1 Running Head: DEVELOPMENTAL CHANGES IN LANGUAGE ACQUISITION Diverging paths: Developmental changes in second language acquisition between three and five years of age Jesse Snedeker1, Joy Geren1 and Carissa L. Shafto2 1 Harvard University 2 University of Louisville Address Correspondence to: Jesse Snedeker 1136 WJH, 33 Kirkland St. Cambridge MA, 02138 Phone: 617-495-3873; fax: 617-384-7944 [email protected] Abstract Language development is characterized by predictable shifts in the words children produce and the complexity of their utterances. Because language acquisition and cognitive development occur simultaneously in infants, it is difficult to determine the causes of these shifts. These studies explore the effects of cognitive maturation on language development examining the acquisition of English in internationally-adopted preschoolers. Parental reports (CDI) were collected from 48 preschoolers, within the first year after they were adopted from China or Eastern Europe. Children who were adopted at two or three years of age showed the same developmental patterns in language production as monolingual infants (matched for vocabulary size). Early on, their vocabularies were dominated by nouns and social words with the proportion of predicates and closed class words increasing with age. Thus shifts in lexical composition appear in older learners and are unlikely to reflect the development of new conceptual resources. Children who were adopted at four or five deviated from this pattern acquiring fewer nouns and more predicates in the early stages of acquisition. Affects of the birth language on acquisition were limited to the older children, suggesting that older children may employ different strategies in word learning. In both groups grammatical development and lexical development were synchronized in precisely the same way that they are in infancy, raising the possibility that word production and grammatical production are causally connected. Keywords: language development, international adoption, word learning, language production, nouns, verbs, critical periods3 In the Biological Foundations of Language (1967) Lenneberg argues that the course of language acquisition is shaped by a biological capacity that matures over the first three years of life, reaches a stable state in early childhood, and then begins to deteriorate at the onset of adolescence. Thus Lenneberg’s critical period hypothesis had two parts. First, the gradual maturation of language accounts for the predictable set of milestones that characterize early acquisition and their correlation with biological growth and motor development. Second, the maturational decline of language accounts for the decline in language abilities that hinders recovery from aphasia and second language learning later in life. In the past twenty years research inspired by Lenneberg has largely focused on the second part of this hypothesis. Numerous studies have confirmed that ultimate attainment declines as age of acquisition decreases (Flege, Yeni-Komshian, & Liu, 1999; Hakuta, Bialystok, & Wiley, 2003; Johnson & Newport, 1989; Newport, 1990) and have documented qualitative differences in language development and processing in late second language learners (Clahsen & Muysken, 1996; Hahne & Friederici, 2001; Weber-Fox & Neville, 1996). Nevertheless the debate rages on about the proper interpretation of these findings and what the definition of a critical period should be (Birdsong, 1999; Hakuta et al., 2003; Newport, Bavelier, & Neville, 2001). In contrast the present study is inspired by the first part of Lenneberg hypothesis. Early language development is marked by a series a qualitative shifts. Infants initially speak in single-word utterances, before they begin to combine words. Young language learners initially produce sparse telegraphic utterances consisting mostly of nouns and verbs and then gradually add in the function morphemes. A central question in language acquisition is what causes children to move through these phases. Lenneberg argued that these intermediate stages reflected the gradual maturation of children’s linguistic capacity. Young children’s utterances were short and sparse4 because of their cognitive limitations. This is one example of a developmental hypothesis for language development. Theories of this kind attribute the order of acquisition or the emergence of new abilities to changes in the learner which are independent of the child’s experience with a given language. Immaturity constrains language acquisition, limiting the kinds of words that a child can learn, the kinds of representations she can create or the kinds of utterances she can produce. When these roadblocks are removed, either by biological maturation or cognitive development, children can acquire new linguistic abilities. In contrast, contingent-acquisition hypotheses attribute the order of acquisition to the interdependence of different linguistic representations or processes. The emergence of new abilities is driven by the child’s growing knowledge of the language. Specifically, if knowledge of form A is necessary for acquiring form B, then the acquisition of B will have to await the acquisition of A. In developmental theories, the initial stages of language acquisition reflect cognitive immaturity, while on the contingent acquisition hypothesis they are viewed as necessary steps in decoding the target language. In developmental theories, the emergence of new linguistic abilities can be driven by the maturation of domain-specific abilities (Wexler, 1998) or the acquisition of new cognitive skills (Shore, 1986). In contingent acquisition hypotheses, new linguistic abilities result from the child’s growing knowledge of language. However, this knowledge may have been acquired via domain-specific mechanisms that evolved to support language (e.g., Snedeker & Gleitman, 2004)or through domain-general associative processes (e.g., Smith, Jones, Landau, Gershkoff-Stowe, & Samuelson, 2002). The popularity of theories linking language development to cognitive development has waned with the erosion of Piagetian dominance in developmental psychology. The failure to find robust correlations between linguistic milestones and