Mixed Initiative in Dialogue: An Investigation into Discourse Segmentation

Mixed Initiative in Dialogue: An Investigation into Discourse Segmentation Marilyn Walker University of Pennsylvania* Computer Science Dept. Philadelphia, PA 19104 lyn@linc.cis.upenn.edu Steve Whittaker Hewlett Packard Laboratories Bristol, England BS12 6QZ HP Stanford Science Center sjw@hplb.hpl.hp.com Abstract Conversation between two people is usually of MIXED-INITIATIVE, with CONTROL over the con- versation being transferred from one person to an- other. We apply a set of rules for the transfer of control to 4 sets of dialogues consisting of a total of 1862 turns. The application of the control rules lets us derive domain-independent discourse structures. The derived structures indicate that initiative plays a role in the structuring of discourse. In order to explore the relationship of control and initiative to discourse processes like centering, we analyze the distribution of four different classes of anaphora for two data sets. This distribution indicates that some control segments are hierarchically related to oth- ers. The analysis suggests that discourse partic- ipants often mutually agree to a change of topic. We also compared initiative in Task Oriented and Advice Giving dialogues and found that both allo- cation of control and the manner in which control is transferred is radically different for the two dia- logue types. These differences can be explained in terms of collaborative planning principles. 1 Introduction Conversation between two people has a number of characteristics that have yet to be modeled ade- quately in human-computer dialogue. Conversa- tion is BIDIRECTIONAL; there is a two way flow of information between participants. Information *This research was partially funded by ARO grants DAAG29-84-K-0061 and DAAL03-89-C0031PRI, DARPA grant N00014-85-K0018, and NSF grant MCS-82-19196 at the University of Pennsylvania, and by Hewlett Packard, U.K. is exchanged by MIXED-INITIATIVE. Each partici- pant will, on occasion, take the conversational lead. Conversational partners not only respond to what others say, but feel free to volunteer information that is not requested and sometimes ask questions of their own[Nic76]. As INITIATIVE passes back and forth between the discourse participants, we say that CONTROL over the conversation gets trans- ferred from one discourse participant to another. Why should we, as computational linguists, be interested in factors that contribute to the interac- tivity of a discourse? There are both theoretical and practical motivations. First, we wish to ex- tend formal accounts of single utterances produced by single speakers to explain multi-participant, multi-utterance discourses[Po186, CP86]. Previ- ous studies of the discourse structure of multi- participant dialogues have often factored out the role of MIXED-INITIATIVE, by allocating control to one participant[Gro77, Coh84], or by assuming a passive listener[McK85, Coh87]. Since conversation is a collaborative process[CWG86, SSJ74], models of conversation can provide the basis for extending planning theories[GS90, CLNO90]. When the sit- uation requires the negotiation of a collaborative plan, these theories must account for the interact- ing beliefs and intentions of multiple participants. ~,From a practical perspective, there is ample evi- dence that limited mixed-initiative has contributed to lack of system usability. Many researchers have noted that the absence of mixed-initiative gives rise to two problems with …

Content truncated to 500 words