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22 Considerations for Pediatric Cochlear Implantation
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.
22.4.2 Imaging of the Auditory System
Imaging of the auditory system allows the CI surgeon to assess
the anatomy of the temporal bone with specific focus on cochlear
anatomy and anomalies. Twenty to thirty-five percent of CI recip-
ients have abnormal or atypical cochlear anatomy (e.g., cochlear
dysplasia, enlarged vestibular aqueduct, cochlear ossification).
Prior knowledge of cochlear anatomy is impor tant, part icularly for
such conditions as an enlarged vestibular aqueduct and cochlear
dysplasia, because they are associated with a higher likelihood of
a perilymphatic gusher during surgery (i.e., ejection of perilymphatic uid when the round window is perforated or cochleostomy created), which can result in vestibular complications after
surgery. Imaging also informs the surgeon of the most appropriate
electrode array for the child’s cochlear anatomy. Moreover, imaging may help to avoid nonauditory complications such as facial
n
erve damage. Of note, the course of the facial nerve is aberrant in
15 to 30% of children with vestibulocochlear anomalies.
Computed tomography (CT) scanning and magnetic resonance
imaging (MRI) are the two most commonly used procedures to
image the auditory system prior to implantation. An MRI is often
preferred because it does not expose a child to radiation, allows
the surgeon to examine the cerebrum to rule out neurologic
abnormalities, and enables the surgeon to evaluate the integrity
of the cochlear nerve. Cochlear nerve deficiency (e.g., an absence
or reduction of the caliber of the cochlear nerve) aects up to
10% of children referred for CI evaluation,
unilaterally.30 Obviously, a CI will provide little to no benefit for a
child with absent cochlear nerves. Preimplant imaging is important because for most modern CIs, the magnet must be removed in
order to conduct a standard MRI; however, a MRI may be possible
with a lower magnetic field.
29
but it often manifests
26,27
27, 28
Pitfall
Cochlear nerve deciency will likely reduce the benet a child
receives from a CI. MRI assessment should be conducted to evaluate the integrity of the cochlear nerve prior to implantation.
is carefully perforated, or a cochleostomy is made just anterior
and inferior to the round window, to allow electrode array
insertion. The surgeon slowly inserts the electrode array into the
cochlea in an attempt to minimize surgical trauma and to keep
the electrode array in the scala tympani throughout the entire
insertion. Some CI teams provide intraoperative assessment
of device function during CI surgery to confirm that electrode
impedance is within normal limits and that the cochlear nerve
is responsive to electrical stimulation from the CI. Following
the completion of the CI surgery, it is highly recommended that
the surgeon order plain-film X-ray imaging to confirm proper
placement and insertion depth of the CI electrode array. The
results of the radiograh should be conveyed to the programming
audiologist.
The recovery process is typically free of major complications
and distress. Within a few weeks, the incision site is largely free of
scarring, and the child usually is not burdened by chronic discomfort, vestibular issues, or healing complications. After surgery, the
ad is usually wrapped with a bandage, which the child wears for
he
several days after surgery. Postoperative follow-up care varies by
surgeon, but in most cases the child is seen approximately 1 week
after CI surgery and then again for a 1-month postoperative examination. The surgeon, then, sees the child for a routine checkup on
an annual or biannual basis.
22.5 Cochlear Implant Activation
and Programming
There are several steps that the audiologist will need to review
with the family to prepare them for activation of the CI, which
are outlined in Table 22.2.
Prior to the activation appointment, the clinician should confer
with the CI surgeon to determine whether any surgical complications occurred, including partial insertion of the electrode array
or unusual observations. Of course, it is also necessary for the
audiologist to know the make, model, and electrode array of the
child’s CI.
Several steps are involved in the preparation of the environment and the activation of the implant, which are reviewed in
Table 22.3.
