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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, & ValdesPerez, 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. Together, these three differences might suggest that it would make little sense to try to develop a Unified Model of first and second language acquisition. In fact, many researchers have decided that the two processes are so different that they account for them with totally separate theories. For example, Krashen (1994) sees L1 learning as involving “acquisition” and L2 learning as based instead on “learning.” Others (Bley-Vroman, Felix, & Ioup, 1988; Clahsen & Muysken, 1986) argue that Universal Grammar (UG) is available to children up to some critical age, but not to older learners of L2. Despite these differences, there are good reasons to want to develop a Unified Model. First, many of the tasks faced by L1 and L2 learners are identical. Both groups of learners need to segment speech into words. Both groups need to learn the meanings of these words. Both groups need to figure out the patterns that govern word combination in syntactic constructions. Both groups have to work to interleave their growing lexical and syntactic knowledge to achieve fluency. For both groups, the actual shape of the input language of the community is roughly the same.