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16 Assessment, Treatment, and Management of Auditory Processing Disorders in 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 quality and quantity of scientific evidence are sucient
to support the existence of APD as a diagnostic entity to guide
the diagnosis and assessment of the disorder and to inform the
development of more customized, deficit-focused treatment and
management plans.
Emanuel et al50 reported that the majority of respondents
surveyed on management/treatment of APD indicated that they
used a customized set of management recommendations based
on actual findings of the diagnostic testing for APD (without using
a system of profiles based on diagnostics). A complication arises,
however, when it was noted that although 81% of respondents
indicated that audiologists were responsible for the development
of treatment and management recommendations for APD, only
40% of respondents indicated that audiologists were actually providing the treatment and management services. However, based
on current research in neuroscience and what might be described
as a renewed interest in aural habilitation/rehabilitation, it is
likely that the types of recommendations oered and how APD is
treated are in transition, with greater involvement of audiologists
being expected.
Historically, a triad approach to management and treatment
has been adopted to address the needs of the individual child with
APD. This triad includes developing environment modifications,
helping the child to develop compensatory skills, and providing
treatment designed to change the auditory system. Although the
triad approach appears to be as relevant today as it has been in
the past, the range of available options has expanded. In addition,
the AAA guidelines reframed this discussion by recommending a
dual approach to intervention, with environmental modification
and compensatory strategies classified as “management” of APD
and direct therapy classified as “treatment.” Specifically, AAA
defined “intervention” as a broad term that refers to one or more
actions that are taken to produce, aect, and alter the course of
the disorder and “management” as compensatory approaches,
including strategies and technologies that are used to reduce the
impact of the disorder.
Another way to frame this is to look at context-centered
management, such as accommodations in the classroom, and
person-centered management, such as aural habilitation/rehabilitation treatment. An overview of approaches will be provided in
this chapter; however, there is considerable current research that
is constantly changing the landscape for both treatment and management, and the reader is encouraged to explore these options on
an ongoing basis. A consistent focus for all aspects of intervention
is to increase both the predictability and the redundancy in the
listening environment. Regardless of the approach, the audiolo-
gist is uniquely qualified to develop, implement, and oversee the
treatment plan, based on knowledge of aural rehabilitation and
the accommodations for hearing and listening disorders and the
ability to coordinate an interdisciplinary team to meet the child’s
needs eectively.
4
16.4.1 Management: Addressing the
Educational Environment
Children spend most of their day in the classroom, with a focus
on listening as the primary means for learning. Listening in a
noisy classroom can be fatiguing for a young child even with
normal hearing acuity and typical auditory processing skills; it
is far more so for a child with a hearing loss or APD. In the past,
a common recommendation was preferential seating, placing
the child close to the source of verbal instruction. Although this
approach has good face validity and is inexpensive to implement,
it does not eectively address the listening and learning impact
of poor acoustics on a child classified as a high-risk listener.
Adults with normal hearing acuity and typically developing
auditory processing skills require a +6-dB signal-to-noise ratio
(SNR) to maximize auditory learning, but typically developing
children require a +10-dB SNR in the classroom.79 Speech-innoise ratios have been consistently reported across classroom as
+5 dB to –7 dB, much poorer than would be adequate for eective
auditory comprehension for learning.80 Leavitt and Flexer,81
using the Rapid Speech Transmission Index (RASTI) approach
as a measurement tool, found a significant loss of speech intelligibility unless the position of the listener was very close to the
position of the speaker (approximately 6 inches), dispelling the
myth that preferential seating is an eective accommodation for
a child with an APD. Additionally, most classrooms are no longer
set up to establish a true preferential seat, reecting instead the
collaborative nature of the classroom where students are seated
in groups, rather than rows. The distance of the student from the
teacher is generally impractical for making a positive acoustic
impact from a peripheral seat. Some children, however, may
benefit from seating in the classroom that allows the student to
have unobstructed view of the teacher or the teacher to access
the student for comprehension checks.
