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19 The Acoustic Speech Signal
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
or produced with more eort. Note, also, that the SII is only a
measure of the amount of useful information in a given acoustic
speech signal that is available to the child. It tells us nothing about
the ability of the child’s auditory system to relay that information
to auditory and language centers in the brain or the child’s ability
to use that information.
Pearl
The SII is an estimate of how much of the useful information in
the acoustic speech signal is accessible to the listener. A value
of 1 (or 100%) requires that the average speech level at each
frequency be at least 15 dB above the listener’s threshold and/or
the background noise.
19.7 SII vs. Speech Intelligibility
The SII and speech intelligibility are not the same thing. The first
is a measure of available information provided to the listener’s
brain. The second is a measure of the listener’s use of that information. It is possible to transform SII into an estimate of speech
intelligibility, but the process is challenging and involves a lot of
assumptions.
In addition to information about sound patterns, the acoustic
speech signal carries information because of what it represents.
This information is usually referred to as linguistic redundancy
or contextual information.14 It has phonological, lexical, syntactic,
semantic, and even pragmatic components. But, just as access to
the acoustic speech signal is restricted by hearing loss, access to
its linguistic redundancy is restricted by the limited linguistic and
cognitive status of the developing child. His phonology, vocabulary, grammar, world knowledge, and people knowledge give him
less access to the contextual information than is the case with an
adult. His need for access to the acoustic speech signal is, therefore,
greater than that of the adult. It is generally assumed, for example,
that an SII of around 60% is adequate for perception of connected
speech by adults with normal hearing. No such assumption can be
made for the developing child.
In spite of these challenges, we can make estimates of the rela-
tionships between SII and various measures of speech recognition.
Such estimates can be used to demonstrate the kind of eects to
be expected for the developing child with hearing loss. The left
panel of Fig. 19.7, for example, shows data based on studies of
speech perception in young adults with normal hearing. The right
panel shows the changes to be expected for a child who is less able
to take advantage of phonological, lexical, and sentential redundancy. In this hypothetical illustration, the child needs an SII of
80% to obtain the same word-in-sentence performance as an adult
listening with an SII of 60%. Standards for listening conditions and
linguistic content considered adequate for adults simply cannot
be applied to developing children.
Pearl
The SII tells us how much information is accessible to the
listener. Speech intelligibility tells us how much use the listener
is making of this information. The relationship between the two
depends on many factors, including the language content of the
speech and the skills and knowledge of the listener. Criteria for
an acceptable SII need to be much higher for children than for
adults, and higher for children with hearing loss than for a child
who is developing normally.
19.8 The Sound Patterns of Speech
The rapid spectral changes in the acoustic speech signal create
sound patterns in the dimensions of amplitude, time, and frequency. These patterns convey information about the speech
movements, the gestures that caused them, and the phonemes,
words, and message they represent.15 The upper panel of Fig. 19.8
shows a spectrogram of the sentence “Wash grease spots soon”
spoken by a man. In the spectrogram, time is shown horizontally,
Fig. 19.7 An illustration of possible relationships between Speech
Intelligibility Index (SII) and three measures of speech recognition for
adults (left panel) and children (right panel). The child needs an SII of
80% to match the word-in-sentence performance of an adult listening
with an SII of 60%.
Fig. 19.8 Spectral and temporal patterns in a recording of the
sentence “wash grease spots soon” spoken by a man. The upper
panel shows a spectrogram. The lower panel shows the variation of
amplitude over time.
211
III Hearing Access Technologies for Infants and Children
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
frequency is shown vertically, and amplitude is represented by
color. The lower panel shows the variation of overall amplitude
over time, measured over a 7.5-millisecond window. These
approaches to examination of the acoustic speech signal are
rather like preparing an X-ray or magnetic resonance image
(MRI) of the speech banana. The most striking feature of the
resulting pictures is the extent and speed of the pattern changes
within the acoustic speech signal. Note, also, that these are patterns of amplitude variation in both frequency and time. Their
perception requires a hearing system that not only detects the
sounds but is also able to preserve frequency and time detail
as the information is relayed to the brain centers dealing with
auditory and language processing.
The fine vertical stripes in the spectrogram of Fig. 19.8 and the
rapid zig-zags in the amplitude plot show individual vibrations
of the vocal folds. We do not hear these variations separately but
perceive their repetition rate as voice pitch and the variation of
pitch over time as melody or intonation.
The broad horizontal stripes in the spectrogram (also known
as formants) are caused by resonance in the vocal tract.17 As the
tongue, jaw, and lips move, the frequencies of these resonances
change. Because of the tongue’s primary role in articulation, the
resonance of the cavity formed between the front of the tongue
and the lips carries very useful information. This resonance (the
second formant) is highlighted in white in Fig. 19.8. Its frequency
rises from a low of around 500 Hz at the beginning of this utterance to a high of just over 2,000 Hz in the “ee” of “grease.” The
frequency range of the second vocal tract formant accounts, in
part, for the large contribution of these frequencies to SII (Fig.
