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By Carol Flexer
1. What
do you mean by "minimal hearing loss"?
Normal hearing for children is 15 dB
HL or better at all frequencies with normal middle ear function.
All else is abnormal and places a child at risk for academic failure.
Because the normal hearing boundary for children is 15 dB HL and
a mild hearing loss is typically considered to start at 25 dB
HL, most people define a minimal or slight hearing impairment
as one that occurs from 16 dB HL to 25 dB HL. Most hearing losses
do not have a flat configuration (they have a slope); therefore,
a hearing loss may be minimal at some frequencies and worse or
better at others. The hearing loss could be sensorineural or conductive.
In fact, most minimal hearing losses are caused by otitis media
with effusion.
Webster defines "minimal" as "the least possible degree or quantity".
Unfortunately, the term erroneously implies without consequence,
insignificant. Implicit in the term "minimal" is permission to
provide the least possible intervention and the fewest management
strategies.
2. How many
children in schools have minimal hearing losses? It couldn't be
too many because hearing loss is considered a low-incidence disorder.
There are about 39.5 million school children in the United
States, and approximately 8 million of them have some type and
degree of hearing loss. Fewer than 700 audiologists are employed
by school systems to manage these 8 million children. Consequently,
fewer than 1% of children with hearing problems are being served,
an appalling figure. Most of the children who are not identified,
not served, or underserved are those with minimal, mild, or unilateral
(stable or fluctuating) hearing impairments. Several colleagues
and I recently conducted a longitudinal study and found that one
quarter to one third of kindergarten and first grade children
in typical classrooms did not hear normally on any given day.
So, we're talking about a lot of children - not just one or two
per school district!
3. What kind
of problems could such a slight hearing loss cause for children
in classrooms?
Children with minimal hearing losses experience problems in
the following areas: hearing faint or distant speech (more than
25% of classroom instruction could be missed); hearing subtle
conversational cues that could cause a child to react inappropriately;
following fast-paced verbal exchanges; and hearing the fine word-sound
distinctions that denote plurality, tense, possessives, etc. In
addition, a child with a minimal hearing loss may appear immature
and become more fatigued than normal-hearing classmates because
of the extra effort needed to hear. In fact, when teachers or
parents notice attention and behavior problems, they often do
not even consider hearing loss as the source of a child's problems.
4. It's hard
to believe that such a slight hearing loss could be so problematic.
Tell me more about the relationship between hearing and classroom
learning.
In mainstreamed classrooms, hearing/listening is the cornerstone
of the educational system. If a child cannot clearly hear the
teacher, the entire premise of the educational system is undermined.
There is a big difference between an "audible" signal and an "intelligible"
signal.
5. Really? What
is the difference?
Speech is audible if the person is simply able to detect its
presence. However for speech to be intelligible, the person must
be able to discriminate the word-sound distinctions of individual
phonemes. As Mark Ross has often said, the major problem with
having a hearing loss is that you can't hear so good! Consequently,
speech might be very audible, but not consistently intelligible
to a child with a minimal hearing loss, causing the child to hear,
for example, words such as "walked," "walking," "walker" and "walks"
all as "_ah."
6. If a child
isn't hearing clearly, won't he or she just tell the teacher?
It seems as though people ought to know when they are missing
verbal information: however, that's not the case, especially with
children. The problem with "not hearing so good" is that you don't
hear what you don't hear, and you don't know that you didn't hear
it - because you didn't hear it! Moreover, most children (and
adults, for that matter) may not know that they "misheard" a message
unless they have already had experience with the language and
topic under discussion. Consequently, children often have an unrealistic
perception of the amount and accuracy of the information that
they are receiving from the environment. So, even if a teacher
asks, "Are you hearing me?", the child will almost always say
"Yes." How can a child estimate the quantity and quality of the
information that he/she did not hear? Because hearing is a first-order
event in a mainstream classroom, if children don't hear clearly
and consistently their academic potential is compromised due to
the acoustic filter effect of hearing loss.
7. What is the
"acoustic filter effect of hearing loss?"
Hearing loss of any degree can interfere with the development
of a child's spoken language, reading and writing skills, and
academic performance. That is, hearing loss can be described as
an invisible acoustic filter that distorts, smears, or eliminates
incoming sounds, especially sounds from a distance - even a short
distance. The negative effects of a hearing loss may be apparent,
but the hearing loss itself is invisible and easily ignored or
underestimated.
8. What does
"distance hearing" have to do with learning?
