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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4507_Библиотеки_им_академика_М_И_Перельмана.pdf
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“slow compression” by keeping it long. Using only one of these methods can result
in loss of temporal and spatial cues or distortion of sounds [9, 10]. Therefore, the
“adaptive compression” system, which uses both types of compression depending
on the situation, is widely preferred for hearing aids. The “multichannel adaptive
compression system,” which works in each sound channel formed by lters, provides highly optimized amplication today [11, 12].
According to the preferred prescription formula and the patient’s audiological
data (hearing thresholds, loudness discomfort levels/LDL, contralateral acoustic
reex thresholds, etc.), compression knee points were determined at different input
levels (generally, mild/45dB, medium/65dB, and high/80 dB input levels), and
compression ratios (CRs) were calculated [6]. Although objective verication is
provided by a Real Ear Measurement (REM) application, hearing aid gain and compression values may not always be optimal for the user. In such cases, the audiologists can ne-tune all input levels and redetermine CRs based on user feedback.
As a result, all technologies used in hearing aids are controlled by the hearing aid
tting software. For an ideal personalized hearing aid tting, it is very important to
enter all necessary audiological data about the patient into the software.
11.4 Hearing Aid Types
Hearing aids can be divided into two models: BTE and custom. BTE models are
physically placed behind the ear and transmit sound to the ear through an earmold.
Over time, different BTE models have been produced. More powerful versions
(140dB SPL+) of the standard BTE models (85 dB SPL) are called BTE SP or
UP.The physically smaller BTE models are called Mini BTE.The RITE models are
an advanced version of the BTE models. They have been made even smaller by
removing the receiver found in conventional BTE models. These models were the
most preferred type of hearing aid, accounting for 79% of all hearing aid models in
the United States in 2020 [13].
Conventional BTE models are used with an earmold and may have a longer lifespan than custom models. They may also have an LED-illuminated warning system,
and volume/program buttons. They may also have a longer battery life than other
models. Almost all BTE models have two different microphones required for directional microphone technology. In addition, most BTE models sold today support
wireless connectivity technologies. This allows users to conveniently make phone
calls and watch television. The “hook” part where the earmolds are attached is easily replaceable, and open ttings can be performed on BTE models using a
“thin tube.”
RITE models have a more aesthetic and modern appearance compared to traditional BTE models and do not use the “bulky” earmolds used in BTE models
(Fig.11.2a). Instead, they use a micro-mold or dome. In addition, receivers of different power levels are made for these models and many models allow for easy
replacement of the receiver in hearing clinics. There are also smaller versions called
Mini RITE and more aesthetic versions called Design RITE.These models, which
D
11 Selection and Application Principles of Hearing Aids in Pediatric and Adult…
Fig. 11.2 (a) BTE, RITE,
and (b) Custom
hearing aids
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offer more limited physical button control than BTE models, can usually be easily
controlled with a smartphone application. Finally, these models may have a shorter
battery life than traditional BTE models and due to their smaller size, may be more
difcult to use for patients with limited physical abilities (vision problems, hand
tremors, etc.).
In addition to the classic RITE models, there are also “special design” RITE
models introduced by some hearing aid manufacturers. The “Transducers in the
Ear” (TIE) hearing aids introduced by the Earnet brand are similar in appearance to
the classic RITE models but differ from them in that the entire speaker and microphone system is placed inside the ear. The “Microphone & Receiver in the Ear”
(M&RIE) hearing aid introduced by GN Resound differs from its competitors in
that the third microphone is placed in the ear in addition to the two microphones
used in the standard RITE models.
On the other hand, custom models are made according to the patient’s ear impression and are placed in the ear (Fig.11.2b). Physically, the models are listed from
smallest to largest: Invisible in The Canal (IIC), Completely In The Canal (CIC), In
The Canal (ITC), and In The Ear (ITE). IIC and CIC models are more aesthetically
pleasing than ITC and ITE models. However, they have lower speaker performance
and do not include a wireless antenna. In addition, these models are typically manufactured with a single microphone. ITC and ITE models, while physically larger,
have volume control/program buttons. They may also have two microphones and
wireless connectivity.