19.5). Note that the typical values of the formant frequencies,
because of their dependence on vocal tract length, are some 15 to
20% higher for women and children than for men.
16
19.9 Labeling the Speech Banana
When discussing audiometric data with parents or students, it
can be helpful to indicate, on the audiogram form, the approximate distribution of the acoustic energy needed for recognition
of selected speech sounds.20 An example is shown in Fig. 19.9.
These illustrations, however, should be used with caution. By
definition, the sound patterns in the acoustic speech signal
cannot be pinned down to a specific frequency or amplitude but
are spread across both and across time. Moreover, as pointed out
earlier, there is a big dierence between hearing a sound pattern
and inferring what it represents.
The reader will note that the sounds of the Ling21 six-sound
test are included in Fig. 19.9 (Chapter 9). This test oers a simple
and convenient way of confirming that the goal of providing the
child with “comfortable audibility of the information-bearing
components of the acoustic speech signal” has been met. But the
dierence between audibility (or SII) and recognition (or speech
intelligibility) cannot be overstressed.
Pearl
A combination of acoustic and intelligibility tests allows us to
label the speech banana in terms of the regions providing most
access to a selection of speech sounds. This approach is, however,
an oversimplication. While useful for illustration, its limitations
need to be recognized by clinicians, educators, and therapists.
Pearl
The acoustic speech signal consists of patterns in amplitude,
frequency, and time. These patterns provide the listener with
evidence about the talker’s speech movements and the phonemes, words, sentences, and meaning these movements are
intended to represent. One of the most important patterns is
that of the second formant, produced by resonance in the cavity
between the lips and the front of the tongue. It accounts for the
high importance of frequencies around 2,000 Hz.
The main energy in the “sh” sound for this utterance is between
3,000 and 5,000 Hz. That for “s” is between 4,000 and 8,000 Hz (or
even higher). Note that these values apply to this utterance only.
The main energy concentration for these two sounds tends to be
considerably higher for women, and this author has encountered
women for whom the main “s” energy is at frequencies higher
than 8,000 Hz.
access to the acoustic speech signal at frequencies higher than the
4,000 Hz shown on the right of Fig. 19.6.
8
It is clear that children with hearing loss need
18,19
Fig. 19.9 Approximate distribution, within the speech banana, of the
spectral energy needed for recognition of a sample of speech sounds.
212
19 The Acoustic Speech Signal
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
19.10 Conclusion
If the goal of management is age-appropriate use and devel-
opment of spoken language, a first step is to give the child as
much access as possible to the information in the acoustic
speech signal. This signal, which has an overall level of around
60 dB SPL when measured at a conversational distance, contains
components that are distributed across a wide frequency range,
from below 125 Hz to higher than 8,000 Hz. Most of the energy
is in frequency regions below 1,000 Hz, but the maximum concentration of useful information is between around 1,000 and
3,000 Hz. This is the range covered by the second vocal-tract
formant, which conveys considerable information about place
of articulation. At any frequency, the short-term amplitude
varies rapidly between 15 dB above and below the average.
Expressing speech levels in relation to normal hearing threshold and transferring them to an audiogram form results in the
speech banana. Examination of this area in relation to a child’s
audiogram can provide insights into the acoustic cues, phonetic
cues, and phonemes that are likely to be accessible to the child
with and without the benefits of assistance with hearing aids or
cochlear implants. It is important to realize that assisted hearing,
regardless of the form that assistance takes, is not perfect and
that diculties of discrimination and noise susceptibility are
likely to remain. Nevertheless, providing comfortable access to
the information contained in the acoustic patterns of speech is
an essential first step in auditory-oral intervention. By addressing this issue at as early an age as possible, we give the normal
developmental processes the best chance of contributing to the
desired outcome.
Pearl
For the acoustic speech signal “accessibility” means “audibility.”
Children cannot learn to recognize sounds they cannot hear.
Discussion Questions
1. Name ve ways of optimizing a hearing-impaired child’s
access to information in the acoustic speech signal.
2. What options exist for providing the child with access to
nonacoustic information in speech?
3. If this is only a rst step in promoting spoken-language pro-
ciency, what are the other steps?
4. Which part of the acoustic speech signal carries the most
useful information and how does that relate to speech
production?
5. How does the distribution of useful information in the acoustic
speech signal relate to the characteristics of normal hearing?