Improving classroom acoustics can include addressing options
for improving overall noise, reducing reverberation, and improv-
ing the SNR, all of which can have a significant impact on speech
intelligibility for all children in the classroom. Eort should be
made to use the American National Standards Institute (ANSI)
standard for classroom acoustics as the goal in every classroom.82
Many classrooms have a classroom audio distribution system
(CADS), previously known as a soundfield frequency-modulated
(FM) or infrared system. In addition, the child with an APD may
benefit from remote microphone (RM) technology, such as FM
and/or digitally modulated (DM) systems, as a method to maximize SNR for the individual listener or a classroom.83 However, use
of assistive technology to address speech intelligibility in children
with APD is not a panacea, nor is this the appropriate and/or
necessary treatment for all students with APD. An overview of
assistive technology can be found in Chapters 23 and 24, and the
reader is directed there for additional information.
Children with APD obtain the same types of benefits from an
improved acoustic environment as all other students do, and
the overall benefits of soundfield amplification in the classroom
is obvious in the general education environment. However, as
noted by Boothroyd,84 a soundfield amplification system is not
a substitute for good room acoustics. In addition, SNR enhancement must be carefully considered and must be matched to the
listener’s needs. Some children with APD benefit from the type of
enhancement provided by the CADS. For others, in keeping with
the “high-risk listener” profile,78 a more favorable SNR is required
than is available through a CADS.
A personal RM system provides a great option for students with
APD, particularly for students with APD who require a greater
SNR enhancement or those with concomitant disabilities, such
as dyslexia. The ASHA85 Guidelines for Fitting and Monitoring FM
78
181
II Diagnosing Hearing Disorders in 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.
Systems provide a framework for this type of fitting; however, FM
fitting, particularly with this population, is less of a standardized
approach, where an audiologist may or may not be involved in the
actual fitting.86 A trial with technology is highly recommended to
determine benefits, with authentic assessment being performed
during this time. Use of the Listening Inventory for Education—
Revised (LIFE-R)87 provides a foundation for documenting perfor-
mance with the system. Not only is the use of RM an eective
management strategy; there is evidence that consistent use of RM
technology may have the added benefit of impacting neuroplasticity in children with APD.
the neural representation of the speech signal, enhancing acoustic
clarity and attention while reducing variability in auditory processing.88 These results suggest that increasing predictability and
redundancy of the speech signal is of benefit to the child with
APD in the classroom; however, the improved SNR may have more
long-lasting and significant impact on the central auditory system
than previously understood.
A recent consideration in improving audibility and addressing
children with APD is the use of hearing aids, set to provide mild
gain to the listener. The advent of open-fit digital hearing aids has
enabled this to be a viable option for children with APD, which
may provide an option for a listener who prefers a more exible
option than can be provided with RM technology or in a wider
variety of settings. Protocols for fitting hearing aids to children
with APD exist,
in the population. The author has similar successful outcomes
in both children and teens with APD who have been fitted with
hearing aids; obviously, medical clearance must be obtained, and
this may take a team approach for the physician to understand the
benefits of amplification for the patient and the careful protocol
implemented in ensuring an appropriate fit.
83,89
83,88
Use of the RM is thought to improve
and successful outcomes have been noted
16.4.2 Management That Incorporates
Compensatory Strategies
Children with APD often have poor ability to compensate for
their listening limitations. Children are not directly taught
the skill of listening, unlike the skills of reading, writing, and
spelling. When a teacher asks students to listen, the child with
APD in the classroom may have little understanding of what is
required to be a successful listener in the educational environ-
ment. Children may benefit from specific instruction in the steps
needed to become an active and eective listener and in orga-
nizing incoming auditory information. Several programs have
been described over the years that focus on developing specific
listening skills in the classroom listening environment; that of
Prelock,90 the Classroom Language and Auditory Strategies for
Success (CLASS),91 and the Kooser program.92 Audiologists may
be able to modify an aural habilitation/rehabilitation program
for another population to work with children with APD.
It is critical to recall that auditory-oral communication is
the responsibility of both the teacher and the student in the
classroom environment. If failure of communication occurs on
the part of the listener, the speaker (such as the teacher, in this
case) should also be provided with strategies that can improve
the student’s comprehension. Often, the speaker will increase the
intensity of his or her voice, which helps neither communicator.