Persons with hearing losses, even minimal ones, cannot receive
intelligible speech well over distances. This reduction in earshot
has tremendous consequences for life and classroom performance
because distance hearing is linked to passive/casual/incidental
listening and learning. Also, the farther away a child is from
the sound source, the poorer the speech-to-noise ratio.
9. How does
speech-to-noise ratio relate to minimal hearing loss?
Speech-to-noise ratio (S/N ratio) is a critical concept relative
to the reception of intelligible speech and the justification
for using S/N-ratio-enhancing technology in addition to or instead
of hearing aids in a classroom. S/N ratio is the relationship
between the primary speech or input signal and background sounds.
The more favorable the S/N ratio, the more intelligible that speech
signal will be for a child. Adults with normal hearing sensitivity
and language abilities typically require a S/N ratio of +6 dB
- speech is twice the sound pressure of the noise - for the reception
of intelligible speech.
Because of internal auditory distortion, children with any degree
of hearing impairment need a more favorable S/N ratio of about
+15 to +20 dB in the classroom, even when they are already wearing
hearing aids. That is, speech needs to be approximately
10 times the level of background noise. Because of noise, reverberation
and frequent changes in teacher and pupil locations in the classroom,
the average classroom S/N ratio is only about +4 dB, and may be
worse than 0 dB, which is far from ideal even for children with
normal hearing sensitivity.
10. Doesn't
preferential seating solve the speech-to-noise ratio problem,
especially if the teacher has a loud voice?
No!
11. Why not?
After all, preferential seating is a routine recommendation?
Because the hearing sensitivity of the child, the classroom
acoustic environment, and the speech of the teacher are all variables
- not constants - preferential seating for acoustic advantage
is ineffective. To explain, due to fluctuating middle ear systems,
many otherwise typical young children do not hear well consistently.
Also, noise levels in classrooms can vary tremendously throughout
the day depending on such factors as hall traffic, windows open
or shut, blowers of fans on or off, lights humming, overheads
in use, not to mention the noise a roomful of children make. And
don't forget, the teacher is not nailed to the floor. He or she
often will walk around the room when teaching. Unless all children
with hearing problems (and there might be as many as 10 per classroom)
can remain very close to the teacher at all times, they will not
receive a consistently intelligible speech signal. Remember, noise
and reverberation are not the only negative factors in classrooms.
Distance from the primary sound source is also a critical variable.
You asked if teachers with loud voices can overcome poor classroom
acoustics. While it might seem as if yelling should solve some
listening problems, actually, it doesn't. An analysis of acoustic
phonetics shows that when someone speaks loudly, vowel energy
in increased, but consonant energy is not increased to the same
degree. Thus, ironically, loud speech or yelling increases audibility,
but it may decrease intelligibility! so, a child might hear more
sound from a loud-spoken teacher, but understand fewer words.
12. So what
do you do?
Recognizing that hearing is a first-order event in the classroom,
I feel that our first responsibility is to provide children with
clear and consistent access to spoken instruction.
13. How do you
do that?
By using some form of S/N-ratio-enhancing technology, such
as a low-gain, low-power-output personal FM system or a sound-field
(classroom) FM amplification system, we can control the intelligibility
of spoken instruction no matter where the teacher or child is
located.
14. Are you
saying that you might not fit a hearing aid first on a child with
a minimal hearing loss; instead you might fit some type of FM
system first? I thought that a hearing aid should always be the
first form of amplification employed.
The type of amplification technology used depends upon your desired
outcome, and the demands and constraints of the listening environment.
If the desired outcome is that the child learn in the classroom,
and, given that a mainstreamed classroom is an auditory-verbal
environment, then we must enable the child to hear clearly and
consistently in order to learn. Because of noise, reverberation,
and distance factors, signal intelligibility is compromised unless
the listener can be very close, physically or technologically
(remote microphone), to the speaker. Therefore, some form of S/N-ratio-enhancing
equipment is imperative. Note that the key to the technologic
improvement of the S/N ratio is the use of a remote microphone
that can be placed very close to the sound source.
15. I know
what a personal FM system is, but what is a sound-field FM system?
A sound-field FM system is an exciting educational tool that allows
control of the acoustic environment in a classroom, thereby facilitating
acoustic accessibility of teacher instruction for all children
in the room. Sound-field FM units are small, wireless, high-fidelity
public address systems that are self-contained in a classroom.
The classroom is amplified through the use of one to five wall- or ceiling-mounted
loudspeakers. The teacher wears a wireless FM microphone transmitter,
just like the one used for a personal FM unit. The radio signal
is sent to an amplifier that is connected to the loudspeakers.
