A Unified Model

There are three obvious differences between first and second language learners. First, infants who are learning language are also engaged in learning about how the world works. In contrast, second language learners already have a full understanding of the world and human society. Second, infants are able to rely on a highly malleable brain that has not yet been committed to other tasks (MacWhinney, Feldman, Sacco, & Valdes-Perez, 2000). In contrast, second language learners have to deal with a brain that has already been committed in various ways to the task of processing the first language. Third, infants can rely on an intense system of social support from their caregivers (Snow, 1999). In contrast, second language learners are often heavily involved in social and business commitments in their first language that distract them from interactions in the new language.