Providing a wider range of communication strategies can enhance
the exchange of auditory information. One example of a program
is clear speech, an approach that is designed to address speech
production parameters, such as decreasing speaking rate; this
type of intervention has been shown to be successful in increasing
speech intelligibility for the listener.
The development of additional metacognitive abilities may
empower the child to implement small but significant accommodations in the classroom, which gives increased control over
the listening and learning environment. Several techniques and
skills, such as providing guided notes or PowerPoint slides prior to
instruction or pretutoring of new vocabulary, provides accommodation in a metacognitive approach. The addition of technology,
such as a speech-to-text tool that is available with a Livescribe
smartpen (Livescribe, Oakland, CA) or with the Lesson Capture
feature in the Juno Connect CADS system (FrontRow, Nundah,
Queensland, Australia), can provide an excellent opportunity for
the student to have real-time information provided in an eective
manner without having to transcribe a recording or obtain notes
from another student in class. The benefit of an interdisciplinary
approach is that often a psychologist or speech-language pathologist will also provide the student with metacognitive strategies,
creating a positive support network.
93,94
16.4.3 Treatment by Direct Therapeutic
Approaches
Historically, speech-language pathologists in the school setting
have implemented auditory training programs for children with
APD. These programs were often implemented as part of language
therapy and have targeted a top-down approach to listening.
Some of these programs have also focused on building reading
and literacy skills, such as the Orton-Gillingham approach
(Institute for Multi-Sensory Education, Northville, MI) or the
Lindamood Phoneme Sequencing (LiPS) program (LindamoodBell Learning Processes, San Luis Obispo, CA). These programs
include a multisensory approach to enhance auditory skills and
often target global listening skills rather than addressing specific
types of auditory processing skills that may be taught. In some
cases, programming has been implemented from preprinted
worksheets or handbooks that purport to address listening skills.
Although these programs may have ecacy, it has been dicult
to measure changes in the auditory system following implementation of these programs or to accept that the focus of the
programs is anything beyond the development of compensatory
skills.
Advances in auditory neuroscience over the past several decades
have ignited renewed interest in treatment of APDs. Phillips20
noted that changes in the auditory cortex, representing the neuroplasticity of the system, are seen as a result of behavioral training,
first noted in animal models and now seen in human auditory
system development. Thompson95 described “representational
182
16 Assessment, Treatment, and Management of Auditory Processing Disorders in 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.
plasticity” of the central auditory nervous system, engaging new
growth in neural networks posttreatment. Recent programs have
used these theories as a foundation for developing treatment
of APD.
Although auditory training programs have historically been
applied to intervention for children with APD, current programs
attempt to capitalize on intensive adaptive training methods.
Some have used specific types of stimuli presented in an adaptive
manner and are incorporated into a computer game format. One
of the earliest programs incorporating these parameters was FastForWord (Scientific Learning Corporation, Oakland, CA), an auditory training program designed to improve temporal processing
skills.96 Although the ecacy of FastForWord as a treatment for
children with APD was debated in the literature, the options for
computer-assisted auditory training have grown because of an
improved eciency and eectiveness with these types of programs and the ability to measure this ecacy.
A number of treatment programs have incorporated the princi-
ples described in this chapter to address specific auditory processing deficits identified in the auditory processing assessment. One
example is dichotic interaural intensity dierence (DIID) training
for binaural integration deficits.97 Temporal processing deficits
have been addressed using training on temporal ordering and
auditory memory tasks, using the game SIMON98 as the vehicle for
auditory training.99 Another example of a deficit specific program
is Auditory Rehabilitation for Interaural Asymmetry (ARIA), a program to strengthen the listening skills of the weaker ear in dichotic listening skills.
101
Results for both programs demonstrated
promising outcomes related to the ability to change the auditory
system with treatment, based on behavioral changes observed in
skills after treatment.
A new generation of treatment programs has emerged for APD,
based on a number of trends, including linking assessment results
to treatment, taking advantage of current technology, and being
able to document actual changes in the auditory system. One
example is LiSN & Learn, developed by Cameron and coworkers
at Australia’s National Acoustics Laboratories.
101
The program
was targeted at remedying spatial processing disorders (SPD) as
identified by the results of the LiSN-S test, described earlier in this
chapter. The program uses a game-based format with adaptive
stimuli and is administered of a period of 10 weeks, with the
child “playing” two games per day, 5 days a week. Children who
participated in the program demonstrated a 10-dB posttreatment
improvement at the conclusion of the 10-week treatment pro-
101
gram.
