SLI as a Model System of Language Acquisition

1. SLI as a Model System of Language Acquisition Mabel L. Rice SRCLD-IASCL 2002 Madison, Wisconsin July 2002

2. Questions • 1. What accounts for growth (nongrowth) in children’s language? • 2. Is growth (nongrowth) synchronized tightly across all elements of language?

3. Possibilities: • Sorting out useful distinctions about linguistic growth and the nature of linguistic competence in children Pitfalls Variance across children in levels of performance Variance across elements of language

4. Background: What are the Mechanisms That Underlie Children’s Acquisition of Morphosyntax? • Assumption of uniform robustness: All “normal” children acquire language effortlessly, following the same timing mechanisms and the same general sequence. An emphasis on invariant properties of language acquisition.  • “In general, language acquisition is a stubbornly robust process; from what we can tell there is virtually no way to prevent it from happening short of raising a child in a barrel.” Pinker, 1984, p. 29.

5. Updated assumption: Otherwise “normal” children can have language impairments (SLI); there is unexpected and unexplained variance across children • Some relatively invariant properties of morphosyntax show unexpected individual variability

6. Variation in onset timing: Late activation of language acquisition mechanisms?

7. A late start for an intact language system versus a late start for an underspecified grammar

9. The value of the 3-group design: Affected, age-matched, language-matched • Affected < Age matches = “Language Impairment” • Affected < language-matched = “Language impairment beyond general language delay”

10.    Variation in acquisition timing mechanisms for TNS, ages 3-8 years • SLI children start later, and show slower acquisition timing although similar growth curves

12. Young children show variation that disappears by age 5 years, at adult grammar

14. SLI children show variation in a range far below age expectations

16. At the Same Time of Variation in TNS- Marking, Other Morphology is Nonvariant

17. Lexical indices Show Consistent Variation Across the Growth Curve, and Do Not Differentiate SLI from Language-Equivalent Group • # Different Words • # Verb Types • # Verb Tokens • % General All Purpose Verbs • PPVT Raw Scores

23. Cross-clinical Comparisons as a Way of Unraveling the Relationship of TNS, MLU, Cognitive and Lexical Acquisition: A Comparison of SLI and WMS Children Matched for MLU, Disparate for Cognitive and Lexical Acquisition • MLU equivalent across SLI and WMS • CA different between SLI and WMS • WMS IQ < SLI • WMS < SLI on number of words comprehended • SLI < WMS on three measures of TNS: regular past –ed 3rd person singular –s BE copula and auxiliary

31. SLI = WMS on non-TNS morphemes • Plural –s • In/On

34. Working Conclusions • Outcomes are compatible with linguistic models of the adult grammar that posit a relatively discrete morphosyntax and TNS-marking as obligatory features of clause construction • Evidence is compatible with a 2-phase maturational model, one that controls initial appearance of language (i.e., “start-up”) and another that controls certain grammatical properties versus general lexical growth and overall clause construction

35. Overall, support for an Extended Optional Infinitive period that co-exists with a generally slowed linguistic system in children with SLI • Selective slowing of certain grammatical properties is evident in the obligatory properties of clausal structure

36. Implications for Genetic Studies • What elements of language acquisition are vulnerable to phenotypic variation — onset? general delay? delay-within-delay? • Is a grammatical marker age-dependent, or also evident in older children and adults?