In addition to the well-known BTE, RITE, and custom models, there are relatively less common hearing aid models. Spectacle and headband hearing aids, which
are designed for conductive hearing losses and have a vibrating receiver for bone
conduction stimulation, may be preferred for patients who are not candidates for or
do not wish to use, bone-anchored hearing aids. In addition, pocket (body worn)
hearing aids, although rarely preferred, may be used by patients with severe hearing
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loss who are not candidates for a cochlear implant system or who do not wish to
undergo surgery. In addition to these models, there are unusual models that are
placed on the mastoid bone or that deliver sound by stimulating the ear cartilage.
11.5 Most Popular Technologies Used inHearing Aids
Today, there are some popular technologies that are supported by powerful hardware and coordinated with DSP in hearing aids. These technologies, which aim to
support the central part of the audio system as well as the peripheral audio system,
are Directional microphones, Digital Noise Reduction (DNR), Frequency lowering,
Feedback canceller, and Bluetooth (BT).
11.5.1 Directional Microphone Technologies
Covering the ear with your hand is the oldest known method of amplication. In this
way, the palm of the hand helps pick up sounds coming from the front, while the
back of the hand blocks sounds coming from the back, increasing the signal-tonoise (SNR) ratio. Directional microphone technology was developed with a similar
philosophy. In BTE and RITE hearing aids, two different microphones are placed
on the hearing aid at a specic angle and distance from each other. The goal of the
directional system is to delay or suppress background noise as much as possible and
increase the SNR ratio [14].
Directional microphones, which began to be used in the 1970s, have evolved
technologically over time [15]. While early designs used a single microphone
with two separate microphone inputs, two different microphones were used in
later years [6]. With a single microphone with two different inputs, factors such as
the angle of the microphone, the distance between the microphones, and the angle
of the microphone input were varied to delay sounds coming from behind, and an
optimum value was tried. After the digital revolution, electronic ltering and digital delays increased the effectiveness of directional microphones [16]. As hearing
aid processors have become more powerful, so have microphone technologies.
For example, “Reverse directionality” can be activated while driving to reduce
noise from the front and allow the driver to focus on speech sounds from behind.
“Split/Pinna directionality” can simulate the directional effect of the pinna, while
“Full directionality” suppresses sounds from the rear. In addition, “Automatic
Switching Directionality” has the ability to switch between microphone modes
based on the SNR of the ambient noise without requiring manual adjustment. As
a result, enhanced directional modes have been implemented in hearing aids under
various brand names. With the proliferation of wireless technologies in hearing
aids, “Bilateral Beamformer Microphones” can operate collaboratively with each
other. These systems increasingly incorporate the shadow effect of the head into
SNR calculations and have gained popularity in the hearing aid industry since
the 2010s.
11 Selection and Application Principles of Hearing Aids in Pediatric and Adult…
213
The increased processing power of hearing aids in recent years has encouraged
manufacturers to develop alternative microphone technologies. While some manufacturers use advanced adaptive systems known as “Multiple Speech Access
Technology,” others have sought to improve system efciency by incorporating a
third microphone into their hearing aids in recent years [17, 18]. Manufacturers aim
to enhance speech discrimination by preserving crucial speech cues while minimizing environmental noise through the use of directional microphone algorithms. To
accomplish this, they utilize diverse directional patterns that can be achieved by
adjusting the sound sensitivity of hearing aid microphones with various mathematical formulas. The range of sensitivity of these patterns to environmental sounds
varies according to the manufacturer’s threshold. “Directional beams” show the
effective directions and range of the hearing aids in the preferred directional microphone mode on a graph. For instance, in omni microphone mode, the hearing aids
are receptive to sounds from all directions, but in xed full directional mode, they
are sensitive only to sounds from the front. The directional patterns commonly used
in the industry are supercardioid, cardioid, omnidirectional, hypercardioid, and
bidirectional.
The microphone modes frequently used by manufacturers are listed below.
1. Omnidirectional Microphone: When this mode is selected, the hearing aid sup-
presses sound in any direction. Instead, it picks up sound equally from all
directions.
