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<Paper uid="P88-1014">
  <Title>DISCOURSE DEIXIS: REFERENCE TO DISCOURSE SEGMENTS</Title>
  <Section position="3" start_page="0" end_page="118" type="intro">
    <SectionTitle>
1. INTRODUCTION
</SectionTitle>
    <Paragraph position="0"> There seem to be at least two constructs that most current theories of discourse understanding have adopted in at least some form. The In'st is the discourse entity, first introduced by Lauri Karmunen in 1976 (under the name &amp;quot;discourse referent&amp;quot;) \[9\] and employed (under various other names) by many researchers, including myself \[18\].</Paragraph>
    <Paragraph position="1"> The other is the discourse segment.</Paragraph>
    <Paragraph position="2"> Discourse entities provide these theories with a uniform way of explaining what it is that noun phrases (NP) and pronouns in a discourse refer to.</Paragraph>
    <Paragraph position="3"> Some NPs evoke a new discourse entity in the listener's evolving model of the discourse (which I have called simply a discourse model), others refer to ones that are already there. Such entities may correspond to something in the outside world, but they do not have to. To avoid confusion with a sense of &amp;quot;referring in the outside world&amp;quot;, I will use the terms referm here, meaning &amp;quot;refer in a model&amp;quot;, and referentm, for the entity in the model picked out by the linguistic expression.</Paragraph>
    <Paragraph position="4"> The basic features of a discourse entity are that (a) it is a constant within the current discourse model and that Co) one can attribute to it, inter alia, properties and relationships with other entities. (It is for this reason that Bill Woods once called them &amp;quot;conceptual coat hooks&amp;quot;.) In some theories, different parts of the discourse model (often called spaces) may represent diffeaent modalities, including hypothetical contexts, quantified contexts, the belief contexts of different agents, etc. Depending on what space is currently being described, the same NP or pronoun may evoke and/or referm to very different discourse entities.</Paragraph>
    <Paragraph position="5"> The other common construct is the discourse segment. While discourse segmentation is generally taken to be a chunking of a linguistic text into sequences of related clauses or sentences, James Allen notes: ... there is little consensus on what the segments of a particular discourse should be ~ how segmentation could be accomplished. One reason for this lack of consensus is that there is no precise definition of what a segment is beyond the intuition that certain sentences naturally group together \[\[1\], p. 398-9\] What is taken to unify a segment is different in different theories: fox example, among computational linguists, Grosz &amp; Sidner \[5\] take a discourse segment to be a chunk of text that expresses a common purpose (what they have called a discourse segment purpose) with respect to the speaker's plans; Hobbs \[8\] takes a discourse segment to be a chunk of text that has a common meaning; while Nakhimovsky \[12\], considering only narrative, takes a discourse segment to be a chunk of text that describes a single event from a single perspective.</Paragraph>
    <Paragraph position="7"> While discourse segment is usually deemed recursively, theories differ in what they take the minimal segment to be. Hobhs takes it to be a sentence, and Polanyi \[12\], a clause. Grosz &amp; Sidner do not state explicitly how much is needed to express a single purpose, but from their examples, it appears to be a single sentence as wen. (Unlike Hohbs and Polanyi, Grosz &amp; Siduer do not consider every sentence to be a discourse segment per so.) Since discourse segment is defmed recm~vely, the resulting segmentation of a text (or at least, large parts of it) can be described as a tree. From the point of view of processing, this means that at any point in the discourse, several segments, each embedded in the one higher, may still be open - i.e., under construction. This is illuswated schematically in</Paragraph>
    <Paragraph position="9"> \[2\] and Rachel Reichman \[15\]) have discussed problems inherent in this discourse parsing task, among which is the lack of precise definition of its basic building block.</Paragraph>
    <Paragraph position="10"> At the point of processing sentence Sj/I in this example, segments DSkl, DSk211 ..... DSk21j are complete (closed - indicated by a *), while DSk, DSk2, and DSk21 are open, able to incorporate sentence Sj+I (or, alternatively, its cones~nding unary discourse segment). Of special interest is the right frontier of the tree - the set of nodes comprising the most recent closed segment and all currently open segments - here {DSk21j, DSk21, DSk2, and DSk}, which I will make use of later in Section 3. Several researchers (including Grosz &amp; Sidner \[5\], Hh-schberg &amp; Litman \[6\], Robin Cohen For the current discussion, the most significant thing about these two constructs is their different associations: discourse entities go with N'Ps (to explain anaphoric and definite refemncem) and discourse segments go with sentences or clauses (to explain textual coherence and d~ourse stmctare).</Paragraph>
