Labiodentalization of bilabial stops in spontaneous english smiled speech

Abstract

The co-occurrence of facial expressions and speech production presents a conflict of opposing muscular activation. Existing English research indicates a pattern of bilabial stops being resolved as labiodentals during smiled speech. Electromyographic data suggests that suppression is imposed on one muscle force to resolve the smiling-lip closure conflict [Liu et al., in ISSP Proceeding (2020), pp. 130–133]. These results have limited generalizability as data was collected from one speaker performing reading tasks under laboratory context. The present study continues the investigation of bilabial productions by investigating bilabial phonemes in spontaneous smiled speech. Natural speech samples from 16 native English speakers were extracted from YouTube interviews and vlogs. Bilabial phonemes in neutral and smiling conditions were analyzed for labiodentalization using facial imaging software. The intensity of Facial Action Units (FAU) “lip corner puller” and “lip tightener” during labial token productions were examined. Results show that labiodentalized variants of bilabial tokens also occurred during natural smiled speech. FAU intensity measurements indicate lower “lip corner puller” intensity during bilabial closures than labiodental ones when smiling. This suggests that smile suppression was observed when lip closure was prioritized, validating earlier laboratory conclusions that selective muscular suppression is utilized in the resolution of conflict between articulators.