2. Fixed Directionality: Sound delay/suppression direction of the microphone is
xed. Typically, sounds from the front are accepted directly into the hearing
aid, while sounds from the back are suppressed. In addition to the full directional pattern, Pinna effect directionality can be used. However, the natural
SNR amplication of the pinna is reduced when using BTE hearing aids. The
goal of this mode is to create a partial directional effect similar to that of
the pinna.
3. Adaptive Directionality: Different directional patterns are used depending on the
user’s sound environment. The hearing aid’s operating system calculates the
most appropriate SNR.The DSP continuously receives information from both
microphones and determines appropriate directional pattern to use.
4. Automatic Switching Directionality: The hearing aid automatically adjusts its
directional patterns to match the user’s listening environment.
5. Bilateral Beamformer: Hearing aids in each ear use different wireless connec-
tion technologies such as BT or near-eld magnetic induction (NFMI) to communicate with each other. The microphones of both devices determine the most
appropriate mode or pattern for the user by analyzing the shadow effect of the
user’s head.
Continuous use of xed directional microphones can result in increased internal hearing aid noise in quiet environments. In addition, speech sounds coming
from the side or behind the wearer may be lost. As a result, hearing aid manufacturers have recently shown interest in operating systems that can provide true
environmental analysis and directional patterns based on the SNR in the
environment.
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11.5.2 Digital Noise Reduction
Hearing aids use the DNR system along with directional microphones to reduce
background noise. It is well known that people with hearing loss have difculty
understanding speech in noisy environments compared to people with normal hearing. As a result, hearing aid manufacturers strive to amplify speech sounds as clearly
as possible to improve users’ speech comprehension scores in noisy environments
and reduce listening effort. Originally developed in the 1970s to lter only lowfrequencies, DNR is now supported by AI [19, 20]. Since the 1990s, the use of DNR
technology in hearing aids has increased signicantly. The technology separates
noise from the signal utilizing modulation-based analysis methods. Furthermore,
different DNR technologies, including frequency-based (short-term sound spectrum) and temporal-based (temporal analysis of environmental sounds), have been
used in digital hearing aids [19].
Most DNR technologies in use today work in harmony with directional systems.
DNR technology plays a critical role in maintaining the overall acoustic environment and speech signals by minimizing noise. In the literature, some studies suggest
that speech perception is not improved by DNR while others report a positive impact
of DNR on listening effort [21–23]. Therefore, the level of use of this technology
may uctuate between users. According to the preference of the hearing aid user,
the noise reduction level can be adjusted using the tting software. Therefore, in
addition to information from microphones, DNR technology also uses information
from “motion sensors” or internal audio libraries trained with “machine learning.”
A variety of DNR technologies are used by hearing aid manufacturers to reduce
wind noise and transient sounds such as horns.
11.5.3 Frequency Lowering
The high-frequency bands play a crucial role in the audio spectrum as they contain
important speech cues and have a direct impact on the ability to discriminate speech.
Research shows that a 6dB gain loss in high-frequencies could reduce speech cues
by 30% [24]. Therefore, it is essential for hearing-impaired individuals to be able to
hear high-frequency bands. However, hearing aids may not be effective at amplifying frequencies of 4000Hz and above, especially in the case of severe or profound
hearing loss. In this scenario, shifting critical speech cues from high to midfrequency bands audible to the patients could be a viable solution.
The rst attempts at frequency-lowering technology were made in 1991 under
the name “Linear Frequency Compression” Today, hearing-aid manufacturers offer
four different frequency transfer techniques: “Frequency Transposition,” “Frequency
Composition,” “Frequency Compression,” and “Frequency Translation.” [25]
First introduced in 2006, frequency transposition technology is commonly
referred to as “Audibility Extender.” It involves copying and pasting high- frequencies
into the mid-frequency bands. The hearing aid then attempts to present the midfrequency and transmitted high-frequency information without distortion [26].
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Alternatively, frequency composition divides the high-frequency information into
segments. Unlike Frequency Transposition, which places segments of highfrequency information side by side in the mid-frequency bands. Frequency
Compression stacks these segments on top of each other. As a result, the transmitted
high-frequency information takes up less space in the mid-frequency range.