References
[1] Boothroyd A. Room acoustics and speech perception. Semin Hear
2004;25(2):155–166
[2] Pittman AL, Stelmachowicz PG, Lewis DE, Hoover BM. Spectral characteristics of
speech at the ear: implications for amplification in children. J Speech Lang Hear
Res 2003;46(3):649–657
[3] Pearsons KS, Bennett RL, Fidell S. Speech Level in Various Noise Environments
(EPA report 600/1–77–025). Washington, DC: Environmental Protection Agency;
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[4] Cox RM, Moore JN. Composite speech spectrum for hearing aid gain prescrip-
tions. J Speech Hear Res 1988;31(1):102–107
[5] Byrne D, Dillon H, Tran K, et al. An international comparison of long-
term average speech spectra. J Acoust Soc Am 1994;96(4):2108–2120.
doi:10.1121/1.410152
[6] Robinson DW, Dadson RS. A re-determination of the equal loudness relations for
pure tones. Br J Appl Phys 1956;7(5):166–181
[7] Sivian LJ, White SD. On minimal audible sound fields. J Acoust Soc Am
1933;4(4):288–321
[8] Boothroyd A, Medwetsky L. Spectral distribution of /s/ and the frequency
response of hearing aids. Ear Hear 1992;13(3):150–157
[9] Fant G. Speech Acoustics and Phonetics: Selected Writings. Norwell, MA: Kluwer;
2004
[10] French NR, Steinberg JC. Factors governing the intelligibility of speech sounds. J
Acoust Soc Am 1947;19(1):90–119. doi:10.1121/1.1916407
[11] Miller GA, Nicely P. An analysis of perceptual confusions among some English
consonants. J Acoust Soc Am 1955;27(2):338–352
[12] ANSI. American National Standard Methods for Calculation of the Speech Intel-
ligibility Index. ANSI S3.5–1997. New York, NY: American National Standards
Institute; 1997
[13] Mueller GH, Killion MC. An easy method for calculating the articulation index.
Hear J 1990;43(9):14–17
[14] Boothroyd A, Nittrouer S. Mathematical treatment of context eects in phoneme
and word recognition. J Acoust Soc Am 1988;84(1):101–114
[15] Raphael L, Borden GJ, Harris KS. Speech Science Primer: Physiology, Acoustics,
and Perception of Speech. 5th ed. Baltimore, MD: Lippincott Williams and
Wilkins; 2007
[16] Moore BCJ. Cochlear Hearing Loss: Physiological, Psychological and Technical
Issues. 2nd ed. Hoboken, NJ: Wiley; 2007
[17] Pickett JM. The Acoustics of Speech Communication: Fundamentals, Speech Per-
ception Theory, and Technology. Needham Heights, MA: Allyn and Bacon; 1999
[18] Stelmachowicz PG, Pittman AL, Hoover BM, Lewis DE. Eect of stimulus band-
width on the perception of /s/ in normal- and hearing-impaired children and
adults. J Acoust Soc Am 2001;110(4):2183–2190
[19] Stelmachowicz PG, Pittman AL, Hoover BM, Lewis DE. Aided perception of /s/ and
/z/ by hearing-impaired children. Ear Hear 2002;23(4):316–324
[20] Boothroyd A, Erickson FN, Medwetsky L. The hearing aid input: a phone-
mic approach to assessing the spectral distribution of speech. Ear Hear
1994;15(6):432–442
[21] Ling D. The Foundations of Spoken Language for Hearing-Impaired Children.
Washington, DC: Alexander Graham Bell Association for the Deaf; 1989
213
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
20 Hearing Aids for Infants, Children, and Adolescents
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
20 Hearing Aids for Infants, Children, and Adolescents
Andrea Pittman and Kathy Laudin Beauchaine
Summary
This chapter provides an overview of hearing aid fitting in
infants, children, and adolescents, including hearing device and
feature selection, real-ear verification, validation, and follow-up
for each age group. Signal-processing schemes (digital noise
reduction, directional microphones) that may be useful for children as their hearing needs become more sophisticated with age
are also described. Finally, this chapter emphasizes the need for
audiologists to modify their clinical and fitting strategies as their
pediatric patients transition through each stage of childhood to
become autonomous young adults.
Keywords
hearing aid selection, real-ear verification, signal processing,
infants, children, adolescents, hearing loss
Key Points
The choice of appropriate earmold, hearing aid, and ampli-
•
cation features can change as rapidly as the child’s physical
size and cognitive abilities change. In the early years, these
choices should address the child’s immediate communication
and amplication needs but should eventually give way to
choices that enable the child to become an autonomous
decision maker and an eective advocate for his own hearing
health care.
Hearing instruments for children should provide an amplied
•
signal that can be shaped to accommodate the conguration
of the hearing loss, provide amplitude compression, be free
of distortion, and prevent the amplication of excessively
loud input.
Objective measures of hearing aid function (i.e., real-ear
•
measures) are critical to the hearing aid tting process in children of any age. Signicant over- or underamplication due
to a failure to measure the level of hearing aid output in the
child’s ear canal can place the child at risk for further hearing
loss and/or delayed communication development.
A wide range of social and personal factors contribute to
•
hearing aid use or rejection during the adolescent years,
including feelings of isolation, poor identity and self-concept,
cosmetic and other hearing aid issues, problem-solving abilities, and self-acceptance.