22.4.3 CI Surgery
For an experienced pediatric CI surgeon, the minimally invasive
surgery is typically an outpatient procedure that requires 45
minutes to 2 hours to complete (Video 22.1). To begin surgery, a
small incision is typically made where the auricle attaches to the
skull. The skin ap is retracted, and a pocket is created under the
skin and muscle to create a location for the implant superior and
posterior to the external ear canal for secure placement of the
body of the implant. Next, a mastoid cavity is facilitated through
careful drilling to allow visualization of the middle ear space and
round window. Often a shallow recess is created in the bone to
help secure the implant as well. Then the overhang of the round
window niche is often drilled away to allow better visualization
of the round window and an easier approach to inser ting the electrode array through the round window. Next, the round window
22.5.1 CI Programming
CI programming involves the process of determining the optimal
signal coding strategy, signal coding/processing parameters,
input processing, and stimulation levels necessary to optimize
the auditory abilities of the user. CI manufacturers oer multiple
signal coding strategies, but the manufacturer’s default (recommended) signal coding strategy and signal coding/processing
parameters is a good place to start and will support excellent
hearing performance in most recipients. The most important and
critical objective of the programming audiologist is to determine
the ideal stimulation levels, which vary considerably across indi-
viduals, because these levels inuence hearing performance with
31,32,33,34,35,36,37
the CI.
modification of coding strategies and processing parameters
should be considered.
If a child is not making appropriate progress,
241
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.
Table 22.2 Steps to prepare child and family prior to implantation
Step Description
1. Healing period Generally, 2–4-week period for incision to heal
2. Establish realistic expectations for activation Expect varied responses to CI activation: (a) happy; (b) tentative, upset, or frightened; and (c)
3. Understand child’s gradual progress with CI
4. Orientation to CI equipment
5. Counsel family on full-time CI use and
strategies to enhance communication
Table 22.3 Activation and programming of the implant
Step Description
1. Prepare programming room
2. Ensure the use of a programming assistant
3. Evaluate the status and integrity of the implant
site and middle ear
4. Check for residual low-frequency hearing If patient had AC thresholds < 75 dB HL from 250 to 1,000 Hz, check hearing AC thresholds using
5. Select magnet strength for external
transmitting coil
Abbreviations: AC, air conduction; CPA, conditioned play audiometry; VRA, visual reinforcement audiometry.
ambivalent
Child will not understand speech immediately
•
Child needs time to adjust to auditory stimulation; activation is child’s hearing birthday
•
May take months to discriminate and identify speech and environmental sounds
•
Provide hands-on training with sound processor
•
Provide user manuals and introductory videos
•
CI should be used during all waking hours (“eyes open, ears on”)
•
Consistent use necessary to expose child to speech and environmental sounds
•
Optimize acoustics and facilitate frequent communication with child and family, friends, and
•
peers
Child-friendly décor and furniture; high chair
•
Equipment for VRA to obtain minimal response levels to electrical stimulation (6–30 mo)
•
Toys for CPA and VRA, keep out of view to avoid distraction
•
Ensures child seated securely with good posture
•
Train child on CPA or VRA task; center toward midline in VRA
•
Maintain child’s attention, cooperation, and behavior
•
Observe child’s responses
•
Inform family about programming procedures and progress
•
Perform otoscopic inspection and perform tympanometry before every programming
•
appointment to check for middle ear issues
Look for inammation or at implant site
•
Refer for otologic consultation, if necessary
•
appropriate test technique
Maintains retention but no excessive pressure on implant site, which could cause discomfort or
•
compromise circulation
Too strong if coil drawn to magnet when 2" from head
•
Too weak if coil dislodges when child walks or turns head
•
The electrical dynamic range (EDR) defines the dierence in
stimulation level between the lowest-level electrical charge the
recipient can detect (T level) and the highest-level electrical
charge the patient perceives as loud but not uncomfortable (upper
stimulation level, called a C level or M level). When converted to
decibels (dB), the EDR of a typical CI recipient is narrow, usually
between 10 and 30 dB. As a result, it is a challenge to present
the wide range of acoustic inputs (e.g., 80 dB; 20 to 100 dB SPL)
into the relatively narrow EDR. CI signal processing possesses
amplitude compression to achieve this objective, but to optimize
recipient performance, clinicians must select the ideal stimulation
levels for each individual. CI programming therefore consists of
making a map of ranges of acoustic inputs to levels within the EDR
for all the channels on the implant. The word “map” in this sense
is often capitalized as if it were an acronym, though it is not, so
the process of creating the map, or MAP, is often referred to as
“MAPping.”
