Department of Speech and Hearing Sciences
University of Washington, Seattle
Previous results have indicated that suspected childhood apraxia of speech (sCAS) may be associated with a central timing deficit that surfaces in speech as well as other activities. To rule out the possibility of a linguistic deficit as the underlying feature of timing inaccuracies during speech, this study examined intrinsic and extrinsic vowel duration effects in monosyllabic words produced by three children with sCAS, one child with phonologic delay (PD), two children with typical development (TD), and one adult. Results indicated that intrinsic and extrinsic influences on vowel durations were not categorically reduced in the participants with sCAS as compared to the children with TD and the adult; the participant with PD showed reduced evidence of these influences. This finding is compatible with the idea that temporal inaccuracies in sCAS are related to deficits in central timing, not linguistic representation.
Childhood apraxia of speech is a proposed disorder label referring to children who struggle with learning to speak, presumably due to difficulties with motor programming aspects of speech production processes. An underlying cause has not been identified. Because this disorder label is not universally accepted in research and clinical communities, the term "childhood apraxia of speech" is often qualified with the adjective "suspected," yielding the acronym "sCAS," which will be used throughout this paper.
While the disorder profiles found in the literature vary widely, a core set of characteristics is cited frequently and includes a limited phoneme inventory, frequent omission errors, vowel errors, inconsistency in error production, disordered prosody, increased errors with increased complexity of utterance, difficulty when imitating speech, predominance of simple syllable shapes, impaired oral motor skills, lower expressive vs. receptive language skills, and slower diadochokinetic rates (Davis, Jakielski and Marquardt, 1998). While subsets of these and other characteristics have been observed and described in children with sCAS, an unambiguous diagnostic marker has not yet emerged in clinical research.
In recent years, one line of research focused on the disordered prosody observed in children with sCAS, exploring the possibility of identifying a diagnostic marker in that domain. For instance, Shriberg, Aram and Kwiatkowski (1997a, b, c) suggested that a perceptual measure of disordered prosody on the level of lexical stress may be characteristic of sCAS or one of its subtypes. This perceptual measure is part of the Prosody-Voice Screening Profile (PVSP; Shriberg, Kwiatkowski and Rasmussen, 1990). The label "excessive/equal/misplaced" captures the percepts of "excessively forceful, punctuated monostress, misplaced word stress and/or sound blocks or prolongations" (McSweeney and Shriberg, 2001) under a single error code. Also investigating prosody as a potential diagnostic characteristic of sCAS, but focusing on aspects of prosody related to timing, Shriberg, Green, Campbell, McSweeny and Scheer (2003) described significant differences between children with sCAS, as compared to children with typical development and children with moderate to severe speech delay of unknown origin, when the variability of pause events and speech events was measured. Specifically, the participants with sCAS showed proportionally greater variability in their pause events and/or less variability in their speech events, when compared to the other two groups, leading the authors to suggest that constraints in speech timing may characterize children with sCAS.
The idea that a deficit in timing may transcend the domain of speech in individuals with a diagnosis of sCAS was investigated by Alcock, Passingham, Watkins and Vargha-Khadem (2000) in a study of family members diagnosed with "verbal dyspraxia." These authors studied prosodic errors during speech tasks as well as music-related tasks and found that timing accuracy in these individuals was affected during both speech and music tasks while pitch accuracy was intact during both types of activities.
Subsyllabic Component Durations in Three Children with Suspected Childhood Apraxia of Speech, Two Children with Typical Development, One Child with Phonologic Delay, and One AdultSubsyllabic Component Durations in Three Children with Suspected Childhood Apraxia of Speech, Two Children with Typical Development, One Child with Phonologic Delay, and One Adult
Department of Speech and Hearing Sciences