Once children reach the age when they and their peers are
•
routinely given responsibility for devices such as cellular
phones or automobiles, smaller ear-level aids or custom
in-the-ear or in-the-canal devices may be considered if their
hearing losses and listening needs permit.
20.1 Hearing Aid Fittings for Infants
and Young Children
In the early years of universal newborn hearing screening, audiologists faced unique challenges as they adapted adult hearing
aid fitting procedures to meet the needs of infants and young
children with hearing loss. These adaptations included earmolds
for smaller, softer ears; obtaining hearing thresholds through
physiologic measures; and real-ear verification procedures for
patients who wouldn’t sit still. Over the years, amplification
recommendations and fitting protocols for infants and small
children were developed and distributed through publications
and professional organizations. These recommendations and
protocols continue to be revised as new procedures are developed and as hearing aid technologies advance.
this chapter is to provide an overview of the current practices
for fitting hearing aids in infants and young children as well
as to provide a summary of the recent research regarding the
use of certain hearing aid features during the first few years
of life. In addition, this chapter provides practical information
regarding hearing aid selection and fitting for older children and
adolescents.
The many developmental milestones that occur between birth
and early adulthood are unmatched by physical changes at any
other time of life. Children change so quickly that the child you are
fitting with a hearing aid today is not the same child you fitted last
year. It is logical then that the procedures used to fit hearing aids
in infants and young children should also mature as they enter
adolescence and adulthood. For example, occluding earmolds
may be appropriate for an infant or young child but may not be
as the child grows and acoustic feedback diminishes. Likewise,
parents may favor brightly colored earmolds and hearing aids for
their young children, while smaller earmolds with less attentiongrabbing colors may better suit a grade-schooler or teenager.
The information provided in this chapter is based on the principle that children with hearing loss are best served by audiologists
who consider both short- and long-term goals of hearing aid
fitting during each clinical interaction. Ideally, short-term goals
address the child’s immediate communication and amplification
needs as well as motivations for hearing aid use, while long-term
goals move the child incrementally toward becoming an autono-
mous decision maker and an eective advocate for his or her own
hearing health care. After all, that child will have a hearing loss for
the rest of his or her life.
1,2
The purpose of
Pearl
Hearing loss in childhood lasts a lifetime.
215
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Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
During infancy and early childhood, the goal of the hearing aid
fitting is to provide access to sound through optimal amplification
and consistent hearing aid use. Research has shown that the bene-
fit that children with hearing loss receive from their hearing aids is
related to the quality of the hearing aid fitting provided, especially
for children with more severe hearing losses.3 A recent large-scale
project examining the outcomes of children with hearing loss
between the ages of 6 months and 7 years characterized the risks
of childhood hearing loss to language development as well as the
benefits of amplification.
was directly related to the audibility provided by hearing aids
during the preschool years regardless of the degree of hearing loss
(mild to severe). Likewise, children who wore their hearing aids
consistently were more likely to demonstrate better language and
auditory outcomes than children who did not. This was particularly true for children with more severe hearing losses. Finally,
and most interesting, children who were fitted with hearing aids
early in the course of the disorder and those who were fitted at
a later age were found to have dierent trajectories of language
development. That is, language developed more rapidly in the
later-fitted children such that the gap between the two groups
narrowed rather than remaining constant or increasing. This is
good news for children who experience a delay in auditory input
for a portion of their early lives (up to 18 months). For children
older than 2 years, however, the developmental trajectory appears
to be constant regardless of degree of hearing loss through 6 years
of age. Overall, the outcomes of this project highlight the benefits
of early identification, best practices for hearing aid fitting, and
consistent hearing aid use for all children with hearing loss.
4,5
Specifically, language development
and timeline involved in the fitting process should be reviewed
with the parents so that they may adopt appropriate expectations
for each of the many appointments that will follow over the first
few months and years.
20.1.2 Taking the Earmold Impression
Most of the techniques used to obtain earmold impressions in
adults are used with infants and small children; however, several
important adaptations must be made. First, children’s ears are
significantly smaller than those of adults in both diameter and
length until about 2 years of age. The most significant of these
is length of the canal. Table 20.1 shows average ear canal length
(in mm) for healthy full-term babies starting at 1 month through
24 months.6 The shorter overall length of the infant ear canal (14
mm) requires special attention when placing an otoblock for an
earmold impression. Fig. 20.1 shows the placement of a small
otoblock (~ 3 mm) about 5 mm from the tympanic membrane.
That leaves only 6 mm for the impression material, which is
equivalent to the width of a paper clip at the narrow end. Because
insertion depth is dicult to estimate from a distal perspective
(i.e., looking into the ear canal), it is recommended that the tip
of the otolight be marked at 6 and 8 mm for 1- to 3-month-old
infants and at 9 and 12 mm for 6- to 12-month-old children and
older to ensure proper insertion depth. However, these depths
should not be applied to premature infants, children who are
small for their age, or those with ear canal stenosis.
