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high-frequency hearing loss. These frequencies can be amplied with the hearing
aid if the test results show that the high-frequencies are functional. If the hearing
thresholds are shadows of adjacent frequencies, frequency-lowering technology
may be used. Although most audiologists consider it a waste of time to repeat the
audiological evaluation in the hearing aid clinic, it is necessary because the patient’s
audiological data are not up to date or because of calibration problems with the
hospital equipment.
In addition to the medical, audiological, physical, and psychosocial assessment
of the candidate, appropriate hearing aid models should be presented to the candidate based on the candidate’s medical history and the results of the COSI assessment. The candidate should be informed about the advantages and disadvantages of
the presented hearing aid models and application styles as well as their prices.
Look-alike demo models made to a 1:1 scale of the actual hearing aids can make it
easier for the candidate to touch and identify the hearing aids.
As a result, the audiologist presents the models that are appropriate for the candidate’s medical, audiological, and physical condition. Later, the candidate prefers
a hearing aid model that meets his/her psychological, social, cosmetic, and nancial
expectations. The audiologist decides how to use the selected hearing aid and plans
the acoustic modication of the hearing aid.
11.8.2.4 Connecting theHearing Aid totheFitting Software
The minimum equipment required to perform a hearing aid tting is a computer, the
manufacturer’s tting software, and a programming interface to connect the hearing
aid tting software. Before the digital sound processing revolution of the 1990s,
analog hearing aids were tted using a small screwdriver. Today, most manufacturers prefer to connect BTE, RITE and BT-enabled custom hearing instruments to a
computer via a wireless interface. Hearing aids from different manufacturers can be
equipped with the “Noahlink Wireless” device from the Hearing Instrument
Manufacturers’ Software Association (HIMSA) using the BLE standard. Some
hearing aids that do not have a wireless connection, such as the IIC, can be connected to a computer using the Hi-Pro 2 device from Natus (Natus Medical
Incorporated, USA). There are still some older hearing aid models that can be connected to a computer through “shoe” adapters, although their numbers are declining.
Fitting software is developed and regularly updated by the manufacturer. It typically includes an “Information” screen for entering patient information, a “FineTuning” screen for frequency-specic ne-tuning, a “Technologies” screen for
setting hearing technologies, a “Data Logging” screen for viewing user data, and a
“Notications” screen for setting audio/LED alerts. The Information screen provides basic information to help customize the hearing aid for the candidate. In addition to general information such as the candidate’s rst and last name, age, gender,
address, phone number and air/bone conduction thresholds, this screen also asks for
LDL and MCL thresholds. All of this information is needed to determine the appropriate prescription formula and to calculate the optimal hearing aid gain. Of course,
entering incomplete or incorrect data into the software can negatively affect the
quality of the hearing aid tting.
11 Selection and Application Principles of Hearing Aids in Pediatric and Adult…
241
Another software commonly used in hearing aid clinics is “NOAH” from HIMSA
(The Hearing Instrument Manufacturers’ Software Association, Denmark). HIMSA
is a community of many hearing aid manufacturers and its goal is to facilitate the
hearing aid tting process for all manufacturers. NOAH software combines the tting software of the hearing instrument manufacturers who are members of this
community. Because NOAH works with hearing aid tting software, audiologists
do not have to enter patient data repeatedly for different brands of hearing aids. With
NOAH, an audiologist can easily t different models from different brands by entering patient information once.
11.8.2.5 Determining the“Safe” Hearing Aid Gain Range: Acoustic
Feedback Control
Acoustic feedback is a common problem in hearing aid applications. Therefore, the
“safe” gain range of the hearing aid should be determined prior to verication and
ne-tuning with REM.To do this, feedback limits should be determined using feedback analyzer technology after the hearing aid has been worn on the candidate’s ear.
After reviewing the feedback risk map, the clinician could change the acoustic
application style if it is determined that the candidate is not achieving the required
auditory gain with the current application style. Consider a patient with a highfrequency hearing loss who is being tted with an open-t hearing aid. If the feedback thresholds after feedback analysis are below the required gain levels, it means
that adequate gain is not being achieved due to potential feedback. Therefore, the
clinician should change the acoustic application style rather than reducing gain to
avoid feedback. An earmold with a 2mm vent or a tulip dome can be used instead
of an open application.
