Bilingual children with specific language impairment: Theoretical and applied issues

Bilingualism is often considered an inappropriate developmental choice for children with specific language impairment (SLI) because, according to a widespread belief, these children’s limited capacity for language would be overtaxed by learning two linguistic systems. However, there has not been adequate empirical investigation of SLI in bilingual children to support, or refute, this belief and the professional practices that are based on it. On the theoretical side, two opposing perspectives concerning the nature of the deficit in SLI make different predictions for the outcome of children with SLI learning two languages, and one set of predictions is consistent with the popular belief stated above. This article is aimed at addressing both the applied concerns and the theoretical debate with evidence from two studies examining the morphological acquisition of French–English bilingual children with SLI as compared to French and English monolinguals with SLI. In the first half of the 20th century it was commonly thought that bilingualism in early childhood was detrimental to children’s linguistic and intellectual development, but an established body of research since that time has shown that bilingualism either has neutral or enhancing effects on children’s cognitive development (see reviews in Bialystok, 2001; Genesee, Paradis, & Crago, 2004; Hakuta, 1986). Although attitudes have shifted greatly toward accepting bilingualism in childhood as healthy and perhaps advantageous, these attitudes only apply to children who are typically developing (TD). Children who present with language-learning disabilities are usually thought to be unsuitable candidates for dual-language learning in childhood. Anecdotal experiences of my own and those of my colleagues with speech–language pathologists, school psychologists, elementary school teachers, pediatricians, and parents have revealed that there is a widespread negative attitude about children with language disorder learning two languages. For example, parents of children with language-learning disabilities are often counseled out of French immersion schools by principals, teachers, and other professionals. In addition, if two languages are spoken in the home of a child with language disorder, speech–language pathologists often recommend © 2007 Cambridge University Press 0142-7164/07 $15.00 Applied Psycholinguistics 28:3 552 Paradis: Bilingual children with SLI that the household switch to using just one language. (For further elaboration, see Genesee et al., 2004; Juarez, 1983; Kohnert, Yim, Nett, Kan, & Duran, 2005.) These practices and the beliefs that underlie them are problematic because they are based on common sense rather than evidence. The common sense notion is that a disordered language faculty could not possibly cope with learning two languages. The majority of the research literature on dual language development and disorders is oriented toward giving advice to educators and speech–language pathologists in their assessment and intervention practices in multilingual settings (Juarez, 1983; Kohnert et al., 2005; Roseberry-McKibbin, 1995; Westernoff, 1991). Studies directly examining bilingual children with language disorders are few, and are limited in terms of what they contribute to our understanding of whether bilingualism impacts negatively on affected children (see Paradis, Crago, Genesee, & Rice, 2003, for elaboration). Consequently, one goal of this article was to provide some grounding for evidence-based practices with bilingual children presenting with language disorders. Bilingualism in children with language-learning disabilities has significant theoretical as well as applied relevance. There is an ongoing debate concerning the mechanisms causing specific language impairment (SLI), which is a developmental language disorder that has no readily identifiable etiology such as hearing loss, autism, or mental retardation. Children with SLI exhibit typical social–emotional development, hearing and motor–speech abilities, and have IQs within the normal limits, but have language abilities significantly below age expectations. (For more information on SLI, see Leonard, 1998.) The debate about the mechanisms causing SLI consists of two main perspectives: cognitive/perceptual processing accounts and linguistic representational accounts. Each of these perspectives makes different predictions for the outcome of children with SLI learning two languages. Therefore, research on bilingual children with SLI could shed light on this theoretical debate, which has hitherto been addressed primarily with data from monolinguals only. Accordingly, another goal of this article is to make a unique contribution to our understanding of the nature of SLI in all affected children through examining bilingual affected children. PROCESSING AND REPRESENTATIONAL ACCOUNTS OF SLI There is a group of explanatory accounts of SLI that have in common the underlying assumption that children affected with this disorder have deficits in some basic cognitive and perceptual processing mechanisms, which cause profound difficulties learning language and also have effects in nonlinguistic cognition (Ellis Weismer, Evans, & Hesketh, 1999; Kohnert & Windsor, 2004; Leonard, Bortolini, Caselli, McGregor, & Sabbadini, 1992; Miller, Kail, Leonard, & Tomblin, 2001). The generalized slowing hypothesis is such a processing-limitation account that claims children with SLI have a generalized deceleration of their ability to intake, store, and access linguistic information (e.g., Miller et al., 2001). Such limitations in processing speed are thought to underlie the very protracted linguistic development in children with SLI because even though they have been exposed to target language input for the same duration of time as their unaffected age peers, they need much more time on task to process that information and develop Applied Psycholinguistics 28:3 553 Paradis: Bilingual children with SLI linguistically. If a child