Using optimality theory to identify rule-based variability in a child with suspected childhood apraxia of speech: A single-subject case study

The framework of Optimality Theory has been recently used to develop constraint-based approaches to the analysis of speech patterns produced by children with phonological disorders. A significant benefit of this type of nonlinear analysis is the power to predict interword and intraword variability of phonological productions. Such variability, also known as inconsistency, is a speech characteristic frequently cited by researchers and clinicians as one that (a) critically aids in differentially diagnosing childhood apraxia of speech and (b) supports the theoretical perspective that childhood apraxia of speech is a motor speech disorder. This study applies a constraint-based approach to the phonological analysis of the speech of a single child suspected to present with childhood apraxia of speech. Transcriptions of the participant's speech were obtained from therapy notes written by the clinicians providing his speech services. A thorough phonological analysis of the sample was performed yielding a consonant inventory, two quantitative measurements of variability, and several constraint-based predictions of variability at the segmental and prosodic levels. The results of this study confirm variability as a characteristic of this child's speech. Relatively common and rare variations were successfully predicted by a phonological constraint hierarchy, revealing a rule-based deficit discordant with the theoretical perspective that childhood apraxia of speech is a pure motor speech disorder. It is suggested that the results presented in this study indicate a breakdown in the transformational stage of speech production similar to that of phonological disorders. Implications of this theoretical perspective for future research and clinical practice are discussed