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Purpose: To investigate the hypothesis that vowel production is more variable in adults with acquired apraxia of speech (AOS) relative to healthy individuals with unimpaired speech. Vowel formant frequency measures were selected as the specific target of focus.
Method: Seven adults with AOS and aphasia produced 15 repetitions of 6 American English vowels in /hVC/ context (hid, head, hat, hot, hub, hoot). Vowel formant frequency measures (F1, F2) were Bark transformed and compared with data from archival sources.
Results: Measures of vowel acoustics in speakers with AOS did not differ from those of unimpaired speakers, including absolute Bark formant values, vowel space area, intervowel distance, and individual trial-to-trial formant variability.
Conclusion: Comparison with normative acoustic measures suggested that vowel production at the word level is unimpaired in the current speakers with AOS, supporting previous studies that have shown vowel production is relatively intact in AOS.
KEY WORDS: apraxia of speech, acquired, acoustic, vowel, aphasia
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Apraxia of speech (AOS) is a speech motor control disorder that results from acquired neurological damage, usually to the left inferior frontal cortex (McNeil, Robin,&Schmidt, 2008; see Robin, Jacks, & Ramage, 2008, for a review of neuroimaging studies in AOS). The disorder is thought to be characterized by inefficient translation of intact phonological representations into appropriate spatiotemporal parameters of articulatory movements (McNeil et al., 2008) and may occur in the absence of neuromuscular and linguistic impairments. Speech production in AOS is marked by articulatory distortions, lengthened speech segment and intersegment durations, and prosodic abnormality (Wambaugh, Duffy, McNeil, Robin,&Rogers, 2006). Other characteristics include consistent speech error types (e.g., distortions, substitutions) and invariable error locations (McNeil et al., 2008; Wambaugh et al., 2006; cf. Shuster & Wambaugh, 2008).
Speech Variability in AOS
Speech variability is a potentially important clinical marker for AOS (Darley, Aronson, & Brown, 1975; Johns & Darley, 1970; LaPointe & Horner, 1976), but definitions of variability have not been consistently applied, leading to difficulty in data interpretation (see Miller, 1992, regarding definitions of variability). Studies of phonetic variability (based on phonetic transcription) have found consistent speech error types and invariable error locations (McNeil, Odell, Miller, & Hunter, 1995, although cf. Shuster&Wambaugh, 2008); specifically, the phrase consistency of error types refers to evidence that speakers...