The primary characteristics considered to define acquired apraxia of speech (AOS) have continued to evolve, but a few characteristics remain controversial among researchers and clinicians (McNeil, Robin, & Schmidt, 2009). Particularly, the consistency or variability of speech sound errors in AOS (Croot, 2002). For years, variability of speech sound errors has been considered a primary characteristic of AOS (Deal & Darley, 1972; Johns & Darley, 1970; Wertz, LaPointe, & Rosenbek, 1984). Apraxic errors were considered to be variable with regard to the location of the error within a word (Johns & Darley; LaPointe & Johns, 1975) and the nature of the error (Johns & Darley; LaPointe & Horner, 1976) across repeated productions of the same stimuli.Conversely, more recent research with “pure” apraxic speakers and speakers with AOS and accompanying aphasia has suggested that speech sound errors may not be variable (Mauszycki, Dromey, & Wambaugh, 2007; Mauszycki, Wambaugh, & Cameron, 2010a, 2010b; Mlcoch, Darley, & Noll, 1982; McNeil, Odell, Miller, & Hunter, 1995; Shuster & Wambaugh, 2003; Wambaugh, Nessler, Bennett & Mauszycki, 2004). However, there are limited data examining sound errors over time (i.e., beyond a single session). Furthermore, the influence of conditions of stimuli presentation on sound errors remains uncertain.The purpose of this investigation was to further examine variability of speech production in individuals with AOS and aphasia. Of specific interest were the effects of repeated sampling and conditions of stimulus presentation (i.e., random and blocked by sound) on the variability of error types identified using narrow phonetic transcription.
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