ABSTRACT
It is estimated that approximately 7% of the general population has a syndrome known as specific language impairment (Tomblin et al., 1997). The term specific language impairment (SLI) is used to identify children who have difficulty with the acquisition and use of language. When compared to their typically developing peers, these children’s scores on standardized measures of language development fall greater than one standard deviation below the mean, yet their cognitive abilities are within normal limits, they have normal hearing acuity, no frank neurological impairment, and no social-emotional problems (Leonard, 1998; Stark & Tallal, 1981). The acquisition and use of grammatical morphology appears to be the aspect of language most severely affected in children with SLI and they often produce grammatical markers less frequently than younger, typically developing children matched for mean length of utterance (MLU; e.g., Leonard, 1998; Rice & Wexler, 1996). The morphemes that appear to be most problematic for children with SLI include inflectional markers (e.g., third person singular: s, regular past tense: ed, contractible copula and auxiliary forms of to be) and functional words (e.g., uncontractible copula and auxiliary forms of to be). These morphemes may be completely absent or produced inconsistently across utterances (Leonard, Eyer, Bedore, & Grela, 1997; Miller & Leonard, 1998). When errors do occur, children with SLI are more likely to make omission rather than commission errors (Leonard et al., 1997; Rice & Wexler, 1996). Furthermore, they often have problems with other aspects of language such as phonology, vocabulary, and syntax (e.g., Leonard, 1998; Rice, 2004). Recent studies of language intervention have shown that while these children do show progress in their acquisition of language as a result of intervention, they are resistant to mastery of language in a timely manner (Bishop, Adams, & Rosen, 2006; Ebbels, van der Lely, & Dockrell, 2007; Leonard, Camarata, Pawlowska, Brown, & Camarata, 2008; Rice & Wexler, 1996). This difficulty with language may persist into adulthood (van der Lely, 1997, 2005).