    <Paragraph position="11"> This leaves a gap in the case of referencem to what can only be token to be some aspect of a sequence of clauses, sentences or utterances (e.g., its content, form, modality, etc.), for example: Example 1 It's always been presumed that when the glaciers receded, the area got very hot. The Folsum men couldn't adapt, and they died out.</Paragraph>
    <Paragraph position="12"> That's what is supposed to have happened. It's the textlx)ok dogma. But it's wrong. They were human and smart. They adapted their weapons and cultme, and they survived.</Paragraph>
    <Paragraph position="13"> Example 2 The tools come from the development of new types of computing devices. Just as we thought of intelligence in terms of  servomechanism in the 1950s, and in terms of sequential computers in the sixties and seventies, we are now beginning to think in terms of parallel computers, in which tens of thousands of processors work together. This is not a deep, philosophical shift, but it is of great practical importance, since it is now possible to study large emergent systems experimentally. \[\[6\] p.176\] The obvious question is whether such refereneem involves the same processes used to explain how a pronoun or NP evokes and/or refersm to a discourse entity or whether some other sort of process is involved. In this paper I win argue for the latter, giving evidence for a separate referencem process by which a linguistic expression is first interpreted as a pointer to the representation of a discourse segment and then further constrained to specify either (a) a particular aspect of the discourse segment (e.g., its form, interpretation, speech act, etc.) or Co) a particular entity within its interpretation.</Paragraph>
    <Paragraph position="14"> In Section 2, I will attempt to justify the existence of a second referringm process linked to a representation of discourse segments per se. In Section 3, I will attempt to justify particular features of the proposed process, and Section 4 summarizes the impfications of this work for discourse understanding.</Paragraph>
    <Paragraph position="15"> 2. Justifying a Second Referring m Process There is ample evidence that subsequent reference can be made to some aspect of a sequence of clauses in text. Besides Examples 1 and 2 above, several other examples will be presented later, and the reader should have no trouble fmding more. So the existence of such a phenomenon is not in dispute. Also not in dispute is the fact that such subsequent reference is most often done via deictic pronouns: Of 79 instances of prominal referencem to clausal material found in five written texts 1, only 14 (-18%) used the pronoun it while the other 65 (-82%) used either this or that (17 instances of that and 48 of this). On the other hand, looking at all instances of pronominal referencem using it to discourse entities evoked by NPs 2, of 41 such references, 39 (-95%) used it while only 2 (-5%) used this or that. Because of this, I will call this type of reference discourse deixis. The f'trst thing to note about discourse deixis is that the referentm is often distinct from the things described in the sequence. For example, Example 3 There's two houses you might be interested in: House A is in Pale Alto. It's got 3 bedrooms and 2 baths, and was built in 1950. It's on a quarter acre, with a lovely garden, and the owner is asking $425K. But that's all I know about it.</Paragraph>
    <Paragraph position="16"> House B is in Portola Vally. It's got 3 bedrooms, 4 baths and a kidney-shaped pool, and was also built in 1950. It's on 4 acres of steep wooded slope, with a view of the mountains. The owner is asking $600IC I heard all this from a friend, who saw the house yesterday.</Paragraph>
    <Paragraph position="17"> Is that enough information for you to decide which to look at? In this passage, that in the second paragraph \[doe s not refer to House A (although all instances of it do): ' rather it refers to the description of House A presented there. Similarly (all) this in the third paragraph does not refer to House B (although again, ~ i ms~ of it do): rather it refers to the description of House B presented there. That in the fourth paragraph refers to the descriptions of the two houses taken together. That in each case it is the given description(s) that this and that are aeces.~g and not the houses, can be seen by interleaving the two descriptions, a technique often used when comparing two items: Example 4 There's two houses you might be interested in: House A is in Palo Alto, House B in Portola Vaily. Both were built in 1950, and both have 3 bedrooms. House A has 2 baths, and B, 4. House B also has a kidney-shaped pool. House A is on a quarter acre, with a lovely garden, while House B is on 4 acres of steep wooded slope, with a view of the mountains.The owner of House A is asking $425K. The owner of House B is ~sking $60(0 #That's all I know about House A. #This I heard from a friend, who saw House B before it came on the markeL Is that enough information for you to decide which to look at7 Here houses A and B are described together, and the failure of that and this to refer successfully in the second paragraph indicates that (a) it is not the houses being referredm to and Co) the individual descriptions available for referencem in Example 3 are no longer available here. One must conclude from this that it is  something associated with the sequences themselves rather than the discourse entities described therein that this and that referm to here.</Paragraph>
