Key Words: Instructional Strategies, Language, K-12
Date: Fri, 4 Oct 1996 04:24:32 EDT
Information travels to your brain where it is interpreted (shortened version
here) as sound/speech/whatever. Think of what happens when you throw a
rock in a pond. Near the site where the rock enters the water, you have
very high/deep pronounced ripples (waves). As the waves get farther away
from the site of original impact, they become less formed, i.e., not so
pronounced, until they eventually disappear to nothing. This is the exact
same thing that noise does. At the source of the noise, the sound waves
are big, crisp and clear. As they travel through space, they get less
sharp, less formed and less easy to interpret. Given enough distance, they
eventually disappear. The high frequencies disappear to nothing faster,
just like throwing a little rock will make smaller, less pronounced ripples
than a larger rock. So, the farther away from the speech signal you are,
the less clear the signal will be when it hits your ear and makes your
eardrum vibrate to send a signal to your brain. On top of this, throw in
some background noise. Now think of throwing two rocks in the water, but
you only want to track the ripples of your personal rock (the speech signal
you're trying to hear). Well, the ripples/waves cross each other and it's
harder to make out which ripples are yours. Throw in about 3-4 more rocks,
and you get a scrambled mess. How do you pick your wave/speech signal out
of all of the others bouncing around the room.
Now, get yourself an assistive listening device. That puts you right at the
center of the point where sound originates. Just as though you're sitting
on top of where that rock goes in. So, you'll get the benefit of those high
waves that send such a strong signal to make your eardrum vibrate from the
noise you're trying to hear. Those other, now quieter noises, are further
away now and won't over-ride or mix in with the vibration (as much) because
the original signal is so much stronger.
If a child is hearing impaired, then they already have trouble understanding
a perfect sound wave. If this sound wave is already weakened, distorted, or mixed in with other sound waves when it gets to that child's ear, then it is
just so much harder for them to hear that sound. If they have any loss in
the high frequencies, it makes their situation even worse, because the high
frequency sounds are the worst ones at making it through. What's the
solution? Get that "perfect" sound wave as close to the ear as possible.
Then, at least the child is starting out with a clear signal to begin with
and can get as much information out of that sound signal as his ears will
let him/her.
This is why a hearing aid cannot substitute for an ALD. The sound signal
has already weakened, ie, the ripples have spread out and become less clear,
by the time the sound signal gets to the hearing aid. The amplification
provided by the aid does not reinstate the original signal, it just
amplifies the "distorted" signal that has changed by traveling through space
to the hearing aid. So, it does not place the child in the same situation
as using an ALD. Some children may still be able to "Cope" without an ALD,
but my position is why should they in any way have to struggle...they spend
enough of their lives struggling to hear in situations where an ALD is not
appropriate. Why put the extra stress on them when you don't have to.
Brad, you're our resident audiologist. Am I missing something in this
analogy that is making me overemphasize the importance of ALD's?
Linda S
Date: Fri, 4 Oct 1996 16:23:21 -0400
Your explaination was correct. Signal-to-noise ratio is essential for kids
with sensorineural loss. BUT even with an ALD, a linear hearing aid can
exacerbate the recruitment in the kid's ear. So it's a matter of ALD's PLUS
hearing aids that reflect our current understanding of hearing loss.
I am tossing around the idea of establishing a not-for-profit (501c3)
foundation that will provide advanced processing hearing aids to kids on a
sliding scale based on gross income. I'll let you all know if and when it
comes about.
Brad Ingrao
Date: Fri, 4 Oct 1996 21:14:57 -0400
In a message dated 96-10-04 17:51:31 EDT, you write:
<< By Soundfield FM are you talking generically about using a sound field
with
a hearing aid or is it a specific name for their FM device. Also, I'm not
familiar with the Lombard effect. Also, when you say compresses the
frequencies, in what fashion are they compressed and what is the impact of
this? >>
I meant generic soundfield FM system.
The Lombard Effect is the tendency for normal hearing people to raise the
volume of their voice and increase vocal effort for high frequency consonants
in background noise. The listener will shift their attention to the higher
frequency speech components and reduces attention for the low frequencies
where background noise will tend to mask more.
If a hearing aid compresses the low frequencies, this is great because it
compensates for the abnormal loudness perception (recruitment) associatedwith sensorineural hearing loss. But, it the aid also compresses the highs,
then the Lombard advantage is lost.
Resound compreses both the lows and highs.
MultiFocus and DigiFocus (Oticon) compress the lows and leave the highs
essentially un-compressed.
A head-to-head study found that in quiet, there was a slight preference for
Resound, but MultiFocus was preferred in noise.
Brad Ingrao
Date: Sun, 6 Oct 1996 23:13:18 -0400
At 10:03 AM 10/4/96 -0400, Linda Semesky wrote:
>Brad, you're our resident audiologist. Am I missing something in this
>analogy that is making me overemphasize the importance of ALD's?
One thing that you left out. There's no question that an FM system is
preferred in a school setting by most, IF it is used properly. The FM
can do great things as long as the teacher wearing the microphone is
constantly aware of a few very important things:
The point of all this being, the FM does no good whatsoever, and can even be
detrimental, if the input coming from the mike is not relevant to all of the children wearing the recievers. At least hearing aids would give a somewhat
equal weighting to all sounds in the room, both essential and nonessential.
Chris
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