Effect of syllable onset, coda, and nucleus on degree of skin stretching over the mandible

Movements of the mandible have been shown to correlate with English speech rhythm, and significant differences have been found between native speakers' mandible movements and those of second-language speakers. A simple, inexpensive method of inferring movements of the mandible is to use video tracking of a chin marker during speech. However, since the skin is free to stretch over the mandible, inferences using the chin marker may not always be accurate. This study examines the degree of skin stretching during vowel production in 18 different CVC syllables (using 3 different stop consonants and 2 different vowels) spoken as the middle word in a 3-word utterance. We made electromagnetic articulometer (EMA) recordings of two North American English speakers (1 male, 1 female). The distance was measured between coils placed on the lower incisor and on the skin of the mental protruberance (chin). For both speakers, the distance significantly differed depending on the vowel. The onset C affected the distance for only the female speaker. The coda C did not significantly affect the distance for either speaker. These results need to be taken into account as we continue to develop a method for video recording jaw displacement patterns in running speech.