An Investigation of Coarticulation Resistance in Speech Production Using Ultrasound
Zharkova, N. (2007) An Investigation of Coarticulation Resistance in Speech Production Using Ultrasound, no. 329.
Sound segments show considerable influence from neighbouring segments, which is described as being the result of coarticulation. None of the previous reports on coarticulation in vowel-consonant-vowel (VCV) sequences has used ultrasound. One advantage of ultrasound is that it provides information about the shape of most of the midsagittal tongue contour. In this work, ultrasound is employed for studying symmetrical VCV sequences, like /ipi/ and /ubu/, and methods for analysing coarticulation are refined. The use of electropalatography (EPG) in combination with ultrasound is piloted in the study. A unified approach is achieved to describing lingual behaviour during the interaction of different speech sounds, by using the concept of Coarticulation Resistance, which implies that different sounds resist coarticulatory influence to different degrees. The following research questions were investigated: how does the tongue shape change from one segment to the next in symmetrical VCV sequences? Do the vowels influence the consonant? Does the consonant influence the vowels? Is the vocalic influence on the consonant greater than the consonantal influence on the vowels? What are the differences between lingual and non-lingual consonants with respect to lingual coarticulation? Does the syllable/word boundary affect the coarticulatory pattern? Ultrasound data were collected using the QMUC ultrasound system, and in the final experiment some EPG data were also collected. The data were Russian nonsense VCVs with /i/, /u/, /a/ and bilabial stops; English nonsense VhV sequences with /i/, /u/, /a/; English /aka/, /ata/ and /iti/ sequences, forming part of real speech. The results show a significant vowel influence on all intervocalic consonants. Lingual consonants significantly influence their neighbouring vowels. The vocalic influence on the consonants is significantly greater than the consonantal influence on the vowels. Non-lingual consonants exhibit varying coarticulatory patterns. Syllable and word boundary influence on VCV coarticulation is demonstrated. The results are interpreted and discussed in terms of the Coarticulation Resistance theory: Coarticulation Resistance of speech segments varies, depending on segment type, syllable boundary, and language. A method of quantifying Coarticulation Resistance based on ultrasound data is suggested.