Automatic Cue-Based Dialogue Act Tagging Discourse & Dialogue CMSC November 3, 2006

Roadmap Task & Corpus Dialogue Act Tagset Automatic Tagging Models –Features –Integrating Features Evaluation Comparison & Summary

Task & Corpus Goal: –Identify dialogue acts in conversational speech Spoken corpus: Switchboard –Telephone conversations between strangers –Not task oriented; topics suggested –1000s of conversations recorded, transcribed, segmented

Dialogue Act Tagset Cover general conversational dialogue acts –No particular task/domain constraints Original set: ~50 tags – Augmented with flags for task, conv mgmt 220 tags in labeling: some rare Final set: 42 tags, mutually exclusive –Agreement: K=0.80 (high) 1,155 conv labeled: split into train/test

Common Tags Statement & Opinion: declarative +/- op Question: Yes/No&Declarative: form, force Backchannel: Continuers like uh-huh, yeah Turn Exit/Adandon: break off, +/- pass Answer : Yes/No, follow questions Agreement: Accept/Reject/Maybe

Probabilistic Dialogue Models HMM dialogue models –Argmax U P(U)P(E|U) – E: evidence,U:DAs Assume decomposable by utterance Evidence from true words, ASR words, prosody Structured as offline decoding process on dialogue –States= DAs, Obs=Utts, P(Obs)=P(Ei|Ui), trans=P(U) P(U): –Conditioning on speaker tags improves model –Bigram model adequate, useful

DA Classification -Words Words –Combines notion of discourse markers and collocations: e.g. uh-huh=Backchannel –Contrast: true words, ASR 1-best, ASR n-best Results: –Best: 71%- true words, 65% ASR 1-best

DA Classification - Prosody Features: –Duration, pause, pitch, energy, rate, gender Pitch accent, tone Results: –Decision trees: 5 common classes 45.4% - baseline=16.6% –In HMM with DT likelihoods as P(Ei|Ui) 49.7% (vs. 35% baseline)

DA Classification - All Combine word and prosodic information –Consider case with ASR words and acoustics –P(Ai,Wi,Fi|Ui) ~ P(Ai,Wi|Ui)P(Fi|Ui) –Reweight for different accuracies Slightly better than raw ASR

Integrated Classification Focused analysis –Prosodically disambiguated classes Statement/Question-Y/N and Agreement/Backchannel Prosodic decision trees for agreement vs backchannel –Disambiguated by duration and loudness –Substantial improvement for prosody+words True words: S/Q: 85.9%-> 87.6; A/B: 81.0%->84.7 ASR words: S/Q: 75.4%->79.8; A/B: 78.2%->81.7 –More useful when recognition is iffy

Observations DA classification can work on open domain –Exploits word model, DA context, prosody –Best results for prosody+words –Words are quite effective alone – even ASR Questions: –Whole utterance models? – more fine-grained –Longer structure, long term features

Automatic Metadata Annotation What is structural metadata? –Why annotate?

What is Structural Metadata? Issue: Speech is messy Sentence/Utterance boundaries not marked Basic units for dialogue act, etc Speech has disfluencies Result: Automatic transcripts hard to read Structural metadata annotation: –Mark utterance boundaries –Identify fillers, repairs

Metadata Details Sentence-like units (SU) –Provide basic units for other processing Not necessarily grammatical sentences Distinguish full and incomplete SUs Conversational fillers –Discourse markers, disfluencies – um, uh, anyway Edit disfluencies –Repetitions, repairs, restarts Mark material that should be excluded from fluent Interruption point (IP): where corrective starts

Annotation Architecture 2 step process: –For each word, mark IP, SU, ISU, none bound –For region – bound+words – identify CF/ED Post-process to remove insertions Boundary detection – decision trees –Prosodic features: duration, pitch, amp, silence –Lexical features: POS tags, word/POS tag patterns, adjacent filler words

Boundary Detection - LM Language model based boundaries –“Hidden event language model” Trigram model with boundary tags Combine with decision tree –Use LM value as feature in DT –Linear interpolation of DT & LM probabilities –Jointly model with HMM

Edit and Filler Detection Transformation-based learning –Baseline predictor, rule templates, objective fn Classify with baseline Use rule templates to generate rules to fix errors Add best rule to baseline Training: Supervised –Features: Word, POS, word use, repetition,loc –Tag: Filled pause, edit, marker, edit term

Evaluation SU: Best combine all feature types –None great CF/ED: Best features – lexical match, IP Overall: SU detection relatively good –Better on reference than ASR Most FP errors due to ASR errors –DM errors not due to ASR –Remainder of tasks problematic

SU Detection FeaturesSU- R SU-PISU- R ISU-PIP-RIP-P Prosody only POS, Pattern,LM Pros,POS, Pattern,LM All+frag