20.1.1 Where to Begin?
The hearing aid fitting process begins when the infant or small
child is identified with a permanent hearing loss that is not
complicated by unresolved middle ear dysfunction (e.g., middle
ear eusion). Individual-ear, frequency-specific hearing thresholds should be obtained if the child is old enough to participate
reliably in behavioral testing (as early as 6 months, but valid
behavioral hearing thresholds are often not obtained until 8 to 9
months for children with hearing loss).
Pearl
Hearing aid prescription begins with individual-ear, frequency-
specic hearing thresholds.
For younger children, thresholds may be obtained with auditory brainstem response (ABR) testing, although these thresholds
should be c
with behavioral measures as soon as possible. Also, all educational,
family support, and necessary medical referrals (otolaryngology,
ophthalmology, genetic counseling) should be made prior to
initiating the hearing aid fitting process. Finally, the procedures
onsidered estimates of auditory function and replaced
Table 20.1 Ear canal length as a function of age
Age (months) Length (mm)
1 14.0
3 16.5
6 17.5
12 20.0
24 21.0
Adult 25.0
Source: Adapted from Keefe et al.
6
Special Consideration
The length of an infant’s ear canal is dicult to determine
from a distal position. The placement of anything in the canal
should be attempted only with a guide displaying increments in
millimeters.
When choosing a material for the earmold, vinyl is recom-
mended because it is soft enough for comfort but rigid enough
o keep the sound bore open when it is inserted into the canal.
t
Also, the shape of a vinyl earmold can be modified easily, and
the material accepts adhesive readily to hold the tubing firmly
216
depth
Eardrum
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
5 mm space
20 Hearing Aids for Infants, Children, and Adolescents
Otoblock (3 mm)
6 mm insertion
Fi g . 20 .1 Placement and dimension of an otoblock within an infant ear
canal.
in place. Standard #13 tubing is recommended if the size of the
sound bore is large enough. It is recommended that the earmold
be inspected when it is received from the manufacturer to ensure
that the sound bore is open and that the tubing, if it extends to
the end of the sound bore, is not pinched closed. For some infants,
the diameter of the ear canal may be equivalent to, or smaller
than, the diameter of the #13 tubing during the fi rst few weeks
or months of life. It may be necessary to use a vinyl earmold with
the tubing inserted partially through the sound bore. Although a
reverse-horn e ect may occur (causing attenuation of the high
frequencies), this problem is short-term and will be resolved
as the child’s ear canal grows and can accommodate a standard
tubing diameter.
20.1.3 Real-Ear-to-Coupler Di erence
(RECD)
Most infants and young children (and some older children) have
di culty participating in the hearing aid fi tting process because
many of the measures (such as real-ear verifi cation) require
them to sit upright, quiet, and still for a period of time. But these
measures are critically important when fi tting hearing aids to
infants and young children. Because of their small ear canals, the
output of a hearing aid in an infant’s ear canal can be substantially higher than in a larger, adult ear canal.
7
Pearl
The output of a hearing aid will be substantially higher in an
infant ear canal than in a larger adult ear canal.
Fig. 20.2 Schematic of the components involved in an RECD measure.
If the sound pressure level (SPL) of the hearing aid output is not
measured, overamplifi cation is a signifi cant risk. To address this
problem, a simple method was devised to capture and represent
the acoustic characteristics of a child’s ear canal in a standard
acoustic coupler.
coupler di erence (RECD) and is exactly that: the di erence
between the acoustic characteristics of the child’s ear and those
of an acoustic coupler used to measure hearing aid output.
Most real-ear verifi cation instruments include a module for
making these measures and for including the values in subsequent
hearing aid analyses. Fig. 20.2 shows a simple schematic of how
the RECD is measured and calculated. Using a probe microphone,
the SPL of a 1 to 2-second broadband noise is measured in the
child’s ear and in an acoustic coupler. The level of the noise in the
ear canal is shown in the graph as a solid line, while the coupler
response is a dotted line. Although the fi gure displays a hypothetical RECD, the di erence between the two measures is representa-
tive of what would be observed in the infant ear canal. That is, the
level of the noise in the infant ear is higher than the same noise
in the coupler. The lower dashed line is the arithmetic di erence
between the ear and coupler measures. This is the RECD. When
these di erence values are applied to hearing aid measures made
in the same coupler, they provide a close approximation to the
amplifi cation levels that would occur in the child’s ear canal.
It is important to bear in mind that the transducer that generates the noise is a component of a real-ear system and can be
coupled to a foam tip or to the child’s personal earmold. However,
the RECD values will be applied to both the child’s hearing thresholds as well as to the hearing aid output to convert these values to
units of SPL. Small errors can be introduced if di erent methods
are used to couple the transducer to the child’s ear (e.g., foam
tip, earmold). A good rule of thumb is to use the same coupling
method for both the RECD and the hearing threshold measures.