    <Paragraph position="18"> The next thing to note is that the only sequences of utterances that appear to allow such pronominal referencem are ones that intuitively constitute a discourse segment (cf. Section I), as in Example 1 (repeated here) and Example 5: Example 1 Ifs always been presumed that \[ lWhen the glaciers receded, the area got very hot. The Folsum men couldn't adapt, and they died out. 1 \] That's what is supposed to have happened. It's the textbook dogma. But it's wrong. They were human and smart. They adapted their weapons and cuimre, and they survived.</Paragraph>
    <Paragraph position="19"> Example 5 ...it should be possible to identify certain functions as being unnecessary for thought by studying patients whose cognitive abilities are unaffected by locally confined damage to the train. For example, \[lbinocular stereo fusion is known to take place in a specific area of the cortex near the back of the head. \[2Patients with damage to this area of the cortex have visual handicaps but show no obvious impairment in their ability to think. 2\] This suggests that stereo fusion is not necessary for thought. 1\] This is a simple example, and the conclusion is not surprising .... \[\[61, p. 183&amp;quot;\] In Example 1, that can be taken to referm to the narrative of the glaciers and the Folsum men, which is intuitively a cohezent discourse segment. (Brackets have been added to indicate discourse segments.</Paragraph>
    <Paragraph position="20"> Subscripts allow for embedded segments.) In Example 5, the fLrst this can be token as referring to the observation about visual cortex-damaged patients. The second this can be taken as referring to the whole embedded &amp;quot;brain damage&amp;quot; example.</Paragraph>
    <Paragraph position="21"> To summarize the current claim: in the process of discourse understanding, a referentm must be associated with each discourse segment, independent of the things it describes. Moreover, as Example 6 shows, this referentm must have at least three properties associated with it: the speech act import of the segment, the form of the segment, and its interpretation (e.g., as a situation, event, object description, etc.) Example 6 A: Hey, they've promoted Fred to second vice president.</Paragraph>
    <Paragraph position="22">  (* that speech act *) BI: That's a lie.</Paragraph>
    <Paragraph position="23"> (* that expression *) B2:: That's a funny way to describe the situation. (* that event *) B3: When did that happen7 (* that action *) B4: That's a weird thing for them to do.</Paragraph>
    <Paragraph position="24">  I have not said anything about whether or not these discot~se segment referentsm should be considered discourse entities like their NP-evoked counterparts. This is because I do not believe there is enough evidence to warrant taking a stand. Part of the problem is that there is no precise criterion for &amp;quot;discourse entity-hood&amp;quot;. 3 However, ff every discourse segment evokes a discourse entity, an account will be needed of (1) wheo in the course of processing a segment such a thing happens, and (2) what the 'focus' status of each of these entities is.</Paragraph>
    <Paragraph position="25">  3. Features of Deictic Referencem I suggest that the process of resolving discourse segment referencem involves the following steps: 1. An input pronoun is first interpreted as a pointer to a representation of a discourse segment on the fight frontier (cf. Section 1).</Paragraph>
    <Paragraph position="26"> 2. As the rest of the clause containing the pronoun is interpreted, pronoun interpretation may be either a. further consuained to some pmpe~ of the discourse segment representation b. extended to one of the discourse entities within the interpretation of the segment 3. As a consequence of whether this or that was  used, the listener characterizes the speakers &amp;quot;psychological distance&amp;quot; to its referentm as either &amp;quot;close&amp;quot; or &amp;quot;far away&amp;quot;. That is, this well-known deictic feature of this/that is not used in the referent-finding process but rather afterwm~, in atm~bufing the speakers relationship to that referentm.</Paragraph>
    <Paragraph position="27"> In this section, I will try to motivate each of the proposed steps.</Paragraph>
    <Paragraph position="28">  I have already argued that some deictic pronouns must be interpreted with respect to a discourse segment. Here I claim that the only discourse segments so available are ones on the right frontier. My evidence for this consists of (a) it being true of the 69 clausally-referfing instances of this and that found in the five texts and Co) the oddity of examples like the following variation of Example 3 where that in paragraph 3 is intended to referm to the description of</Paragraph>
    <Section position="1" start_page="116" end_page="116" type="sub_section">
      <SectionTitle>
House A.
