Tongue-jaw coordination in vowel production: Isolated words versus connected speech

Abstract

This study investigates the positions of the tongue body and the jaw in the production of Italian vowels /i/ and /a/ in different phonetic, prosodic and utterance contexts, with the aim of assessing the role of and the coordination between the two articulators in the processes of coarticulation, reduction and compensation. The data indicate that, within the same phonetic context, a change in utterance type (from isolated words to words in connected speech) or in lexical stress position (from stressed to unstressed vowels) induces decreased displacement of the jaw and the tongue from their rest position along the high/low dimension for both vowels. Thus prosodic and utterance contexts induce vowel reduction through a decrease in displacement of both jaw and tongue. Variation in vowels as a function of the consonantal context (/t,d,z,f,l/) was observed in jaw displacements only in the front/back dimension: vowels were more fronted when adjacent to fricatives. All the other coarticulatory effects concern tongue body movements and tend to increase, as does reduction, from isolated words to connected speech. In symmetric VCV sequences extensive compensatory tongue displacements in the back direction were observed during the production of reduced /a/ vowels: thus, if vowel reduction causes a decrease in the articulatory distance between /i/ and /a/ along the high/low dimension, this compensatory tongue movement appears to counteract such effect by increasing the articulatory distance along the front/back dimension. In asymmetric sequences, the V-to-V effects seem to overrule the compensatory movements, and, adding to the reduction effects, cause a further decrease in the articulatory distance between the two vowel types.