An intra-twin phonological study: the phonologies of an SLI twin and her normally developing brother

This study examined the phonological systems of fraternal twins, at 6;1 and again at 7;6. The male twin is acquiring language normally, while the female has been diagnosed as being language impaired. Phonetic and phonological inventories, substitution patterns, phonological processes, syllable structures and proportion of correct consonants for each twin were analysed following the assessment procedures outlined in Ingram (1981, 1989a). Results indicate that the SLI twin omitted consonants most frequently in syllable final position and consistently reduced consonant clusters. Her results reveal a language delay of approximately four years in terms of segmental acquisition, and five or more years in the acquisition of syllable structures, compared with her brother. It is argued that this mismatch between the degree of delay in segmental and syllabic acquisition demonstrates a type of phonological deviance.