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Ability to Listen to Two Things at Once
Is Largely Inherited
Your ability to listen to a phone message in one ear while a friend
is talking into your other ear and follow what both are saying
is heavily influenced by your genes, according to a new study.
Your brain analyzes the sounds you hear so you can make sense
of them. This "auditory processing" enables you to, among
other things, tell where a sound is coming from, the timing and
sequence of a sound, and whether a sound is a voice you need to
listen to or background noise you should ignore. Auditory processing
skills play a role in a child's language acquisition and learning
abilities. Disorders in this system may affect as many as 7% of
school-aged children in the U.S. and often appear alongside language
and learning disorders, including dyslexia. Auditory processing
disorders also affect older adults and stroke victims and can limit
the successfulness of hearing aids.
To learn whether our auditory processing skills are inherited,
researchers at NIH's National Institute on Deafness and Other Communication
Disorders (NIDCD) studied identical and fraternal twins who attended
a national twins festival in Twinsburg, OH, during the years 2002
through 2005. A total of 194 same-sex pairs of twins, ages 12 through
50, participated. DNA tests confirmed that 138 of them were identical
twins and 56 fraternal, and hearing tests made sure they had normal
hearing.
The volunteers took 5 tests that are frequently used to identify
auditory processing difficulties. In 3 of the tests, 2 different
one-syllable words or nonsense syllables (short word fragments
such as ba, da and ka) were played into their right and left ears
simultaneously, and they were asked to name both. In 2 other tests,
volunteers listened to digitally altered one-syllable words played
into the right ear and tried to identify the word. One test artificially
filtered out high-pitched sounds, which tends to obscure consonants,
while the other sped up the word.
The researchers reported in the August 2007 issue of Human
Genetics that in all but the filtered-words test there was
a significantly higher correlation among identical twins than
fraternal twins, demonstrating a strong genetic component in
auditory processing. Participants showed the widest range of
abilities when they were asked to identify competing words entering
each ear—called dichotic listening ability. As much as
73% of the variation in dichotic listening ability was due to
genetic differences. Conversely, the ability to understand the
filtered words showed high correlation among all twins, indicating
that variation in that skill is primarily influenced by the environment.
"Our auditory system doesn't end with our ears," says
Dr. James F. Battey, Jr., director of NIDCD. "It also includes
the part of our brain that helps us interpret the sounds we hear.
This is the first study to show that people vary widely in their
ability to process what they hear, and these differences are due
largely to heredity."
The finding will help researchers further understand auditory
processing and the role it plays in the development of language
and learning disorders.
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