with SLI were to learn two languages instead of one, the generalized slowing hypothesis would predict that this child would show delays not only compared to monolingual unaffected age peers in each language, but also compared to monolingual age peers with SLI. This is because the decelerated processing mechanisms of this child would have twice as much linguistic information to deal with in the same amount of exposure time as monolinguals. Note that the generalized slowing hypothesis predictions for bilingual development in children with SLI is highly consistent with the common-sense belief discussed above. Another set of explanatory approaches to SLI claims that children affected with this disorder have selective deficits within the domain of linguistic representation itself (Clahsen, Bartke, & Göllner, 1997; Jakubowicz & Nash, 2001; Rice, 2003; van der Lely, 2003; Wexler, 2003). Although the hypothesized locus of the deficits varies between accounts, the central assumption they all share is that the criteria determining these deficits can be expressed in terms of domain-specific linguistic complexity alone and need not be derived from extralinguistic, domain-general cognition and perception. The disruption within delay account argues that children with SLI show overall delay in their language development compared to unaffected age peers, but also show pernicious difficulties with individual linguistic structures that go beyond what their general delay would indicate (Rice, 2003, 2004). These “disrupted” structures are those that require certain linguistic computations for which children with SLI have incomplete or faulty abilities to establish the appropriate representation (Wexler, 2003). Rice, Wexler, and colleagues have argued that morphology marking the grammatical feature tense in English (e.g., past [-ed] or BE as an auxiliary verb) is a prime example of a disrupted structure (Rice & Wexler, 1996; Rice, Wexler, & Hershberger, 1998), and disrupted structures could be construed as clinical markers because measuring children’s accuracy in using them could circumscribe the clinical from the nonclinical population (Rice & Wexler, 1996, 2001). Even if a child with SLI was learning two languages, this would not necessarily change their proficiency with respect to those aspects of language that are considered to be clinical markers for monolingual children with SLI. This is because the mechanism causing the difficulty with these particular linguistic structures is internal to linguistic representation, and therefore, the reduced input a bilingual child receives in each language compared with monolinguals would not impact on their (in)ability to represent the structure. The processing and representational accounts contrast not only in their predictions for dual-language development in children with SLI, but also in their approach to explaining uneven linguistic profiles displayed by all children with SLI. Take the example that English-speaking children with SLI show significantly greater difficulties producing grammatical morphology that marks tense than they do with other kinds of grammatical morphology (Bedore & Leonard, 1998; Leonard, Eyer, Bedore, & Grela, 1997; Rice, 2003; Rice & Wexler, 1996). Although a representational account like disruption within delay is clearly compatible with uneven profiles, and in fact, has been conceived around them, processing accounts offer less straightforward explanations for this phenomenon. It is possible that a proponent of the generalized slowing hypothesis might argue that selective deficits on tense morphemes are nothing more than an outcome of the Applied Psycholinguistics 28:3 554 Paradis: Bilingual children with SLI generalized delay children with SLI display in their language development; after all, in the acquisition sequence of grammatical morphemes in English in TD children, the ones marking tense tend to be acquired later (Brown, 1973; de Villiers & de Villers, 1973). However, TD children show a gap between their mastery of nontense marking morphemes and tense marking morphemes of about 12 months (Brown, 1973, de Villiers & de Villiers, 1973); whereas children with SLI show a gap of about 4 years between their mastery of plural [-s] and third person singular [-s], for example (Rice, 2003; Rice & Wexler, 2001). Thus, the magnitude of the gap for children with SLI is much greater than their overall language delay would suggest. Another line of explanation within the processing perspective to account for uneven profiles is the surface hypothesis that claims children with SLI find less phonetically salient morphemes more difficult to acquire because these children have perceptual in addition to processing limitations (Leonard et al., 1992; Leonard & Eyer, 1996; Leonard et al., 1997). On this hypothesis, grammatical morphology would pose difficulties in many languages because these morphemes are often affixes of brief phonetic duration, for instance, English tense morphemes like [-ed] and [-s] are most often pronounced with single consonantal, nonsyllabic allomorphs. Leonard (1998) proposes that the surface hypothesis, together with the generalized slowing hypothesis, could potentially explain some uneven developmental profiles: the morphemes that show extremely protracted acquisition in affected children, like tense morphemes in English, would be those that are less phonetically salient. To test whether the processing or representational account best explains uneven linguistic profiles, morphemes that are equivalent in saliency but different in terms of clinical marker status need to be examined. In this article, results from two studies examining the acquisition of grammatical morphemes in bilingual children with SLI and their monolingual peers are discussed in terms of their pertinence to the predictions of representational and processing accounts.1 The validity of each account is assessed by comparisons between bilinguals and monolinguals as well as between different grammatical morpheme types. TENSE MARKING MORPHEMES IN BILINGUALS AND MONOLINGUALS