| Summary: | This study examined the phonological development of a set of 6-year-old male dizygotic twins with protracted phonological and morphosyntactic development. Each twin was given 16 weeks of therapy, 8 weeks of morphosyntactic treatment and 8 weeks of phonology treatment. These 8-week treatment blocks were ordered oppositely so that one twin received morphosyntactic treatment first while the other received phonology treatment first. The study investigated phonological changes after morphosyntax treatment (cross-domain generalization), after phonological treatment (direct treatment effect), and after the full 16 weeks (overall effects and treatment order effect). Specific changes within the phonological systems of the twins were interpreted from a constraint-based non-linear phonology point of view. Twin 1, who received morphosyntax treatment first, did not show an increase in phonological matches to adult targets after the morphosyntax treatment block. After the phonology treatment block, an increase in percentage match for treated word structures and phonological features was seen. Twin 2, who received phonology treatment first, showed an increase in percentage match for treated structures and features after phonology treatment. After morphosyntax treatment, a continued increase in phonological matches to adult targets was seen. These results imply that it may be important to target phonology directly with children who have both protracted phonological and protracted morphosyntactic development. Results also indicate that both morphosyntax treatment first and phonology treatment first strategies can facilitate phonological development and that phonology treatment first may allow for greater generalization in the phonological domain during morphosyntax treatment.
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