Date of Degree

9-2018

Document Type

Dissertation

Degree Name

Ph.D.

Program

Speech-Language-Hearing Sciences

Advisor

Douglas H. Whalen

Committee Members

Raymond D. Kent

Erika S. Levy

Klara Marton

Subject Categories

Speech and Hearing Science | Speech Pathology and Audiology

Keywords

Down syndrome, Ultrasound, Vowels, Acoustics, Speech intelligibility

Abstract

The present study investigated the articulatory and acoustic characteristics of vowel production in individuals with Down syndrome (DS). Speech production deficits and reduced intelligibility are consistently noted in this population, attributed to any combination of phonological, structural, and/or motor control deficits. Speakers with DS have demonstrated impaired vowel production, as indicated by perceptual, acoustic, and articulatory data, with emerging evidence of vowel centralization. Participants in the study included eight young adults with DS, as well as eight age- and gender-matched controls. Ultrasound imaging was utilized to obtain midsagittal tongue contours during single-word productions, specifically targeting the corner vowels /ɑ/, /æ/, /i/, and /u/. Measurements of tongue shape, as related to its curvature and vowel differentiation, were calculated and contrasted between the participant groups. Acoustic measures of vowel centralization and variability of production were applied to concurrent vowel data. Single-word intelligibility testing was also conducted for speakers with DS, to obtain intelligibility scores and for analysis of error patterns.

Results of the analyses demonstrated consistent differentiation for low vowel production between the two speaker groups, across both articulatory and acoustic measures. Speakers with DS exhibited reduced tongue shape curvature and/or complexity of low vowels /ɑ/ and /æ/, and high-vowel /u/, than did TD speakers, as well as some evidence of reduced differentiation between tongue shapes of all four corner vowels. Acoustic analysis revealed a lack of group differentiation across some metrics of vowel centralization, while a reduction in acoustic space dispersion from a centroid was demonstrated for the low vowels in speakers with DS. Increased variability of acoustic data was also noted among speakers in the DS group in comparison to TD controls. Single-word intelligibility scores correlated strongly with measures of acoustic variability among speakers with DS, and moderately with measures of articulatory differentiation. Clinical implications, as related to understanding the nature of the impairment in DS and effective treatment planning, are discussed.

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