As discussed in Chapter 20, detailed evidence-based protocols
are available to determine the appropriate output of a hearing
aid using objective measurements with children. Unfortunately,
the same type of evidence-based protocol does not exist for
determining appropriate CI stimulation levels. Determination of a
child’s CI stimulation levels is a multifaceted process involving the
use of a number of conventional audiologic behavioral measures,
objective measures, informal observations, and feedback from the
child’s caregivers and therapist. An overview of the programming
process is provided in Table 22.4.
Pearl
The most important objective in CI programming is the determination of a child’s optimal stimulation levels (e.g., T levels and
upper stimulation [C or M] levels).
22.5.2 Objective Measures in CI
Programming
Young infants as well as children with neurologic disorders or
other disabilities may not respond behaviorally to stimulation
242
22 Considerations for Pediatric Cochlear Implantation
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.
Table 22.4 Overview of cochlear implant programming procedures
Step Description
1. Determine the electrical threshold (T level)
2. Determine upper stimulation levels (USL)
4. Elicit feedback
Abbreviations: BOA, behavioral observation audiometry; CPA, conditioned play audiometry; LSLS, Listening and Spoken Language Specialist; MRL, minimal response
level; VRA, visual reinforcement audiometry
Use BOA, VRA, or CPA to obtain MRL or threshold
•
LSLS can help to train child for CPA task during weekly therapy
•
Ascending programming stimulus (biphasic pulses) presented to several channels (remaining
•
channels interpolated)
Clinical bracketing procedure used to determine the lowest level of electrical stimulation that is
•
audible to a recipient
Inputs at T level result in electrical stimulation, which is perceived as an audible but soft level
•
T level may be raised slightly if patient hears low-level ambient noise
•
Aided soundeld thresholds should yield responses: 20–25 dB HL across speech frequencies
•
(< 15 dB HL means T level may be too low; > 40 dB HL means insucient audibility)
For some manufacturers, T levels estimated based on upper stimulation levels rather than
•
measured
Loudness determinations are dicult for children
•
Set USL to mirror T levels
•
Gradually increase to desired setting, which is determined by child’s behavior and typical USLs
•
for that implant
Use observation for young children; loudness scaling charts for older
•
Reduce USL if child shows signs of overstimulation (blinking)
•
For older children, balance loudness across channels by presenting stimulus to 2 channels at a
•
time
Elicit feedback from caregivers, teachers, and therapists to assess appropriateness of the
•
program
If no response to certain speech sounds, adjust levels in appropriate channel (e.g., if the child
•
does not respond to /s/, increase T levels and USLs in high-frequency channels)
If child has adverse responses, reduce levels in appropriate channel
•
a b
from the implant during the initial activation appointment. As
a result, the use of objective measures, such as the electrically
evoked compound action potential [eCAP] and the electrically
evoked stapedial reex threshold [eSRT], may be useful in
estimating appropriate stimulation levels. These children will
require several programming sessions, and feedback will be
required from the child’s family, SLP, and LSLS in order to guide
the process of setting stimulation levels. A brief overview of eCAP
and eSRT will be provided; however, more detailed information
may be found in a review by Hughes.
The eCAP is a recording of the synchronous response of a large
number of cochlear fibers in response to an electrical stimulus
delivered from the CI. Manufacturers provide special software
programs to perform simple measurement of the eCAP (Advanced
Bionics: Neural Response Imaging; Cochlear: Neural Response
38
Fig. 22.5 Examples of (a) an electrically
evoked compound action potential (eCAP)
and (b) an electrically evoked stapedial
reex threshold (ESRT) response. (Images
courtesy of Cochlear Americas.)
Telemetry; MED-EL: Auditory Response Telemetry). The primary
component of the eCAP is the N1 potential shown in Fig. 22.5a
and is analogous to wave I of an ABR, occurring at 200 to 500 milliseconds. The eCAP threshold indicates a level of stimulation that
should be audible to the recipient, which can be used to establish
a conditioned response, guide program levels (i.e., T level should
not exceed eCAP threshold), confirm stimulation to the cochlear
nerve, and monitor physiologic responsiveness over time.