The RECD is a quick and easy measure to make. Generally, the
setup takes longer than the test itself. Once the RECD is obtained,
the child does not need to be present while the hearing aids are
programmed. There are, however, several important considerations to keep in mind when measuring RECDs. First, the placement and insertion depth of the probe microphone changes as the
child grows. The probe tube should be positioned below the earmold or foam tip during testing. Although convenient, the probe
tube should not be inserted through the vent of the earmold. As
8
This method is referred to as the real-ear-to-
9
10
217
III Hearing Access Technologies for Infants and Children
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
for the depth of insertion, it is recommended that the tip of the
probe tube exceed the medial surface of the foam tip or earmold
(i.e., the sound bore) by 3 mm in young infants and by 5 mm in
older infants and young children.11 Finally, it is best to measure
individual RECDs for each ear. If circumstances prevent measuring
both ears, there are temporary solutions that can be used until
these measures can be obtained at a later date. If an RECD is available for one ear but not the other, the values obtained can be used
for both ears as long as no significant medical conditions are present that might alter the acoustic characteristics of the ear canal
or middle ear on one side.12 If RECDs are not available for either
ear, age-specific normative values are available for infants and
older children.13 However, the variability in RECDs across healthy
infants and young children is considerable, such that the error can
be as large at 5 to 10 dB at certain frequencies. It is recommended
that normative values be used only when absolutely necessary
and only until the next opportunity to obtain individual RECDs.
20.1.4 Choosing and Fitting a Hearing
Instrument
Hearing instruments for infants and young children should: (1)
provide an amplified signal that can be shaped to accommodate
the configuration of the hearing loss, (2) provide amplitude compression to make low-level sounds suciently audible while lim-
iting the maximum output of the device for comfort and safety,
(3) be free of distortion due to limitations of the microphone and
receiver, and (4) prevent the amplification of excessively loud
input through output-limiting technology.
2
Pearl
Hearing instruments should provide an amplied signal that can
be shaped to accommodate the conguration of the hearing
loss, be free of distortion, include amplitude compression, and
prevent overamplication.
These requirements can be met with most commercially
available digital hearing aids. In addition, many hearing aid
manufacturers oer features designed specifically for the needs
of young users. These features include pediatric tone hooks and
retention cords to position the aid better on the ear and prevent
loss if the device comes o of the ear. Parents and teachers benefit
from LED lights on the devices oered by some manufactures that
indicate the status of the device (e.g., on/o, low battery). Newer
devices for children may also be shock and moisture resistant
to withstand the rough-and-tumble lifestyle of most children.
Tamper-resistant battery doors are also a standard feature on
pediatric devices, preventing young children from removing and
swallowing the button-sized batteries. Although battery ingestion
can occur at any age, the incidence is highest in children under
the age of 5 years, with boys more likely to swallow batteries than
14
Parents should be counseled regarding techniques for the
girls.
prevention of battery ingestion or the oral manipulation (sucking)
of the hearing aids. Given the abuse that children’s hearing aids
must endure, parents are encouraged to purchase extended warranties as well as loss and damage insurance.
F
inally, the latest generation of hearing aids now oer wireless
connectivity to remote microphone (RM) systems or personal
devices such as tablets, computers, or cellular phones. While
infants and young children may not use many of these features in
the first years of life, they are likely to become useful as the children grow and expand their communication environments and
needs. For example, communication with a child in the back seat
of a car is dicult due to noise and an inability to see the parent’s
face. An RM worn by the driver and connected via radiofrequency
(RF) transmission to the child’s hearing aids enables the parent to
monitor the child’s needs better and provides an opportunity for
communication and language learning, particularly during long
commutes.
Ear-level (behind-the-ear) devices are considered the best
option for infants and young children for several reasons: (1)
They are more resistant to wear and tear than custom devices,
(2) ear canal growth can be accommodated for a much lower cost
by replacing the earmolds in ear-level devices than by recasing
the shell portion of custom devices, (3) ear-level devices can be
immediately replaced with a similar device while the child’s per-
sonal device is being repaired or replaced, and (4) unlike custom
devices, ear-level hearing aids are large enough to accommodate
more amplification features that may be useful to the child. For
example, severe hearing losses require more powerful hearing
aids and therefore a larger battery, which can be housed only in
these devices. Some assistive listening devices require a physical
port on the exterior of the device to couple connectors for direct
audio input. Also, larger telephone coils can be accommodated in
an ear-level device, providing a stronger receiver for electromagnetic signals. Finally, better microphone alignment for directional
technologies can be achieved in ear-level devices, whereas port
alignment is challenging in custom devices.
