Relationship Between Jaw Opening and Phonetic Complexity: A Cross-Language Study

The current study employs a simultaneous cross-system monitoring technique to examine the impact of jaw opening on articulatory and vocal behaviours. The purpose of the study is to determine whether an increased jaw opening posture can improve speech and voice quality in a variety of phonetic contexts. Participants were 20 healthy non-smoking adults, including 10 New Zealand English (Mean = 36.5 years, SD = 14) and 10 Mandarin (Mean = 27.5 years, SD = 9.3) native speakers, with five females and five males in each group. Participants were asked to say, with and without an exaggerated jaw opening posture, monosyllabic consonant-vowel (CV) couplets which contained a vowel (/i/, /a/, or /u/) and a consonant selected from the phonemes in their native language. Signals recorded with the acoustic, electroglottographic (EGG), and marker-based video tracking devices were analyzed to yield (i) acoustic measures, including consonant length, fundamental frequency (F0), percent jitter (%jitter), percent shimmer (%shimmer), signal-to-noise ratio (SNR), and frequencies of Formants One and Two (F1 and F2), (ii) EGG measures, including open quotient and speed quotient, and (iii) maximum jaw displacement. A series of two-way Analysis of Variances (ANOVAs) and repeated measures ANOVAs were conducted on the experimental measures to determine whether there was an effect of task (normal vs. exaggerated jaw opening), language (English vs. Mandarin), consonant, or tone (Tones 1 to 4, for the Mandarin group only). Results showed that an exaggerated jaw opening posture resulted in an expansion of vowel space (as shown in the F1-F2 plot for vowels /i/, /a/, and /u/), increased F0, and positive changes in phonatory stability, including decreased %jitter and %shimmer and increased SNR. These findings highlighted the importance of jaw manipulation in speech treatment and supported the hypothesis that an open mouth approach was useful for speech and voice enhancement, suggesting that jaw opening had a universal effect of reducing phonetic complexity. In addition, some changes of the experimental measures were also shown to be a function of language, consonant, and tone