normal tone of voice, as we start at the bottom of your
volume control taper and work my way up. You may notice
a pressure sensation or stuffy feeling on your voice at
first, which should clear up as I raise the volume. If I
get past the best point of comfort, you may hear your
voice echo or sound hollow---that means we are too loud,
and we need to back off some. When I get to the point
where your voice sounds just right, raise your hand. Are
you ready?"
Then, hand them a card or laminated sheet with Helen
Keller’s statement to read slowly and aloud:
"I am just as deaf as I am blind. Deafness is a worse
misfortune, for it means the loss of the vital
stimulus..." to assess their voice as the specialist
raises or lowers the VC while in the ear.”
An alternative to the Helen Keller quotation is to
instruct the patient to slowly count to 10 until you
have adjusted the volume control to be ideal level.
Remember, part of the purpose for this method is to
overcome occlusion effects, both acoustic and
non-acoustic. At the other extreme is to avoid over
amplification of their voice, which brings the hollow
effect. Since they are the closest voice to the speaker
of their instruments, it is absolutely imperative that
the patient uses their own voice first for
quantification of comfortable loudness, instead of using
another's voice. The importance of setting the volume
control to the user's own voice first cannot be
emphasized enough!
Adjust the other side in like manner. It is also
important to note that in many cases the binaural
summation effect may cause a slight over-loudness of the
resulting setting, in which case a slight VC reduction
on both instruments may be in order. Ascertain by again
asking for a report on their own voice quality. Note: Of
course, to hear high frequencies (or lack of) in one’s
own voice for the first time in years can be initially
very disconcerting. This must be pointed out, counseling
the patient that, over time, their “new” voice should
sound more normal as they become more accustomed to
hearing it as others do.
4. Determining directional/localization ability. A
simple test to determine directional ability of a
binaural fitting is by using the handles of the two
tuning forks (or other like objects) to produce sharp
"clicks". The client will be instructed,
"Now, I would like you to close your eyes and point the
direction from which you hear a series of clicking
noises. Follow these noises with your finger."
The specialist will then begin at about 3 feet from the
user's head, by clicking the fork handles near the right
ear, while the user points in the direction of the
sound. Next, go to the left ear and do the same until
they point in that direction. Then, clicking in the
center (azimuth) position, continue until they point
precisely at the sound source. If there is difficulty
for them to ascertain center position, a slight
adjustment of the lateralized (loudest) instrument may
be in order by reducing the gain slightly. Be careful
that they do not turn their head or "cock their ears"
for finding the signal. That will only invalidate the
procedure. This is also an ear-training exercise to
assist them in localization in the amplified state. For
further ear-training, the specialist may also sweep from
side to side, asking the patient to point (with the same
hand) from where the sound is coming.
5. Noise tolerance and sensitivity.
In this section the specialist will find out whether the
instruments’ output is within comfortable limits. While
there are many more scientific approaches, this
practical test is quick and will alert to most potential
problems. Also, this constitutes excellent ear training
for the patient so that THEY can determine what to
expect of these kinds of sounds. Otherwise, they may be
under the impression that hearing such noises in the
everyday environment is something that should be
adjusted out, thereby rejecting an adequate amount of
amplification. The specialist will begin this test by
explaining,
"I am going to make various sounds and noises to find
out if they are too loud for the volume control setting
that we are now on. I'd like you to tell me if these
sounds bother you or sound piercing on the ear."
Then, by making sharp sounds in the following manner,
one may determine not only the type of sound that may be
unacceptable but the approximate frequency range of the
offending noises:
1. Striking metal to metal (>700-1KHz)
2. Striking metal to glass (>1K-1.5KHz)
3. Striking glass to glass (>1.5K-2KHz)
If adjustments need to be made, the specialist may lower
output slightly by use of a potentiometer or by
programming. In cases where neither potentiometer or
computer programmability are available the use of
Knowles filters or lamb's wool (Chartrand, 1989) may be
used as trial or temporary filters until more effective
changes may be made by the manufacturer. The best rule
of thumb is to be conservative on the use of filters.
