To determine if auditory processing skills are hereditary, National Institute on Deafness and Other Communication Disorders (NIDCD) researchers studied 194 same-sex pairs of identical and fraternal twins. All twins received a DNA test to confirm whether they were identical or fraternal and a hearing test to make sure they had normal hearing.
If a trait is purely genetic, identical twins, who share the same DNA, will be alike nearly 100 percent of the time, while fraternal twins, who share roughly half of their DNA, will be less similar. The volunteers took five tests that are frequently used to identify auditory processing difficulties in children and adults.
In three of the tests, volunteers listened as two different one-syllable words were played into their right and left ears simultaneously, and then tried 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 artificially filtered out high-pitched sounds, which tended to obscure the consonants, while the other sped up the word.
In all but the filtered-words test, researchers found a significantly higher correlation among identical twins than fraternal twins, indicating that differences in performance for those activities had a strong genetic component. The tests in which different one-syllable words were played simultaneously into each ear showed the widest degree of variation as well as the highest correlation among twins, especially identical twins. As much as 73 percent 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 due to differences in environment.
MEDICA.de; Source: NIH/National Institute on Deafness and Other Communication Disorders