Phonetic inventory changes after treating distinctions along an implicational hierarchy

Dinnsen, Chin, Elbert, and Powell (1990) described an implicational hierarchy of feature distinctions that characterized five inventory types for a group of phonologically disordered children. The presence of a feature associated with a more complex phonetic inventory implied the presence of all the distinctive features from less complex levels. In the present study two phonologically impaired subjects, ages 2;8 and 2; 10, with limited phonetic inventories, received treatment to add phonetic distinctions based on this implicational hierarchy. One subject was treated on a distinction from a more complex level in the hierarchy and the other on a less complex distinction. Treatment was applied in two 9-week blocks separated by 5-week withdrawal periods in which generalization probes were administered. Both children learned their target sounds; however, only the child treated on the complex distinction added sounds reflecting less complex distinctions without direct treatment. This subject added 12 sounds compared to his baseline inventory. Change observed in both subjects' phonological systems supports the application of implicationally related feature distinctions in treatment to expand phonetic inventories. Results also lend support to planned no-treatment periods as facilitative of system-wide phonological change.