11.8.2.6 Hearing Aid Fitting
The hearing aid tting software calculates a frequency-specic gain based on the
entered data and provides recommendations for the use of the technology. Auditory
gain is calculated using prescription formulas. The candidate’s gain is calculated
using the patient’s age, gender, hearing thresholds, Loudness Discomfort Level
(LDL), Long Term Average Speech Spectrum (LTASS) and Speech Intelligibility
Index (SII) data and presented by the software. This “preset” is then veried with
REM, ne-tuned if necessary, and the tting is complete.
Selection ofPrescription Formula
Prescription formulas are algorithms that mathematically calculate the auditory
gains of individuals with hearing loss. While the most commonly used formula for
the pediatric group is the Desired Sensation Level (DSL) v5.0 pediatric, the National
Acoustic Laboratories (NAL)-NL2 is used for adults.
The rst NAL formula was developed for linear gain analog hearing instruments.
This formula, which aimed to normalize the normal loudness perception of individuals with hearing loss at moderate input levels, was updated in 1999 with the
development of nonlinear gain digital hearing aids and was named NAL-NL 1 [73].
This formula was updated again in 2011 and renamed NAL-NL2 to provide optimal
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loudness and maximum speech discrimination with the NL2 version. [203]
NAL-NL2 incorporates the updated SII into the calculation. In addition, the gains
available for the low and high-frequencies have been increased compared to NL1,
while the mid-frequencies have been slightly reduced. In addition, version 2 applies
no gain to frequencies below 50Hz and above 16kHz. Obviously, NAL-NL 1 and
NAL-NL 2 produce completely different auditory gain/output curves [74].
Another feature of NAL-NL2 is the inclusion of the effect of tonal and nontonal
languages on auditory gain. For example, the low-frequency gain of hearing aid
users who speak tonal languages commonly used in Asian and African countries
becomes more important and is calculated accordingly. In addition, the CR calculation in NAL-NL2 has been updated. In this new calculation, no compression is
applied to speech stimuli below 50dB SPL. In addition, CR rates different from
NL1 are recommended for users with severe/profound hearing loss.
Other features updated in NAL-NL2 include the inclusion of gender effect and
user experience in the calculation. Women are offered 2dB less gain than men at an
input level of 65dB SPL [75]. In addition, new users with moderate, severe, and
profound hearing losses are offered less gain than older users. Finally, the NL2 version incorporates age into the gain calculation [74].
DSL, known for its DSL v5.0 pediatric formula developed primarily for pediatric
hearing aid applications, was also used in analog hearing aids. The formula, revised
in 1995, was called DSL [i/o] [76]. This formula, adapted for digital hearing aids, is
intended to optimize the auditory dynamic range of individuals with hearing loss
[77]. However, studies have shown that this formula results in a loudness perception
that is higher than desired [78–80]. As a result, the DSL [i/o] formula was revised
again in 2005 to calculate auditory gains using “multistage” signal processing technology. This new algorithm involves signal processing in 4 stages: amplitude expansion, linear gain, amplitude compression, and output limiting. The updated formula
is called DSL m[i/o] by adding the rst letter of the word “multistage.” However, it
is often referred to as DSL v5.0 [81]. Although DSL [i/o] and DSL v5.0 calculate
the similar auditory gain for at hearing losses, the new formula applies less gain at
low frequencies for hearing losses that increase toward the front and at highfrequencies. A pediatric version of DSL v5.0 has also been developed. The pediatric
version takes into account the acoustic properties of the external ear canal, which
vary with age, and electrophysiological measurements [82].
Although NAL-NL2 is the formula often preferred by adults, DSL v5.0 stands
out for its success in speech perception. In addition, there are also “brand-specic”
tting formulas developed and suggested by manufacturers.
Objective Verification ofCalculated Auditory Gain
REM can be used to objectively verify that the hearing gain calculated by the prescription formula is properly reaching the eardrum. A REM instrument, computer,
and software for the REM unit are required to perform REM verication. REM
devices typically have a loudspeaker to deliver the stimulus and two different microphones to pick up the delivered stimulus. The “reference microphone” is placed in
front of the tragus, while the “probe microphone” is placed 5mm in front of the
11 Selection and Application Principles of Hearing Aids in Pediatric and Adult…
243
tympanic membrane. The basic principle is that the stimuli presented by the REM
device speaker are reected on the software screen before and after hearing aid
amplication. According to one study, only 29% of ttings performed without REM
can deliver the target gain to the user [83]. Therefore, the use of probe measurements is essential for hearing aid tting in both pediatric and adult populations.