Pitfall
The eCAP is not a good predictor of an individual child’s optimal
stimulation levels.
243
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.
The eSRT, shown in Fig. 22.5b, is a measure of the time-locked
change in admittance secondary to the contraction of the stapedius muscle in the response to electrical stimulation from the
CI. The eSRT measure is conducted by continuously measuring
middle ear admittance (usually in the ear contralateral to the
CI) while presenting trains of biphasic pulses at progressively
increasing stimulation levels. The eSRT occurs at the lowest level
of electrical stimulation that produces a time-locked change in
the ongoing admittance of the middle ear.
The eSRT helps to predict the CI upper stimulation level and is
valuable for programming in children. When upper stimulation
levels are set near eSRTs, it may be easier to achieve equal loudness across the channels.
clinician should set upper stimulation levels at the eSRT levels and
then globally decrease upper stimulation levels to a level that is
comfortable to the recipient. Next, the program should be acti-
vated in “live speech mode” (e.g., microphone of processor enabled
so that recipient can hear environmental sounds), and upper
stimulation levels should be slowly increased to a level providing a
satisfactory EDR while the programming audiologist and assistant
observe for signs of discomfort or aversion from the recipient. The
limitations of the eSRT include the necessity for the child to sit
still and cooperate for 5 to 15 minutes and the impossibility of
measuring eSRT if there is even slight middle ear dysfunction.
34,36,39,40,41
Once the eSRT is obtained, the
Pearl
The eSRT is the optimal objec tive measure for use in predicting CI
upper stimulation levels.
of each of these outcome measures is provided in Table 22.5.
Assessments should occur every 3 months for the first 2 years
after the child receives a CI and at least every 6 months thereafter.
Chapter 9 in this volume provides more information about
speech perception procedures and tests, and Uhler and Giord42
provide an overview of the Pediatric Minimum Speech Test Battery
(PMSTB), a collection of clinical measures of speech recognition
and a protocol for how to administer each test.
Historically, pediatric CI recipients have achieved a wide range
of outcomes in auditory, speech, and language development.
A number of factors inuence outcomes, including the age of
implantation, child’s nonverbal IQ, presence of additional disabilities, significant anatomical abnormalities (e.g., cochlear nerve
aplasia, common cavity cochlea), maternal education, maternal
support, SES, proximity of the electrode array to the modiolus,
the scalar location of the electrode array, and aided soundfield
detection thresholds.
implanted under 12 months of age achieve normal vocabulary
and receptive and expressive language by the time they enter
kindergarten.
with good outcomes include connexin 26 mutations, enlarged
vestibular aqueduct, and Usher syndrome, whereas etiologies
that may hinder or result in variable outcomes include cochlear
nerve aplasia, meningitis with cochlear ossification, and common
cavity cochleae. Auditory brainstem implants may be considered
for children who have one of these etiologies and receive limited
benefit from a CI. The child’s communication mode may also
inuence outcome. Children who communicate solely through
listening and spoken language achieve better auditory, spoken
language, and literacy outcomes than children who use a total
communication (sign language and speech) approach.
reason, it is imperative for a child who receives a cochlear implant
to receive therapy from an SLP or LSLS.
2,3
3,43,44,45,46
However, the majority of children
Etiologies of hearing loss that are often associated
1,2,3
For this
1,3,43
22.6 Outcomes of Cochlear
Implantation in Children
The outcomes CIs in children should be determined with
subjective questionnaires, evaluation of audibility of low-level
sounds, assessment of speech recognition in quiet and in noise,
and assessment of speech and language progress. A description
Table 22.5 Summary of outcome measures for children with CIs
Measure Description
Subjective questionnaires
Audibility and speech recognition measures
Speech-language
Abbreviations: HL, hearing loss; SLP, speech-language pathologist
Questionnaires or rating scales to enable comparison to normal-hearing peers
•
Assess functional auditory performance in the real world
•
Determine family perceptions of child’s strengths and weaknesses
•
Document family concerns or satisfaction
•
Monitor child’s progress in daily situations
•
Obtain thresholds in the 20–25 dB HL range
•
Use recorded speech stimuli to determine audibility across speech frequencies
•
Use aided thresholds with warble tones/narrowband noise for frequency-specic info
•
Use Ling six sounds to determine audibility for low-, mid-, and high-frequency speech
•
Formal evaluations of child’s speech, language, and listening skills using standardized, norm-
•
referenced measures
SLP and audiologist should confer when progress lags behind peers or when child fails to make 1
•
year of progress in 1 chronological year
Pearl
Audiologists and SLPs should work together to evaluate the
child’s functional auditory and spoken language progress associated with CI use.
