How Languages Construct Time

Disentangling the Effects of Cognitive Development and Linguistic Expertise: A Longitudinal Study of the Acquisition of English in Internationally-Adopted Children (Article begins on next page) The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters. Citation Snedeker, Jesse, Joy Geren, and Carissa L. Shafto. Forthcoming. Disentangling the effects of cognitive development and linguistic expertise: A longitudinal study of the acquisition of English in internationally-adopted children. Cognitive Psychology. Accessed January 4, 2015 5:40:30 PM EST Citable Link http://nrs.harvard.edu/urn-3:HUL.InstRepos:5149081 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-ofuse#OAP1 Running Head: INTERNATIONAL ADOPTION AND LANGUAGE DEVELOPMENT Disentangling the effects of cognitive development and linguistic expertise: A longitudinal study of the acquisition of English in internationally-adopted children. Jesse Snedeker1 , Joy Geren1 and Carissa L. Shafto2 1 Harvard University 2 University of Louisville (Accepted pending revision, Cognitive Psychology) Address Correspondence to: Jesse Snedeker 1136 WJH, 33 Kirkland St. Cambridge MA, 02138 Phone: 617-495-3873; fax: 617-384-7944 snedeker@wjh.harvard.edu 2 Abstract Early language development is characterized by predictable changes in the words children produce and the complexity of their utterances. In infants these changes could reflect increasing linguistic expertise or cognitive maturation and development. To disentangle these factors, we compared the acquisition of English in internationally-adopted preschoolers and internationallyadopted infants. Parental reports and speech samples were collected for one year. Both groups showed the qualitative shifts that characterize first-language acquisition. Initially, they produced single-word utterances consisting mostly of nouns and social words. The appearance of verbs, adjectives and multiword utterances was predicted by vocabulary size in both groups. Preschoolers did learn some words at an earlier stage than infants, specifically words referring to the past or future and adjectives describing behavior and internal states. These findings suggest that cognitive development plays little role in the shift from referential terms to predicates but may constrain children’s ability to learn some abstract words. Keywords: language development, international adoption, word learning, one-word stage, language production, nouns, verbs.3 Early language production can be characterized as a series of roadblocks that are gradually removed. Most infants use single-word utterances for many months before they begin combining words (Nice, 1925; Bloom, 1973). Children’s first words are largely limited to social routines and labels for the people and things around them. Verbs, adjectives and closed-class words only become common at larger vocabulary sizes (Doran, 1907; McCarthy, 1930; Gentner, 1982, Bates, Marchman, Thal, Fenson, Dale, Reznick, et al., 1994). Two central questions in language acquisition are: What accounts for these early limitations, and how are they overcome (Lenneberg, 1967; Bloom, 1973; Cromer, 1974; Gleitman, 1981)? Specifically, are the initial stages present because the child is cognitively or perceptually immature, or do they represent necessary steps in decoding the target language? Are new linguistic abilities partially due to broad changes in the cognitive abilities of the learner, or are they solely attributable to the child’s growing knowledge of the language itself? These questions are difficult to answer because cognitive development and language acquisition are confounded in typically developing children. Young infants are cognitively immature and limited in their linguistic knowledge, while older children are more sophisticated in both respects. When confronted with confounds like this, developmental psychologists often turn to special populations in which the variables of interest can be disentangled. Much of what we know about language development comes from studies of atypical populations (see e.g., Bellugi, Marks, Bihrle & Sabo, 1988; Cromer, 1974; Curtiss, 1989; Goldin-Meadow & Feldman, 1977; Landau & Gleitman, 1985; Senghas, 2003). These natural experiments allow us to explore the effects of factors that are impossible or unethical to manipulate. International adoption is one such natural experiment, creating the opportunity to disentangle the effects of linguistic expertise and cognitive maturation (Snedeker, Geren & 4 Shafto, 2007). About 17,000 internationally-adopted children enter the U.S. each year (U.S. Department of State, 2008). While most are infants or toddlers, thousands of older children are also adopted. Many of these children are well within the critical or sensitive period for learning language (Newport, 1990). These older children appear to rapidly lose their birth language (Glennen & Masters, 2002) and become fluent speakers of their adoptive language (Pallier, et al., 2003). But we know almost nothing about how they get there. While a number of researchers have studied language development in children adopted as infants or toddlers (see e.g., Glennen & Masters, 2002; Roberts, Pollock, Krakow, Price, Fulmer & Wang, 2005; Pollock, 2005), there is little work on acquisition in children who were adopted after 30 months. The learning problem faced by internationally-adopted preschoolers is broadly similar to that of infants learning their first language: they are exposed to child-directed speech in the context of daily routines; they must learn the new language to communicate with their families; they have little access to text or bilingual informants; and they lack many of the metalinguistic skills available to older children and adults (Gombert, 1992). However, these children are more cognitively and physically mature than their infant counterparts and have already started to learn one language. Thus international adoption could provide a way to explore the role that cognitive development and maturation play in shaping the course of first language acquisition, by allowing us to see how acquisition proceeds when these roadblocks have been removed. Such a tool would be useful for distinguishing between two broad classes of hypotheses about qualitative changes during language acquisition: 1) Developmental Hypotheses: Theories of this kind attribute the order of acquisition or the emergence of new abilities to changes in the learner that are independent of her experience with a given language. Immaturity constrains language acquisition, limiting the kinds of words that a 5 child can learn, the kinds of utterances she can produce or the kinds of representations she can create. When these limitations are removed, by biological maturation or cognitive development, new linguistic abilities can emerge. 2) Contingent-Acquisition Hypotheses: These theories attribute the order of acquisition to the interdependence of different linguistic representations, processes, and learning algorithms. Critically, the emergence of new abilities is driven by the child’s growing knowledge of the language. If knowledge of form A is necessary for acquiring form B, then the acquisition of B will have to await the acquisition of A.1 Critically, this distinction is orthogonal to the nativist/empiricist and domainspecific/domain-general dichotomies that typically organize theoretical discussions of language development. Contingent-acquisition hypotheses necessarily attribute shifts to the child’s growing knowledge of the language, but they differ in their claims about how the child acquires that knowledge in the first place. Thus there are contingent-acquisition hypotheses which invoke innate language-specific representations and highly-constrained learning mechanisms (e.g., Snedeker & Gletiman, 2004) and others which posit that language ac
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isition is largely driven by domain-general learning abilities (e.g., Bates & Goodman, 1997). The developmental hypotheses are even more diverse. For example, Wexler has argued that the development of tense and agreement depends on the maturation of domain-specific innate syntactic knowledge (Wexler, 1999). In contrast, others have suggested that the length of children’s early utterances depends on a domain-general increase in memory capacity (see e.g., Shore, 1986). These two proposals differ in the mechanisms they invoke and the phenomena they seek to explain, yet both are developmental hypotheses because they attribute changes in linguistic abilities to events that 1 The contingent-acquisition hypotheses under consideration make the weaker claim that one type of knowledge is needed for efficient acquisition or utilization of another type. This is desirable since the generalizations under consideration are strong but violable. For example, children do learn some verbs early on (Bates et al. 1995). 6 are distinct from the process of language acquisition itself and are tightly linked to the child’s biological or cognitive development. Consequently, both theories predict that older learners, with mature grammars and longer memory spans, would initially produce more complete utterances than young children who begin acquiring the language in infancy. Our work tests central predictions of developmental hypotheses by tracking the early language development of internationally-adopted children. Developmental hypotheses deal with diverse phenomena, ranging from the timing of babbling in infancy to the mastery of complex constructions during the early school years, thus no single method or population can be used to address all of these proposals. In the present study, we focus on two qualitative changes that typically occur between 12 and 30 months of age: 1) the systematic shift in the composition of the child’s lexicon from concrete nouns to more abstract words such as verbs, adjectives and grammatical function words and 2) the end of the one-word stage and the emergence of combinatorial speech. These phenomena were selected because they are robust, easy to observe and central to theories about children’s early word learning and language production. In the remainder of this introduction, we examine these two shifts in greater detail. For each one, we describe the relevant developmental and contingent-acquisition hypotheses and briefly review the prior research. We conclude that the evidence to date is consistent with both classes of explanation. Finally, we describe our initial work on language acquisition in internationallyadopted children (Snedeker et al., 2007) laying out the motivations for the present study. 