Prosodic and lexical indications of discourse structure in human-machine interactions

From a discourse perspective, utterances may vary in at least two important respects: (i) they can occupy a different hierarchical position in a larger-scale information unit and (ii) they can represent different types of speech acts. Spoken language systems will improve if they adequately take into account both discourse segmentation and utterance purpose. An important question then is how such discourse-structural features can be detected. Analyses of monologues and human-human dialogues have shown that a good indicator of these factors is prosody, defined as the set of suprasegmental speech features. This paper explores whether speakers also use prosody to highlight discourse structure in a particular type of human-machine interaction, viz., information query in a travel-planning domain. More specifically, it investigates if speakers signal (i) the start of a new topic by marking the initial utterance of a discourse segment, and (ii) whether an utterance is a normal request for information or part of a correction sub-dialogue. The study reveals that in human-machine interactions, both discourse segmentation and utterance purpose can have particular prosodic correlates, although speakers also mark this information through choice of wording. Therefore, it is useful to explore in the future the possibilities of incorporating prosody in spoken language systems as a cue to discourse structure.