244
22 Considerations for Pediatric Cochlear Implantation
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.
Table 22.6 Overview and description of postactivation appointments
Time postactivation Duration Basic overview of typical procedures
1 week 1 hour
3 weeks 1 hour This appointment necessary only when T and USL levels not determined at 1 week
1 month 1 hour
2 and 3 months 1 hour
Every 3 months 1 hour
Every 6 months 1 hour For children > 7 years with a minimum of 2 years of implant experience:
Abbreviations: eCAP, electrically evoked compound action potential; eSRT, electrically evoked stapedius reex threshold; LSLS, Listening and Spoken Language
Specialist; T, threshold levels; USL, upper stimulation levels.
Visually examine incision site, perform otoscopy impedance measures
•
Measure T levels, eCAP, and eSRT for remaining electrodes
•
Make adjustments to USL in live speech mode
•
Reduce the volume range available via remote control
•
Discuss maintenance and care of devices and demonstrate accessories
•
Children: Provide with only one program
•
Adolescents: Obtain aided soundeld thresholds; create situation-specic programs
•
Visually examine incision site and perform otoscopy
•
Similar protocol to week 1 appointment
•
Visually examine incision site and perform otoscopy
•
Query patient about progress and discuss duration of daily use of implant
•
Visually examine device and do biologic listening check on processor
•
Obtain aided sound eld thresholds and speech recognition
•
Measure electrode impedances and T-levels
•
Optimize USL and measure ESRT
•
Reduce the volume range available via remote control or disable
•
Provide patient with situation-specic programs
•
Visually examine incision site and perform otoscopy
•
Obtain soundeld detection thresholds and speech recognition
•
Similar procedures as 1-month appointment
•
Children: Ensure access to soft sounds; conrm appropriate program settings/ levels
•
Adolescents: See at 2 months only if patient is struggling, otherwise see at 3 months
•
Visually examine incision site and perform otoscopy
•
Obtain soundeld detection thresholds and speech recognition
•
Conduct a visual exam of device as well as a biologic listening check on processor
•
Measure electrode impedances and eSRTs
•
Make necessary adjustments to T levels, USL, parameters, and programs
•
Assess auditory skills; collaborate with LSLS
•
Visually examine incision site and perform otoscopy
•
Obtain soundeld detection thresholds and speech
•
Procedures similar to 3-month appointment
•
22.7 Other Considerations
in Pediatric Cochlear
Implantation
Several other considerations and options may greatly enhance
performance with CIs, including timeline for follow-up programming and testing and other technology options, such as bilateral/
bimodal stimulation, advanced signal processing, remote
microphone (RM) technology, and electric-acoustic stimulation
(EAS),47 which is shown in Fig. 22.6. A timeline and overview of
appointments following implantation are provided in Table 22.6.
In addition to these follow-up appointments, children will need
to be managed by a team of professionals focused on hearing,
speech-language development, and educating the child in the
least restrictive environment.
An overview of other technology options is provided in Table
37,48,49,50,51,52,53,54,55,56,57,58,59,60
22.7
options should be considered for pediatric users of CIs. Additional
information on RM technologies is provided in Chapter 24.
, and when possible, all of these
a b
Fig. 22.6 (a) Hybrid CI sound processor that possesses both an
acoustic component to deliver amplication for low-frequency
inputs and a CI coil to deliver electrical stimulation for mid- to
high-frequency inputs. (b) Hybrid electrode array, which is shorter
in length than a conventional electrode array. (Images courtesy of
Cochlear Americas.)
245
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.
