Discourse Structure in Generation

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Discourse Structure in Generation

• Julia Hirschberg
• CS 4706

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Today

• Models of Discourse Structure
• Do we have them?
• Grosz Sidner 86
• What identifies discourse structure to Hearers?
• Textual cues
• Spoken cues
• How can we produce appropriate discourse
  structure in TTS systems?
• Can we identify discourse structure
  automatically, from speech?

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Is there structure in this discourse?

• A beautiful mallard spotted the dove I was
  feeding.
• The duck dove supply is small this year.
• That dove was history in a minute.
• Well, to recover from this horrible scene, I went
  to the park snack bar for a cup of cocoa.
• To my surprise, I ran into a friend from back
  home.
• When I told her of my recent experience she
  questioned my sanity.

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Is this a reasonable structure?

• A beautiful mallard spotted the dove I was
  feeding.
• The duck dove supply is small this year.
• That dove was history in a minute.
• Well, to recover from this horrible scene, I went
  to the park snack bar for a cup of cocoa.
• To my surprise, I ran into a friend from back
  home.
• When I told her of my recent experience she
  questioned my sanity.

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This?

• A beautiful mallard spotted the dove I was
  feeding.
• The duck dove supply is small this year.
• That dove was history in a minute.
• Well, to recover from this horrible scene, I went
  to the park snack bar for a cup of cocoa.
• To my surprise, I ran into a friend from back
  home.
• When I told her of my recent experience she
  questioned my sanity.

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This?

• A beautiful mallard spotted the dove I was
  feeding.
• The duck dove supply is small this year.
• That dove was history in a minute.
• Well, to recover from this horrible scene, I went
  to the park snack bar for a cup of cocoa.
• To my surprise, I ran into a friend from back
  home.
• When I told her of my recent experience she
  questioned my sanity.

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What information do we use in segmenting a
discourse?

• Topic coherence?
• Repeated reference?
• Cue phrases?
• ????

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Structures of Discourse Structure (Grosz Sidner
86)

• A leading theory of discourse structure
• Based upon Speaker intentions and Speaker and
  Hearer attentional state
• Identifies a few, general relations that hold
  among Speaker intentions
• Identifies a model of attentional state
• Three components
• Linguistic structure
• Intentional structure
• Attentional structure

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Linguistic Structure

• What is actually said or written
• How is the linguistic structure represented?
• Assume discourse is segmented into Discourse
  Segments (DS)
• What is the basic unit of analysis?
• Do we all segment alike?
• Do we all use the same cues?

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Linguistic Structure of Discourse D

• S1 A beautiful mallard spotted the dove I was
  feeding.
• The duck dove supply is small this year.
• That dove was history in a minute.
• S2 Well, to recover from this horrible scene, I
  went to the park snack bar for a cup of cocoa.
• To my surprise, I ran into a friend from back
  home.
• When I told her of my recent experience she
  questioned my sanity.

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Intentional Structure

• Discourse purpose (DP) basic purpose of the
  Speaker in producing the discourse
• Discourse segment purposes (DSPs) the Speakers
  purpose in producing the segment
• Segments are related to one another by their
  purposes
• Satisfaction-precedence DSP1 must be satisfied
  before DSP2
• Dominance DSP1 dominates DSP2 if fulfilling
  DSP2 constitutes part of fulfilling DSP1

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Linguistic Structure of Discourse D

• DSP1 Describe murder of dove by duck.
• S1 A beautiful mallard spotted the dove I was
  feeding.
• The duck dove supply is small this year.
• That dove was history in a minute.
• DSP2 Describe meeting of old friend.
• S2 Well, to recover from this horrible scene, I
  went to the park snack bar for a cup of cocoa.
• To my surprise, I ran into a friend from back
  home.
• When I told her of my recent experience she
  questioned my sanity.

