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

Snedeker and Trueswell (2003)

Psych 526

Eun-Kyung Lee

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

Previous Findings

Inconsistent The use of prosodic cues in syntactic disambiguati

on is limited (Allbritton et al, 1996) vs. reliable (Schafer et al. 2000)

Speaker’s reliable use of prosodic cues depends on Whether other cues disambiguate the structure Whether speakers are aware of the potential for a

mbiguity

Limitations

Data Artificially manipulated prosody Obtained mostly from trained speakers with

explicit instruction No examination of interaction between the speaker

and the listener

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

NP attachment

VP attachment

Referential Communication Task[1]

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

Referential Communication Task[2]

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 experimenter’s action

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)

Experiment 1

Methods[1]

32 pairs of participants Identical sets of toy animals for the speaker and the liste

ner Attribute-possessor relation is demonstrated by a small

object attached to them Speaker’s utterances are audiotaped and the listener’s

actions are videotaped Post-experiment interview

to assess participants’ awareness of the experimental manipulation and the ambiguity in the critical items

Methods[2]

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)

Target instrument

Unmarked animal

Marked animal

Marked animal

Distractor animal Distractor object

Methods[3]

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

Coding

Listener’s actions Instrument responses Modifier responses

Speaker’s 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

Results[1] Listener’s actions

Proportion of instrument responses

66% for instrument demonstration

24% for modifier demonstration

Reliably lower performance on ambiguous structure compared to unambiguous structure

Results[2]Acoustic 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

Results[3]Phonological Analysis

Modifier demonstration A relatively frequent IP break after the verb

Instrument demonstration A relatively frequent IP break after DO Pitch accent on preposition

Results[4]Phonological 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

Results[5]Awareness of Ambiguity

97% of the speakers and 91% of the listeners were coded as aware of the ambiguity

Prosodic disambiguation arises due to the speaker’s awareness of the ambiguity in the critical items

Experiment 2

Methods[1]

Differences in stimuli from Exp.1 The speaker’s referential context supports only the

intended meaning of the ambiguous phrase Listener’s 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

Methods[2]

32 pairs of participants + additional 10 pairs (unaware pairs / aware pairs depending on the speaker’s awareness of the ambiguity)

2 lists 16 critical sentences, 24 fillers

2 reverse order lists Coding

Same as in Exp. 1

Results[1]Listener’s 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, p>.05)

Results[2]Acoustic 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

Results[3]Phonological 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

Results[4]Awareness 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 -> but decreased relative to Exp. 1 Due to verb bias: action verbs, more likely instrument attachment

Results [5]Awareness and Listener’s Performance

In Modifier condition Instrument responses: no significant difference

between when speakers were aware of the ambiguity (40%) and unaware (38%)

the speaker’s awareness alone does not determine prosodic disambiguation

Results [6]Awareness and Listener’s 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 doesn’t do the work for them

Results [7]Awareness 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

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

Experiment 3

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

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

Results[1]Actions, 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

Results[2]Online interpretation

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

Results[3]Proportion of fixation to direct object noun

(150ms) Program an

eye movement

Modifier

Instrument

Time slice 1200-300

Time slice 2300-400

Time slice 3400-500

Significant difference in

fixation to unmarked animal

Results[4]Proportion 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)

Results[5]Prosody vs. phonologically driven effects

Results[4]Proportion 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

Results[6]Proportion of fixation to prepositional object

Onset of the prepositional object

Modifier

Instrument

Significant

Marginally significant

(due to ceiling effect)

Target instrument

Marked animal

Summary & Discussion[1]

Referential context affects the speaker’s 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

Summary & Discussion[2]

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

Summary & Discussion[3]

Listeners are sensitive to the existing prosodic cues Prosodic effects are found prior to the onset of the

ambiguous phrases Affect the listener’s initial interpretation of

utterance Predict material which has yet to be spoken

Thank you!