(By the end of 2017, LiSN & Learn had been updated and
turned into an iPad app titled Sound Storm, available through the
iTunes App Store.
102
) CAPD Online Therapy System (CAPDOTS)—
Integrated (The Listening Academy, Vancouver, BC, Canada) is an
online program that claims to target the treatment of binaural
integration deficits characterized by diculties with dichotic
listening (integrative type) and atypical interaural symmetry.
103
It is reported to be evidence-based and deficit-specific and is
administered by an audiologist or speech-language pathologist.
Acoustic Pioneer has introduced Zoo Caper Skyscraper and Insane
Earplane, auditory training games that purport to address dichotic
listening and temporal processing respectively. These programs
are designed to be administered on an iPad, remediation directed
by results of assessment, and can be administered either in the
home or clinical environment. Initial results show ecacy for
both programs.
104,105
Computerized auditory training programs will continue to
grow as additional research is performed in this area. These types
of programs will have a significant impact on developing auditory
processing skills in all children. However, the ability to generalize
these skills to reading or spoken language has not yet been clearly
established, and research shows conicting results.
106,107
Six studies in which children with APDs participated in auditory training
programs that included nonspeech stimuli and/or simple speech
sounds were reviewed; the training was eective in improving
APD skills but was not found to generalize to improving reading,
academic, or language skills.
107
Recent interest has also been in the
area of the use of musical training to improve auditory processing
abilities.
108,109,110
Transfer in training has been optimized when
some stimulus dimensions (e.g. speech, modulated noise, tonal
frequency) in the treatment program are shared between tasks
and outcomes; outcome-specific materials for auditory training
are recommended.
111
Treatment outcomes as measured by behavioral changes can be
confounded by a number of factors, including age of the child and
treatment bias. A more objective approach to assessing treatment
outcome, such as changes in a measurable electrophysiologic
response, is the gold standard. This was proposed decades ago
looking at pre-posttreatment measures in the P300 response
and recently has been observed in improvements in both behavioral skills and changes in the cABR following speech-in-noise
training.
113
These findings support plastic changes in the auditory
system as the result of treatment, and as tools such as functional
magnetic resonance imaging (fMRI) become more commonplace
in clinical settings, these types of outcomes will become more
available.
114
16.5 Conclusion
Assessment, treatment, and management of auditory processing
skills in children are time- and labor-intensive clinical endeavors
but a worthwhile investment on the part of the audiologist. This
chapter focuses on the pediatric patient. However, assessment
and management of APD across the lifespan are certainly within
the scope of practice of the audiologist, recognizing the role of
the brain in hearing and listening, and acknowledging that hearing and listening do not stop at the level of the inner ear. APDs are
on the continuum of auditory disorders, and addressing these for
children provides a necessary service.
Exciting changes based on cutting-edge science in areas such
as genetics and expansion of the use of fMRI as a clinical tool will
certainly inuence both the evaluation and the treatment of APD.
The auditory system’s capacity to learn and change supports why
audiologists enter the profession. The ability of the audiologist
to identify an underlying disorder eectively and to intervene to
improve the quality of the person’s life and communication are
germane to the area of APD.
112
183
II Diagnosing Hearing Disorders in 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.
Discussion Questions
1. Describe how APD ts on a continuum of hearing loss in
children. Considerations in this answer should include educational perspectives and functional information from a World
Health Organization (WHO) perspective.
2. What factors should be considered in the development of
a test battery for auditory processing? What tests might
be selected with an emphasis on behavioral testing and/or
electrophysiologic testing and why?
3. APD in children appears to continue to engender controversy.
List some of the main controversies related to the assessment
of APD in children. Provide evidence, if any, that supports APD
as a clinical diagnosis.
4. Describe the development of a treatment program for a child
with an APD. What are the main considerations?