Table 22.7 Considerations and options that may improve cochlear implant outcomes
Option Description
Bilateral/bimodal stimulation
Advanced signal processing
Remote microphone (RM)
technology and HAT
Electric-acoustic stimulation
(EAS)
Abbreviations: HA, hearing aid; HAT, hearing assistive technology
Pearl
Bilateral (2 CIs) and bimodal stimulation (HA+CI) provide superior performance over a unilateral CI
•
Bilateral CI provides better speech recognition in quiet and noise, localization, language development, and
•
educational outcomes
Better bilateral outcome with simultaneous CIs or short gap between sequential CIs
•
Bimodal provides better speech recognition in quiet and noise with modest improvements in localization
•
Noise reduction processing aims to decrease steady-state noise; improves speech recognition and, likely, comfort
•
Directional microphone technology focuses on sounds in front of user while decreasing sound from side or
•
behind; signicantly improve speech recognition
In children, directional technology could hinder audibility of sounds from behind. When available, fully adaptive
•
directional microphone systems are recommended
RM technology signicantly improves speech recognition in quiet and in noise by 30–70% over CI alone
•
Benecial for children in schools, social situations, some sports, and car
•
Wireless phone and TV technologies may improve speech recognition by 20–30% over CI alone
•
Soft surgical techniques/shallow electrode array insertions can preserve low-frequency hearing sensitivity
•
When residual hearing is preserved, an electric-acoustic processor may be used
•
EAS may result in better speech recognition in quiet and noise, localization, sound quality, and music aptitude
•
Hybrid CIs (short electrode arrays) are not currently approved by the FDA for commercial use in children
•
[4]
[5] U.S. Food and Drug Administration. Devices@FDA. https://www.accessdata.fda.
All children with bilateral hearing loss should use optimally tted
hearing technology for each ear.
22.8 Conclusion
[6]
[7]
[8] Telmesani LM, Said NM. Eect of cochlear implant electrode array design on
Children who are implanted at an early age are able to achieve
age-appropriate auditory, speech, language, and academic performance. Clinicians are tasked with identifying children with hearing loss who should be considered for implantation. The FDA has
[9] von Wallenberg E, Briggs R. Cochlear’s unique electrode portfolio now and in the
[10] Adunka OF, Pillsbury HC, Kiefer J. Combining perimodiolar electrode placement
approved guidelines for CI candidacy, but ultimately, the clinician
should determine individual candidacy by seeking to determine
whether a CI will improve a child’s quality of life and optimize
the child’s overall development beyond what would be achieved
[11]
[12] Kerr A, Schuknecht HF. The spiral ganglion in profound deafness. Acta Otolaryn-
with hearing aids. Optimal success with CIs is dependent upon
many factors including the CI programs (maps) created by the
clinician. Development of the optimal CI program is predicated
on the use of a number of behavioral and objective measures and
[13] Spoendlin H. Neuroanatomical basis of cochlear coding mechanisms. Audiology
[14] Adunka OF, Pillsbury HC, Adunka MC, Buchman CA. Is electric acoustic stimu-
procedures. Audiologists should work with the child’s family and
LSLS to ensure that optimal progress is being made after implan-
[15] Bruce IA, Bates JEHM, Melling C, Mawman D, Green KMJ. Hearing preservation
tation. Furthermore, outcomes should be routinely evaluated via
the use of a battery of audiologic, speech-language-listening,
educational, and social-emotional measures.
[16] U.S. Food and Drug Administration. [Notice of approval for Cochlear Nucleus Hy-
[17] Incerti PV, Ching TYC, Cowan R. A systematic review of electric-acoustic stimula-
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23 Acoustic Accessibility in the Classroom and Beyond
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copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
23 Acoustic Accessibility in the Classroom and Beyond
Joseph Smaldino and Carol Flexer
Summary
The classroom is a listening and learning environment. Barriers
exist in this environment in the form of undesirable room
acoustics. The intent of this chapter is to overview the barriers,
identify standardized methods to measure them, and suggest
remedies to lessen their impact on speech perception and, ultimately, classroom learning.
Keywords
model of communication, classroom acoustics, classroom acous-
tic standard, identification of acoustic problems, remedies for
acoustic problems
Key Points
The classroom is an auditory verbal environment in which
•
accurate transmission and reception of speech between the
teacher and students, or between students and students, is
critical for eective learning to occur.