For instance, just a 2-4dB drop in peak SSPL90 can make
a tremendous difference in achieving adequate “headroom”
response, while not degrading necessary frequency and
gain parameters significantly. An added psychological
benefit of this procedure is that the patient and third
party know how the patient is going to respond to those
types of sounds. Rather than being startled or surprised
after leaving the controlled environment of the office,
they will now be more apt to subconsciously accept the
sharp, extraneous noises of life once they leave the
specialist's office.
6. Paper rattling. There seems to be a strong
psychological component to the sound of paper rattling
in new hearing aid users. The problem lies in the fact
that this is a noise closely related or intermingled
with the critical range of speech. Because of its
prevalence in modern society, it is important to
demonstrate that they can hear paper rattle without
destroying their ability to function. In most cases,
this is actually an ear training exercise, but there
will be some legitimate situations that warrant
frequency response adjustments. With the following
instructions, the specialist will instruct, while
rattling a thin sheet of paper in their hands,
"Now, I am going to rattle this paper and ask you to
tell me if you still understand my voice over this paper
rattling. Can you still separate my voice from this
paper rattling?" (You may continue to talk until they
have had a chance to assess your voice over the noise).
Usually the affirmative answer is an indication that the
patient can subconsciously accept the sound of amplified
paper rattling, and, hopefully, will not be disturbed by
it next Sunday at church or at work, etc. This factor
should never be overlooked or the specialist may find
themselves in the formidable position of trying to
appease a patient who insists they want to be completely
rid of the sound of paper rattling without subduing the
speech range----an impossible task at that!
Whisper test. And, finally, it is important to
demonstrate that hearing sensitivity has not been
sacrificed while damping, filtering, and adjusting for
loud sounds. This may be accomplished in several ways,
probably the most dramatic being the "whisper test".
This is accomplished by the specialist leaning down near
the right ear of the client and whispering,
7. "Can you hear me whisper?". Many first time patients
have not heard a whisper, or at least heard it clearly,
for many years. The consonant sounds that comprise a
whisper are the very same sounds that we strive most to
amplify with hearing aids. To help the patient get an
idea of the sound of a whisper in the amplified state,
and to gain confidence in hearing it, it is important to
take a moment and demonstrate it. This will also help
the third party appreciate the fact that improvement has
been enjoyed with amplification. Going from ear to ear,
in a voiceless whisper, the specialist will ask,
“Can you hear me whisper in this ear? How about over on
this side, can you hear me?"
The successful response to this test will be an
assurance to the client and the observing third party
that indeed the potential is there for the client to
hear softer speech with their new instruments. Caution
should be taken in utilizing this procedure when it is
not feasible, because of degree or type of hearing loss.
8. Validation by pure-tone and speech soundfield. This
section can be the most important section from a
validation standpoint (Chartrand, 1993), and one in
which we will render a little more explanation. Keep in
mind that we have adjusted the volume controls, but we
have not permanently marked them or otherwise "set" them
in place. We do not want the patient to touch the volume
controls until we have run all tests and we have marked
the VC position with the markers, which we will do at
the end of this section.
We are assuming that the VCs are set at an appropriate
use-gain setting. The patient's own voice sounds
comfortable, various noises have been demonstrated to be
tolerable, and both instruments are relatively balanced
for directionality. Now, we want to use pure-tone
soundfield, which this author and others (Goldberg,
Duffy, etc.) advocate as an excellent comparative method
with the air-conduction audiogram. While the traditional
methodology has heretofore been in SPL (sound pressure
level), we will herein provide a brief rendition of
pure-tone soundfield in HTL-calibration so that we may
superimpose the completed soundfield audiogram over the
air-conduction audiogram taken earlier on the client's
ears.
