Phonetic learning is not enhanced by sequential exposure to more than one language

Several studies have documented that international adoptees, who in early years have experienced a change from a language used in their birth country to a new language in an adoptive country, benefit from the limited early exposure to the birth language when relearning that language's sounds later in life. The adoptees' relearning advantages have been argued to be conferred by lasting birth-language knowledge obtained from the early exposure. However, it is also plausible to assume that the advantages may arise from adoptees' superior ability to learn language sounds in general, as a result of their unusual linguistic experience, i.e., exposure to multiple languages in sequence early in life. If this is the case, then the adoptees' relearning benefits should generalize to previously unheard language sounds, rather than be limited to their birth-language sounds. In the present study, adult Korean adoptees in the Netherlands and matched Dutch-native controls were trained on identifying a Japanese length distinction to which they had never been exposed before. The adoptees and Dutch controls did not differ on any test carried out before, during, or after the training, indicating that observed adoptee advantages for birth-language relearning do not generalize to novel, previously unheard language sounds. The finding thus fails to support the suggestion that birth-language relearning advantages may arise from enhanced ability to learn language sounds in general conferred by early experience in multiple languages. Rather, our finding supports the original contention that such advantages involve memory traces obtained before adoption.