Using prosody to avoid ambiguity: Effects of speaker awareness and referential context

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Using prosody to avoid ambiguity Effects of
speaker awareness and referential context

• Snedeker and Trueswell (2003)
• Psych 526
• Eun-Kyung Lee

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Prosody in Sentence Processing

• The role of prosodic information in either
  comprehension or production of syntactically
  ambiguous sentences
• Based on the finding of the relation between
  syntax and prosody

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Previous Findings

• Inconsistent
• The use of prosodic cues in syntactic
  disambiguation is limited (Allbritton et al,
  1996) vs. reliable (Schafer et al. 2000)
• Speakers reliable use of prosodic cues
• depends on
• Whether other cues disambiguate the structure
• Whether speakers are aware of the potential for
  ambiguity

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Limitations

• Data
• Artificially manipulated prosody
• Obtained mostly from trained speakers with
  explicit instruction
• No examination of interaction between the speaker
  and the listener

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The Current Paper

• Examines the effect of referential context and
  awareness on both the production and
  comprehension of prosodic cues to structure
• Untrained speakers
• Target structure
• Globally ambiguous PP attachment
• Tap the frog with the flower

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Referential Communication Task1

• Referential context sets of objects
• The speaker and the listener are separated by a
  divider
• Allows manipulations of referential effects
  independently on the comprehension and the
  production task

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Referential Communication Task2

• Procedure
• The experimenter demonstrates an action to the
  speaker
• The speaker produces a scripted sentence
  describing that action
• The listener performs the action described by the
  speaker
• The effectiveness of prosodic cues is assessed
  depending on how well the listener replicates the
  experimenters action

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Research Questions

• How prosodic cues are used by the speaker when
  the referential context
• supports both meanings of the target sentence
  (Experiment 1)
• Strongly favors the intended meaning of the
  utterance (Experiment 2)
• When the prosodic information is used by the
  listener, based on the eye movement test
  (Experiment 3)

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Experiment 1
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Methods1

• 32 pairs of participants
• Identical sets of toy animals for the speaker and
  the listener
• Attribute-possessor relation is demonstrated by a
  small object attached to them
• Speakers utterances are audiotaped and the
  listeners actions are videotaped
• Post-experiment interview
• to assess participants awareness of the
  experimental manipulation and the ambiguity in
  the critical items

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Methods2
Target instrument

• Stimuli (on each trial)
• Support both interpretations of the ambiguous
  sentence by providing
• a potential instrument (large flower)
• two possible direct objects (the frogs) for the
  VP attachment
• a potential direct object for the NP attachment
  (frog holding flower)

Unmarked animal
Marked animal
Marked animal
Distractor animal
Distractor object
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Methods3

• 4 Conditions
• Ambiguous, instrument demonstration
• Tap the frog with the flower
• Ambiguous, modifier demonstration
• Tap the frog with the flower
• Unambiguous, instrument demonstration
• Tap the frog by using the frog
• Unambiguous, modifier demonstration
• Tap the frog that has the flower
• 4 counterbalanced presentation lists
• 16 target trials, 30 fillers
• 4 reverse-order lists

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Coding

• Listeners actions
• Instrument responses
• Modifier responses
• Speakers prosody
• Acoustic analysis word and pause durations
• Tap the frog with the flower
• Phonological analysis
• Break indices for the break following the verb
  and the noun
• Presence or absence of pitch accent on the
  preposition

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Results1 Listeners actions

• Proportion of instrument responses
• 66 for instrument demonstration
• 24 for modifier demonstration
• Reliably lower performance on ambiguous structure
  compared to unambiguous structure

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Results2Acoustic Analysis

• Instrument demo.
• For 68 of the trials
• Lengthening of the direct object (DO)
• Pause after DO
• Modifier demo.
• For 40 of the trials
• Lengthening of the verb
• Pause after the verb

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Results3Phonological Analysis

• Modifier demonstration
• A relatively frequent IP break after the verb
• Instrument demonstration
• A relatively frequent IP break after DO
• Pitch accent on preposition

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Results4Phonological Analysis

• 68 of the trials with appropriate and
  disambiguating phrasing
• 22 with neutral prosodic phrasing
• 10 with phrasing that was more appropriate
  for the alternate interpretation
• ? Prosodic cues are a highly effective but
  imperfect means of syntactic disambiguation

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Results5Awareness of Ambiguity

• 97 of the speakers and 91 of the listeners were
  coded as aware of the ambiguity
• ? Prosodic disambiguation arises due to the
  speakers awareness of the ambiguity in the
  critical items

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Experiment 2
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Methods1

• Differences in stimuli from Exp.1
• The speakers referential context supports only
  the intended meaning of the ambiguous phrase
• Listeners context was the same ambiguous context
  as in Exp. 1
• Listeners and speakers were told that they would
  receive an identical set of objects
• The type of Demonstration serves as a
  between-subject variable
• Syntactically ambiguous conditions only

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Methods2

• 32 pairs of participants additional 10 pairs
  (unaware pairs / aware pairs depending on the
  speakers awareness of the ambiguity)
• 2 lists
• 16 critical sentences, 24 fillers
• 2 reverse order lists
• Coding
• Same as in Exp. 1

