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<Paper uid="P94-1014">
  <Title>AN EMPIRICAL MODEL OF ACKNOWLEDGMENT FOR SPOKEN-LANGUAGE SYSTEMS</Title>
  <Section position="5" start_page="96" end_page="96" type="metho">
    <SectionTitle>
3 DIALOGUE ANALYSIS
</SectionTitle>
    <Paragraph position="0"> In this section, we describe the task characteristics and the corpus used for this study, present a theoretical model of acknowledgment acts in task-based dialogue, and present an analysis of acknowledgment acts based on corpus material.</Paragraph>
  </Section>
  <Section position="6" start_page="96" end_page="96" type="metho">
    <SectionTitle>
3.1 THE VEHICLE NAVIGATION
SYSTEM CORPUS
</SectionTitle>
    <Paragraph position="0"> The corpus we analyzed was collected by U S WEST Advanced Technologies in the domain of a vehicle navigation system (VNS). A VNS is intended to provide travel directions to motorists by cellular telephone: the system interacts with the caller to determine the caller's identity, current location and destination, and then gives driving directions a step at a time under the caller's control. U S WEST collected the dialogues through a Wizard-of-Oz experiment (Brunner et M., 1992) in which the wizard was free to engage in linguistically unconstrained interaction in the VNS task. Each of the 21 subjects performed three tasks in the VNS domain. As a whole, the corpus contained 2499 turns and 1107 acknowledgments.</Paragraph>
    <Section position="1" start_page="96" end_page="96" type="sub_section">
      <SectionTitle>
3.2 A TASK-BASED MODEL OF
</SectionTitle>
      <Paragraph position="0"/>
    </Section>
  </Section>
  <Section position="7" start_page="96" end_page="97" type="metho">
    <SectionTitle>
ACKNOWLEDGMENT ACTS
</SectionTitle>
    <Paragraph position="0"> The generally accepted view of acknowledgments, as noted earlier, distinguishes between two classes--namely continuers and assessments (Schegloff, 1982). Indeed, there were many occurrences of continuers (and a few assessments) in the VNS corpus. However, our analysis suggests that acknowledgments perform functions beyond these two classes. For instance, we observed several instances of acknowledgment being used at the beginning of a turn by the same speaker. This contrasts with the notions of continuers and assessments which, by definition, occur as unitary productions in the context of extended turns by another speaker. Clearly, an acknowledgment occurring at the beginning of a turn is not serving as a prompt for the other speaker to continue.</Paragraph>
    <Paragraph position="1"> To account for the evidence provided by the VNS corpus, we propose to extend Schegloff's classification scheme into a task-based model of acknowledgment acts. This model formalizes the meaning and usage characteristics of acknowledgments, based On an analysis of what acknowledgments mean and when acknowledgments are used in the VNS dialogues.</Paragraph>
    <Paragraph position="2"> A useful way of looking at the role of acknowledgments in the context of turns is to consider the basic structural context of exchanges. We begin by reviewing the concept of an adjacency pair (Schegloff and Sacks, 1973; Clark and Schae- null fer, 1989). An adjacency pair is formed by two consecutive utterances that have a canonical relationship, such as question-answer and greetinggreeting. An acknowledgment can be produced as the second phase of an adjacency pair or following a complete adjacency pair; in each case, the utterance may contain multiple acceptances. Of course, an acknowledgment can be produced also as a single turn that does not relate to an adjacency pair. Thus, based on exchange structure one can distinguish three broad structural classes of acknowledgments: 2  * Other-*ackn, where the acknowledgment forms the second phase of an adjacency pair; * Sclf--*other--*ackn, where Self initiates an exchange, Other (eventually) completes the exchange, and Self then utters an acknowledgment; and * Self/ackn, where Self includes an acknowledgment in an utterance outside of an adjacency  pair.</Paragraph>
    <Paragraph position="3"> In the other--*ackn class, the exchange is a basic adjacency pair; Other's act will be composed of a single turn. In the self--*other-*ackn class, the exchange initiated and eventually acknowledged by Self may be composed of multiple turns, with multiple utterances by both Self and Other. In the self/ackn class, the acknowledgment occurs in a single, extended turn by Self that may contain multiple utterances.</Paragraph>
    <Section position="1" start_page="97" end_page="97" type="sub_section">
      <SectionTitle>
3.3 A CATALOGUE OF
</SectionTitle>
      <Paragraph position="0"/>
    </Section>
  </Section>
  <Section position="8" start_page="97" end_page="99" type="metho">
    <SectionTitle>
ACKNOWLEDGMENT ACTS
IN TASK-BASED DIALOGUE
</SectionTitle>
    <Paragraph position="0"> In this section, we elaborate the structural classes of acknowledgment through a catalogue of patterns of speech acts that occur in each class.</Paragraph>
    <Paragraph position="1"> This catalogue provides broad coverage of patterns typically encountered in task-oriented discourse.</Paragraph>