7 Accounting for changes in early vocabulary composition Children’s early vocabularies are dominated by social routines (“bye bye”) and nouns that refer to people, animals, and small moveable objects. Although adults speak to children in full sentences, complete with verbs and grammatical function words, these elements are massively underrepresented in children’s early vocabularies (Gentner, 1982, Bates et al., 1994; Behrens, 2006). As children’s lexicons grow the proportion of social words declines and more verb, adjectives and function words appear, resulting in systematic correlations between vocabulary size and vocabulary composition (Bates et al., 1994). These systematic shifts lend themselves to both developmental accounts and contingent-acquisition hypotheses (see Conboy & Thal, 2006). Developmental accounts of vocabulary shifts appeal to a range of mechanisms. For example, some theorists have suggested that the skewed nature of children’s early lexicons may reflect their conceptual limitations (Huttenlocher, Smiley & Ratner, 1983; O’Grady, 1987). Perhaps the relative dearth of verbs and adjectives is attributable to the infant’s inability to conceive of relations, states or actions, while the overabundance of nouns is attributable to the conceptual primacy of object categories. As children overcome these limitations and develop the relevant concepts, they are able to acquire the words that encode them. This account provides a particularly intuitive explanation for young children’s failure to learn words, like mental state verbs or temporal connectives, that are very frequent, highly abstract, and known to cause conceptual difficulties later in childhood. The maturation of perceptual mechanisms could also play a role in the diversification of vocabulary. Closed-class words (or function words) are typically short in duration, rarely receive stress, and often have reduced vowels (Morgan, Shi & Allopena, 1996; Selkirk, 1996). These factors could make them difficult for infants to accurately perceive or produce, raising the 8 possibility that their emergence between 24 and 30 months is caused by improvements in perception or motor control. But the changing composition of children’s lexicons is equally amenable to contingentacquisition hypotheses. For example, Gleitman and her colleagues have argued that shifts in lexical composition reflect the child’s growing mastery of a particular language, rather than conceptual or perceptual development (Gillette et al., 1999; Snedeker & Gleitman, 2004; Gleitman, Cassidy, Papafragou, Nappa & Trueswell, 2005). An infant who is just breaking into language can only learn the meanings of words by observing the situational contexts in which they are used. This information may be sufficient for learning social routines, names for people, and labels for objects, because the meanings of these words can be readily inferred from nonlinguistic social cues (e.g., points or eye gaze). But as the child’s knowledge of language grows, she is increasingly able to decode the sentence in which a new word appears and use this information to infer its meaning. This strategy (syntactic bootstrapping) could allow her to acquire more abstract relational words, such as verbs, adjectives and closed-class items. Perceptual bootstrapping could also play a role in vocabulary diversification. Closed-class words rarely appear in isolation (Brent & Siskind, 1999), instead they are typically part of the same prosodic unit as an adjacent open-class word (Selkirk, 1996). Thus stable representations of open-class words may be necessary for the accurate segmentation (and acquisition) of many closed-class words. Although vocabulary composition is a well-studied topic, only a few lines of research appear to bear on the distinction between developmental and contingent-acquisition hypotheses. First, there is an extensive literature documenting that early vocabulary composition varies across linguistic and cultural contexts. Specifically, children who are learning object-dropping 9 languages like Mandarin or Korean produce more verbs early in development than those who are learning languages like English (Tardif, 1996; Choi & Gopnik, 1995). If a given ability emerges early in one language and late in another, it seems reasonable to conclude that its emergence in the later language cannot be attributed to cognitive or maturational changes. There are two reasons, however, to reject this conclusion. First, the phenomenon of interest appears to be universal—under the correct description. As Gentner points out, the relevant question is not whether every child knows more nouns than verbs, but rather whether children systematically learn more nouns than we would expect given their frequency in the input (Gentner & Boroditsky, 2001). If the noun bias is characterized in this way, the current evidence suggests that it is a cross-linguistically robust feature of development (see e.g., Kim, McGregor & Thompson, 2000; Tardif, Gelman & Xu, 1999; Bornstein et al., 2004). Second, it is possible for shifts which are specific to particular languages to be caused by universal developmental changes. For example, suppose that the acquisition of function words in languages like English is driven by the maturation of perceptual abilities that allow children to accurately represe

