Auditory lateralization in monozygotic twins.

In an attempt to investigate whether auditory lateralization has a heritable component, 20 monozygotic (MZ) twin pairs were examined with four different dichotic listening tests known to produce reliable right-ear advantages (REAs) in right-handers. Ten twin pairs were concordantly right-handed (MZ-RR), and ten twin pairs were discordant for handedness (MZ-RL). Intraclass correlations for MZ twin pairs were weak or nonexistent for ear advantage, but relatively strong for overall correct scores and mean reaction times, measures unrelated to laterality scores. These results support the hypothesis that auditory lateralization, as measured with dichotic tests, is nongenetic in origin. A comparison of MZ twins and right-handed siblings (n = 20) showed that right-handed siblings exhibited strong REAs, whereas left-handed siblings (n = 20) and MZ twins showed weak or absent REAs, indicating that twins may be atypically lateralized with respect to auditory lateralization.