Incidental word learning in a hearing child of deaf adults.

It is unclear how children develop the ability to learn words incidentally (i.e., without direct instruction or numerous exposures). This investigation examined the early achievement of this skill by longitudinally tracking the expressive vocabulary and incidental word-learning capacities of a hearing child of Deaf adults who was natively learning American Sign Language (ASL) and spoken English. Despite receiving only 20% of language input in spoken English, the child's expressive vocabularies at 16 and 20 months of age, in each language, were similar to those of monolingual age-matched peers. At 16 months of age, the child showed signs of greater proficiency in the incidental learning of novel ASL signs than she did for spoken English words. At 20 months of age, the child was skilled at incidental word learning in both languages. These results support the methodology as it applies to examining theoretical models of incidental word learning. They also suggest that bilingual children can achieve typical vocabulary levels (even with minimal input in one of the languages) and that the development of incidental word learning follows a similar trajectory in ASL and spoken English.