The Role of Visibility in Silent Speech Tongue Movements: A Kinematic Study of Consonants

Abstract

Purpose To better understand the role of tongue visibility in speech, this study compared the spatiotemporal patterns of silent versus audible speech for lingual consonants of American English. Kinematic data were obtained for articulatory features assumed to be visually salient, including tongue movement (anterior displacement and midsagittal area), lip aperture, and consonant duration. Method Electromagnetic articulography was used to measure 11 native speakers' productions of five consonants (/ɡ/, /w/, /ɹ/, /l/, and /ð/), selected to represent a continuum of tongue visibility. Nonword consonant–vowel syllables were elicited during a procedure designed to convey a dyadic communication environment. A method of kinematic-based consonant segmentation was developed for data processing, and results were analyzed with repeated-measures analysis of variance. Results Findings indicated increased consonant duration and lip aperture in the silent condition (vs. audible) for all five consonants. Tongue forward displacement was slightly greater in the silent condition, compared to audible, for all consonants except /ɡ/, the only consonant without a visible tongue component. In addition, the extent of tongue forwarding in silent speech corresponded with the degree of tongue visibility. Conclusion During silent speech, talkers increased their lip aperture and consonant duration and tended to shift their tongues forward for the most visible lingual consonants, suggesting that talkers may be aware at some level of the need to increase articulatory visibility of the tongue in the presence of an interlocutor during adverse speech conditions.