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Dr. Dillion, one thing I know that is underway at NAL, is a lot of work with the
LISN, can you talk about that? Sure, the LISN is the Listening in
Spatialized Noise - Sentences test.
This is a test aimed at
diagnosing one particular type of central auditory processing disorder. We
think CAPD is a big umbrella term, and there is a whole range of different
things underneath it. The one that
we have been focusing on are children with what we've termed spatial
processing disorder. These are children with normal hearing. They may not, but
most of them have normal hearing,
and what they haven't developed is the ability to focus on sounds from one
direction and suppress sounds from other directions.
If you measure them in a speech test where everything is coming from the same
place or out of the same pair of headphones, they seem
normal,
but as soon as you separate the speech from the noise, suddenly they are different from other
children around them, and that causes some problems in the classroom.
So what we've done is we've processed sounds
so they are coming actually out of headphones, but they sound like target is straight
in front,
it sounds like there is one distractor over on that side and one on that side.
Now if you know a bit about CAPD, you'll immediately think
Oh it's a speech test. How can we diagnose CAPD? Wouldn't a language
problem cause it to look like CAPD?
So what we've done is we've got the two conditions, one where everything is
straight ahead
and the other one way where we have the separated noises out to the side. So, yes,
language problems might cause a suppression of the score or someone
who's just learned English, for instance, will need a
better signal to noise ratio,
but what we're interested in is the difference between the two
signal-to-noise ratios and that way we think language is constant and we can
really pick out those children whose only problem is an inability to
spatially separate sounds and attend to the one they are trying to attend
such as the teacher.
So once this has been diagnosed, what can be done for it? Well that's the good news.
Look this could be the first time that an audiologist has actually been able to, well I don't
use the word lightly, but it looks like cure the problem.
So we have a remediation strategy which consists of practice at doing the thing
they can't do.
They take home some software; we called it Listen and Learn,
and every day, five days a week,
fifteen minutes a day, they play computer games where their job is to click
on the icons that match the sounds they hear coming from straight ahead and ignore
the, what we call the tricky people,
talking at them from the sides,
and of course they better they get at it, the harder the signal to noise ratio becomes.
And what we see is over three months a very gradual improvement, but adding up
to a 10 dB improvement in signal to noise ratio over
three months.
And the self-report data at the end
from the parents, teachers, children, all support the fact that this generalizes
to real life.
So these children have got a very specific form of a central auditory processing disorder and
by giving them
very specific training in that
skill they haven't developed, they learn it.
We've done a randomized control trial, a small one, but it was very convincing
results.
All the children thought they were getting an auditory training program, and
they were, half of them got the Listen and Learn, and half of them got another well-known training program,
but it did not train spatial skills,
and sure enough, the ones with the spatial training got better at spatial
things, and the other ones didn't.
Now is this remediation something that could help people with hearing loss as well?
Because we know that people with hearing loss often have the same problem. Yes people with
hearing loss all have this problem.
Now it seems a bit strange, why would people with a hearing loss have a central auditory processing
disorder?
Well it may just seem like a central auditory processing disorder.
We think it's a product of the degraded output from the cochlea which is
actually giving the same symptoms. So they definitely have the same problem, an inability
to focus in one direction and suppress sounds from others, but it's not something
that's coming from up at the top, if you like, it's a problem with the
signal that's coming up from the bottom.
We are actually training some people right now.
Our strong expectation was that it wouldn't work, but we thought we had
to try it, and the first two or three people who finished, indeed, got no
benefit from the training.
So if you have normal hearing and spatial processing disorder and you are a child,
we have not tried it on adults, then we can fix it.
If you've got a hearing loss, then no, we can't. And then really you are up to
FMs or directional microphones to physically improve the
signal to noise ratio instead.