Communication Disorders Ph.D. Dissertations

The Aerodynamic, Glottographic, and Acoustic Effects of Clear Speech

Date of Award


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Communication Disorders

First Advisor

Ronald Scherer (Committee Chair)

Second Advisor

Steven Boone (Other)

Third Advisor

Brent Archer (Committee Member)

Fourth Advisor

Jason Whitfield (Committee Member)


This dissertation investigated aerodynamic, glottographic, and acoustic differences between habitual and clear speech. Nine normal-speaking individuals (five cis female, 4 cis male) were asked to read six short sentences in four reading conditions: habitual reading, habitual reading while holding a mask to the face to capture airflow and oral air pressure, clear reading, and clear reading while holding the mask to the face. Mask-off conditions in both habitual and clear reading manners were used for acoustic analyses, and mask-on conditions were used for aerodynamic and glottographic analyses. The instruction for eliciting habitual speech was “Read each sentence as if you are talking with a friend across the table.” The instruction for eliciting clear speech was “Read the sentences as clearly as possible by enunciating well, as if someone is having trouble understanding you.” Acoustic and time-related results indicated that from habitual to clear speech: (1) sentence duration increased, (2) speaking rate decreased, (3) duration of stressed vowels and unvoiced fricatives increased, (4) voice onset time increased for some unvoiced plosives, (5) stop gap duration increased, (6) fundamental frequency did not change except for two stressed vowels in female speakers for which fo increased, and (7) intensity of stressed vowels and stop consonants increased, but not for unvoiced fricatives (except for /ʃ/). Aerodynamic results indicated that from habitual to clear speech, there was greater (1) oral air pressure, (2) average airflow, (3) total air volume, and (4) peak flow during the release of the voiceless bilabial stop, suggesting the influence of greater subglottal pressure. In contrast, there was little to no change in glottal dynamics such as EGG width, EGG height, EGG contact and open quotients, and glottal airflow timing measures. In this study, it might be inferred that clear speech was a phenomenon that is more related to subglottal pressure and oral cavity kinematics than to vocal fold adduction and vibratory dynamics.