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<Paper uid="P90-1010">
  <Title>Mixed Initiative in Dialogue: An Investigation into Discourse Segmentation</Title>
  <Section position="14" start_page="75" end_page="76" type="concl">
    <SectionTitle>
5 Discussion
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    <Paragraph position="0"> It has Often been stated that discourse is an inherently collaborative process and that this is manifested in certain phenomena, e.g. the use of 9The higher, percentage of Interruptions in the keyboard TODs in comparison with the t ~1 ~ ./.hone TODs parallels Oviatt and Cohen's analysis, showing that participants exploit the Wider bandwidth of the iptoractive spoken channel to break tasks down into subtaskstCoh84 , OC89\].</Paragraph>
    <Paragraph position="1"> anaphora and cue words \[GS86, HL87, Coh87\] by which the speaker makes aspects of the discourse structure explicit. We found shifts of attentional state when shifts in control are negotiated and agreed by all participants, but not when control is seized by one participant without the acceptance of the others. This was reflected in different distribution of anaphora in the two cases. Furthermore we found that not all types of anaphora behaved in the same way. Event anaphora clustered at segment boundaries when it was used to refer to preceding segments and was more likely to cross segment boundaries because of its function in talking about the proposed plan. We also found that control was distributed and exchanged differently in the ADs and TODs. These results provide support for the control rules.</Paragraph>
    <Paragraph position="2"> In our analysis we argued for hierarchical organization of the control segments on the basis of specific examples of interruptions. We also believe that there are other levels of structure in discourse that are not captured by the control rules, e.g. control shifts do not always correspond with task boundaries. There can be topic shifts without change of initiation, change of control without a topic shift\[WS88\]. The relationship of cue words, intonational contour\[PH90\] and the use of modal subordination\[Rob86\] to the segments derived from the control rules is a topic for future research.</Paragraph>
    <Paragraph position="3"> A more controversial question concerns rhetorical relations and the extent to which these are detected and used by listeners\[GS86\]. Hobbs has applied COHERENCE RELATIONS to face-to-face conversation in which mixed-initiative is displayed by participants\[HA85, Hob79\]. One category of rhetorical relation he describes is that of ELABORATION, in which a speaker repeats the propositional content of a previous utterance. Hobbs has some difficulties determining the function of this repetition, but we maintain that the function follows from the more general principles of the control rules: speakers signal that they wish to shift control by supplying no new propositional content. Abdications, repetitions and summaries all add no new information and function to signal to the listener that the speaker has nothing further to say right now. The listener certainly must recognize this fact.</Paragraph>
    <Paragraph position="4"> Summaries appear to have an additional function of synchronization, by allowing both participants to agree on what propositions are mutually believed at that point in the discussion. Thus this work highlights aspects of collaboration in discourse, but  should be formally integrated with research on collaborative planning\[GS90, LCN90\], particularly with respect to the relation between control shifts and the coordination of plans.</Paragraph>
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