But first, we must explain a few things about pure-tone
soundfield testing. Because we are not able, within the
scope of this text, to cover the mechanics of set-up,
facilities, equipment, and applied physics of sound, we
will make only reference to those items that will be
most pertinent to counseling for expectations from
pure-tone results. It is further recommended that the
student attend courses on soundfield testing and study
printed materials in this regard (Speaks, 1992). Here
are the considerations:
· Because of tremendously varying---and often
unpredictable----suprathreshold loudness growth rates
for many individuals, we cannot expect the soundfield
results to show a great deal of discrete frequency
correction where thresholds fall below the 70dB line of
the audiogram. If, for instance, the pure-tone audiogram
already indicates a threshold @2KHz of 80dB, it would be
unrealistic to expect the corrected threshold to rise
above the 35-40dB line of the audiogram without
intruding upon the individual's discomfort level at that
particular frequency. In this case, attempting to
approach audiometric zero is totally unfeasible....but
this may need to be explained to the client in the
course of counseling. A good rule of thumb is correction
of no more than 40-50dB at any given frequency for
sensorineural cases, and especially for presbycusis.
· Should the patient have normal or near-normal
thresholds at a given frequency (let's say, 500Hz @
15dB), the corrected threshold should look little
different than the uncorrected threshold. It is easy
enough to explain that no amplification is needed in
that region.
· When the pure-tone audiogram is "off the chart" in a
given region (let's say @4KHz), it is possible they
might respond to the mechanical noises of equipment
switches instead of the tones themselves. It is
important for the specialist to ascertain that
possibility before recording the response. Also, a quick
check for diplacusis---comparing a given pitch in one
ear with the other---would be in order in cases where
"off the chart" frequencies are responded to during
aided soundfield.
· Generally, it is not possible and certainly not ideal,
to approach "0" HTL in corrected thresholds at any
frequency. A better goal is to achieve what is called
the long-term spectrum of speech (Berger, Hagberg, and
Rane, 1979), which presents a curve starting at a point
about 25dB (on the HTL scale) in the lowest frequencies,
ascending to about 10dB in the mid and high frequencies,
and then gradually descending again to about 25dB in the
highest frequencies. The shaping of this "curve" is
reportedly the most realistic shape for most users in
achieving optimum speech understanding within the
inherent idiosyncrasies and limitations of hearing
instruments. Especially when one considers the nature of
cochlear mechanics, and the possibility of introducing
cochlear distortions by over-stimulation via tectorial
membrane action against the outer hair cells (OHCs). In
such an event, it would be highly probable to
noise-induce even more hearing loss with amplification.
Observe figures 5.6, 5.7, and 5.8 for illustrations of
how pure-tone HTL soundfield scoring might be
superimposed over the covered-ear air conduction
audiogram. These represent typical examples of three
types or patterns of losses. The small superimposed "o"
and "x" marks represent binaural pure-tone responses.
The stimulus may be given in pure-tones; however,
warble-tones or narrow band noise is much preferable for
soundfield testing. Furthermore, witness how the
specialist might visually point out the expected
benefits and/or limitations of a given amplification
fitting to the client and interested third parties.
Figure 5.6 Typical Bilateral Presbycusis Loss: Aided HTL
soundfield thresholds superimposed over TDH-39 headphone
thresholds
Figure 5.7 Typical Unilateral Moderately Severe
Conductive Case (left ear dead): HTL aided soundfield
superimposed over TDH-39 earphone thresholds.
Figure 5.8 Typical bilateral sensorineural loss with
moderate recruitment: HTL aided soundfield thresholds
superimposed over unaided TDH-39 earphone thresholds.
A comparative study of an individual's aural correction
which is derived by superimposing the pure-tone "aided"
soundfield over the "unaided" air-conduction audiogram
will allow the specialist to quantifiably and
graphically assess the degree of threshold correction
achieved in a given fitting in each of the four crucial
frequency bands (500Hz-1KHz, 1-2KHz, 2-4KHz, 4-6KHz).
We'll list here a few considerations that will assist
the specialist in counseling the client and/or adjusting
the instruments as a result of the pure-tone soundfield
audiogram as it relates to the air-conduction audiogram
by frequency region:
250Hz-1000Hz region: If there is evidence of
over-amplification in this region we may expect a
significantly negative signal-to-noise ratio.