5. How might genetics be involved in APD?
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Appendix 16.1 Distributors of
Auditory Processing Materials
Acoustic Pioneer
Email: info@acousticpioneer.com
Website: https://acousticpioneer.com
Materials include:
Feather Squadron for assessment of APD skills
•
Auditory training “games”:
•
Zoo Caper Skyscraper (dichotic listening)
•
Insane Earplane (tonal-pattern training)
•
Auditec of St. Louis
2515 South Big Bend Blvd.
St. Louis, MO 63143
Phone: 800-669-9065
Email: auditecinfo@auditec.com
Website: http://www.auditec.com
Materials include:
Dichotic Digits
•
Masking Level Dierence
•
Multiple Auditory Processing Assessment (MAPA)
•
Pitch Pattern Sequence Test
•
Spanish versions of test materials
•
Educational Audiology Association
700 McKnight Park Drive
Suite 708
Pittsburgh, PA 15237
Phone: 800-460-7322
Email: admin@edaud.org
Website: https://edaud.org
Materials include:
Children’s Auditory Performance Scale (CHAPS)
•
Fisher’s Auditory Checklist
•
The Listening Academy, Inc.
Suite 304
650 West 41st Ave
Oakridge Centre, South Tower
Vancouver, BC Canada V5Z 2M9
Phone: 1-778-891-0037
Email: info@capdots.com
Website: http://www.capdots.com
Materials include:
CAPDOTS-Integrated: A Dichotic Integration Listening
•
Training Program
CAPDOTS-Selected: A Dichotic Selection/Separation Listening
•
Training program
National Acoustic Laboratories (NAL)
Level 4, Australian Hearing Hub
16 University Avenue
Macquarie University
NSW, 2019
Australia
Phone: +61 2 9412 6800
Email: shop@nal.gov.au
Website: https://shop.nal.gov.au/
Materials include:
SoundStorm (available from https://itunes.apple.com/us/app/
•
sound-storm/id1062466584?ls=1&mt=8)
Pearson
PO Box 599700
San Antonio, TX 78259
Phone: 800-627-7271
Website: https://www.pearsonclinical.com/
Materials include:
SCAN-3:A Tests for Auditory Processing Disorders in
•
Adolescents and Adults
SCAN-3:C Tests for Auditory Processing Disorders in Children
•
ASA: Auditory Skills Assessment
•
186
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copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
Phonak LLC
4520 Weaver Parkway
Warrenville, IL 60555
Phone: 800-777-7333
Website: https://www.phonakpro.com
Materials (under “Resources”) include:
Listening in Spatialized Noise—Sentences (LiSN-S)
•
LiSN-S PGA (one step; tests ability to understand speech in
•
no i se)
Precision Acoustics, Inc.
13410 SE 26th Circle
Vancouver, WA 98683
Phone: 360-447-8403
Email: contact@precisionacoustics.org
Website: http://precisionacoustics.org
Materials include:
Staggered Spondaic Word (SSW) test
•
Phonemic Synthesis Test
•
Competing Environmental Sounds (CES) Test
•
Supporting Success for Children with
Hearing Loss
15619 Premiere Drive/Suite 101
Tampa, FL 33624
Phone: 888-963-8991
Email: teachertools@successforkidswithhearingloss.com
Website: https://successforkidswithhearingloss.com/
Materials include:
Listening Inventories for Education—Revised (LIFE-R)
•
Screening Identification of Targeting Educational Risk Listening
•
Inventories for Education (SIFTER; editions include Preschool
SIFTER, SIFTER (Elementary), and Secondary SIFTER)
187
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.
17 Evaluation and Management of Vestibular Function in Infants and Children with Hearing Loss
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.
17 Evaluation and Management of Vestibular Function in
Infants and Children with Hearing Loss
Richard E. Gans
Summary
The identification, evaluation, and management of infants and
young children with the comorbidities of sensorineural hearing
loss and vestibular dysfunction is of critical importance in the
habilitation process and quality of life issues. The audiovestibular
system is the first sensory organ to develop embryologically and
is therefore subject to syndromic, nonsyndromic, and mitochondrial conditions. Likewise, acquired medical disorders as well
as migraine variants and trauma may cause an array of balance
dysfunctions in this young population. This chapter will provide
the reader with a comprehensive overview of the conditions
that may cause dysfunction, and the appropriate behavioral and
electrophysiologic evaluation protocols.