Example 3'
</SectionTitle>
      <Paragraph position="0"> There's two houses you might be interested in: House A is in Palo Alto. It's got 3 bedrooms and 2 baths, and was built in 1950. It's on a quarter acre, with a lovely garden, and the owner is asking $425K.</Paragraph>
      <Paragraph position="1"> House B is in Ponola Vally. It's got 3 bedrooms, 4 baths and a kidney-shaped pool, and was also built in 1950. It's on 4 acres of steep wooded slope, with a view of the mountains. The owner is asking $600K. I heard all this from a friend, who saw the house yesterday. #But that's all I know about House A 4 Is that enough information for you to decide which to look at? (Note that this very limited availability of possible referentSm and the ability to coerce referents to any of their parts which I shall argue forshorfly suggests parallels between this phenomenon and definite NP and temporal anaphora.) Because at any time, there may be more than one discourse segment on the fight frontier, part of the reference resolution process involves identifying which one is intended. To see this, re-consider the fhst part of Example 5.</Paragraph>
    </Section>
    <Section position="2" start_page="116" end_page="116" type="sub_section">
      <SectionTitle>
Example $
</SectionTitle>
      <Paragraph position="0"> ...it should be possible to identify certain functions as being unnecessary for thought by studying patients whose cognitive abilities are unaffected by locally confined damage to the brain.</Paragraph>
      <Paragraph position="1"> For example, binocular stereo fusion is known to take place in a specific area of the cortex near the back of the head. Patients with damage to this area of the cortex have visual handicaps but show no obvious impairment in their ability to think.</Paragraph>
      <Paragraph position="2"> This ....</Paragraph>
      <Paragraph position="3"> At this point in the discourse, there are several things that this can be taken as specifying.</Paragraph>
      <Paragraph position="4"> Considering just the things associated with clauses (and just this segment of text, and not what it is embedded in), this can be taken as specifying either the segment associated with the previous sentence (as in the original text - &amp;quot;This suggests that stereo fusion is not necessary for thought.&amp;quot;) or the segment associated with the description of the whole example &amp;quot;This is only a simple example, and the conclusion is not surprising...&amp;quot;). The listener's choice depends on what is compatible with the meaning of the rest of the sentence. 5 As with other types of ambiguity, there may be a default (i.e. context-independent) preference for one particular form of construal over the others (cf. \[3\]) but it is easily over-fidden by context.</Paragraph>
      <Paragraph position="5"> This ambiguity as to the intended designatum of a pointer is very similar to the ambiguity associated with the more fundamental and historically prior use of deixis in pointing within a shared spatio-temporal context, as in the following example:</Paragraph>
    </Section>
    <Section position="3" start_page="116" end_page="117" type="sub_section">
      <SectionTitle>
Example 7
</SectionTitle>
      <Paragraph position="0"> \[,4 and AJunior are standing in A's art gallery\] A: Someday this will all be yours.</Paragraph>
      <Paragraph position="1"> Here this could be interpreted as either the business, the pictures, or the physical gallery. 6 Both Quine \[14\] and Miller \[10\] have observed in this regard that all pointing is ambiguous: the intended demonstratum of a pointing gesture can be any of the infinite number of points &amp;quot;intersected&amp;quot; by the gesture or any of the slzuctures encompassing those points. (Or, one might add, any interpretation of those structures.) The ambiguity here as to how large a segment on the fight frontier is encomp .a.~ by a this or that is very similar.</Paragraph>