20.1.5 Programmable Amplication
Features
During the hearing aid selection process, choices must be made
regarding several amplification features. At least two of these
features are built into the platform of the hearing aid, with no
possibility for adjustment by the audiologist. One of these is
the number of independently adjustable frequency regions
(bands) to accommodate deviations in the hearing thresholds
between adjacent frequencies. Another is the speed of the widedynamic-range amplitude compression (fast vs. slow). For both
of these features, the audiologist must select a device having
the desired characteristics from the range of options oered
across manufacturers. It is recommended that the device have
a reasonably high number of adjustable frequency regions, with
the understanding that more is not always cost eective. That
is, the benefit of increased frequency-shaping precision may not
justify the increased cost. Finally, there is currently no direct evi-
dence regarding the benefits of fast or slow wide-dynamic-range
amplitude compression in infants and young children. Research
in older children (8–12 years) indicates little to no dierence to
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Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
perception between fast and slow compression, whereas adap-
tive compression may oer significant benefits over both.
Another feature that is useful for hearing aid fitting in infants
and young children is feedback management. The prevalence
of feedback in infant ears is high, despite measures designed to
prevent the amplified signal from leaking around or through the
earmold by providing a soft occluding earmold. When these measures are successful, feedback is reduced, and high-frequency gain
is optimized. However, feedback management can degrade audibility of high-frequency input over time as the ear canal grows and
the physical fit of the earmold is no longer optimal. Any feedback
management strategy should be monitored regularly to ensure
that high-frequency gain has not decreased substantially. This
can be done by deactivating the feature and listening for feedback
when the aid is in the ear or with the more comprehensive measures provided by real-ear instruments. Feedback management
should not be used to prolong the use of poorly fitting earmolds.
The remaining amplification features that audiologists may
choose to enable are designed to optimize speech perception through
bandwidth or noise management. Bandwidth management involves
access to the widest possible frequency range, either through
direct amplification at frequencies from 0.25 to 8 kHz or through
frequency lowering when the residual hearing at high frequencies is
insucient for amplification. For these children, frequency-lowering technology can be used to represent the acoustic signal in those
regions at lower frequencies, where there is more residual hearing.
However, direct evidence regarding the eectiveness of either
approach to bandwidth management is not available for infants and
young children. In these cases, evidence of benefit in older children
(provided in the next section) can be extrapolated to young children.
15
Pearl
Amplication should provide as much access as possible to the
full bandwidth of the speech signal.
Finally, many commercially available products oer noise man-
agement through directional microphone technology or through
gital noise reduction feature. While there is no direct evidence
a di
regarding the ecacy of digital noise reduction in infants and
young children, directional microphone technology has been
suggested for use in young children when they are old enough
to localize to sound. This is based, in part, on reports that gradeschool children with hearing loss consistently turn their heads
toward a sound source more than children with normal hearing
do,16 suggesting that they are able and willing to do so for the
sake of communication. While this may be true for older children,
directional microphone technology is not advisable for infants
and young children, for several reasons. The most important of
these is the safety of the child. Once a child learns to walk, the
opportunity for orientation and movement away from caregivers
is greater. Because directional technology, including automatic
switching technologies, prioritize input to the front microphones,
the caregiver’s voice may be attenuated from behind the child, particularly dangerous given the hazardous scenarios young children
are drawn to. Another limitation of this technology for infants and
young children is the requirement that the user position himself
between the noise and the signal of interest. Young children are
unlikely to understand this constraint and even if they did, they
may lack the ability to position themselves accordingly.
20.1.6 Verication
Once fitted, the output of the hearing aid should be verified
through real-ear measures that indicate the level of the ampli-
fied signal reaching the child’s tympanic membrane. During the
first year of life, simulated real-ear measures are the only option,
eventually giving way to traditional real-ear measures when the
child is old enough to tolerate the length and constraints of the
procedure. Until then, it is not possible to evaluate some hearing
aid features on-ear (e.g., feedback management, directional
microphones). However, simulated real-ear measures do allow
precise shaping of the frequency response to targets calculated
by fitting protocols designed to provide children with sucient
audibility for optimal speech perception: Desired Sensation
Level (DSL)
linear fitting procedure.18 These protocols are evidence-based,
and deviation from them is not recommended.
17
and the National Acoustic Laboratories (NAL) non-
20.1.7 Validation
As young children mature, they can begin to participate in the
fitting process. In addition to real-ear measures, which should
be obtained with any change in hearing, earmolds, or hearing
aid settings, aided thresholds can be added to confirm that the
amplified signal is perceived at the level of the auditory cortex.
These thresholds can be obtained using warble tones or narrow
bands of noise with visual reinforced audiometry in children 8
to 30 months of age and with play audiometry through 4 years
of age. Suprathreshold measures of word or sentence recognition
can be obtained as well as once the child is able to participate
in play audiometry. Both real-ear and aided measures provide
independent and valuable information regarding the hearing aid
fitting. Neither should be used in the absence of the other unless
constrained to do so by the limitations of the device or the child.
For example, aided thresholds and speech measures are the
only way to verify the function of implantable devices such as
bone-anchored hearing aids or cochlear implants. Also, in cases of
auditory neuropathy spectrum disorder, aided measures are the
only way to determine the agreement between the audibility predicted by real-ear measures and those experienced by the child.