The REM instrument has a loudspeaker to present different stimuli and probes
for measurement. With REM, hearing aid gain is checked separately for soft (50dB
SPL), moderate (65dB SPL), and loud (80dB SPL) input levels. After the measurements, gain targets are achieved by increasing or decreasing hearing aid gain in the
appropriate frequency bands and input levels, as needed. Today, most hearing instrument manufacturers have introduced hearing instrument software that can be synchronized with certain REM devices. In this automated system, called “REM
Auto-t,” the hearing instrument software makes the necessary gain changes as a
result of the REM measurement for all input levels.
For all probe measurements to be accurate, both the reference and probe microphones must be equally sensitive to the stimulus. Therefore, prior to verication
measurements, the microphones are positioned close to each other and the calibration process is performed by holding them in front of the REM speaker (approximately 20–30cm).
After calibration, the client is seated in front of the REM speaker at 0 degrees of
azimuth in the range of 0.5–1 meter. The SNR ratio, especially at low input levels,
may increase and cause erroneous measurements if the subject is seated closer to
this distance. On the other hand, placing the candidate farther away may cause the
REM procedure not to start. After the REM procedure has been explained to the
user, the probe microphone is placed in the “clean” ear canal of the otoscopically
examined candidate. Probe microphone measurements are not recommended for
candidates with earwax in the ear canal because the probe microphone is easily
blocked by earwax. Before the hearing aid is placed on the ear, some probe measurements are taken to measure the characteristics of the ear canal resonance. The
hearing aid is then placed on the ear and gain verication measurements are taken.
The probe microphone is usually placed in the ear canal using 3 different techniques: manually placing the probe about 5mm from the eardrum, attaching the
probe to the earmold or custom hearing aid with a band, and placing it according to
the frequency response of the probe. The verication process is completed after the
microphones measure sound or speech stimuli presented through a hearing aid at
50, 65, or 80dB SPL.
After probe placement and correct positioning of the candidate in the REM
application, another important issue is the correct entry of hearing aid application
parameters into the REM software, in addition to the candidate’s audiogram information. Data such as the selected hearing aid model, earmold or dome type, vent
diameter, prescription formula, age, and gender of the candidate should be entered
into the REM software. In other words, the information entered into the hearing aid
tting software and the REM software should be the same.
Verication with REM may consist of tonal stimuli covering all frequencies as
well as speech stimuli based on the Long Term Average Speech Spectrum (LTASS)
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[84]. The International Speech Test Signal (ISTS), which is considered to be more
representative of everyday life, was developed according to the LTASS standard. In
this speech stimulus, a woman reads the text “North Wind and Sun” in six different
languages (American English, Arabic, Chinese, French, German, and Spanish) [85].
Directional microphone and DNR technologies should be turned off during all
probe microphone measurements as they can affect the measurement results. Most
hearing aid tting software allows the clinician to easily turn off these technologies
during the measurement. On the other hand, probe microphone tests can be used to
measure the effectiveness of technologies such as contralateral routing of signal/
bilateral contralateral routing of signal (CROS/BiCROS) hearing aid applications
and frequency reduction.
Real Ear Measurements (REM) are probe microphone measurements that include
several subtests. Each subtest has a specic purpose and use. These subtests and
their uses are described below.
Real Ear Unaided Response (REUR) This is a measurement taken after the probe
microphone is properly placed in the ear canal, without a hearing aid or earmold in
the ear. It shows the distribution of sound pressure level (SPL) in the ear canal at all
frequencies.
Real Ear Unaided Gain (REUG) This is the measurement in which the REUR is
expressed in terms of auditory gain. For example, when measuring a 60dB input
signal in a normal adult ear canal, a 77dB SPL REUR is measured in the 3000Hz
frequency band and a 77–60=17dB REUG is obtained at that frequency.