Adjustments to reduce the low frequency response of the
instrument may be required. In fact, most losses, even
"reverse slope" losses do not require a great deal of
amplification below 500Hz. "Mirroring" the audiogram is
definitely not the goal in the low frequency range.
Otherwise, recruitment---and increased tinnitus, in some
cases---may develop from noise exposure. On the other
hand, if low frequency responses are deficient there may
be difficulty in the patient hearing vowels, plosives,
liquids, and stops; in distinguishing from men's and
women's voices; and in adequate localization and spatial
separation. Furthermore, there may be a "plugged" or
occluded feeling if lows are too subdued. A delicate
balance between not enough and too much must be
achieved.
1KHz-2KHz region: Undue amplification in this range will
bring discomfort and speech-masking effect in the
presence of noises, such as paper rattling, dishes
clinking in the cafeteria, or background music.
Underamplification, on the other hand, can reduce aided
speech understanding.
2KHz-4KHz region: This range is extremely critical for
speech understanding, and for optimum signal-to-noise
function. Coincidentally, the 2-4KHz range is also where
many presbycusis cases experience a lessening of
critical bandwidth sensitivity (Durrant and Lovrinic,
1985)---in such cases they may not be able to
distinguish between 2.5Hz and 3KHz, which could be
crucial in distinguishing various consonant sounds,
particularly the letter "s". This letter is the most
common and most critical consonant sound in the English
language. It is also important to restore this region of
frequencies without exceeding suprathreshold sensitivity
(recruitment) and UCL. When unaided thresholds exceed
80dB in sensorineural cases it is unrealistic to expect
more than a 35-40dB aided improvement in this region.
Such threshold levels may respond to loudness growth
strategies such as wide range dynamic compression.
4KHz-8KHz region: This range is also critical for speech
understanding, but more importantly in difficult
listening situations, and at distances.
Overamplification concerns rest primarily within the
UCL/difference parameters. Underamplification may cause
a severe reduction in speech understanding in the
presence of background noise, as well as a lessening of
distance discrimination.
9. Speech Discrimination Soundfield Testing
It is not possible for a counseling textbook to
adequately cover the procedures and techniques of speech
discrimination testing. Again, the recommended
methodology is the Duffy (1985) method or Phoneme
Recognition Quick Test which utilizes comparative aided
and unaided soundfield testing as its function. If, on
the other hand, the situation is not within the
possibility of proper equipment and environment, it is
recommended that some form of comparative soundfield
speech testing take place.
For instance, in cases where soundfield equipment is not
available or feasible: Using the PB word list, the
specialist may provide live-voice testing at 60-65dB (on
the SPL meter) @ 3' with the patient facing them, eyes
closed. Note: The author does not recommend the covered
mouth approach because of the notable reduction high
frequency speech sounds. Therefore, the
facing-with-eyes-closed method is much preferable in
live-voice situations, and lessens the problem of
involving the examiner’s hearing acuity! This must be
performed unaided first and then aided, utilizing a
different list. Recording the number of correct phonemes
will provide a viable basis of comparison for adjustment
and counseling. Frequency response and gain adjustments
may reveal an improvement in speech understanding using
this method. For a more complete understanding of
soundfield testing protocols, see the author's
explanation in "Soundfield and Sound Control in the
Dispensing Practice" (Chartrand, 1993).
Probe Microphone Measurements: A Primer. Several
excellent texts have recently been published to fully
explain the techniques, rationale, and equipment
necessary for effective probe mic validation (Mueller et
al, 1992)(Zelnick et al, 1987). At the risk of breaking
continuity in the reader's understanding of the hearing
aid delivery and validation procedure, however, we will
spend a little time here to explain some of the facets
of probe mic testing. Of course, this will be no more
than a rudimental introduction, requiring the serious
student to pursue further instruction elsewhere.
Probe mic measurements are an objective in situ
assessment methodology to determine the following
parameters:
· Real Ear Unaided Response (REUR)
· Real Ear Aided Response (REAR)
· Real Ear Insertion Response (REIR)
Other measurements, of course, can be taken, but these
three fulfill the purposes for basic hearing aid
validation. See Figure 5.9 for a superimposed comparison
of a typical ear canal measurement using probe mic
equipment.