      <Paragraph position="2"> (Another featme that Quine and Miller mention, that will come up later in this discussion, involves constraints on the demonswatum of a pointing gesture to being something present in the shared context or some mutually recognizable re-interpretation of it. The latter is what Quine has called deferred ostension. It enables one, given the fight audience, to point to the ceiling, with wires dangling from the center, say &amp;quot;That's off being cleaned&amp;quot; and effectively refer to the chandelier. Most examples of deferred ostension, both in spatio-temporal deixis and discourse deixis, are not that extreme. However, as I will try to show, both these features - ambiguity and &amp;quot;required ~ce&amp;quot; -- are characteristic of discourse deixis as well.) Having taken the initial step of interpreting a pronoun as pointing to the representation of a discourse segment, the proposed process must then be  able to further coerce \[8,11\] that interpretation to be some property of the discourse segment representation or to some entity within it. Example 6 (above) illustrates the first type of coercion, Example 8, the latter.</Paragraph>
      <Paragraph position="3"> Example 8 A: In the Antarctic autumn, Emperor penguins migrate to Tasmania.</Paragraph>
      <Paragraph position="4"> BI: That's where they wait out the long Antarctic winter.</Paragraph>
      <Paragraph position="5"> (* that place *) B2: So that's what you're likely to see there in May.</Paragraph>
      <Paragraph position="6"> (* that species of birds *) B3: That's when it begins to get too cold even for a penguin.</Paragraph>
      <Paragraph position="7"> (* that time *)  The reason for miring discourse segment identification and coercion as two separate steps in the process is to accommodate the fact that most instances of this and that are as the fh-st NP in a clause. 7 Since the listener cannot say for sure what they referm to until more evidence comes in from the rest of the sentence, a two-stage process allows the fLrSt stage of the process to be done immediately, with the second stage done as a subsequent constraint satisfaction process. This would resemble spafio-temporal uses of this and that, where the listener recognizes the general pointing gestm-e, and then tries to figure out the intended demonslratum based on what the speaker says about it (and on general heuristics about what might be worth pointing to).</Paragraph>
      <Paragraph position="8"> Notice that this step of further constraining a pointing gesture also allows for a uniform treatment of this and do this (that and do that). A preposed this/that may be the object of do or of some other verb, but the listener will not know which, until s/he reaches the verb itself, as in Example 9. Considering actions as properties of their respective events, the listener should be able to coerce that to be some appropriate facet of the discourse segment (or to some entity within that segment - as I will discuss next) that can be said or done. 8 Example 9 Gladys told Sam last night that Fred was a complete jerk.</Paragraph>
      <Paragraph position="9"> a. Anyway, that's what Fred believes that Gladys said.</Paragraph>
      <Paragraph position="10"> b. Anyway, that's what Fred believes that Gladys did. 9 On the other hand, what appears to be an additional ambiguity in resolving this/that may not be one at all That is, a listener who is asked what a given this/that refersm to must describe the representation that s/he has created. This act of description is subject to alot of variability. For example, given a segment in which a statement A is supported by several pieces of evidence {B,C,D}, the listener might just describe A (the top level of the representation) or s/he might verbalize the whole representation.</Paragraph>
      <Paragraph position="11"> As with anaphoric pronouns, when a deictic pronoun specifies an NP-evoked discourse entity, it must actually be part of its corresponding discourse segment interpretation. The interesting thing is that the same holds for deictlc NPs, distinguishing them from anaphoric definite NPs, which can easily referm to things ~ in some way with an exisiting entity, as in Example 10 John and Mary decided to go on a picnic.</Paragraph>
      <Paragraph position="12"> While they remembered most things, they forgot to put the picnic supplies in the cooler.</Paragraph>
      <Paragraph position="13"> So when they got to the park, the beer was warm.</Paragraph>
      <Paragraph position="14"> By contrast, a similar example with a demonstrative NP sounds definitely odd -</Paragraph>
    </Section>
    <Section position="4" start_page="117" end_page="118" type="sub_section">
      <SectionTitle>
Example II
</SectionTitle>
      <Paragraph position="0"> John and Mary decided to go on a picnic.</Paragraph>