Real Ear Occluded Response (REOR) This test measures how the hearing aid
affects the acoustics of the ear canal when placed in the closed ear, in terms of sound
pressure level.
Real Ear Occluded Gain (REOG) This test measures how the hearing aid affects
the acoustics of the ear canal when placed in the closed ear, in terms of auditory gain.
Real Ear Aided Response (REAR) This is a measurement taken after the hearing
aid is placed in the ear in working condition. It measures how much SPL the hearing
aid produces at what frequency.
Real Ear Aided Gain (REAG) This is obtained by subtracting the amount of the
input stimulus on which the test is performed from the REAR values obtained at all
frequencies. This test can be used to determine the amount of gain provided by the
hearing instrument at each frequency.
Real Ear Insertion Gain (REIG) This is obtained by subtracting the REAR and
REUR values and is used to verify the gain of the hearing aid.
Real Ear Saturation Response (RESR) The maximum output of the hearing aid
after tting is measured. ANSI S4.46-2013 recommends the use of REAR 85 or
REAR 90 instead of RESR.
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245
Real Ear Coupler Difference (RECD) When REIG measurements cannot be
obtained, the RECD may be used to verify hearing aid gain in the pediatric
population.
Fine-Tuning
Although hearing aids veried by probe measurements are assumed to provide optimal amplication for adults, some changes in hearing aid gain may be required
based on the candidate’s feedback. These “small” changes, which can be made in
the “ne-tuning” screen of the tting software, provide an “optimal” gain for the
hearing aid user.
On this screen, you will primarily nd frequency-based tting bands for auditory
gain in three different input levels (soft, moderate, and loud), as well as MPO tting
bands. Frequency-specic compression settings can also be made using these bands.
Some manufacturers include some automatic ne-tuning algorithms as a result of
their research. These are practical algorithms based on common user complaints
such as “sounds are too loud” or “I have difculty hearing soft sounds.” As a result,
manufacturers have attempted to address user complaints through changes in tting
bands and technologies such as DNR.However, it is important to fully learn the tting software and perform manual ne-tuning to maintain auditory gain.
Fine-tuning should be performed within the “safe” range of auditory gain. The
candidate’s gain can be optimally adjusted with very small changes to the tting
bands. If the gain is reduced more than necessary for the candidate’s “comfort,” the
hearing aids may not provide the necessary amplication. For example, most candidates with high-frequency hearing loss will be satised with hearing aids that provide as little high-frequency amplication as possible. They expect the hearing aid
gain to be compatible with their current audiogram conguration. Candidates do not
want to leave their auditory comfort zone. According to the candidate’s feedback,
reducing the high-frequency gain eliminates the hearing gain the candidate needs
and makes the hearing aid an accessory, like an “earring.” Therefore, a balance
should be struck between the candidate’s hearing comfort and hearing needs. The
candidate should be prepared for the new “normal” as the current “normal sound”
perception will be replaced by the hearing aid.
Another important aspect of the ne-tuning process is that tuning is performed
only at the “required” input levels and frequency bands. Fine-tuning is performed at
the “soft” input level for soft sounds at a distance, “moderate” for sounds at a social
distance, and “loud” for unpleasant sounds around one’s voice. For example, if the
user indicates that he or she has difculty hearing distant sounds, only the “soft”
input levels should be increased slightly. If the user indicates that he has difculty
understanding his wife over coffee at home, even though he can hear trafc sounds
on the street, the soft input levels can be decreased a few steps and the moderate
sounds increased. In order for ne-tuning to be truly “ne,” it is important for the
candidate to provide detailed feedback to the clinician. For example, if a user says,
“I hear voices too loud,” the clinician can ask the patient, “Your voice or my voice?”
and ask the patient to provide details of the complaint. If it is his voice that is bothering him, it is only “loud”; if it is the audiologist’s voice that is bothering him, it is
only “moderate”; the input level can be reduced by a few levels. Once the input level
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has been determined, the frequency range to be adjusted should also be determined.
For example, for a candidate who complained of “I hear my voice echoing,” only
the high-frequency bands should be reduced slightly at the “loud” input level.
