Multitaskers Are Born, Not Made

The finding, detailed in the August issue of the journal Human Genetics, could help researchers understand a diverse group of disorders in which people hear perfectly fine but have trouble comprehending.

“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,” said study team member James Battey, director of the National Institute on Deafness and Other Communication Disorders, one of the National Institutes of Health (NIH).

Ears are important for picking up sound, but what we call “listening” takes place largely in the brain, which is responsible for extracting information from what would otherwise just be noise. Thus, many hearing disorders are actually brain disorders that interfere with our ability to interpret the world.

Auditory processing disorders, or APDs, are estimated to affect as many as 7 percent of school-aged children in the United States, as well as older adults and stroke victims.

Hearing tests

The researchers tested the hearing of 138 identical and 56 fraternal twins who attended a national twins festival in Twinsburg, Ohio, from 2002 to 2005. Ages ranged from 12 to 50, and all participants had normal hearing.

The volunteers took five tests routinely used to identify auditory processing difficulties. In three of the tests, volunteers listened as two different one-syllable words or nonsense syllables (words such as ba, da and ka) were played into their right and left ears simultaneously. They were then asked to name both words or syllables.

In two other tests, volunteers listened to digitally altered one-syllable words played into the right ear and tried to identify the word. One test sped words up. The other test artificially filtered out high pitched sounds, which tends to obscure consonants.

The researchers found that performance in all but the last test was heavily influenced by genetics. The test in which different one-syllable words were played in each ear simultaneously showed the highest degree of correlation among twins, especially identical twins.

Because identical twins share the same DNA, they will exhibit the same trait nearly 100 percent of the time if it is genetic. In contrast, fraternal twins share about half of their DNA and are less similar.

If a trait is primarily due to a person’s environment, the idea is that both identical and fraternal twins should exhibit the same degree of similarity, since most twins grow up in the same household.

In the study, the ability to understand filtered words showed high correlation among all twins, an indication that variation in this skill was due primarily to upbringing.

More widespread

Scientists previously thought that problems with listening to two things simultaneously, called “dichotic listening,” was due to lesions or disconnects between the brain’s two hemispheres.

The new findings show this isn’t always the case. “It means that these kinds of differences in people’s abilities are not always necessarily caused by an environmental insult like a stroke … [and] that these kinds of differences are to a large extent hereditary,” said NIDCD geneticist Richard Morell, who was involved in the study.

Because the tests were conducted in twins with seemingly normal hearing, the findings also suggest many more people have some degree of APD than is commonly thought.

“We took these [clinical] tests and gave them to people have no problem,” Morell told LiveScience. “We just recruited them at a festival … and we saw that there was quite a large variation in people’s ability to perform in these tests.”

• Top 10 Mysterious Diseases

• Top 10 Things You Didn't Know About You

• Nobody is Listening to the Modern Hearing Problem