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Orofacial Movements Associated With Fluent Speech in Persons Who Stutter

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294 Journal of Speech, Language, and Hearing Research • Vol. 47 • 294–303 • April 2004Michael D. McCleanWalter Reed Army Medical Center,Washington, D.C.Stephen M. TaskoWestern Michigan University,Kalamazoo, MICharles M. RunyanJames Madison University,Harrisonburg, VAThis study was intended to replicate and extend previous findings that (a) duringfluent speech persons who stutter (PS) and those who do not (NS) differ in theirvocal tract closing movements (L. Max, A. J. Caruso, & V. L. Gracco, 2003) and(b) ratios relating lip and tongue speed to jaw speed increase with stutteringseverity (M. D. McClean & C. R. Runyan, 2000). An electromagnetic system wasused to record movements of the upper lip, lower lip, tongue, and jaw of 43 NSand 37 PS during productions of a nonsense phrase and a sentence. Measure-ment and analysis of movement speeds, durations, and ratios of lip and tonguespeed to jaw speed were performed on fluent productions of a nonsense phraseand sentence. Statistical comparisons were made between PS with low and highstuttering severity levels (LPS and HPS) and NS. Significant variations acrossgroups in movement speed and duration were observed, but the pattern of theseeffects was complex and did not replicate the results of the two earlier studies. Inthe nonsense phrase, significant reductions in lower lip closing duration, jawclosing duration, and jaw closing speed were seen in PS. In the sentence task,HPS showed elevated tongue opening and closing durations. For tongue openingin the sentence, LPS showed elevated speeds and HPS showed reduced speeds.The elevated speeds for LPS are interpreted as a contributing factor to speechdisfluency, whereas the reduced speeds and increased durations in HPS areattributed to adaptive behavior intended to facilitate fluent speech. Significantgroup effects were not seen for the speed ratio measures. Results are discussed inrelation to multivariate analyses intended to identify subgroups of PS.KEY WORDS: stuttering, orofacial movements, tongue, jaw, lipsOrofacial Movements AssociatedWith Fluent Speech in PersonsWho StutterJournal of Speech, Language, and Hearing Research • Vol. 47 • 294–303 • April 2004 • ©American Speech-Language-Hearing Association1092-4388/04/4702-0294Beginning primarily with the investigations of Zimmermann (1980a),there has been a continuing effort to characterize possible differ-ences in the movements underlying the fluent speech of personswho stutter (PS) and those who do not (NS) (Caruso, Abbs, & Gracco,1988; Kleinow & Smith, 2000; Max, Caruso, & Gracco, 2003; McClean &Runyan, 2000; Smith & Kleinow, 2000). This work has revealed moder-ate differences between PS and NS in a variety of kinematic measures.A central issue regarding interpretation of these findings was highlightedby Max et al., who pointed out that kinematic differences in PS and NSmay reflect acquired behaviors intended to enhance speech fluency, ormore general neuromotor mechanisms that are operative during speechand nonspeech movements. In support of the latter view, they presenteddata indicating differences between PS and NS in the characteristics offinger flexion movements and combined lip and jaw movements as theycontribute to vocal tract closing for speech and nonspeech oromotorMcClean et al.: Orofacial Movements and Stuttering 295behaviors. Max et al. interpreted these various results asreflecting differences between PS and NS in basic prop-erties of the general neuromotor system that are specificto vocal tract closing and limb flexion movements.An alternative perspective on kinematic differencesin speech between PS and NS is that they, in part, re-flect processes specific to the speech motor system of PSthat are intended to enhance speech fluency. Such pro-cesses are reflected in increased movement durationsin the fluent speech of PS following some forms of speechtherapy (McClean, Kroll, & Loftus, 1990; Samar, Metz,& Sacco, 1986; Story, Alfonso, & Harris, 1996). There isalso modest evidence that more severe PS who have notundergone therapy tend to display increased movementdurations and reduced velocities in their fluent speech(McClean, Kroll, & Loftus, 1991). This finding suggeststhat in some PS, childhood and/or adult experience withspeech disfluency promotes acquired adaptive behaviorsthat enhance fluent speech.In summary, initial findings on orofacial movementsduring fluent speech in adults suggest that differencesbetween NS and PS may reflect general motor systemproperties and/or acquired motor processes intended toenhance speech fluency. However, we are far from un-derstanding how these factors are realized in terms ofinherited traits and experiences that shape the speechmotor system in children and adults who stutter. It isour view that progress in this area will depend in parton more detailed information on differences in the kine-matics of fluent speech in adult NS and PS. Due to thevariable nature and modest size of reported differences,replication and refinement of certain studies are needed(Muma, 1993).One result we see as particularly important is thatof Max et al. (2003), which indicated differences betweenPS and NS in vocal tract closing but not opening move-ments. Specifically, they observed greater movementdurations and extents in PS compared to NS for vocaltract closing movements and no significant differencesin opening movements. This finding has broad implica-tions for both theory and clinical approaches to stutter-ing. Insofar as vocal tract opening and closing movementsinvolve distinct neuromotor mechanisms as suggestedby Max et al. (see also Gracco, 1994), solidification of theirfindings could speak directly to the nature of centralneural processes contributing to speech disfluency.Hence, the first major objective of this study was to rep-licate the observations of Max et al. regarding vocal tractclosing movements in PS and to assess whether relatedtrends vary with stuttering severity. Max et al. studiedcombined lip and jaw opening and closing movementsassociated with closure and release of bilabial stop con-sonants, where consonant position within utterances ofvarying length was systematically controlled. The speechsample used here was not specifically designed to repli-cate their method. Rather, the kinematic recordings froman existing dataset were used to evaluate the general-ity of their findings regarding group differences in vocaltract closing movements and the absence of


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