Subjective Verification ofFine-Tuned Auditory Gain
After ne-tuning, some simple tests can be used to assess whether the candidate has
sufcient and well-balanced hearing gain. These tests can be useful both to observe
the benet of the hearing aid in daily life and to demonstrate to the candidate and
his or her companions that the hearing aid is “really” useful. These evaluations can
be grouped under three headings: symmetry check for binaural tting, distance
check for soft speech intelligibility, and speech discrimination check in noise.
Symmetry control should be performed in all hearing aid applications, particularly for asymmetrical hearing losses. After tting, it is important to ensure that both
ears are the same so that the candidate has the correct localization skills with the
hearing aids. The application of the test is quite simple: walk behind the seat where
the candidate is sitting and stand behind the candidate at 0 degrees of azimuth. After
the hearing aids have been tted, various words or sentences are read to the candidate in a mixed fashion from the right, left, or center line and the candidate is asked
to indicate exactly from which side he or she heard the sounds clearly. For example,
if the words are read from the mid-right side, the candidate is expected to indicate
that he or she hears more from the right side. Based on the candidate’s feedback,
small changes are made to the hearing gains in the right and left hearing aids to
ensure that the candidate has the correct localization skills. After changing the gains
in different frequency bands, the candidate should hear the words or sentences read
from the midline “equally” in both ears.
Another assessment is “soft speech control.” The purpose of this test is to determine whether the calculated and veried auditory gains at the soft input level meet
the candidate’s expectations in everyday life. The test is performed as follows: a
suitable area of 8–10 meters is designated in the hearing aid clinic and a chair is
placed in the designated area. After the candidate is seated in the chair, the audiologist stands in front of him and asks him to repeat the words with 3 syllables. After
each word that the candidate knows correctly, the distance is gradually increased. At
this point, it is recommended that the clinician cover his mouth to avoid providing a
visual cue. The “soft” input levels may be increased by a few units if the client is
unable to repeat words read in a normal tone of voice at a distance that is not excessive. The optimal distance for this test may vary depending on the patient’s or clinician’s comfort level.
Evaluation of the candidate’s ability to discriminate speech in noise is also part
of the subjective assessment. This test can be used to evaluate both the challenging
daily life experiences of the hearing-impaired individual and the noise reduction
technologies of the hearing instrument. The test can be conducted in a structured
environment with a multi-speaker system or in “real life.” In this condition, the
candidate is tested in the street and word tests are performed in this “real” environment. Comparisons with/without hearing aids or basic/premium hearing aids can
also be made quickly with this test. If the test shows that the SNR of the hearing aid
11 Selection and Application Principles of Hearing Aids in Pediatric and Adult…
247
is not sufcient, the use of DNR technologies can be increased or a hearing aid with
a higher SNR can be selected.
For a more comprehensive evaluation and detailed ne-tuning, the candidate
may be asked to “note” the hearing aid experience until the follow-up appointment.
At the follow-up appointment, the candidate can discuss issues such as sound environments that are challenging or comforting, and satisfaction with watching television and talking on the phone.
In addition to quick post-tting tests, questionnaires such as The International
Outcome Inventory for Hearing Aids or The Abbreviated Hearing Aid Benet
Prole can be used to assess long-term hearing aid satisfaction [86, 87]. Because
they can be scored, these scales can be used to mathematically determine and compare the user’s hearing aid satisfaction. Therefore, completing these scales at each
follow-up appointment and keeping them in the patient’s record is valuable for retrospective evaluation of the user. Some of the scales that can be used are
described below.
11.8.2.7 Accessories andAssistive Technologies
When taking a holistic approach to hearing aid tting, accessories should also be
considered as part of the hearing aid application. Accessories consist of technologies that support or complement hearing aid technologies. These accessories, which
transmit sound from electronic devices such as televisions, computers, and telephones to the hearing aid, both increase the SNR ratio and make life easier for the
hearing impaired.
Hearing aids and accessories should be considered when completing the history
and COSI forms. For example, a candidate who expects to watch a movie on television should be offered the necessary accessories for a TV connection along with
hearing aids. In addition, the clinician should observe the candidate’s needs and
recommend appropriate accessories as needed. For example, a student may be recommended the use of remote microphone technology. This accessory allows the
student to listen to lectures in the lecture hall as well as participate in online courses
by connecting to the computer.
