The nature of theme and rheme accents

Abstract

It has increasingly been recognised that appropriate intonation is essential to create believable voices for speech synthesis. This is particularly true in dialogue, where the link between intonation and meaning is especially important. Here we report two experiments, a production and perception study, which test an aspect of Steedman's (2000) theory relating information and intonation structure with a view to specifying intonation in a speech synthesis system. He claims that themes and rhemes, the basic building blocks of information structure, are marked by distinctive pitch accents in English, which he identifies with L+H* and H* in the ToBI system respectively. After reviewing problems with the identification of these ToBI accents, we show that speakers do produce and listeners do distinguish different pitch accents in these discourse contexts, but that the ToBI labels may not be helpful to characterise the distinction. The exact phonetic nature of theme and rheme accents remains unclear, but the alignment of the start of the rise, pitch height and the fall after the pitch peak all appear to be factors. Speakers also appear to be more sensitive to the distinction at the end of an utterance than utterance-medially.