    <Paragraph position="2"> These patterns describe the context of acknowledgments in terms of exchanges and are derived from utterances in the VNS corpus. Each act in an exchange is represented in terms of speech-act verbs based on the set described by Wierzbicka (1987) . Table 1 summarizes the speech-act patterns in the catalogue. In the following sections, we will consider each of the structural classes in turn and provide examples of selected patterns from the VNS corpus. We also consider embed2The notation for structural class names indicates turns delimited by arrows (--*). Acts combined within a turn are joined with a plus (+) symbol. Other and self refer to non-acknowledgment acts by the respective conversants. &amp;quot;Self&amp;quot; refers to the party producing the acknowledgment; &amp;quot;Other&amp;quot; is the other party. ded exchanges, in which basic patterns are used to build more complex patterns.</Paragraph>
    <Paragraph position="3">  other--*ackn class relate principally to the immediately antecedent utterance as opposed to the prior exchange, which is covered by the self-*other-*ackn class. In Clark and Schaefer's (1989) terms, Self's acknowledgment in the other-*ackn class serves as the acceptance phase for Other's presentation. As listed in Table 1, the canonical other--* ackn patterns axe inform--* ackn, inform-*ackn+mrequest, request-*ackn/inform, mdirect-~ackn and preclose-*ackn. 3 In each of these cases, the first turn is by Other and the second turn is Self's acknowledgment. In some cases, Self's turn also extends to include other significant utterances. We illustrate the other-*ackn class through examination of the inform-*ackn and inform-*ackn+mrequest patterns.</Paragraph>
    <Paragraph position="4"> Inform-*Aekn The inform-*aekn pattern covers cases where Other performs an inform act and Self responds with an acknowledgment of that act. In the following example 4 of an inform-* ackn, the wizard gives directions to the user, who acknowledges these directions. This is an example of an acknowledgment that Schegloff (1982) would call a continuer. Example 1 (U6.3.1) 5  (1.1) Wizard: On Evans, you need to turn left and head West for approximately three quarters of a mile to Clermont.</Paragraph>
    <Paragraph position="5"> (1.2) User: Okay.</Paragraph>
    <Paragraph position="6"> (1.3) Wizard: And, urn, on Clermont you  turn left, heading South for about two blocks to Iliff.</Paragraph>
    <Paragraph position="7"> Here, the &amp;quot;okay&amp;quot; at turn 1.2 indicates the user's acceptance of the wizaxd's utterance. That is, the acknowledgment implies that the user understood information given by the wizard-more emphatically than a simple next-relevantcontribution response. Use of the acknowledg- null interest is highlighted.</Paragraph>
    <Paragraph position="8"> ~All examples are extracted from a corpus of telephone dialogues from a task-oriented &amp;quot;Wizard-of-Oz&amp;quot; protocol collection study described in Section 3.1. The examples in this paper are notated with the corpus dialogue reference number and each turn is numbered for purposes of reference.</Paragraph>
    <Paragraph position="9">  ment would be strong evidence of understanding in Clark and Schaefer's (1989) terms. An important point to stress here is that the wizard cannot rely on the user necessarily having received the information that was actually conveyed or formed the intended interpretation. Rather, the wizard is left with the user's response indicating that the user was apparently satisfied with the wizard's original presentation.</Paragraph>
    <Paragraph position="10"> Inform--* Ackn+ MRequest The inform--*ackn+mrequest class represents a significant functional variation on the inform--~ackn class just considered. It covers cases where Other performs an inform act, Self responds with an acknowledgment of that act and then goes on to seek clarification of the content of the inform act. Requests for clarification are kinds of metaact because they are concerned with aspects of dialogue control rather than the task itself. That is, requests for clarification are concerned with the specifics of old information rather than seeking to elicit largely new information--unlike request-inform acts.</Paragraph>
    <Paragraph position="11">  (2.1) Wizard: Okay. Then you want to go north on Speer Boulevard for one and one half miles to Alcott Street.</Paragraph>
    <Paragraph position="12"> (2.1) User: Okay. I want to go right on Speer? (2.2) Wizard: It will be a left.</Paragraph>
    <Paragraph position="13">  In this example, the repair is a potential request for specification (Lloyd, 1992). That is, the user's clarification at 2.2 (&amp;quot;I want to go right on Speer?&amp;quot;) focuses on information which was missing from the surface structure of the original inform act but which is potentially available-namely &amp;quot;right&amp;quot; instead of &amp;quot;north.&amp;quot;  in the self--~other--*ackn class relate to the previous exchange, rather than just the previous utterance. Broadly speaking, they express the current state of the dialogue in addition to embodying the functionality of other--~ackn acknowledgments. That is, they explicitly mark the completion of the antecedent exchange and indicate that the dialogue will either enter a new exchange or resume an existing exchange. Furthermore, self--~other--~ackn acknowledgments signal understanding and acceptance of both the previous exchange and the previous utterance. The canonical patterns of the self--* other--* ackn class, as listed in Table 1, include inform--*ackn---~ackn, request-* inform-~ ackn, mrequest-* inf orm--~ ackn and mdirect--~ackn--*ackn. We illustrate the self--*other--~ackn class through examination of the request-~inform--, ackn pattern.</Paragraph>