The integration of hearing instruments and smartphones offers several conveniences for today’s users. Many hearing instrument manufacturers offer rich content
smartphone applications in the app stores. There are also some features that are
exclusive to Apple. For example, a hearing aid user with an iPhone can make phone
calls through the hearing aid and use the phone as a remote microphone without the
need for accessories. An Android smartphone user who is compatible with the
ASHA BT protocol can stream audio directly between the phone and the hearing
aid. In addition, some manufacturers offer wireless connectivity for feature phones
with older versions of BT.
In addition to accessories that increase sound transmission or SNR, there are
some assistive listening devices that are designed to improve the quality of life for
people with hearing loss. These devices, which consist of a transmitter sensor and a
receiver, can be used for a variety of purposes. The transmitter works with baby
monitors, re/smoke alarms, doorbells, and telephones and is connected to tabletop
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or wrist receivers that provide vibration or light alerts to the user. For example, a
mother with profound hearing loss can place the transmitter in her baby’s room and
wear the receiver on her wrist to alert her to her baby’s crying when she is not using
her hearing aids. When the baby cries, the receiver on the wrist vibrates and alerts
the mother. If the mother prefers, she can also choose the receiver that is placed
under the pillow, which has a stronger vibrating stimulus. Similarly, vibrating
devices are being made for people with hearing loss that can be used as morning
wake-up alarms.
B. Celikgun et al.
11.9 Conclusion
Hearing loss is an important sensory loss that many people today do not pay enough
attention to. Hearing impairment alienates people rst from their friends, family,
and society, and then from themselves. Although people’s hearing and discrimination problems are sometimes ridiculed, the “neural” part of hearing loss is the invisible part of the iceberg. To protect people from the audiological, psychological,
neurological, and social consequences of hearing loss, early diagnosis and early use
of hearing aids are essential. Therefore, ENT specialists and audiologists should
work together and consider hearing aid rehabilitation without hesitation, even in
cases of mild hearing loss.
11.10 Case Studies
11.10.1 Case 1
The case with “moderate” sensorineural hearing loss according to Goodman classication has a speech discrimination score of 68% in both ears. According to the
Uncomfortable Levels evaluation performed during the speech audiometry; the
dynamic range of the case is signicantly reduced. When the case’s bilateral thresholds and speech discrimination scores are evaluated together, all hearing aid models
could be recommended audiologically. However, the segment of the model could be
determined by considering the social/psychological needs and the economic situation of the patient. Even if the individual expects an aesthetic aspect from hearing
aids, a custom model such as CIC is not recommended due to the risk of progression. Instead, the use of a binaural RITE may be recommended, as RITE models
have both replaceable receiver systems and wireless connectivity technologies. A
bass dome or ventless micro-mold may be preferred with RITE models. On the
other hand, if the patient’s ear produces dense earwax or the patient has limited ne
motor skills, BTE hearing aids may be recommended. A ventless half-shell hard
mold may be preferred with BTE hearing aids (Fig.11.7).
11 Selection and Application Principles of Hearing Aids in Pediatric and Adult…
Fig. 11.7 Case study 1.
SRTs (Speech Reception
Thresholds); SDSs (Speech
Discrimination Scores);
UCLs (Uncomfortable
Levels)
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11.10.2 Case 2
Case 2 has normal hearing in the left ear and a profound sensorineural hearing loss
in the right ear. Speech audiometric results are also consistent with hearing thresholds. In addition, type A tympanograms were obtained in both ears. While ipsilateral and contralateral thresholds were obtained in the left ear, no acoustic reexes
were observed in the right ear. Several different applications could be tried for this
case. For example, a BTE UP hearing aid with a full-shell soft ear mold might be
preferred for the right ear. However, since the patient’s speech discrimination in the
right ear is quite poor, BTE hearing aids are unlikely to be effective in terms of quality of life. Another option is a CROS hearing aid. When CROS is applied, the patient
has a non-amplifying receiver in the left ear and a transmitter in the right ear that
sends the sound to the left ear. Thus, sounds coming from the patient’s right ear are
transmitted to the left ear through the CROS application. For such asymmetrical
hearing losses, a BAHS or a cochlear implant for the right ear may be considered in
addition to the hearing aid. Finally, in cases of asymmetrical hearing loss where
both ears cannot be effectively amplied, additional wireless accessories such as a