Keywords
audiovestibular system, behavioral testing, BPV of infancy,
congenital, electrophysiological evaluation, maturational milestones, phylogeny, vestibular evoked myogenic potentials
Key Points
While we could survive without vision or hearing, as some
•
species do, it would be impossible to survive without the
ability to resist the pull of gravity or safely navigate within
our environment.
The majority of equilibrium problems that occur in infants
•
and children manifest as delayed gross motor and balance
problems, not as vertigo or dizziness.
Muscle tone is another important aspect of an infant/child
•
vestibular evaluation because it is closely associated with the
integrity of the vestibular system.
Multiple investigators have reported as high as 90% abnormal
•
vestibular evoked myogenic responses in children with congenital sensorineural hearing loss.
Children with unilateral sensorineural hearing loss have also
•
been shown to have poorer balance than normal-hearing
children.
Hearing loss does not make a child immune from vestibular
•
migraine, concussion, or other conditions causing vestibular
dysfunction in normal-hearing children.
Children who receive cochlear implants prior to 3 years of age
•
may have better balance function than those implanted at an
older age.
in prevalence through adolescence. Considering the similar
anatomy and phylogeny of the vestibular and cochlear mecha-
nisms, it is not dicult to understand that the causes of cochlear
dysfunction may also aect the balance mechanism. Although
not considered highly prevalent, vestibular conditions do occur
in children.2 Numerous investigators have reported a higher
incidence of vestibular problems in children with congenital or
acquired sensorineural hearing loss (SNHL) than in the general
pediatric population.
of SNHL and vestibular deficits, it is equally as important to
provide early identification and intervention for children with
balance issues as it is for those with hearing loss. The global
acceptance and success of early neonatal hearing testing has
improved our ability to identify those infants who are also at risk
for vestibular dysfunction.
3,4
Based on the well-known comorbidities
Pearl
Vestibular loss or dysfunction should be considered a possibility
for all neonates, infants, and children who are identied as
having SNHL.
In the literature, pediatric vestibular testing and normative
data has focused primarily on school-aged children with modi-
fication of adult protocols utilizing videonystagmography (VNG),
rotary chair testing, and computerized dynamic posturography
2,5,6,7,8
(CDP).
facilities and that even where they are, testing may not be obtained
until the child is at least 3 years old, the focus of this chapter will
be to provide the reader with an overview of vestibular function,
common disorders, and evaluation methods for infants ranging
from 3 months to 3 years of age. The good news is that with a
proper case history, interview of the parents, an understanding
of the vestibular system’s multiple reex systems and their role
in maturational motor milestones, most at-risk infants and young
children can be identified by most practitioners prior to comprehensive electrophysiologic examination.
Given that these technologies are not available in most
Pearl
Balance is the primary function of the inner ear; the ability to
detect gravity and navigate through space is critical to the
normal development of motor skills and coordination.
17.1 The Mechanisms of
Equilibrium
Hearing loss is the most common congenital abnormality in
infants,1 accounting for 1 to 3 per 1,000 newborns and increases
The inner ear’s contribution to mechanical equilibrium is signif-
icant. In fact, its primary function is equilibrium, not hearing. The
estibular labyrinth portion of the inner ear is the first sensory
v
system to develop embryologically; it actually precedes cochlear
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II Diagnosing Hearing Disorders in 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.
development (the phylogenic development of the cochlea follows
that of the saccule). Like other species, we have a developmental
hierarchy based on importance to survivability. While we could
survive without vision or hearing, as some species do, it would
be impossible to survive without the ability to resist the pull of
gravity or safely navigate within our environment. The labyrinth
is fully developed anatomically in utero by 49 days gestation. Its
neural connections with the central pathways continue to develop
through the 8th month of gestation.9 The system will continue to
mature, myelinate, and evolve through childhood up to about 6
years of age.
Equilibrium requires more than just the vestibular labyrinth.