Special Consideration
Objective verication of hearing aid output is critical for infants
and young children because they cannot participate in the tting
process. As they mature, behavioral measures should be intro-
duced into the verication process.
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III Hearing Access Technologies for Infants and Children
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
20.1.8 Follow-Up
Follow-up after fitting should occur frequently during the first 6
years of life. It is recommended that the child return every month
for the first 6 months, then at 3-month intervals through 3 years
of age. At that age, intervals can increase to 6 months until age 7.
Frequent visits are necessary to replace earmolds, obtain accurate
and current hearing thresholds, reprogram the devices to accom-
modate growing ear canals, and monitor the function of specific
hearing aid features. If this schedule is followed, the audiologist
will see the child 22 times in the first 6 years. This allows the audiologist many opportunities to prepare the family and the child
incrementally for the implications of lifelong hearing loss and to
provide support and counseling to ensure optimal outcomes.
20.2 Hearing aid Fittings in School-
For school-aged children and adolescents, a primary goal of
hearing aid fitting and follow-up is to promote consistent device
use. Research has shown that older children’s use of hearing aids
declines as they mature. While no large-scale studies have been
conducted in the United States, studies in Germany, Cyprus,
Finland, Canada, and England suggest that half of children with
hearing loss opt to wear only one hearing aid during the grade
school years, while many more reject their aids altogether when
they reach junior high and high school.
discard their hearing aids, they are at greater risk for social, academic, vocational, and emotional problems during their delicate
preteen and teenage years.
To better understand hearing aid use and rejection, Elkayam and
English28 surveyed a group of adolescents (12–18 years) with hearing loss through questionnaires and interviews. The responses they
received were organized into five categories: (1) inherent isolation,
(2) identity and self-concept, (3) cosmetic and other hearing aid
issues, (4) problem solving, and (5) self-acceptance. These categories
highlight the prominent role that social and emotional factors play
in adolescents’ decisions to discard hearing aids, while cosmetic
concerns are less of an issue. For example, the decision to discard
hearing aids was often due to the frustration they experienced when
having to explain their hearing loss and hearing aids to others. This
problem is compounded further by the fact that the vocabularies
of children with hearing loss are, on average, 2 years behind those
of their normally hearing peers,
respond articulately to the questions and comments of others.
A common solution oered by professionals is to reduce the
visibility of the devices; however, Elkayam and English warn that
cosmetics is just one facet of the long-term social and emotional
eects of hearing aid use in adolescents. While more cosmetically
appealing hearing aids may improve adolescents’ confidence in
their visual appearance, the hearing aids themselves serve as a
reminder that they have hearing loss. Thus, a wide range of social
and personal factors contribute to the conscious rejection of hear-
ing aids despite the significant consequences to communication
that can occur. Indeed, “The teens who ceased using hearing
aids did not necessarily do so because they underestimated the
listening diculties they experienced. On the contrary, most were
keenly aware of their communication challenges.”
25,26,27
19,20,21,22,23,24
29
making them ill-equipped to
When children
29[493]
20.2.1 What Can the Audiologist Do?
During the challenging adolescent years, a focus on maintaining
a healthy professional relationship will likely be more fruitful
than insisting on consistent hearing aid use. This period is an
opportunity to transition children from pediatric to adult hearing aid styles and technologies in the same way that glasses
can be transitioned to more stylish frames or contact lenses
as children grow older. Some children mistakenly consider
their hearing aids to be temporary like orthodontia (braces on
teeth); a notion supported by the fact that most of the adults
they know, including their parents, do not use hearing aids.
Finally, it may also be helpful to refer some adolescents to an
audiologist of the same gender if it fosters a healthier professional rapport.
Pearl
Children with hearing loss need guidance from professionals to
become autonomous decision makers and eective advocates of
their hearing health care.
20.2.2 Selecting and Fitting a Hearing
Instrument
By the grade school years, the ear impression and fitting process
is similar to that of adults. When selecting the earmold and hearing aid characteristics, however, it is helpful to bear in mind that
a child’s preferences will change faster than either the earmolds
or the hearing aids will wear out.
Pearl
Children’s preference for color and style will change faster than
the earmolds and hearing aids will wear out.
For example, the brightly colored earmolds and hearing aids
that were desired in first grade may no longer be acceptable in
third grade. Even in early childhood, brightly colored earmolds
and hearing aids are more likely to invite regular and unsolicited
attention from others, which may initiate the social and emotional
responses that contribute to later hearing aid rejection. Thus, the
choice of earmold style, color, and features for older children can,
in many cases, be the first step in the transition to adult features.
It is recommended that audiologists resist the urge to please
the child and parent with brightly colored earmolds and select
a clear- or esh-colored material (acrylic, vinyl, silicone) that is
less likely to draw attention and more likely to remain in the ears.
Also, once the earmold features that were necessary to reduce
feedback during infancy are no longer necessary, a vent should be
provided to allow input through the direct pathway for frequency
220
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