Mechanisms for Mixed-Initiative Human-Computer Collaborative Discourse

In this paper, we examine mechanisms for automat ic dialogue initiative setting. We show how to incorporate initiative changing in a task-oriented human-compute r dialogue system, and we evaluate the effects of initiative both analytically and via compute r -compute r dialogue simulation. 1 Motivation: Initiative in Task-Oriented Dialogues Efficient human-compute r dialogue requires immediate ut terance-by-ut terance accommodat ion to the needs of the interaction. The part icipants must continuously focus all concerns on the goals of the task and avoid extraneous paths. This means tha t the dialogue i n i t i a t i v e should always pass immediately to the part icipant who is best able to handle the current task. An agent is said to have dialogue initiative over a mutual goal when tha t agent controls how that goal will be solved by the collaborators. In the implemented voice dialogue system "The Circuit Fix-it Shop" (Smith et al., 1992; Smith and Hipp, 1995), the dialogue fragment given in Figure 1 occurs between a human user and a computer collaborator. Utterances 2 and 4 indicate tha t the computer is directing the search for the missing wire in the faulty circuit. However, in Utterance 5 the user takes the initiative and suggests a different wire than has been proposed by the computer. In this paper we will present a theory explaining how initiative changes between participants and how computat ional agents can evaluate who should be in control of solving a goal. 2 Automat ing Dialogue Init iative Center for Digital Systems Engineering Research Triangle Institute Box 12194 Research Triangle Park, NC 27709 cig~rt±, org 1 U The LED is displaying an alternately flashing one and the top corner of a seven. 2 C There is supposed to be a wire between connector nine nine and connector one zero zero. 3 U It is there. 4 C There is supposed to be a wire between connector nine eight and connector one zero two. 5 U There is no wire on connector o n e ze ro four . [emphasis mine] 6 C There is supposed to be a wire between connector one zero four and connector one zero two. Table 1: A Dialogue Fragment in the Circuit Fix-it Shoppe Domain is in control and the other agent is passive (the master-slave assumption). For instance, in the LADDER system (Hendrix et al., 1978) the user has the initiative while the computer is passive. In contrast, the VODIS system (Young and Proctor , 1989) has the computer taking the initiative while the user is passive. Some dialogue systems (like GUS (Bobrow et al., 1977)) allow for a more mixed-initiative interaction; however, the places where the user can take the initiative are limited and defined a priori. The dialogue model of Smith (1995) allows for either the computer or the user to assume degrees of initiative; however, Smith presents no algorithm for the computer to change initiative during a dialogue. Our model of mixed-initiative dialogue allows either part icipant to be in control of the dialogue at any point in time. Like Smith (1995) we believe tha t the level of iniMany implemented dialogue systems are questiontiative in the dialogue should mirror the level of inianswer systems with fixed initiative where one agent tiative in the task (which is a corollary to Grosz's