Frequency Compression technology, introduced in its nonlinear version in 2008, is
commonly known as “SoundRecover.” [26] This technology compresses, highfrequencies into a smaller space and pushes them toward lower frequencies.
Frequency Translation technology, also known as “Spectral Envelope Twist,” transfers important high-frequency spectral segments of speech to the mid-frequency
regions. When the system identies high-frequency sounds, it translates this information to a lower, audible frequency and then makes it audible [27].
According to the literature, frequency reduction technologies are of “moderate”
benet to individuals with high-frequency hearing loss [25]. The hearing aid tting
software allows for the individualized adjustment of all frequency-lowering techniques, including frequency-lowering range and level, based on user feedback or
objective test results, such as cortical testing.
11.5.4 Feedback Canceller
It is possible for amplied sound waves from the hearing aid to hit the eardrum and
escape the ear canal through earmolds or domes. In cases where these escaped
sound waves are picked up by the hearing aid microphones, an unpleasant highpitched sound called feedback may be heard. This is a common occurrence, especially for hearing aid users with severe to profound hearing loss. The presence of
feedback is not only annoying but it also degrades the sound and amplication quality of hearing aids.
The simplest approach to preventing feedback is to reduce the hearing aid gain at
high frequencies. However, this can result in a decrease in the user’s speech discrimination ability. Therefore, hearing aid manufacturers incorporate “feedback
canceller” technology as part of their DSP to avoid such problems. It minimizes the
feedback problem by using a variety of methods. For example, the “frequency shift”
method identies and alters the frequency causing the feedback [28]. Another
method is “phase shifting.” The phase of the frequency causing the feedback is
determined and the phase is reversed to prevent the loop [29].
In “combined systems,” in addition to these two methods, the hearing aid gain
can be reduced at certain frequencies that cause feedback. In recent years, as hearing aid hardware has become more sophisticated, combined systems have evolved
into “Spectro-Temporal Modulation.” This system uses extremely fast frequency
and time detectors that continuously scan sounds more than 50,000 times per second to identify potential feedback before it becomes audible to the user [24].
Finally, there are AI-based feedback cancellation systems. The deep neural network system is trained with multiple feedback loops, allowing it to intervene in
potential feedback situations and prevent the occurrence of feedback [30].
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The most common causes of feedback in clinical practice are inaccurate earmold/dome selection, punctured earmold hoses, the presence of earwax in the ear
canal, deformation of the earmold structure over time, and the receiver output of the
custom hearing aid matching the ear canal wall. The key point is that the clinician
cannot simply solve the feedback problem by reducing gain. It is crucial to identify
and eliminate the underlying cause of the feedback.
Some custom hearing aids may have internal feedback problems due to assembly
errors. These problems are not related to acoustics and can be corrected by the hearing
healthcare professional. Similarly, internal feedback may occur in defective BTE models.
11.5.5 Bluetooth
BT technology, which enables wireless data transfer, was developed in 1998 under the
leadership of the Swedish telecommunications company Ericsson, with support from
brands such as IBM, Intel, Toshiba, and Nokia [31]. The group has over 35,000 members worldwide under the brand name Special Interest Group (SIG) [32]. The name
“Bluetooth” is derived from the Danish king “Harald Blåtand.” He was a tenth-century
king who ruled over Sweden, Denmark, and Norway. BT technology was named after
him because of his ability to bring important manufacturers together, much like BT connects devices. In 2005, the hearing aid industry adopted BT technology, which enables
wireless sound transmission through a module attached to the hearing aid. With continued development and improved stability over the years, BT’s presence in the hearing aid
industry has grown. Since 2011, hearing aids have been using 2.4GHz wireless connection technology (Bluetooth Low Energy/BLE). Currently, the ASHA (Android
Streaming for Hearing Aids) protocol allows smartphones running both Android OS and
iOS to establish a high- quality connection with hearing aids. The LE Audio LC3 Codec,
which was initially deployed by the hearing aid industry in 2024, provides enhanced
sound transmission with precise synchronization and minimal battery consumption. In
addition, the wireless connection between two hearing aids has enabled many “binaural” technologies such as directionality. CROS hearing aids, which previously relied on
cables, are now available wirelessly thanks to advances in BT technology.
