Prosodic Influences on the Acoustics of Vowel Sequences

Abstract

This dissertation examines prosodic influence on the acoustic properties of tautosyllabic vowel sequences (TVS) using acoustic data. The analyses focused on how the duration of the TVS, the excursion of the formants, and the movement of the TVS are influenced by prosodic boundaries that follow the speech sound. The prosodic structure is understood as an abstract hierarchical structure of prosodic phrasing in this research. At the boundaries of prosodic constituents, prosodic phrase boundaries introduce systematic phonetic variation in the temporal and spatial properties of segments. Four different TVS (/ai, au, ae, ou/) in three languages with different prosodic characteristics (Chinese as a tone language, English as a stress language, and Japanese as a language with mora as its basic prosodic unit) were investigated. This research serves as the first research to cross-linguistically study how TVS are influenced by prosodic structure.

The results show that first, the pre-boundary lengthening is confirmed in all three languages but implemented differently cross-linguistically. Chinese TVS were less affected by prosody than those in English and Japanese. Monophthongs are less lengthened than TVS pre-boundarily. However, the difference between the lengthening of monophthongs and TVS is yet unclear.

Second, TVS are hyperarticulated by prosodic boundaries with more extreme acoustic properties indicating enhancement of the distinctive features of the vocalic targets. Japanese TVS are different than those in Chinese and English in that the onset vocalic targets are also influenced by prosodic boundaries while the onsets of those in Chinese and English are not. This suggests that in Japanese TVS, the first vocalic target is more salient than in Chinese and English.

Third, the strategy of modulation on the TVS trajectory in the F1/F2 vowel space mainly involved stiffness reduction and target rescaling. This is somehow different than the result reported in the literature of articulatory study on pre-boundary strengthening since stiffness reduction has been found to be the major strategy in pre-boundary prosodic modulation. This result suggests a discrepancy between the acoustic and the articulatory domain.

In general, this dissertation demonstrated that TVS is influenced by prosodic structures, although the effect differs for languages and specific TVS. The effect is slightly different than those on monophthongs, and those found in the articulatory study.