Lexical, Prosodic, and Syntactic Cues for Dialog Acts

Lexical, Prosodic, and Syntactic Cues for Dialog Acts Daniel Jurafsky*, Elizabeth Shribergt, Barbara Fox*, and Traci Curl* University of Colorado* SRI Internationalt Abstract The structure of a discourse is reflected in many as- pects of its linguistic realization, including its lexi- cal, prosodic, syntactic, and semantic nature. Multi- party dialog contains a particular kind of discourse structure, the dialog act (DA). Like other types of structure, the dialog act sequence of a conversation is also reflected in its lexical, prosodic, and syntac- tic realization. This paper presents a preliminary in- vestigation into the realization of a particular class of dialog acts which play an essential structuring role in dialog, the backchannels or acknowledge- ments tokens. We discuss the lexical, prosodic, and syntactic realization of these and subsumed or re- lated dialog acts like continuers, assessments, yes- answers, agreements, and incipient-speakership. We show that lexical knowledge plays a role in distinguishing these dialog acts, despite the wide- spread ambiguity of words such as yeah, and that prosodic knowledge plays a role in DA identifica- tion for certain DA types, while lexical cues may be sufficient for the remainder. Finally, our investi- gation of the syntax of assessments suggests that at least some dialog acts have a very constrained syn- tactic realization, a per-dialog act 'microsyntax'. 1 Introduction The structure of a discourse is reflected in many as- pects of its linguistic realization. These include 'cue phrases', words like now and well which can in- dicate discourse structure, as well as other lexical, prosodic, or syntactic 'discourse markers'. Multi- party dialog contains a particular kind of discourse structure, the dialog act, related to the speech acts of Searle (1969), the conversational moves of Car- letta et al. (1997), and the adjacency pair-parts of Schegloff (1968) Sacks et al. (1974) (see also e.g. Allen and Core (1997; Nagata and Morimoto (1994)). Like other types of structure, the dia- log act sequence of a conversation is also reflected in its lexical, prosodic, and syntactic realization. This paper presents a preliminary investigation into the realization of a particular class of dialog acts which play an essential structuring role in dialog, the backehannels or acknowledgements tokens. We discuss the importance of words like yeah as cue-phrases for dialog structure, the role of prosodic knowledge, and the constrained syntactic realiza- tion of certain dialog acts. This is part of a larger project on automatically detecting discourse structure for speech recogni- tion and understanding tasks, originally part of the 1997 Summer Workshop on Innovative Techniques in LVCSR at Johns Hopkins. See Jurafsky et al. (1997a) for a summary of the project and its relation to previous attempts to build stochastic models of dialog structure (e.g. Reithinger et al. (1996),Suhm and Waibel (1994),Taylor et al. (1998) and many others), Shriberg et al. (1998) for more details on the automatic use of prosodic features, Stolcke et al. (1998) for details on the machine learning archi- tecture of the project, and Jurafsky et al. (1997a) on the applications to automatic speech …

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