nt reduced syllables at the beginning of a phonological phrase. This skill would be unnecessary in languages in which function words have full vowels or appear at the end of phonological phrases. Consequently, the age at which function words appeared would vary across languages, but their emergence in English would (by hypothesis) depend on perceptual maturation. A second line of research has explored the contingent-acquisition hypothesis by simulating the effects of linguistic development in the absence of cognitive limitations. In a series of studies, Gleitman and her colleagues asked adults to identify common words from different representations of the contexts in which they occurred in child-directed speech (Gillette et al., 1999; Snedeker & Gleitman, 2004). When limited to situational cues, adults could only identify 10 the concrete nouns. However, when they were given information about the linguistic context, they were able to learn abstract nouns and verbs as well. These experiments demonstrate that changes in vocabulary composition are not necessarily attributable to changes in the learner’s conceptual repertoire. But there are several differences between these human simulation experiments and the experiences of young language learners which might limit their validity. The adult observers are not participants in the interactions, which may affect both their level of motivation and their access to information about the participants’ goals. Unlike infants, the participants in these studies do not have to segment utterances or create a representation of the phonological form of the word. While young children must simultaneously grapple with several unknown words, the adults in these studies were given massed presentations of each target item, drastically reducing the memory demands of the task. If these differences merely improve or hinder performance equally for words of all kinds, then the simulations would still allow us to conclude that situational cues are more informative for nouns than for verbs. However, if these factors have differential effects on words of different classes, then such studies may not provide the relevant characterization of the input. In contrast, the task and input of the adopted child appear to closely parallel that of the typically developing infant. Like the infant, the adopted child gets prolonged exposure to her new language in the context of meaningful social interactions. Like the infant she must simultaneously isolate the words and determine what they mean. However, like the adults in the human simulations, the adopted child is cognitively more mature than the infant. If shifts in vocabulary composition primarily reflect the changing cognitive capacities of the learner, then adopted children should acquire words from a variety of categories, much like their monolingual 11 age mates. If vocabulary composition is largely a function of linguistic knowledge, then the adopted child should initially resemble the infant learner. The emergence of combinatorial speech For about four to six months after they begin speaking, children primarily produce singleword utterances. Short telegraphic utterances appear at about 16 – 19 months of age, when the child has acquired a vocabulary of about 100 words (Nice, 1925; Bates, Dale & Thal, 1995). Between 24 and 30 months, children’s utterances continue to grow in complexity as they add determiners, auxiliaries and inflectional markers to their initially sparse statements (Brown, 1973). Both of these grammatical developments are tightly correlated with the child’s productive vocabulary, suggesting that lexical and grammatical development are linked (Bates & Goodman, 1997). Two types of developmental hypotheses have been proposed to account for the development of combinatorial speech. Some theorists have suggested that the transition to multiword speech is driven by the development of a domain-general cognitive capacity to isolate and combine elements in novel ways (see e.g., Shore, 1986; Brownell, 1988). Others have argued that the onset of combinatorial speech depends on the maturation of a domain-specific grammatical capacity (Lenneberg, 1967; Locke, 1997). However the onset of combinatorial speech could also reflect a pattern of contingent acquisition. The tight correlation between vocabulary size and the complexity of children’s utterances raises the intriguing possibility that children may have to learn a critical mass of words before they are able to acquire the grammatical knowledge that they need to combine them. While this proposal has been associated with theories in which grammatical knowledge emerges from the lexicon (Bates & Goodman, 1997), it is compatible with any theory of 12 acquisition which proposes that lexical knowledge is essential for the creation (or proper identification) of grammatical representations (see e.g., Pinker, 