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 disambiguation 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 ambiguity

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 listener 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 Distractor animalDistractor 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 Time slice Time slice Significant difference in fixation to unmarked animal

Results[4] Proportion of fixation to direct object noun The reliable effect of Demonstration in the ms 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 ms 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!