Speech intelligibility is based on the science of signal-to-noise
•
ratio, the relationship of the desired signal to all background
and competing noises; children need the desired signal to be
~ 10 times as intense as, or 15 to 20 dB louder than, background noise to identify words clearly.
The acoustic environment in a classroom is an important
•
variable in ensuring accessibility of teacher instruction for all
children in the room.
Identication of barriers to acoustic accessibility is important
•
and can be accomplished inexpensively using observational
and smartphone applications.
The purpose of all acoustic management strategies is to
•
enhance the reception of clear and intact acoustic signals
to access, develop, and organize the auditory centers of the
brain.
Accordingly, this chapter will discuss classroom acoustics and
•
their measurement and management, in order to improve
brain access to instructional information for all children.
paper, “A Mathematical Theory of Communication.”
fying this theory, an understanding of the classroom acoustic
environment and ways to maximize communication can occur.
Fig. 23.1 is an example of such an information transfer model.
In this model, the speaker and listener bring important variables
to the communication process. The speaker must speak loudly
enough for speech to be audible. This audibility variable is inuenced by the vocal eort of the speaker and the distance between
the speaker and listener. The speaker must also present a clear,
undistorted speech signal. Finally, the speaker can use speech that
is either simple or complex, and the speech can be familiar or
unfamiliar to the listener. The listener must have enough speech
and language competency to use the eciencies and redundancy
resident in speech and language syntax, semantics, and phonology. In addition, the listener must have certain cognitive and
processing competencies to retain and form auditory-linguistic
linkages in the speech and language centers of the brain.
Separating the speaker and listener is the acoustic transmission
path of the speech signal and encoding capacity of the listener.
The transmission pathway can be quiet, or it can be noisy. If
noisy, the noise can derive from loss of information caused by
inaudibility such as background noise that masks information, or
reverberation that distorts and ultimately masks information. The
encoding capacity of the listener is a measure of the intactness
of the peripheral, brainstem, and central auditory mechanisms.
Loss of hair cells or auditory neurons also can reduce the child’s
encoding capacity—the child’s ability to perceive the message.
Any of these variables can inuence the adequacy of the
communication between speaker and listener and can occur in
a multitude of combinations. The best-case scenario would be a
speaker whose speech was audible and clear, using simple and
familiar speech, standing close to a normal-hearing listener who
has fully developed and normal speech, language, and cognitive
processes, in a room with little noise. The worst case would be
a speaker whose speech is inaudible or distorted, using complex
and unfamiliar speech, some distance from an individual who is
deaf or severely hard of hearing with incomplete speech, language,
or cognitive processes, in a room with a lot of noise. Classroom
1
By simpli-
23.1 Introduction to Acoustic
Accessibility
The classroom is an auditory verbal environment in which accurate transmission and reception of speech between the teacher
and students and among students is critical for eective learning
to occur. In other words, the acoustic speech signal must be
accessible to the brains of pupils for listening and learning to
occur. Because information is exchanged in a classroom, this
exchange can be modeled using an information theory approach.
Modern information theory arose from Claude Shannon’s 1948
Fi g . 23 .1 A simplied version of Shannon’s mathematical theory of
communication.
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communication environments are somewhere between these two
extremes.
Although there has been much research on the eects of room
acoustics on speech perception of individuals with hearing loss,
Fig. 23.1 shows that hearing impairment is only one of several
variables that can be managed to improve information transfer.
The other variables can and should also be managed if inadequacy
in one variable produces loss of information transfer. Management
could include auditory processing therapy, speech and language
therapy, cognitive therapy, hearing-assistive devices, and management of the noise in the transmission path. Also, Fig. 23.1 shows
that breakdowns in information transfers are not solely dependent
on hearing status. In other words, students with normal hearing
but with weaknesses in any other of the highlighted variables will
also have an information transfer problem. In addition, some of the
variables, such as speech and language competency or cognitive
competency, are developmental, so the younger the student, the
more impact these variables will have on information transfer,
simply because the young child’s brain has not fully developed.
Each variable shown in Fig. 23.1 is worthy of in-depth consider-
ation, but this discussion will focus on the acoustic components.
Pearl
The adequacy of the acoustic speech signal is an important variable in a classroom learning environment that can deleteriously
aect accurate listening and successful learning.
