Hannah Rohde, Andy Kehler, & Jeff Elman UC San Diego Where to next? Pronoun interpretation as a side effect of discourse direction Hannah Rohde, Andy Kehler, & Jeff Elman UC San Diego CUNY Conference on Human Sentence Processing, March 29-31 2007

Transfer of possession (Stevenson et al. 1994) handed a book to . ______________. John John He Bill He Bill He thanked John recommended it Source (subject) Transfer Verb Goal (to-phrase) Ambiguous Pronoun Prompt 50/50: Goal continuations / Source continuations No subject preference or grammatical parallelism Two explanations considered: Thematic Role Preference Event Structure Bias

Outline Background: Rohde et al. 2006 Test Thematic-Role and Event-Structure biases Alternative account: Discourse Coherence Experiments 1 & 2: test predictions of a coherence- based model using story continuations Preliminary results: discourse effects in relative clause attachment

Explaining salience of Goal (Rohde et al. 2006) Thematic role preference or event structure bias? handed a book to . ______ . JohnSOURCE BillGOAL He was handing a book to . ___ . Equivalent thematic roles but different event structure Effect of aspect F(1,48)=50.622 p<0.0001 Goal bias ~ side effect of Event Structure

Effects of coherence (Rohde et al. 2006) Establishing coherence: infer a relationship between the meanings expressed by two sentences (P&Q below) (Hobbs 1979, Kehler 2002) Causal relations (Explanation, Result, Violated Expectation) Matt passed a sandwich to David. He didn’t want David to starve. [Explanation: Q  P] Matt He Matt passed a sandwich to David. He said thanks. [Result: P  Q] David He

Coherence cont. Similarity relations (Parallel, Elaboration) Matt passed a sandwich to David. He did so carefully. [Elaboration: infer P from both S1 and S2] Matt He Contiguity relations (Occasion) [Occasion: infer initial state of event described in S2 to be final state of event described in S1] Matt passed a sandwich to David. He ate it up. David He

Discourse coherence effects (Rohde et al.) Goal bias following perfective context sentences limited to Occasion & Result (see Arnold 2001) Interpretation as side effect of coherence distribution

Shift coherence  shift interpretation Test predictions of a coherence-driven model More Occasion/Result  more Goal resolutions More Explanation/Elaboration/Violated-Exp  more Source

Experiment 1: objects-of-transfer Proposal: elicit different continuations with different objects Stimuli: normal and bizarre objects John handed a book to Bill. He ___________ . John handed a bloody meat cleaver to Bill. He __ . Predictions: If… Abnormal objects  more Explanations and Explanations  Source bias More Source continuations for (9) than (8)

Methodology Subjects: 69 monolingual English speakers Task: write 50 continuations, just like Rohde et al. Stimuli: 21 transfer-of-possession like Rohde et al. (+ bizarre objects) Evaluation: judges assess coherence/interpretation Analysis: Effect of within-subject factor of Object Type on Coherence (Elab/Expl/Occ/Par/Res/Viol-Exp) Pronoun interpretation (Source/Goal) Mixed-effects logistic regression Controls for random effects of Subject and Item

} Results Coherence varies by object Consistent prob(Source|coh) Exp 1 Rohde et al. Coherence Elaboration 0.87 Violated-expectation 0.75 Explanation 0.99 0.16 Result 0.20 Occasion 0.45 Parallel p<0.0001 Source 0.81 0.82 0.99 0.05 0.17 0.71 Goal }

Results No effect of object type on pronoun interpretation Subjects: F(1,68)= 0.052 p<0.820 Items: F(1,20)=0.111 p<0.743

Experiment 2: ‘What next?’ or ‘Why?’ John handed a book to Bill. He ___________ . Stimuli & Design: identical to Rohde et al. 2006 Instructions: write continuations answering either “What happened next?” or “Why?” Predictions: “What next?”  more Occasions  Goal bias “Why?”  more Explanations  Source bias

Methodology Subjects: 42 monolingual English speakers Task: identical to Rohde et al. 2006 (w/instructions) Stimuli: identical to Rohde et al. 2006 Evaluation: judges assess coherence/interpretation Analysis: Effect of between-subject factor of Instruction Type on coherence distribution & pronoun interpretation

Results Coherence varies w/instruction (p<0.0001) Consistent prob(Source|coh) Exp 2 Rohde et al. Coherence Elaboration 0.87 Violated-expectation 0.75 Explanation 0.99 0.16 Result 0.20 Occasion 0.45 Parallel 0.81 1.00 0.11 0.28 0.46 Source Goal

Results Effect of Instruction type on pronoun interpretation

Predicting pronoun interpretation Predict % Source Resolutions in Exp 2 using: Exp2 coherence breakdown Exp1 conditional probabilities Coherence p(Source) Explanation 0.82 Elaboration 0.99 V-E 0.81 Occasion 0.17 Result 0.05 Parallel 0.45

Capturing subject variation “What next” “Why” linear regression R2=0.604 F(1,40)=61.097, p<0.0001

Consistency of biases across conditions R2 value/ANOVA Conditional Probability Estimator Exp1: perf, normal objects R2=0.606, F(1,40)=61.612* Exp1: imp, normal objects R2=0.627, F(1,40)=67.371* Exp1: perf, abnormal objects R2=0.561, F(1,40)=51.165* Exp1: imp, abnormal objects R2=0.586, F(1,40)=51.165* Exp1: average across verbal aspects & object types R2=0.604, F(1,40)=61.097* * Indicates p<0.0001

Summary Shift coherence  Shift pronoun interpretation No model relying only on surface-level cues can account for observed variation, since stimuli were near-identical (Exp 1) or identical (Exp 2) Need richer models incorporating discourse-level factors (see Wolf et al. 2004; Kertz et al. 2006)

What else can discourse do for you? Relative clause attachment ambiguity high low Beth babysits the children of the musician who ____ musical prodigies themselves. are the children at the club downtown. plays the musician Function of a relative clause John despises the employee who is always late. Implicit Causality (NP2 IC) verbs attribute cause to direct object Proposal: try to shift RC attachment using verbs that require Explanations and that attribute cause to the referent occupying higher NP

Predictions & results nonIC: Beth babysits the children of the musician who _____ plays at the club downtown. the musician  low IC: Beth despises the children of the musician who ______ and yell during rehearsals. scream the children  high F(1,51)=31.082 p<0.0001 p<0.0001  Further evidence that discourse influences interpretation

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Variation by instruction and aspect Coherence (instr x aspect interaction p<0.0001) Interpretation (instr x aspect interaction p<0.0001) John was giving a book to Bill. He ___________ . John gave a book to Bill. He ___________ . …“What happened next?”

Discourse coherence effects