People who can't follow a movie when someone else is talking can blame their genes. The ability--or inability--to listen to more than one thing at once is largely inherited, according to a study of twins. The finding could help scientists better understand disorders that involve problems in auditory processing.
A few years ago, scientists at the National Institute on Deafness and Other Communication Disorders (NIDCD) in Bethesda, Maryland, discovered that being "tune-deaf" is mostly determined by genes. Now, NIDCD geneticist Robert Morell and colleagues have gauged the heritability of several other auditory abilities by rounding up 194 pairs of same-sex identical and fraternal twins at the annual Twins Day Festival in Twinsburg, Ohio.
In a trailer on the site, twins were given auditory tests that involved piping a different sound into each ear simultaneously. Such dichotic listening tasks are often used for studying brain asymmetry. In the competing words test, subjects had to identify two monosyllables, such as "ma" and "ka," one presented to each ear. A more difficult version, the consonant-vowel-consonant test, required subjects to identify two similar-sounding words, such as "bit" and "get."
To estimate the genetic contribution to performance, the researchers compared the scores of the fraternal twins, who share, on average, 50% of their genes, with those of the identical twins, who share 100% of their genes. The ability to identify the competing words turned out to be the most heritable. The scientists estimated the genetic contribution at 73%--comparable to the heritability of height or of Type I diabetes, they report in the August issue of Human Genetics. The scientists hope the findings will help unravel auditory processing disorders, in which people with normal hearing have trouble understanding words. In particular, the dichotic listening tasks track the efficiency communication between the brain's two hemispheres.
"This is the first study to show that [normal] people vary widely in their ability to process what they hear, and these differences are due largely to heredity," NIDCD director James Battey said in a statement. That's important, says Deborah Moncrieff, an audiologist at the University of Connecticut, Storrs, because skeptics had questioned attributing difficulties in listening, learning, and reading to problems in the auditory pathway. Moncrieff has developed a method for training children to strengthen the transmission of signals from the ear to the speech center of the brain.
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