CONTACT: BECKY SOGLIN
2130 Medical Laboratories
Iowa City IA 52242
(319) 335-6660; fax (319) 335-8034
Release: Sept. 27, 1999
UI study: adjusting speech pitch may compensate for certain types of hearing
IOWA CITY, Iowa -- Amplifying sound through a hearing aid does not always
help people with hearing loss better understand speech. However, compressing
sound frequency -- decreasing its pitch -- through new computer technology
seems to help people with high-frequency hearing loss better understand sounds,
according to University of Iowa research findings.
"Theoretically, there was potential promise of taking speech to lower
frequencies, so we wanted to try this technique one more time using new computer
technology," said Christopher W. Turner, Ph.D., UI professor of speech pathology
and audiology and lead investigator. "We were able to lower speech frequencies
(pitch) to the region where certain individuals have usable hearing."
High-frequency hearing loss affects millions of people as they age and
can also be caused by disease, injury, exposure to excessive noise or medication
with adverse side effects. Hair cells in the ear normally transmit messages
to the brain for interpretation. In people with severe high-frequency hearing
loss, the hair cells at these levels are dead or injured. An option, as in
this study, is to lower sound frequencies so that healthy hair cells at the
lower frequencies can perceive the sound.
Individuals with high-frequency hearing loss have difficulty perceiving
the softer sounds of speech or words with "f," "s" or "sh." They may also
have trouble hearing women's and children's voices or comprehending others'
speech amidst background noise.
Turner said that in contrast with earlier research, improved computer
programs can change speech in a way so that it can be manipulated yet still
be understandable. In addition, the UI study focused on people with hearing
loss only in the high frequencies, so there was more likelihood of their benefiting
from the technique.
Turner and co-investigator Richard Hurtig, Ph.D., UI professor and head
of speech pathology and audiology, studied three people with normal hearing
and 15 people who could hear lower-pitched sounds normally but had severe
hearing losses for higher-pitched sounds.
The participants listened to nonsense syllables at normal and adjusted
frequencies and volume. Using nonsense sounds allowed researchers to better
track the effectiveness of the
frequency adjustment. Listeners might otherwise have "understood" familiar
words because of prior knowledge.
Turner described how new technology helped make the research possible.
"You can't simply tape-record speech then slow it down because that would
change the important timing cues of some sounds," he said. "Also, over time
you couldn't keep up with the conversation. In addition, older technology
shifted the frequencies in a way that muddled sounds and didn't maintain the
frequency ratios within those sounds. The newer technology uses a commercially
available musical algorithm to preserve the frequency ratios with a negligible
change in the timing of speech."
Turner and Hurtig have also developed their own algorithm that would
be even faster. Turner used a visual analogy to explain the importance of
"The brain is set up to perceive ratios so we don't have to recognize
things by remembering absolute numbers. When the brain perceives a square,
it recognizes that all sides are equal, regardless if the sides are one inch
or two inches long," he explained.
Similarly, the brain perceives frequency based on ratios, not absolute
frequency. A syllable uttered by a man may show frequency peaks at 500, 1500
and 2500 hertz, while the same syllable uttered by a woman could peak at 700,
2100 and 3500 hertz. The computer technology will shift the woman's voice
down about 70 percent so that it peaks at approximately the same points as
the man's voice yet maintains its original frequency ratios. The speech cues
are then perceived by working hair cells and can reach the brain. The manipulation
also shifts the male's voice to even lower frequencies.
"Participants said the adjusted female voice was understandable but sounded
unusual," Turner said. "However, they agreed it was better to understand the
speech. I'm glad we didn't give up on this idea of frequency compression."
Turner said the compression technology is not a cure-all but might eventually
be used to create more sophisticated hearing aids. The researchers' next step,
however, is to test frequency adjustment using real sentences. Turner and
Hurtig will also test how well the adjustment improves people's comprehension
when background noise is present.
The study was supported in part by a grant from the National Institute
on Deafness and Other Communication Disorders, a branch of the National Institutes
The findings appeared in the August issue of the Journal of the Acoustical
Society of America. In September, Turner was appointed as an associate editor
of the journal.
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medical education and research programs and services they provide.