Past tense -ed omissions by children with specific language impairment: The role of sonority and phonotactics.

Children with Specific Language Impairment (SLI) frequently omit past tense -ed. Omission rates are subject to phonological context. Two phonological characteristics were manipulated; the sonority profile of the stem-final phoneme plus affix, and the phonotactic probability of the word-final phonemes (/i:pt/ in beeped). Seventeen children with SLI (mean age 6;7) and 21 language-matched children (mean age 4;8) repeated sentences containing regularly inflected verbs according to a 2 (sonority) by 2 (phonotactic legality) design. Affix omissions were analysed. There was a significant effect of sonority only, characterised by a difficulty with level-sonority clusters, and no interaction. Syllabic affixes, e.g. head-ed, were produced relatively accurately. It is argued that -ed omissions in SLI may reflect a low-level speech or articulation difficulty which surfaces in uniquely challenging clusters. This is not an alternative to morphosyntactic accounts; rather past tense omissions are best explained according to complexity in multiple domains; syntactic, morpho-syntactic and phonological.