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NIH funds
research that may lead to improved hearing
for some
Newswise —
Electric-acoustic stimulation research by an
Arizona State University professor could
help discover important acoustic cues used
to improve the hearing of certain profoundly
hearing-impaired people.
Professor Sid P. Bacon,
dean of natural sciences in the College of
Liberal Arts and Sciences, was recently
awarded a National Institutes of Health
grant – $1.1 million over three years – that
will contribute to his ongoing research into
electric-acoustic stimulation, or EAS.
This technology
combines electric stimulation in the mid- to
high-frequency (or mid- to high-pitch)
region via cochlear implants with normal
acoustic stimulation in the low-frequency or
low-pitch region.
Cochlear implants are
surgically implanted devices that use
electricity to imitate the effects of sound
in individuals who are deaf or nearly deaf.
Only recently have they been implanted in
individuals with at least some hearing in
the low-pitch region.
Electric stimulation
and acoustic stimulation separately might
improve hearing a small amount, Bacon says,
“but the sum is much greater than its parts.
There is a synergistic effect when electric
and acoustic stimulation are combined,” he
says.
The long-term goal of
the research is to gain a better
understanding of the cues and processes
underlying the benefits of EAS.
“The combination of
electric and acoustic stimulation enables
individuals to do quite well, even in
environments where there is background
noise; these are typically very difficult
listening situations, especially for people
with hearing loss,” he says.
Bacon’s research
focuses on why there is such a dramatic
improvement. The research will test what he
suspects are the acoustic cues in speech
that account for this improvement.
“When people talk,
their voice has a pitch that varies up and
down during the course of speaking. Men tend
to have a lower overall pitch than women and
children. That voice pitch is known as the
fundamental frequency, and it tends to be
below 400 Hz for all speakers” Bacon says.
“It stands to reason
that one of the cues from the low-frequency
region is this fundamental frequency, this
low voice pitch.
“I decided to test this
cue directly,” he says.
Bacon and his research
team, including Christopher Brown and
several doctoral students, use software to
extract cues from the low-frequency region
of speech that he believes may be important
for EAS.
He then replaces the
speech with a tone that carries the cues,
either alone or in combination. He has found
that voice pitch is an important cue.
For some cochlear
implant patients, a tone carrying this cue
provides as much benefit as speech itself.
“On a theoretical
level, it tells us what cues are important
for EAS, which is what drove me to look at
this initially,” he says.
Bacon’s research
includes evaluating EAS in people with
cochlear implants, as well as simulating EAS
in normal-hearing individuals. He has
another NIH grant to study various aspects
of normal hearing.
“We have access to a
lot more individuals with normal hearing,”
Bacon says, explaining that researchers are
able to simulate the experience of electric
hearing in normal hearers, enabling them to
experiment with new technology and sound
processing before extending that technology
to implant patients.
“We often see the same
pattern of results in the two groups of
listeners. Thus, we can experiment
extensively in normal-hearing people, and
then apply our most promising findings to
people with an implant.”
Bacon’s findings could
potentially expand the range of people who
are able to benefit from EAS technology.
“Right now people
are candidates for EAS only if they have
hearing up to a frequency of at least 500
Hz,” Bacon says. His research with
simulations of EAS in normal-hearing
individuals indicates that the tone carrying
the acoustic cues can be shifted to a very
low frequency without loss of benefit.
“If we can show similar
results in individuals with a cochlear
implant, it would suggest that you might
only need to have hearing up to 100 Hz.”
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