Figure 5.9 Shown above is a composite graph of three
probe mic measurements: REUR, REAR, and REIR. Also,
shown is a "target gain" parameter based upon pure-tone
thresholds of the user. Note the similarity between the
target gain line and the Real Ear Insertion Response.
Theoretically, this is an ideal match of amplification
to the natural ear canal response.
Since the factory-provided electroacoustic readout on
the instrument's frequency response etc. is based upon
ANSI 2cc coupler specifications, there is actually
little relationship between the readout it and the in
situ data. Hence, probe mic testing provides data that
can only be compared with itself, not with ANSI. Plus,
test-retest with probe mic is much less reliable as
compared to ANSI 2cc. Even the bases of parameters can
be quite divergent. Probe mic data are snap-shots of the
ear canal resonance properties in specific settings,
which can be changed dramatically by simply opening a
hearing aid vent, loosening the earmold, moving the
probe tube +/- 5mm, moving away from or changing the
angle of a soundfield speaker, etc. (Dirks and Kincaid,
1987)(Revit, 1987)(Ickes et al, 1991).
The Real Ear Unaided Response (REUR) is the acoustic
"fingerprint" of the user's ear canal in the unaided
setting (Mims, 1993). This might be considered the
starting point with which all other real ear
measurements relate. In fact, the REUR has nothing to do
with hearing thresholds, but simply shows how sound is
shaped as it passes through the user's ear canal. The
next measurement is actually an output measure. In this
way the Real Ear Aided Response (REAR) represents the
output level of the instrument in the ear at each
frequency and is shown in dBSPL.
The final, but most important measure is the Real Ear
Insertion Response (REIR) which is actually a measure of
in situ gain. The REIR is derived by subtracting the
REUR value from the REAR value at each frequency tested
by the probe mic system. The REIR, furthermore, ideally
represents an approximation of "target gain" which is
preprogrammed into the computerized real ear measurement
system. Consequently, the differences between the
"ideal" target gain and what is actually found in the
REIR indicate where changes may be needed in the
response of the hearing instrument. Adjustments of both
gain and frequency response may be needed as shown by
the results and user preferences. Keep in mind that all
changes should be made while the instrument is in the
user's ear. While adjustments are being made, however,
it is advisable to ask the user to assess "quality"
components of speech (and possibly other sounds),
ascertaining that the response and peak modifications
are preferable.
As a side note: It may be advisable to take probe mic
measurements before administering pure-tone and speech
soundfield, or, in some cases, concurrent with
soundfield testing. Also, it is important to note that
while real ear probe mic testing has evolved into a
much-needed scientific and objective approach to hearing
instrument validation, it still only measures what is
taking place up to the tympanic membrane (TM)---i.e.,
replacement of lost canal resonance from insertion and
wearing of the hearing instrument. Therefore, soundfield
testing may provide a more complete and final
subjective/objective profile of a given fitting. For
trouble-shooting and resolution of post-fitting
complaints, however, the probe mic approach is the most
effective approach to-date.
10. Marking the V.C. Position. Now, after all
adjustments and verification have been completed, it is
time to accept the VC position as the correct one. It
has taken about 30-40 minutes to arrive at this point,
and the last thing one needs is to start from "square
one" because the VC position was lost! Therefore, it is
advisable that the specialist develop methods of removal
of the instrument from the ear without moving the VC.
This might entail opening the battery door, and using it
as a "removal handle" or possibly carefully reaching
around the concha to get a better grip of the shell. Do
not let the patient remove the instrument or you will
lose all that hard work!
There are two simple methods in which the VC may be
marked:
· Using a ballpoint pen, the specialist may make a deep
impression on the faceplate next to the dot located on
the VC. Having done this, we now have two small
"impressions" in which we may fill with black ink from
the fine or medium point of a felt tip Exacto pen. The
two "dots" should be easily seen, yet not spread over a
large area, obliterating their precise setting.
· Another method is with bright red fingernail polish.
