Clinical Linguistics & Phonetics
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This article was downloaded by:[Macquarie University] [Macquarie University] On: 9 July 2007 Access Details: [subscription number 778261146] Publisher: Informa Healthcare Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Clinical Linguistics & Phonetics Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713693308 A diagnostic marker for childhood apraxia of speech: the lexical stress ratio Lawrence D. Shriberg a; Thomas F. Campbell b; Heather B. Karlsson a; Roger L. Brown c; Jane L. Mcsweeny a; Connie J. Nadler a a Waisman Center, University of Wisconsin-Madison. WI. USA b Children's Hospital of Pittsburgh. Pittsburgh, PA. USA c Research Design and Statistics Unit, School of Nursing, University of Wisconsin-Madison. WI. USA Online Publication Date: 01 October 2003 To cite this Article: Shriberg, Lawrence D., Campbell, Thomas F., Karlsson, Heather B., Brown, Roger L., Mcsweeny, Jane L. and Nadler, Connie J. , (2003) 'A diagnostic marker for childhood apraxia of speech: the lexical stress ratio', Clinical Linguistics & Phonetics, 17:7, 549 - 574 To link to this article: DOI: 10.1080/0269920031000138123 URL: http://dx.doi.org/10.1080/0269920031000138123 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. © Taylor and Francis 2007 CLINICAL LINGUISTICS & PHONETICS, 2003, VOL. 17, NO. 7, 549–574 A diagnostic marker for childhood apraxia of speech: the lexical stress ratio LAWRENCE D. SHRIBERG {,THOMASF. CAMPBELL §, HEATHER B. KARLSSON {, ROGER L. BROWN {,JANEL.MCSWEENY{ and CONNIE J. NADLER { { Waisman Center, University of Wisconsin-Madison, WI, USA { Research Design and Statistics Unit, School of Nursing, University of Wisconsin-Madison, WI, USA § Children’s Hospital of Pittsburgh, Pittsburgh, PA, USA (Received 12 August 2002; accepted 30 October 2002) Abstract This report includes an extended review of the contemporary inclusionary criteria used to identify children with suspected apraxia of speech (sAOS) and Downloaded By: [Macquarie University] At: 06:46 9 July 2007 describes findings supporting a lexical stress marker for sAOS. The thesis is that although a deficit in speech praxis is the core disorder in sAOS, only a few diagnostic markers for sAOS assess this speech motor control construct. The proposed marker is a composite lexical stress ratio (LSR) that quantifies the acoustic correlates of stress (frequency, intensity, duration) in bisyllabic word forms. Responses to a lexical stress task were obtained from 35 participants referred for a study of apraxia of speech. Eleven of the children were classified as sAOS, because they met one or both of two investigator groups’ provisional criteria for sAOS. The 24 remaining children who did not meet either group’s criteria were classified as having speech delay (SD). The first question posed was whether the LSR scores of children with sAOS differed from those of children with SD. Findings were affirmative. Of the six LSRs at the upper and lower extremes of the obtained distributions of LSR scores (approximately 8% of scores at each end), five (83%) were from speakers with sAOS (pv0.003). The second question was whether findings for the sAOS speakers were more consistent with deficits in speech motor control or with deficits in underlying phonological representational aspects of lexical stress. A parsimonious inter- pretation of the present findings, together with findings from other studies, suggests that they reflect the prosodic consequences of a praxis deficit in speech motor control. Keywords: Assessment, diagnosis, praxis, lexical stress, speech disorders Address correspondence to: Lawrence D. Shriberg, Phonology Project, Waisman Center, University of Wisconsin-Madison, 1500 Highland Avenue, Madison, WI 53705, USA. e-mail: [email protected]; website: http://www.waisman.wisc.edu/phonology/index.htm Clinical Linguistics & Phonetics ISSN 0269-9206 print/ISSN 1464-5076 online # 2003 Taylor & Francis Ltd http://www.tandf.co.uk/journals DOI: 10.1080/0269920031000138123 550 L. D. Shriberg et al. Introduction The goal of the present and a companion study (Shriberg, Green, Campbell, McSweeny and Scheer, 2003) is to identify diagnostic markers for children whose significant speech disorders are due to a deficit in speech praxis. The following