Cheng, Hei Yan (2007). A PHYSIOLOGIC INVESTIGATION OF SPEECH MOTOR DEVELOPMENT PhD Thesis, School of Health and Rehabilitation Sciences, University of Queensland.

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Author Cheng, Hei Yan
School, Centre or Institute School of Health and Rehabilitation Sciences
Institution University of Queensland
Publication date 2007
Thesis type PhD Thesis
Supervisor Professor Bruce Murdoch
Abstract/Summary To date, very little is known about the physiologic development of speech production. Information pertaining to tongue movements during speech in children and adolescents is particularly scarce. An improved understanding of the fundamental motor processes for speech will remarkably strengthen our ability to differentially diagnose and treat a number of speech and language disorders in chldren and adolescents. Using advanced instrumental techniques, this thesis aimed to comprehensively examine the developmental process of tongue movement during speech production over the age span of 6 years to adulthood. A total of 48 speakers participated in the current investigations, with six males and six females in each of the following age groups: (i) aged 6- to 7-years; (ii) 8- to 11- years; (iii) 12- to 17-years; and (iv) adults. All participants were native speakers of Australian English and achieved within age appropriate ranges on a battery of speech and oral motor tests. Two physiological assessments, electropalatography (EPG) and electromagnetic articulography (EMA), were conducted to determine the spatial and temporal characteristics and stability of tongue-tip and tongue-body speech movements in developing speech motor systems. EPG recorded details of the tongue motion and contact at the hard palate during production of lingual consonants. With age, there was a reduction of tongue-to-palate contact and an anterior shfi in the place of articulation for alveolar and post-alveolar sounds. Maturation of the velar consonant, in contrast, was primarily marked by greater stability of tongue-to-palate contact. In the timing domain, duration of the consonant closure phase (i.e., when the tongue is in direct contact with the palate) reduced with age, although no changes in duration variability was seen. A concurrent trend of declining duration and duration variability over entire sentences was also identified. Development of tongue-tip - tongue-body coordination was inferred fiom EPG examination of the transition of velar - alveolar articulatory gestures (i.e., during production of the /kl/ consonant cluster). With advanced motor control, older speakers demonstrated more coherently organized gestures within a phonetic sequence and increased differentiation of tongue-tip - tongue-body movement, resulting in phonetic segments that were more distinct and precisely timed. As EPG assessment focused primarily on tongue-to-palate contacts in speech production, EMA was used to identify changes in tongue motion (i.e., movement distance, duration, speed, acceleration and deceleration) in the closing and opening segments of lingual consonant production. In general, it was found that closing and opening durations decreased across the age spans studied; however, changes in movement distance, speed, acceleration and deceleration were less consistently observed. In contrast, the token-to-token variation for each parameter declined as a function of age. Additionally, adults continued to exhibit more stable spatiotemporal patterning of their tongue movements during sentence production compared to both children and adolescents. Lastly, given that the tongue and jaw appear to be closely related in speech motor development, EMA was used to examine the kinematic coordination of the two articulators during consonant production. Interestingly, development of tongue-tip and jaw coordination for speech was manifested in more tightly synchronized movements. In contrast, with maturity, tongue-body and jaw retained movement independence but developed a more consistent kinematic relationship from trial-to-trial. The present EPG and EMA findings suggested that continual, though nonlinear and nonuniform, changes are occurring in the speech motor system from 6 years, to adolescence, and into adulthood.

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Created: Fri, 21 Nov 2008, 16:00:33 EST