Today, hearing aids that offer optimal smartphone compatibility utilize wireless
connectivity for more than just audio transmission. Their smartphone connectivity
allows them to connect to online “assistant applications,” such as If This Then That
(IFTTT), and remote hearing aid tting applications such as “Remote Fitting.”
Advances in these applications have revolutionized hearing aids, transforming them
into modern “personal assistants.”
11.6 Other Hearing Aid Technologies
In the 1930s, a graduate student at the Massachusetts Institute of Technology demonstrated the modern applicability of George Boole’s nineteenth-century theory of
“machine thinking,” once considered fantastic. Since then, AI technology has
11 Selection and Application Principles of Hearing Aids in Pediatric and Adult…
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continued to evolve and is now used in nearly every aspect of daily life. AI research
for hearing aids began in the 2000s [33]. In 2004, a hearing aid manufacturer used
AI to identify and prioritize speech sounds. More recently, advanced AI technology
supported by various sensors was introduced to the hearing aid community in 2019.
Hearing aids trained with millions of sound environments through “Deep Learning,”
have begun to improve the lives of individuals with hearing impairment [34].
When a hearing aid can utilize the sensors of a connected smartphone, the hearing aid industry experienced a new technology in 2017in the form of motion sensors. In 2019, data collected from sensors in the hearing aid, including the
magnetometer, gyroscope, and accelerometer, were transmitted to the DSP [35],
which improved the stability of the hearing aid.
Another assistive technology used in hearing aids is “sound therapy,” which was
developed for individuals who suffer from tinnitus. Research shows that more than
half of people with hearing loss also suffer from tinnitus [36, 37]. In addition, nearly
half of people with hearing loss and tinnitus nd that using a hearing aid can alleviate or eliminate their tinnitus, according to another study [38]. In addition to amplifying sound, hearing aids include a therapy module that can produce different
sounds, such as ocean waves, to aid in treatment. This technology, developed to
support sound therapy, is used effectively by experienced professionals in the treatment of tinnitus.
Recently, due to the COVID-19 pandemic, the hearing aid industry has integrated remote tting technology. Today, this technology has made it increasingly
common to use smartphone applications and internet connections for hearing aid
tting.
11.7 Pediatric Hearing Aid Application
11.7.1 Negative Effects ofHearing Loss inPediatric Populations
Even in cases of mild hearing loss, the frequency selectivity of the cochlea is
impaired. In addition, the spectral and temporal coding of stimuli and the balance
between inhibition and excitation are disturbed [39]. Due to incomplete neural coding in the peripheral auditory system, sound representation in the central auditory
system is distorted. In addition, auditory deprivation leads to morphological and
functional changes in auditory pathways, differentiation in synaptic transmission,
neuronal degeneration, and cross-modal reorganization in the auditory system [40].
These impairments in the peripheral and central parts of the auditory system
primarily affect the infant’s speech and language development. Depending on the
type and degree of hearing loss and the conguration of the audiogram, the degree
of adverse effects of hearing loss on speech and language development may vary.
Problems such as delays in receptive-expressive language development, slow
vocabulary development, grammatical errors and sentence formation problems,
articulation problems, or inability to acquire language at all are commonly observed
in infants and children with hearing loss [41, 42]. During the school years, problems
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such as learning difculties, cognitive decline, communication and socialization
problems, lack of self-condence, difculty understanding speech in noise,
increased listening effort and decreased academic success are added to the language
problems [43–45]. In particular, the crowded and noisy classroom environment
reduces the learning ability of hearing-impaired school-age children due to their
inadequate speech discrimination skills in noise. The immaturity of the central auditory system and hearing loss may adversely affect their cognitive abilities.
Unfortunately, some parents have reported that some elementary school teachers, inexperienced with hearing-impaired students, consider these children to be
mentally retarded. Even when using a hearing aid, hearing-impaired children who
do not use an assistive listening device that increases the SNR ratio experience
learning difculties due to increased listening effort. These children are trying to
understand both the conversations in the classroom and what the teacher is saying.