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• DSP2 Describe recovery process.
• S2
• DSP3 Describe snack
• S3 Well, to recover from this horrible scene, I
  went to the park snack bar for a cup of cocoa.
• DSP3 Describe meeting old friend.
• S4 To my surprise, I ran into a friend from back
  home.
• DSP5 Describe friends reaction
• S5 When I told her of my recent experience she
  questioned my sanity.

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Attentional State The Focus Stack

• Stack of focus spaces, each containing objects,
  properties and relations salient during each DS,
  plus the DSP
• State changes transition rules controlling the
  addition/deletion of focus spaces
• Information at lower levels may or may not be
  available at higher levels
• Focus spaces are pushed onto the stack when
• A new DS is begun

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• An embedded DS (e.g. a DS dominated by another
  DS) is begun
• Focus spaces are popped when they are completed
• State of focus stack models felicitous reference,
  coherence in discourse

S2 DSP2, scene, Speaker, snack_bar Cocoa,
friend, home,sanity
S1 DSP1, duck, dove, Speaker, duck_dove_supply
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Limits of the Theory

• Assumes discourses are task-oriented
• Assumes a single, hierarchical structure shared
  by S and H
• Questions
• Do people really build such structures when they
  converse?
• Use them in interpreting what others say?
• How could they do it?

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How might people recognize discourse structure?

• Linguistic markers?
• tense and aspect
• cue phrases
• Inference of Speaker intentions?
• Inference from task structure?
• Intonational Information?

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Acoustic and Prosodic Cues to Discourse Structure

• Intuition
• Speakers vary acoustic and prosodic cues to
  convey variation in discourse structure
• Systematic? In read or spontaneous speech?
• Evidence
• Observations from recorded corpora
• Laboratory experiments
• Machine learning of discourse structure from
  acoustic/prosodic features

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Prosodic Correlates of Discourse/Topic Structure

• Pitch range
• Lehiste 75, Brown et al 83, Silverman 86,
  Avesani Vayra 88, Ayers 92, Swerts et al 92,
  Grosz Hirschberg92, Swerts Ostendorf 95,
  Hirschberg Nakatani 96
• Preceding pause
• Lehiste 79, Chafe 80, Brown et al 83,
  Silverman 86, Woodbury 87, Avesani Vayra 88,
  Grosz Hirschberg92, Passoneau Litman 93,
  Hirschberg Nakatani 96

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• Rate
• Butterworth 75, Lehiste 80, Grosz
  Hirschberg92, Hirschberg Nakatani 96
• Amplitude
• Brown et al 83, Grosz Hirschberg92,
  Hirschberg Nakatani 96
• Contour
• Brown et al 83, Woodbury 87, Swerts et al 92

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Issues

• Do we find significant and reliable cues to
  discourse structure in prosodic variation
• When tested against an independent theory of
  discourse structure?
• In spontaneous as well as read speech?
• Are Hearers interpretations of discourse
  structure influenced by intonational variation?

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Grosz Hirschberg 92

• Small corpus of read AP newswire
• Read by professional speaker
• Labeled for discourse structure from text alone
  or from text and speech
• Pre-ToBI labeled
• Acoustic-prosodic features extracted for each
  intermediate (level 3) phrase
• Pitch range and change from prior phrase
• Intensity (rms) and change in db from prior
  phrase
• Preceding and subsequent pause
• Speaking rate

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• Analysis of phrases in different segment
  positions SBEG, SF, parentheticals, quoted
  speech
• ANOVAs and t-tests on means
• Results
• Direct quotes larger pitch range
• Parentheticals smaller range, neg change from
  prior phrase, neg change in db, faster rate
• SBEG larger range, louder, greater preceding
  pause, less subsequent pause
• SF greater subsequent pause

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• Machine learning experiments identified
• SBEG with 91.5 est. accuracy (x-validation)
• SF, 92.5
• Attributive tags, 96.9
• Direct quotations, 86.4
• Indirect quotations, 88.5
• Parentheticals, 89.2
• Conclusion Acoustic/prosodic information is
  available to permit Hearers to identify discourse
  structure

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Next

• The midterm
• Closed book, no notes or electronic devices
• Will include material through today