Now Let’s Talk About Now; Identifying Cue Phrases Intonationally

NOW LET'S TALK ABOUT NOW: IDENTIFYING CUE PHRASES INTONATIONALLY Julia Hirschberg AT&T Bell Laboratories Murray Hill, New Jersey 07974 Diane Litman AT&T Bell Laboratories Murray Hill, New Jersey 07974 ABSTRACT Cue phrases are words and phrases such as now and by the way which may be used to convey explicit information about the structure of a discourse. However, while cue phrases may convey discourse structure, each may also be used to different effect. The question of how speakers and hearers distinguish between such uses of cue phrases has not been addressed in discourse studies to date. Based on a study of now in natural recorded discourse, we pro- pose that cue and non-cue usage can be distinguished into- nationally, on the basis of phrasing and accent. I. Introduction Cue phrases are linguistic expressions -- such as okay, but, now, anyway, by the way, in any case, that reminds me -- which may, instead of making a 'semantic' contribution to an utterance (i.e., affecting its truth conditions), be used to convey explicit information about the structure of a discourse [4], [16], [5]. 1 For example, anyway can indi- cate a topic return and that reminds me can signal a digres- sion. The recognition and generation of cue phrases is of considerable interest to research in natural language pro- cessing. The structural information conveyed by these phrases is crucial to tasks such as anaphora resolution [6], [5], [16] and the identification of rhetorical relations among portions of a text or discourse [11], [8], [16]. It has also been claimed that the incorporation of cue phrases into natural language processing systems helps reduce the complexity of discourse processing [21], [4], [10]. Despite the recognized importance of cue phrases, many questions about how they are defined both individually and as a class -- and how they are to be represented, gen- erated, and recognized -- remain to be examined. For example, in the general case, each lexical item that can serve as a 'cue phrase' also has an alternate interpreta- tion. 2 While the 'cue' interpretation provides explicit 1. Previous literature has employed the terms 'clue word', 'discourse marker' or 'discourse particle' for these items [16], [4], [14], [18]. More recently Grosz and Sidner [5] have proposed the term cue phrase for these items, which we will adopt in this paper. 2. If 'non-lexical' items such as uh are classed as cue phrases, then this generalization may not hold for all cue phrases. However, information about the structure of a discourse, the 'non- cue' interpretation provides quite different information, such as conjunction (but) or adverbial modification (any- way). Distinguishing between these two uses is critical to the interpretation of discourse. In this paper, we address the problem of how this distinction might be made: We propose that, in speech, this distinction is made intona- tionally. We support our hypothesis by an analysis of cue and non-cue uses of the item now in recorded naturally occurring discourse. In Section 2 we discuss the general problem …

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