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Results1Listeners actions

• In Exp. 2, 41 instrument responses for
  instrument Demo. And 34 for modifier Demo.
• Reliable difference in the distribution of
  responses between the two experiments
  (?2(1)4.04, pgt.05)

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Results2Acoustic Analysis

• No significant effect of Demonstration in both
  word and pause durations in critical regions
  (verb, DO)
• Reliable but smaller effect on duration of the
  PP, compared to Exp. 1

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Results3Phonological Analysis

• Instrument Demo.
• Clear distinction between the rate of 3 coding
  categories, but low proportion of correct
  phrasing
• But for Modifier Demo.
• Greater rate of incorrect and ambiguous coding
• ? The relation between particular prosodic cues
  and syntactic structure is weak and probabilistic

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Results4Awareness of ambiguity

• Listeners
• As likely to notice the ambiguity as those in
  Exp. 1
• Speakers
• 6 of the speakers in the instrument condition
• 56 in the modifier condition -gt but decreased
  relative to Exp. 1
• ? Due to verb bias action verbs, more likely
  instrument attachment

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Results 5Awareness and Listeners Performance

• In Modifier condition
• Instrument responses no significant difference
  between when speakers were aware of the ambiguity
  (40) and unaware (38)
• the speakers awareness alone does not determine
  prosodic disambiguation

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Results 6Awareness and Listeners Performance

• In Instrument condition
• Better performance of listeners in Exp. 1 (66
  instrument actions) than in Exp. 2 (41)
• Speaker awareness seems to have an effect in
  contrast to in the modifier condition
• Referential context differs
• ? Speakers only produce reliable disambiguating
  prosody when the context doesnt do the work for
  them

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Results 7Awareness and duration

• Small but reliable differences between Aware and
  Unaware modifier utterances at the noun, the noun
  pause and prepositional phrase
• listeners were rarely sensitive to these
  differences
• No reliable difference between the Unaware
  modifier and instrument utterances

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Summary of Exp. 1, 2

• No reliable prosodic cues (enough for listeners
  to rely on) produced by speakers in Exp. 2
• Speakers provide reliable prosodic cues only when
  the referential context is ambiguous and perhaps
  when speakers become aware of this

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Experiment 3
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Goals

• Based on the real-world eye-gaze paradigm
  combined
• with the referential communication task
• Sees whether the prosodic cues produced by
  speakers could shape online interpretation (the
  rapidity with which prosody influences parsing)
• Examines when and how early the prosodic
  information appears in the utterance

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Methods

• 24 pairs of participants
• ISCAN eye-tracking visor
• Ambiguous referential contexts both for listeners
  and speakers
• No unambiguous conditions
• 2 stimulus lists (8 target items, 24 filler items
  in each list) 4 reversing order lists

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Results1Actions, prosody, and awareness

• Replicate the findings of Exp. 1
• Actions prosody
• Listeners responses to the ambiguous sentences
  reflected the intentions of the speaker
• Speakers prosody clearly varied with intended
  structure
• Significant effect of Demonstration in each of
  the critical regions
• Awareness of ambiguity
• 92 of the speakers, 96 of the listeners

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Results2Online interpretation

• Re-synchronize the utterances at each word and
  conduct the analyses on small time windows
• Direct object noun
• Prepositional object

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Results3Proportion of fixation to direct
object noun
Significant difference in fixation to unmarked
animal
Modifier
(150ms) Program an eye movement
Time slice 1 200-300
Time slice 2 300-400
Time slice 3 400-500
Instrument
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Results4Proportion of fixation to direct
object noun

• The reliable effect of Demonstration in the
  400-500ms time slice
• Within 250ms of the onset of the direct object
  noun
• At about the same time as phonologically driven
  effects (Animal identification)

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Results5Prosody vs. phonologically driven
effects
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Results4Proportion of fixation to direct
object noun

• The reliable effect of Demonstration in the
  400-500ms time slice
• Within 250ms of the onset of the direct object
  noun
• At about the same time as phonologically driven
  effects (Animal identification)
• Prosody influences interpretation prior to the
  ambiguous region
• May be due to the difference in a pause after
  verb

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Results6Proportion of fixation to
prepositional object
Modifier
Marked animal
Target instrument
Marginally significant (due to ceiling effect)
Onset of the prepositional object
Significant
Instrument
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Summary Discussion1

• Referential context affects the speakers use of
  prosodic cues to disambiguate the sentence
• When the context fails to disambiguate the
  sentence
• ? reliably used
• When the context supports only the intended
  meaning
• ? rarely used

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Summary Discussion2

• Why conflicting findings with Shafer et
  al.(2000)?
• In Shafer et al. (2000)
• Likelihood that NP with PP phrases became
  lexicalized (e.g. the square with the triangle)
• Subtler contextual cues to disambiguation
• Longer and more complex sentences

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Summary Discussion3

• Listeners are sensitive to the existing prosodic
  cues
• Prosodic effects are found prior to the onset of
  the ambiguous phrases
• Affect the listeners initial interpretation of
  utterance
• Predict material which has yet to be spoken

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Thank you!