Using a toothpick or other fine-pointed object, one may
dip the toothpick into the bottle, careful to remove
excess polish at the neck of the bottle, and apply a
small "dot" in the proper positions on the faceplate and
VC cap. Allow enough drying time before handling.
Now, the client is ready to be instructed on the proper
setting of the VC to this effect,
"When you want to turn the instrument off, simply turn
the volume control this way (demonstrate). And when you
want to turn the instrument on, turn it this way
(demonstrate). The point of amplification, which we've
found to be best from our tests on you today, is at this
point (line up the two marks for them to see). You may
want it a little louder of softer than this, but we'll
use this as our point of reference. Before you place the
hearing aid in your ear, be sure to line up these two
dots. You might hear a high-pitch whistle, but it will
stop once the instrument is in position."
The client is now set to "practice" manipulating the VC
in and out of their ear. By repeating insertion,
removal, VC adjustment, etc. several times they will
begin to feel more confidant. Of course, there will come
a time when the marks will wear off. That is expected.
By that time they should be able to judge the proper
level of volume by listening instead of pre-setting the
VCs.
11. Battery, wind-noise, and other instructions. It is
also imperative that adequate time be spent practicing
insertion and removal of the battery. Care and basic
technical information should be covered, as well as
future battery purchasing information. If there is a
"battery club" or some easy-purchase system, this will
be a good time to explain the program. Be sure to cover
the HIA-recommended battery safety cautions.
12. Wind Noise. Wind-noise, until the advent of custom
canal instruments, had been a major concern. In any
event, if the specialist will talk to the patient about
the probability of wind-noise, giving instructions on
how to "deflect" the wind by moving the head away etc.,
the patient will subconsciously accept the presence of
wind-noise. Wind-noise, in actuality, is not just an
extraneous by-product of wearing a hearing aid. Wind
generally causes bothersome sounds against the pinna of
normal hearing persons, also. But one who has gone years
without hearing wind at the usual level of intensity may
feel that this is unnatural, or an artifact of
amplification. Upon correction, the wind noise will
return to the pre-loss level, and can be quite
disturbing to the unsuspecting user.
13. Wearing Schedule. A viable wearing schedule is
important. It must also be applicable according to each
user’s experience and needs. It is not feasible for the
new user to merely place the hearing aid in their ear
and wear it for extended periods of time, for the
lymphatic response will cause swelling and, eventually,
soreness, sometimes prompting shell modifications or
remakes that should not be made (Chartrand, 1999).
Experienced users, though old hands with hearing aids,
will also need a wearing schedule, albeit not as limited
or as well-defined as the new user.
For new users, it is generally recommended:
Week one: Practice inserting and removing hearing
aid(s), wearing no longer than 1-2 hours twice daily,
giving the ear(s) a rest for a minimum of 2 hours.
Listening should be confined to one or two people,
restricting use in crowds or noisy places.
Week two: Increase wearing time to 3 hours twice daily,
with at least a 2 hour rest. Listening situations may be
expanded to small groups and non-intensive listening.
Focus listening on one person at a time.
Week three: Increase wearing time to 4 hours twice daily
with at least a 2 hour rest. Listening can now expand to
larger groups, listening at Church, and other controlled
situations.
Week four: Increase to wearing 6 hours per day twice
daily with a 1-2 hour rest. Listening area can expand to
most sound environments.
Week five: Increase wearing time to full-time use. If
the ears have not completely adjusted, give them a rest
at some point during the day.
Week six: Full-time wear---from rising in the morning
until bedtime--- without periods of rest. But keep in
mind that optimal speech understanding, especially in
noise, should continue to improve over the next 8 weeks
before optimal correction is available.
For experienced users it is generally recommended:
Week one: Wear 3-4 hours three times daily, giving the
ear(s) a rest for at least one hour between. Avoid loud
and noisy listening situations.
Week two: Wear 6 hours twice daily, giving the ear(s) a
rest for at least one hour between. Minimize noise
situations.
Week three: Wear full-time with a 1-hour rest break at
mid-day. General listening situations of all kinds OK
now.