It is a complex integration of the vestibular system, vision,
somatosensory-proprioception, and the central nervous system
(CNS). Various sensory modalities interact to provide information
to the postural control system from three frames of reference:
(1) proprioception, the sense of position and movement of one
part of the body relative to another via muscle, joint tactile, and
visual receptors; (2) exteroception, the the sense of relationship of
objects in the environment to each other, via primarily visual and
tactile inputs; and (3) exproprioception, or information about the
body parts relative to the external environment from all types of
sensory receptors. The vestibular system serves as an exproprioceptive sense that reports velocity and acceleration of the head
relative to gravity and inertia, so it is especially helpful in correcting erroneous information from the other sensory inputs. The
vestibular system is the primary sensory modality, contributing
approximately two-thirds of the critical data about where we are
in space, including our sense of motion, speed, and direction. All
sensory modalities must work together within several complex
reex arcs for accurate perception and response to the dynamic
world. The four otolith organs and six semicircular canals are the
end organ receptors of the vestibular system. To begin to develop
an understanding of methods available to evaluate the vestibular
function of infants, a discussion of the underlying physiology and
reexes is presented.
17.2 Physiology of Equilibrium:
Vestibular Reexes
The vestibular system is a critical sensory component within
multiple complex reex arcs. As there are actually no direct
tests of vestibular function, all established and commonly used
vestibular function tests evaluate and record only the motor
(output) portion of one or more of three vestibular reex arcs:
vestibuloocular (VOR), vestibulospinal (VSR), and vestibulocollic
(VCR). The test interpretation is an extrapolation of the inuence
of the inner ear on the results as to whether one has intact or
dysfunctional vestibular participation. Ideally, for infants, just as
with adults, we prefer to evaluate all three reex arcs to obtain
the best comprehensive picture of equilibrium function. Ideally,
as there are three distinct vestibular reexes, one or more or
preferably all three may be evaluated even with behavioral
techniques. The best test of the VCR is arguably the vestibular
evoked myogenic potential (VEMP), which is an electrophysiologic assessment tool.
17.2.1 Vestibuloocular Reex
The VOR allows st abilized vision in th e presence of head movement.
Without this function the world would appear to jiggle or bounce
each time the head was moved. This blurred vision or drop in
visual acuity does occur with individuals who have a defect in the
VOR and is termed oscillopsia. The VOR is an ascending pathway
through the upper brainstem and contributes to the production
of an accurate compensatory eye movement. For each and every
head movement there must be equal and opposite eye movements.
Adult VOR testing typically includes VNG, rotary chair testing, and
dynamic visual acuity tests. Naturally, with infants these evaluation protocols will not be appropriate. The VOR receives some
additional help to stabilize vision at lower movement frequencies
provided by the optokinetic (OKN) reex. While the vestibular end
organs are providing the brain with information about gravity
and velocity, the OKN system produces eye movement based on
motion of the external world. The eyes will follow in the direction of the movement and then quickly return to the center. This
p
roduces an involuntary eye movement termed nystagmus, with a
slow and fast phase. It is this integration that allows the individual
to correctly perceive and respond to whether it is the individual or
the world that is moving. It can be elicited at birth and is adultlike
in its operation by about 6 months of age.
17.2.2 Vestibulospinal Reex
The VSR provides the musculoskeletal system with information
through the lower brainstem and descending motor tracts to the
extremities to correctly maintain our postural stability under
both static and dynamic conditions. Vestibular signals interact
in a complex manner with other systems to produce several
postural reexes. The cerebellum appears to play a key role in
these interactions, which can involve limb and neck propriocep-
tion, touch, vision, and descending cortical inuences relayed
to the vestibular complex primarily via the reticular formation.
Descending pathways responsible for postural reexes include
the vestibulospinal and reticulospinal tracts. Both receive signals
from the vestibular end organs, and both are strongly inuenced
by cerebellar eerents. Descending motor control of the neck
musculature is more closely linked to the vestibular end organs.
Limb muscle reexes are more closely linked to input from several sensory systems.
17.2.3 Vestibulocollic Reex
The VCR is considered to be a righting reex. In essence it is the
gravity sensor within the inner ear communicating with the
neck musculature, keeping the head steady in response to body
tilt. Originating within the saccule portion of the otolith mech-
anism, the reex then courses through the lower brainstem in a
descending pathway with its motor portion being cranial nerve
XI, the accessory nerve, innervating the sternocleidomastoid
neck muscle. This reex has gained much attention over the past
decade, as its measurement is the cervical cVEMP.
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