1984; Tomasello, 1991; Locke, 1997; Redington, Chater & Finch, 1999). Two lines of research support a developmental hypothesis for the emergence of combinatorial speech. First, in typical children, this milestone in language acquisition is associated with milestones in other domains (Lenneberg, 1967). For example, combinatorial speech usually appears around the same time as symbolic play (Fenson & Ramsay, 1980), block construction (Greenfield, 1978), sequenced imitation (McCall, Parke, Kavanaugh, 1977), and changes in nonverbal categorization (Sugarman, 1983). Many of these associations are reliable even when age is controlled or factored out. For example, Shore and colleagues found reliable correlations between the length of children’s utterances at 20 months and the complexity of their symbolic play sequences (Shore, O’Connell & Bates, 1984). Such findings have led many to suggest that combinatorial speech may have to await the development of some domain-general cognitive ability affecting memory, sequencing, or symbolic representation (Shore, 1986; Brownell, 1988; Bauer, Hertsgaard, Dropnik & Daly, 1998). Additional support for this developmental hypothesis comes from studies of early language acquisition in children with developmental disorders. Children with both Down syndrome and Williams syndrome show substantial delays in early language production which are roughly proportional to their cognitive delays, resulting in productive vocabularies that are roughly the size of mental age matched controls (Singer Harris, Bellugi, Bates, Jones, & Rossen, 1997; Vicari, Caselli, Gagliardi, Tonucci & Volterra, 2002; Laing et al., 2002). This early association between general cognitive ability and language production is quite robust; even mentally-13 retarded persons who go on to develop extraordinary linguistic skills appear to have had early language delays proportional to their cognitive impairments (Rondal, 2003). In Williams syndrome, the onset and growth of combinatorial speech is also synchronized to vocabulary size and mental age, just as it is in typical children (Singer Harris et al., 1997; Vicari et al., 2002). In contrast, children with Down syndrome produce fewer and shorter combinations than typical children of the same mental age. These findings are consistent with the hypothesis that the onset of combinatorial speech is usually triggered by the development of a domaingeneral cognitive capacity closely linked to general intelligence. In typical development and in Williams syndrome, acquisition of this ability is sufficient for combinatorial speech. In children with Down syndrome, other impairments may stand in the way (or the critical cognitive skill itself is slow to develop). However, while these findings are compatible with the developmental hypothesis, they do not provide definitive evidence for it. Patterns of association—in typical children or in developmental disorders—are consistent with multiple causal accounts. These associations could reflect effects of general cognitive development on language development, or they could reflect effects of linguistic abilities on nonlinguistic tasks. Alternatively, language and cognitive development could procee

d along independent lines but still be associated, so long as the pace of development in each domain was sensitive to some of the same variables (e.g., differences in general learning abilities, neural efficiency or the pace of biological maturation). Support for the contingent-acquisition hypothesis comes from studies exploring the close relation between vocabulary growth and the development of combinatorial speech. Bates and her colleagues have demonstrated that the same pattern of lexical grammatical synchrony which characterizes typical development is also present in early-talkers, late-talkers and children with 14 Williams syndrome, suggesting that lexical learning may fuel syntactic development (Bates & Goodman, 1997). These studies, however, cannot rule out the possibility that both aspects of language depend upon the development of some other cognitive ability, one which is accelerated for early-talkers, delayed for late-talkers, and proportional to mental age in children with Williams syndrome. The goal of the present study is to test the contingent-acquisition hypothesis by examining the relation between lexical and grammatical development in children who acquiring English as preschoolers. If vocabulary acquisition and combinatorial speech are causally connected, then this relationship should persist in maturationally-advanced learners. In contrast, if the correlation is created by rate-limiting development in another domain, then it should be possible to find disassociations in older learners. A similar motivation underlies two recent studies of language production in young SpanishEnglish bilinguals (Marchman, Martinez-Sussman & Dale, 2004; Conboy & Thal, 2006). Because bilingual children split their time between two languages, vocabulary growth in each language is often delayed relative to monolinguals. Thus bilingual learners could potentially be maturationally-advanced learners, reaching each stage of acquisition at a later age than monolinguals. Both studies used a