      <Paragraph position="1"> While they remembered most things, they forgot to put the picnic supplies in the cooler.</Paragraph>
      <Paragraph position="2"> #So when they got to the park, that beer was warm.</Paragraph>
      <Paragraph position="3"> Another example illustrates this in another way: given that both anaphoric reference and deictic refeaence are possible in a particular context, an anaphoric ~ and a deictic NP will be interpreted differently, even if in all other ways the NPs are the same. The anaphoric NP may refer m to something with the c~t focus, while the deictic NP must point to something already explicitly included there. For example,  b. To screw up some one's directory, look at those files.</Paragraph>
      <Paragraph position="4"> c. They will tell you which of his f'des is absolutely vital to him.</Paragraph>
      <Paragraph position="5"> In Example 12, the files is anaphoric, specifying the fries in that person's directory, the entity currently in focus. In Example 13, those files is deictic, pointing to the fries that are superfdes, i.e., to a discourse entity explicitly in the interpretation of the just current discourse segment.</Paragraph>
      <Paragraph position="6"> Now, nothing in the process so far described distinguishes this and that. This is because with respect to discourse segment referencem, it is rarely the case that the two cannot be used interchangeably. 10 Thus it must be the case that this &amp;quot;psychological distance&amp;quot; feature of the deictic only comes into play after the referentm is found. This does not imply though that this and that cannot have diffeaent eff~m on the discourse: in Sidne~s 1982 theory \[17\] and in Schuster's theory of refm-ence to actions and events \[16\], this and that are also distinguished by their effect (or lack thereof) on the discourse focus. This is compatible with it being a side effect of judging the speaker's &amp;quot;distance&amp;quot; from the referent m, that the listener's beliefs about their shared discourse focus are revised.</Paragraph>
      <Paragraph position="7"> To summarize, in Section 2, I argued for the existence of a second refening process associated with discourse segments per se rather than what they describe. In this section, I have argued for it having the features of pointing to the representation of a discourse segment on the right frontier, followed by further refinement to a property of the segment or an entity within its interpretation.</Paragraph>
      <Paragraph position="8"> Here I want to argue for the proposed process having one additional feature. I have separated it out because it is not essential to the above arguments. However, it does permit an account of the common pattern of reference illustrated in Examples 1, 2, 14 and 15. Example 1 It's always been presumed that when the glaciers receded, the area got very hoL The Folsum men couldn't adapt, and they died out.</Paragraph>
      <Paragraph position="9"> That's what is supposed to have happened.</Paragraph>
      <Paragraph position="10"> It's the textbook dogma. But it's wrong.</Paragraph>
      <Paragraph position="11"> They were human and smart. They adapted their weapons and culture, and they survived.</Paragraph>
      <Paragraph position="12"> Example 2 The tools come from the development of new types of computing devices. Just as we thought of intelligence in terms of servomechanism in the 1950s, and in terms of sequential computers in the sixties and seventies, we are now beginning to think in terms of parallel computers, in which tens of thousands of processors work together. This is not a deep, philosophical shift, but it is of great practical importance, since it is now possible to study large emergent systems experimentally. \[\[6\], p.176\] Example 14 I don't think this can be taken seriously either. It would mean in effect that we had learned nothing at all from the evaluation, and anyway we can't afford the resources it would entaiL Example 15 The Texas attorney general said that the McDonald's announcement represented &amp;quot;a calculated effort to make the public think that they were doing this out of the goodness of their heart when, in fact. they were doing it because of pressure fiom our office. \[Philadelphia Inquirer,</Paragraph>
    </Section>
  </Section>
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