In other words, these children may use more cognitive resources such as perception,
attention, and memory than their hearing peers. As a result, they may feel more tired
at the end of the day than their peers.
11.7.2 Learning Process andParticipation inLife
When babies are born with normal hearing, there is a neural “big bang” in their
brains, and it begins to make neural connections at an extraordinary rate. From this
point on, babies show tremendous cognitive development. Within a few months,
they begin to actively interact with their environment, develop vocalization skills,
begin to babble, and eventually begin to use “words.” During the learning stage,
babies try to learn everything around them. For example, you may hear your children using an inappropriate word that they will never learn from you, and you may
wonder where they heard it. Meanwhile, your children may have been listening to
your phone conversations while playing and learned that word. A learning-hungry
brain can make neural connections at an extraordinary rate through this “incidental
learning process.” [46] It allows children to quickly acquire receptive and expressive language skills. Therefore, hearing-impaired children need a wide range of
sound environments to achieve the language skills of their peers. In this process,
infants and children with hearing loss need access to the full environmental sound
scene without loss of speech cues, especially in the high-frequency bands [47]. High
frequencies allow for increased speech intelligibility, speech intelligibility in noise,
improved sound quality, and localization/spatial awareness [48, 49].
The rapid neural connection capacity that babies have from birth should be fed
with high quality peripheral encoding. Incomplete coding due to hearing loss should
be completed with hearing aids. The incidental learning process should be completed without loss, especially between 0 and 3years of age, which is the critical
period for language acquisition, and babies should be exposed to intense auditory
stimuli [50, 51]. It is important that the stimuli are presented to babies in a lossless
and intense way because when the baby is 4–6years old, the brain enters the “pruning” process, and the noncontinuous, weak neural connections are deleted by the
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brain. The sounds that hearing-impaired babies cannot hear or hear in poor quality
are dened by the brain as “non-continuous” neural connections and are deleted
[52]. Therefore, it is necessary to use a hearing aid and make sure that the hearing
aid is properly tted.
It is clear that hearing loss in the pediatric population is not simply a sensory
loss. For this reason, careful evaluation of the pediatric patient, close communication with the family, observation and follow-up of the child by the family, correct
diagnosis, correct determination of hearing thresholds, quality hearing aid tting,
and auditory-verbal rehabilitation are important touches in the child’s life.
11.7.3 Hearing Aid Fitting Process inthePediatric Population
The most important factor in eliminating the negative effects of hearing loss in the
pediatric population is early diagnosis. A “denitive” diagnosis without any doubt
about the hearing loss is an important step. The next important step is the application of the hearing aid. Another step is “aural rehabilitation” and “follow-up of the
baby.” The otolaryngologist, audiologist, family, and rehabilitation teacher should
work in harmony so that the baby has healthy peripheral hearing. If adequate peripheral hearing cannot be achieved with a hearing aid, the alternative of a cochlear
implant should be considered.
11.7.3.1 Welcoming theFamily forHearing Aid Application
It is important for parents of a hearing-impaired child to feel welcome, relaxed, and
condent in the hearing care center. A friendly and smiling welcome and an attitude
that encourages parents to ask questions and communicate can be a good start to the
rst meeting. It is recommended that all staff working in the hearing care center
should be professionals who understand and give due importance to the psychology
of the individual with hearing loss and the psychology of being a parent of a baby/
child with hearing loss. Making eye contact with the parents, showing them that
their concerns are understood, and encouraging the family for the future will help
the family in this process.
Brochures/yers describing the hearing aid application process in the clinic can
be helpful. Similarly, non-advertising informative posters on the wall and expert
explanations about hearing loss in the pediatric population that can be played on
monitors/TVs in the clinic can also be informative for parents.
Hearing aid clinics that work with the pediatric population should be prepared
for parents in terms of both physical and psychological conditions. For example, a
small playground for babies and children or a nursery is essential for parents.
11.7.3.2 Anamnesis andAudiological Examination oftheBaby
An anamnesis is an important tool that builds a “health” based bridge between the
audiologist and the family. Through the anamnesis form, the audiologist not only
investigates the etiology of the baby’s hearing loss but also establishes a bond with
the family that will last for many years. Therefore, audiologists should listen