The Intonational Structuring of Discourse

THE INTONATIONAL STRUCTURING OF DISCOURSE Julia Hirschberg and Janet Pierrehumbert AT&T Bell Laboratories 600 Mountain Avenue Murray Hill NJ 07974 USA ABSTRACT We propose a mapping between prosodic phenomena and semantico-pragmatic effects based upon the hypothesis that intona- tion conveys information about the intentional as well as the atten- tional structure of discourse. In particular, we discuss how varia- tions in pitch range and choice of accent and tune can help to con- vey such information as: discourse segmentation and topic struc- ture, appropriate choice of referent, the distinction between 'given' and 'new' information, conceptual contrast or parallelism between mentioned items, and subordination relationships between proposi- tions salient in the discourse. Our goals for this research are prac- tical as well as theoretical. In particular, we are investigating the problem of intonational assignment in synthetic speech. 1. Introduction The role of prosody in discourse has been generally ack- nowledged but little understood. Linguistic pragmaticists have noted that types of information status (such as glven/new, toplc/comment, focus/presupposition) can be intonationally 'marked' [1,2,3,4], that reference resolution may depend criti- cally on intonation [5, 6], that intonation can be used to disambigu- ate among potentially ambiguous utterances [7,8], and that indirect speech acts may be signalled by intonational means [9,10,11]. Conversational analysis of naturally occurring data has found that speakers may signal topic shift, digression, and interruption, as well as turn-taking, intonation- ally [12, 13, 141 . And the fact that intonational contours contribute in some way to utterance interpretation is itself unexception- able [8]. To date, however, identification of the prosodic phenomena involved -- and the proper mapping between thcse phenomena and their semantico-pragmatic effects -- has been largely intuitive, and the intonational phenomena involved have not been precisely described. Here, we describe how certain of the resources of the intona- tional system are employed in discourse. In particular, we discuss how speakers' choice of pitch range, accent, and tune contribute to the intentional and attentlonal structuring of discourse -- the way speakers communicate the relationships among their discourse goals and the relative salience of entities, attributes, and relation- ships mentioned in the discourse) Our findings emerge from an intensive study of a simple example of speech synthesis: the script of a computer-aided instruction system, TNT (Tutor 'n' Trainer) [16], which employs synthetic speech to tutor computer novices in the text editor vi. Using the Text to Speech system (TTS) i17], we have been able, by systematic variation of pitch 1. Grosz and Sidaer [15] propose a tripartite view of discourse structure: a llngnlstlc structure, which is the text/speech itself; an attentlonal struc- ture, including information about the relative salience of objects, properties, relations, and intentions at a given point in the discourse; and an Intentional structure, which relates dlscourse segment purposes (those purposes whose recognition is essential to a segment achieving its intended effect) to one another. range and by a principled choice of accent and tune, to highlight the structure of the tutorial text and thus to enhance its coherence. …

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