    <Section position="1" start_page="98" end_page="99" type="sub_section">
      <SectionTitle>
Request --*Inform--~Aekn
</SectionTitle>
      <Paragraph position="0"> The request--~inform--*ackn class covers cases where Self requests an inform act of Other. Other then performs that inform act and Self acknowledges. Note that the acknowledgment in this case follows a completed request-inform adjacency pair.</Paragraph>
      <Paragraph position="1"> Earlier, we mentioned that question-answer adjacency pairs can be regarded as special cases of request-inform adjacency pairs (Searle, 1969). In the following example, the wizard requests the user's start location. The user satisfies this request by communicating the desired information and the wizard then acknowledges. Here the acknowledgment at 3.3 serves to indicate acceptance (that is, receipt, understanding and agreement) of the user's inform act and is a signal that the request initiated by the wizard at 3.1 has been satisfied and thus the exchange is complete.</Paragraph>
      <Paragraph position="2"> Example 3 (U2.1.1)  (3.1) Wizard: Okay and uh, what's your starting location? (3.2) User: I'm at 36th and Sheridan at the Park-n-Ride.</Paragraph>
      <Paragraph position="3"> (3.3) Wizard: Okay, one moment please.</Paragraph>
      <Paragraph position="4"> 3.3.3 Self-bAckn Self-acknowledgments occur when Self issues an acknowledgment following  some action (either verbal or physical) performed by Self. These are not responsive acts, unlike other acknowledgment usages considered; however, they are still closely tied with the idea of establishing mutual beliefs. The canonical patterns, as  listed in Table 1, include inform+ackn+inform, mrequest+ackn, and mdirect+ackn. We illustrate the self+ackn class through examination of the inform +ackn +inform pattern.</Paragraph>
      <Paragraph position="5"> Inform+Ackn+Inform In this pattern, Self uses an acknowledgment in the middle of an extended turn. Consider the following example: Example 4 (U5.3.1) (4.1) Wizard: All right, urn, the first thing you need to do is go South on Logan Street for one and a half miles to Evans Avenue.</Paragraph>
      <Paragraph position="6"> Then turn left on Evans Avenue and go one and a quarter miles to South Josephine Street. Okay, then you'll turn left on South Josephine Street. Nineteen Forty South Josephine is within the first block.</Paragraph>
      <Paragraph position="7"> This particular self-acknowledgment is very similar to a continuer--indeed it may be regarded as a self-continuer. The wizard's acknowledgment in this example represents a sort of temporizing, a chance for the wizard to &amp;quot;catch his mental breath.&amp;quot; For the user, this sort of &amp;quot;Okay&amp;quot; thus signals that the wizard intends to continue his turn. This is functionally distinct from a meta-request of the form &amp;quot;Okay?&amp;quot; because there is no rising intonation and the wizard does not wait for a response. In fact, use of a self-acknowledgment at the end of a turn would be peculiar.</Paragraph>
      <Paragraph position="8">  that basic patterns can used to build more complex patterns. This can lead potentially to variations in patterns of acknowledgments. In particular, it is possible to observe cascades of acknowledgments as nested exchanges are &amp;quot;popped&amp;quot; one by one. Simple acts may be replaced by more complex exchanges, so that an inform act may be replaced by an exchange that accomplishes an inform via a sequence of informs, clarifications and acknowledgments. In this section we will consider one of the variations encountered in the VNS corpus; where an {nform---*ackn--~ackn replaces the inform act in an inform--*ackn sequence. In the following example, there are three successive acknowledgment acts. The first acknowledgment at 5.2 is accompanied by a verbatim response by the user. It is the second phase of the inform--*ackn adjacency pair, indicating understanding and acceptance of the wizard's inform act in which a direction was clarified. The second acknowledgment, issued by the wizard at 5.3, marks the completion of the inform--*ackn exchange. That is, the wizard recognizes that it is his or her turn yet has nothing more to add, so indicates passing up the turn with an acknowledgment. The third acknowledgment, issued by the user at 5.4, is associated with the user recognizing that the wizard has finished clarifying directions; the user thus acknowledges this embedded inform act. The user then indicates satisfaction and approval of the wizard's directions with the assessment &amp;quot;Sounds good.&amp;quot; Example 5 (U6.2.1)  (5.1) Wizard: Okay, it was, urn, on Evans it's three and three quarter miles to Jasmine. null (5.2) User: Three, okay.</Paragraph>
      <Paragraph position="9"> (5.3) Wizard: Okay.</Paragraph>
      <Paragraph position="10"> (5.4) User: All right, sounds good.</Paragraph>
    </Section>
  </Section>
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