Week four: Wear full-time without rest. Learning curve
will continue, however, depending on the amount of new
information being provided in the new instruments.
10. Scheduling Post Fitting Visits. It is recommended
that the first post-fitting visit take place within the
first three days of delivery. The second visit should
occur no later than one week from the previous visit,
and the third visit one week later. Visits should
continue until all concerns and problems have been
resolved. It would be good to make the patient aware of
this so that they will not feel as if they are intruding
on the specialist’s time, but instead need to continue
visits as needed. In this way, the specialist may better
manage the adaptation process, making adjustments as
needed, pre-empting problem fitting cases, and offering
ongoing counsel. This will essentially alleviate the
tendency toward "mole hills" becoming "mountains".
Neglecting timely post-fitting visits has caused many
hearing aid failures, and hard-feelings between some
patients and the specialist. Remember, we are asking
them to go out into deep water, with myriad
neurological, psychoacoustic, and psychosocial changes
happening in a relatively short period of time in their
lives. They need to know the specialist is there for
them, listening and counseling them through the new
challenges through which they must navigate.
11. Other Instructions. Other considerations too
numerous and rudimentary to cover here should involve
care, maintenance, warranties, FDA warnings and
disclosures (if applicable), etc. If the patient will
require compensatory training, such as speechreading,
improved listening skills, use of assistive devices,
considerations in the workplace, etc., this is the time
to outline their program. Be ready to make referral to
deaf educators, speech pathologists, or aural
rehabilitation counselors in cases where overlay
problems exist (CAP, aphasia, etc.). Also, consumer
self-help and publications can be a vital educational
and support experience for those with moderate and
severe losses.
12. Third Party Counseling. Up to this point the third
party has been somewhat of an observer of the
proceedings. Now it is time to address their concerns
directly. Here are a few areas to consider, by way of
dialogue:
"Mrs. Jones, we are going to need your help to make this
a successful experience with your husband. For one
thing, it is going to take him some time to become
reacquainted with the sounds he's been missing. In fact,
for at least a period of time these sounds may even
confuse him. People are going to expect him to hear
perfectly, like with the flick of a light switch. But
that will not happen. For even after all we can do he
will still have a (slight)(mild) hearing loss."
And, continuing on, after pausing for their response...
"When you wish to speak to him, it is still important
that he can see your face, when possible. Also, good
lighting for speechreading will remain necessary. Please
don't expect him to understand perfectly when you call
him from another room of the house, especially when
there is background noise present."
And....
"One very noticeable change that you will notice,
however, is that the television can be turned down. He
should be able to hear the phone and doorbell ring.
He’ll know when you're talking to him, even though he
might still misunderstand some words. It'll be easier to
get his attention. Furthermore, he will be able to relax
more when attending church and other meetings. He'll
become more involved and feel more confident in social
situations....Help him follow his wearing schedule. It
may seem a little restrictive at first, but it gets
better with time until he graduates to full-time wear.
He is going to need your encouragement to make this a
successful experience."
These instructions provide a basis for understanding the
patient's probable and worst-case scenario, while, at
the same time, providing hope and encouragement in the
positive changes that are about to take place.
The "Ultimate" validation
Needless to say, the ultimate validation method is not a
very efficient one, for it involves the final analysis
of the new hearing aid user. One of the most important
roles of the specialist is to remove as many extraneous
obstacles, unnatural resonances, and technical barriers
from the way of the user before they must make an
assessment themselves. When the specialist does not do
their job in a sincere and scientific manner, a great
deal of frustration and failure can be experienced by
all involved parties, and, hence, delay in achieving
timely and effective aural rehabilitation.
Now, the path back to normality or near-normality has
just begun. For most, the trek will be arduous, and will
take more time and patience than they may have
anticipated. By following the above considerations for
delivery and validation, and then continuing on to serve
in the years to come, extending long-term care and
service, the specialist may be able to keep the promises
made to the patient during the earlier stages of the
evaluation. Further, they may be instrumental in opening
new doors of opportunity and quality of life for all
that are affected by the hearing impairment.
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