A Developmental Framework For Linking Phonological And Morpho-syntactic Sequential Pattern Rules In Developmental Language Disorder

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Abstract A hallmark of English-learning children with developmental language disorder (DLD, AKA specific language impairment) is the inconsistent production of grammatical morphology. However, recent work also implicates the phonological domain, as indicated by deficits in producing word and nonword forms. The hypothesis driving the current proposal is that morphological and phonological deficits are causally linked by a broader deficit in sequential pattern learning. The unique approach taken here combines what we already know about morpho-syntactic deficits in DLD with recent developments in the fields of linguistics and language acquisition. First, it is possible to divide phonological and morphological patterns into three pattern types (Single Feature, OR/Disjunction, Family Resemblance/Prototype), with these types having a long history of study in visual pattern learning. Importantly, children with DLD appear to have maximum difficulty with morpho- syntactic patterns of the OR type (e.g., regular past tense). In contrast, studies using artificial grammars show that infants who are typically developing are highly adept at learning Single Feature and OR pattern types; Family Resemblance patterns may be weaker. Typical adults are adept at Single Feature and Family Resemblance patterns, but appear to be, at least superficially, more like children with DLD in their performance on the OR pattern. With these intriguing findings as a starting point, the proposed research links phonological and morphological sequence learning in children with DLD. In Aim 1, we ask if 4- to 6-year-olds (typically developing (TD), DLD alone, DLD + speech sound disorder (SSD), and SSD with no morpho-syntactic deficit) and adults are sensitive to input examples that fit one of these three patterns. We predict that, consistent with their long-documented morpho-syntactic deficit, children with DLD will have particular difficulty with the phonological OR pattern. Consistent with their intact morpho-syntactic skills, children with SSD should show no deficits in the OR pattern, revealing a link between OR pattern learning, phonology, and morpho-syntax. Aim 2 explores whether the inclusion of a semantic subcategory cue facilitates learning the OR pattern. Aim 3 asks if dependence on the associatively organized lexicon can account for the infant-to-adult developmental changes observed for the OR pattern (which is not associatively organized) and thereby explores the possibility that children with DLD rely on their lexicons to compensate for their sequential pattern learning deficit. The results of the proposed studies promise to help identify the underlying mechanism(s) of DLD and to suggest possible intervention strategies, such as employing semantic cues to the OR pattern and strengthening lexical organization.