16. Which
has a better S/N ratio, a personal FM or a sound-field FM?
Good question. A major difference between sound-field FM units
and personal FM systems is that the personal FM, if fit appropriately,
can provide the most favorable S/N ratio: +20 dB to +30 dB. When
a personal FM unit is used, the speech signal travels directly
from the microphone transmitter, which is positioned about 6 inches
from the teacher's mouth, into the ear of the child who is wearing
the FM receiver. In the case of a sound-field unit, the teacher's
speech is transmitted from the microphone worn 6 inches from his
or her mouth to the amplifier/loudspeakers, which are located
at some distance from the children. The students can be consistently
closer to loudspeakers than they can be to the teacher, but not
as close as a child is to the headphones of his or her personal
FM receiver. Typically, sound-field FM units improve the classroom's
S/N ratio by about 10 dB to 15 dB. Therefore, the decision
as to which type of S/N-ratio-enhancing technology will be most
appropriate depends upon the specific population of children to
be served and their particular educational placements and needs.
17. What about
unilateral hearing loss? Wouldn't a CROS hearing aid be most appropriate?
It depends on the situation. If the child is in a classroom and
the desired outcome is the clear and consistent reception of spoken
instruction, then an FM unit would be essential. In typical classrooms,
a CROS hearing aid does not improve the S/N ratio.
18. How do
you fit a personal FM unit on a child with a unilateral hearing
loss?
After evaluating numerous coupling operations (Walkman
headphones, earbud, standard earmold), we found that a custom
standard earmold designed to accommodate the FM button receiver,
with a short canal portion, belled bore, IROS venting, and a helix
lock, appeared to be the most effective and comfortable way of
coupling a low-gain, low-power-output personal FM unit to the
better ear of children with unilateral hearing impairments. Such
coupling allowed the children to hear the teacher at a favorable
S/N ratio while not occluding their ears to their own and classmates'
voices. The value of also coupling the FM to the poorer ear of
a child with unilateral hearing loss would need to be determined
on an individual basis.
In addition, we are in the process of collecting data about using
sound-field amplification instead of a personal FM unit, and seating
the child with his or her better ear toward a loudspeaker. Sound-field
FM amplification seems to hold promise for improving and controlling
acoustic accessibility for this population as well.
19. Promoting
S/N-ratio-enhancing technology is very nice, but children with
minimal and unilateral hearing loss typically do not qualify for
special-education services. How can we help these kids get what
they need?
Special services for children with hearing problems in schools
are mandated by two main federal laws. One is the Education for
All Handicapped Children Act of 1975 (Public Law 94-142). In 1990,
this law was amended and its name changed to the Individuals with
Disabilities Education Act (IDEA). The other law is the Rehabilitation
Act of 1973, Section 504, which was amended in 1992.
IDEA provides access to special-education funds by developing
an IEP (Individualized Education Plan) to identify who has a disability.
Most students who experience minimal, mild or unilateral hearing
impairments would not qualify for special school services through
IDEA because their hearing impairments might not be severe enough
or the child might not yet have failed enough.
Thus, Section 504 of the Rehabilitation Act of 1973 is usually
the most relevant legislation. By using the concept of "acoustic
accessibility," we can recommend S/N-ratio-enhancing technology
for children with minimal hearing losses. That is, we can advocate
proactively, stating that a child's hearing problem interferes
with his or her access to spoken instruction; therefore, the child
is being denied an appropriate education.
20. It seems
that "minimal" is certainly not "simple." Would you say that advocacy
and information provision are as critical as fitting S/N-enhancing-technology
when dealing with this population of children?
Absolutely! Who will advocate for acoustic accessibility if we
don't? Nobody! And who will recommend and fit FM technology if
we don't? Nobody! The problem is not that other professionals
care less than we do about children's opportunities to learn.
The problem is that hearing loss is invisible, and minimal hearing
loss seems as if it should be "insignificant." Therefore, hearing
is an underestimated factor in a child's educational progression.
By providing information about hearing and by advocating for and
accessing the critically important auditory modality, we can help
this neglected population of children with minimal hearing impairments
succeed in a mainstreamed classroom.
Copyright 1995
by Lippincott Williams & Wilkins. Reproduced with permission
of LWW from The Hearing Journal 1995;48(9):10. No part of this
article may be reproduced in any form or by any means, including
photocopying, without written permission from the publisher."
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