extended overviews provide the empirical background and methodological rationales for the study to be reported. To accommodate nosological needs reviewed elsewhere (Shriberg, Aram and Kwiatkowski, 1997a; Odell and Shriberg, 2001), four terms will be used as follows: (a) apraxia of speech refers to the construct of a speech disorder due to impaired praxis; (b) the capitalized and abbreviated term Apraxia of Speech (AOS) refers to the acquired form in adults or children; (c) the capitalized and abbreviated term Childhood Apraxia of Speech (CAS) is reserved for children considered true positives for a developmental form of apraxia of speech; and (d) the capitalized and abbreviated term suspected Apraxia of Speech (sAOS) is used for children whose speech and prosody-voice error patterns, performance on non-speech tasks and/or case histories are consistent with apraxia of speech. No conceptual or clinical distinctions are intended by use of the term apraxia rather than dyspraxia in these four classifications. Research overview Downloaded By: [Macquarie University] At: 06:46 9 July 2007 Behavioural studies A review of English language journals indicates that over 75 case study reports and case-control studies of children with sAOS have been published in the past approximately 50 years. Secondary sources that provide reviews of this literature over the past three decades include Morley (1972), Yoss and Darley (1974), Guyette and Diedrich (1981), Thompson (1988), Stackhouse (1992), Crary (1993), Hall, Jordan and Robin (1993), Velleman and Strand (1994), Ozanne (1995), Shriberg et al. (1997a, c), McCabe, Rosenthal and McLeod (1998) and Caruso and Strand (1999). The goals of descriptive-explanatory studies are to explicate the proximal speech processes underlying apraxia of speech and to speculate on its possible distal etiology, pathophysiology, and implications for treatment. Statistical analyses for descriptive-explanatory goals have typically emphasized tests linking the variable under study with speech processing variables in a number of domains and disciplines (e.g. descriptive linguistic, psycholinguistic, neurolinguistic, speech motor control). There have been few programmatic research findings with sufficient empirical support for theoretical convergence. Rather, the interpretation of descriptive and explanatory findings from the many isolated case studies and case-control reports must be evaluated on their individual conceptual coherence. Evaluative reviews of this body of literature have uniformly concluded that there is little consensus either on the complex of behaviours that defines the disorder or on the explanatory framework that best accounts for its occurrence and natural history. Genetic studies A few behavioural and molecular genetic studies have also used a form of case- control design for descriptive-explanatory research in sAOS. Cases have been The lexical stress ratio in childhood AOS 551 identified by the same sets of inclusionary and exclusionary criteria used in non- genetic designs, but controls are the non-affected relatives of the proband (the index case) and non-affected children and their families matched sociodemographically to proband families. In contrast to the limited number of substantive findings in the sAOS designs referenced above, findings from several programmatic genetic studies offer the promise of an eventual neurobiological account of this disorder. The major ongoing source of neurobiological information is the study series describing a multigenerational British family, half of whose members have an orofacial apraxia and a speech-language disorder. Molecular genetics findings to date include the identification of a susceptibility gene (FOXP2) that co-segregates with the orofacial apraxia and is inherited as an autosomal dominant trait (Lai, Fisher, Hurst, Levy, Hodgson, Fox, Jeremiah, Povey, Jamison, Green, Vargha- Khadem and Monaco, 2000; Lai, Fisher, Hurst, Vargha-Khadem and Monaco, 2001). Neuroimaging and psycholinguistic studies have yielded a number of candidate speech processing loci for the orofacial apraxia, and by inference, for the pattern of speech errors that are presumed to be specific for developmental apraxia of speech (Vargha-Khadem, Watkins, Alcock, Fletcher and Passingham, 1995; Vargha-Khadem, Watkins, Price, Ashburner, Alcock,