Laryngeal-acoustic relations in smiled speech

Smiling is a social signal that can be both seen and heard. Smiling can increase speech amplitude and raise F0 and formants. However, experimental research on the role of larynx height in smiled speech is limited. 21 English speakers (6 M) repeated words in a carrier phrase with a neutral face or while smiling. The participants were recorded with audio, video and laryngeal ultrasound. F0, F1 and F2 were extracted for the duration of target vowels /i/, /u/ and /a/. Ultrasound images of laryngeal position were measured using Optical Flow. The laryngeal and acoustic data were analyzed in R with linear mixed models with smiling condition, timepoint-in-vowel, and gender as fixed effects. There was a significant effect of timepoint-in-vowel for larynx height (raising towards the end) and a smile-timepoint interaction effect (the larynx raised more at the end for smiling condition). Acoustically, smiling led to significantly higher F0 across vowels, and significantly higher F1 and F2 for /a/ but not /i/ or /u/. F2 timepoints were significant for all three vowels (F2 trajectories differed) across smile conditions. Results indicate smiling has a consistent effect on larynx height and variable effect on specific speech sounds.