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Speech Rhythm in American English: A Corpus Study
Doctoral Committee Chair(s)
Department of Study
Degree Granting Institution
University of Illinois at Urbana-Champaign
This dissertation investigates speech rhythm in American English based on the speech from the Boston University Radio News corpus, comparing the patterns of rhythmic shortening in two different types of prosodic domains, the ISI (inter-stress interval) and the IAI (inter-accent interval). The main finding is evidence for rhythmic shortening in the domain defined in terms of lexical stress: the duration of vowels (especially stressed vowels) decreases as the size of the ISI increases. Another important finding is that shortening of vowels occurs only when the ISI is inside the intermediate phrase. A comparison of the effects of ISI size and word size further demonstrates that rhythmic shortening in American English operates only at the ISI level, not at the word level. Based on these findings, we conclude that the ISI, a unit headed by lexical stress, is the basic rhythmic unit in American English, and rhythmic regularization in American English is manifested not in terms of isochronous ISI duration, but through an adjustment of the duration of stressed vowels. Furthermore, it is shown that the intermediate phrase plays a characteristic role as a bounding domain of rhythmic shortening in American English. This study confirms that the ISI (as a representative of metrical foot structure) and the intermediate phrase are phonological units that should be encoded in the grammar of prosody in American English.