CLASSROOM ACCOMMODATIONS AND HEARING
ASSISTANCE
The classroom environment
Classrooms are a critical auditory
environment for children yet many do not provide favorable conditions for
hearing. The classroom environment is one that must be controlled to provide
favorable conditions for hearing. There are three important variables to be
noted: Noise, reverberation, and distance from the teacher. Sources of
classroom noise may include the children themselves, furniture noise,
ventilation systems, and external ambient noise. Ambient noise levels often
exceed an optimum 35 dBA (unoccupied), and hard surfaces can reduce hearing
effectiveness by increasing reverberation time beyond an optimum maximum of 0.3
to 0.6 seconds (American Academy of Audiology; AAA, 2011a). Signal level and
SNR decrease with distance from the signal source.
Children require a greater SNR than adults
for speech recognition. Young children require speech levels that are at least
20 dB above those of interfering noise and reverberation (AAA, 2011b). In
practice, this is difficult to achieve without amplification. Consequently,
even children with normal hearing may experience difficulty hearing in class. Many
children with CAPD particularly have difficulty hearing in background noise.
The noise level does not need to be loud to disrupt auditory input. Adults with
CAPD describe how noise from a fan or refrigerator
can interfere in properly decoding speech. Some children with CAPD are
overwhelmed by all classroom noise levels, becoming distressed and unable to
function. Such children are sometimes withdrawn from school.
Sometimes, minor modifications to a
classroom, for example, sealing obvious entry points of external noise and
introduction of absorbent materials, may improve the acoustic classroom
environment, but are unlikely to sufficiently improve the audibility for a
child with CAPD. This
is because some children with CAPD may
need amplification of the primary signal, not just an improved SNR, to hear
well (see Section “Amplification”). Hearing assistive technologies (HATs) and
in particular remote microphone systems can alleviate or overcome all three
sources of signal degradation in the classroom: Noise, reverberation, and
distance from the talker.
Other
Environments
Children with CAPD have difficulty when
speech is rapid or degraded by distance, acoustic conditions, or accent, when information
streams are complex or lengthy, and when competing sounds are present. It
follows that HAT can be helpful to them in many aspects of their lives besides
the school environment. Moreover, given the positive neuroplastic changes that
occur over time from wearing amplification (Friederichs and Friederichs, 2005;
Hornickel et al.,
2012), children with CAPD should be
encouraged to use their HAT as much as possible.
Amplification
Terminology
The majority of recent studies of
amplification for children with CAPD have used remote microphone hearing aids,
with body- or head-worn receivers, which receive a signal from a microphone
worn by the speaker. The transmission medium has typically been frequency
modulation (FM). Hearing systems of this type are usually referred to as “personal
FM systems.” This term is ambiguous, because it refers to accessory FM systems
used by wearers of conventional hearing aids or cochlear implants. Furthermore,
FM is increasingly being replaced by digital modulation (DM) technology. From
the point of view of advocacy as well as accuracy, use of the term “remote
microphone hearing aids” reinforces the point that children with “central
deafness” require amplifying hearing aids in much the same way as do children
with peripheral hearing loss. Until remote microphone hearing aids become
recognized as simply another type of hearing aid they remain classified as
assistive listening devices (ALDs) or, in more current terminology, a type of
hearing assistive technology (HAT).
CLASSROOM AMPLIFICATION SYSTEMS
Classroom amplification systems, also
referred to as sound distribution or sound field systems, provide amplification
of the teacher’s voice through loudspeakers. Their efficacy is variable,
depending in particular on the room acoustics. Classroom amplification systems
typically improve SNR by 3 to 5 dB, but may worsen SNR in classrooms with very poor
acoustics. Adaptive systems which increase the amplification as the noise level
increases can achieve better than 5 dB. Portable desktop systems in which a
small loudspeaker is placed on the desk of an individual child provide a
slightly better SNR, perhaps 10 dB, for that child. Remote microphone hearing
aids can provide at least 20 dB improvement in SNR. A meta-analysis by Schafer
and Kleineck (2009) comparing speech discrimination in noise with various FM systems
in trials involving cochlear implant users showed no significant improvement
with sound field systems but 17% improvement with desktop systems and 38%
improvement with personal direct auditory input FM systems.
CANDIDACY
FOR AMPLIFICATION
It is sometimes mistakenly assumed that only children with CAPD
who complain of difficulty hearing in noise, or who score poorly on a
speech-in-noise test, will benefit from remote microphone hearing aids. In
fact, research results and clinical experience indicate that nearly all
children with CAPD show classroom benefit from personal amplification as long
as the classroom teacher is cooperative. Results range from children whose
hearing ability in class is instantly transformed through to those in whom
benefits are more subtle and slower to manifest. There is no known predictive test
of degree of benefit to be derived from amplification
(though the Hornickel et al. study
reported above shows an interesting correlation between initial inconsistency
of the brainstem response and subsequent benefit). However, recommendation of
amplification only for children with abnormal scores on tests of hearing in
noise undoubtedly denies potential benefit to many children.
Electroacoustic verification of remote microphone hearing aid. Upper curve(vertical hatches) represents
audibility of the amplified pathway. Lower
curve (horizontal
hatches) represents audibility of the unamplified
pathway through the open ear canal.
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