The acoustic characteristics of the classroom mainly determine
the adequacy of the speech signal received by the students. Of
importance is the signal-to-noise ratio (SNR) of the teacher’s
speech received by the student and the reverberation time (RT)
of the room. The SNR represents the relative intensity of the
teacher’s speech compared with the level of any background
noise present in the classroom as measured at the location of the
student. RT expresses the length of time a signal persists in a room
after the original signal has ended. Sometimes this persistence of
sound is referred to as sound reection or echoes in the classroom.
Research has demonstrated that inappropriate levels of classroom
noise or reverberation can compromise not only speech perception but also reading scores, spelling ability, behavior, attention,
oncentration in children with normal hearing and are even
and c
more deleterious to children with hearing loss or children who are
at risk for listening and learning.
2,3
the desired sig nal to the intensity of the undesired signal or noise.
This ratio is reported as the decibel dierence between the two
intensities. For example, if the speech were 15 dB louder than the
background noise, the SNR would be +15 dB. Speech perception
is generally better when speech is considerably louder than the
noise and decreases as the SNR of the environment is reduced.
Speech recognition ability in adults with normal hearing is not
significantly reduced until the SNR is below 0 dB.
Ample evidence indicates that children require a much better
SNR than adults do.6 The rationale for the better SNR is derived
from the fact that children do not have fully developed auditory-linguistic and cognitive systems. Their immature systems limit
the use of language redundancy and cognitive mechanisms, such
as short-term memory, that can be used to overcome the masking
eects on speech of too much background noise. To obtain speech
recognition scores equal to those of normal hearers, listeners with
sensorineural hearing loss (SNHL) require the SNR to be improved
by 4 to 12 dB.7 An additional 3 to 6 dB are needed in rooms with
moderate levels of reverberation.8 Based on these data, acoustic
guidelines for populations who experience hearing loss suggest
that SNRs should exceed +15 dB for accurate speech recognition.
5
23.3 Eects of RT
RT60 is the amount of time it takes for a steady-state sound to
decrease 60 dB from its peak amplitude. In a reverberant room,
speech is reected from various hard room surfaces, so some of
the speech elements are delayed in reaching the ear of the lis-
tener. The reected speech overlaps with the direct speech signal
(the signal not reected before reaching the listener’s ear) and
covers up or masks certain acoustic speech components.9 Because
vowels are more intense than consonants, a long RT tends to
produce a prolongation of the spectral energy of vowels, which
then covers up less intense consonant components. A reduction
of consonant information can have a significant eect on speech
recognition, as much acoustic information that is important for
speech recognition is provided by consonants.10 Speech recognition, therefore, tends to decrease with increases in RT. Speech
recognition in adults with normal hearing is not significantly
degraded until the RT exceeds ~ 1 second. Listeners with SNHL,
however, need considerably shorter RT (0.4 to 0.5 seconds) for
optimal communication.11 Because of this increased diculty,
acoustic guidelines for populations who experience hearing loss
suggest that RT should not exceed 0.4 to 0.5 seconds in communication environments frequented by these individuals.
12
23.4 Eects of SNR and RT Together
4
23.2 Eects of Room Acoustics and
SNR
Background noise in a room reduces speech recognition by
covering up or masking important acoustic/linguistic cues in the
message. This is especially true of the consonants, which carry
much of the intelligibility of speech necessary for accurate perception. Background noise in a room tends to mask the weaker
consonant phonemes significantly more than it does the more
intense vowel phonemes. The most important factor for accurate
speech recognition, in this regard, is the ratio of the intensity of
The eects of RT and SNR interact. When the factors are combined (which is the case in virtually all real-world listening
environments), the combination aects speech recognition more
than either of the factors does alone. Finitzo-Hieber and Tillman4
were the first to demonstrate this combination eect eloquently.
A summary of their findings is shown in Table 23.1.
Table 23.1 shows the mean speech recognition scores of children with normal hearing and children with SNHL for monosyllabic words across various SNRs and RTs. At an SNR of +12 dB and
RT of 0.4 seconds, children with normal hearing do not recognize
speech perfectly (83%), and children with SNHL perform even more
250
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