AmbiCoref: Evaluating Human and Model Sensitivity to Ambiguous Coreference
What it is about
The paper asks whether coreference models react to pronoun ambiguity as people do. It builds AmbiCoref, a corpus of minimal sentence pairs: an ambiguous and an unambiguous sentence differ only in one verb phrase (for example "Abby told Brittney that she upset Courtney" against "hugged"). The templates come from four psycholinguistic effects (experiencer constraints for objects and subjects, implicit causality, transfer of possession) and use VerbNet classes; the corpus has over 96,000 sentences. In a crowdsourced study of 625 sentences with three judgements each, unambiguous items get the intended referent (likely or definitely) for 83.2%, 91.9%, 85.8% and 68.3% of cases in the four types, while ambiguous items show a clear shift toward uncertainty. Five models (three CoreNLP variants, SpanBERT, NeuralCoref 4.0) are compared by the Earth Mover's Distance between their cluster-case distributions for matched pairs. Four of the five hardly change (mean EMD 0.6 to 4.0); SpanBERT changes most (11.7).
Ideas
- I1. Minimal-pair set for Mova: generate ambiguous and unambiguous pairs in
coref/from the same templates (verb class decides the constraint), and check thatcoref/src/sieve.rschanges its output between the pair. A sieve that outputs the same cluster for both members is missing the verb's effect. - I2. Use the paper's distribution, not the final decision, as a rule output: the sieve can report a confidence per case (A, B, singleton, other) and "abstain" when two cases are close. Log this in
pragas a clarification trigger, explainable per rule. - I3. Human-judgement check for the rules: a small annotation of 50 pairs by the operator, with the confidence scale as in the paper, to fix which template types Mova should treat as ambiguous before any gain is claimed.
For Mova
Code: coref/src/sieve.rs (case output and abstention), coref/src/eval.rs (the minimal-pair measure), and prag for a clarification response. Chapters: languages/en/35-reference-and-coreference.md, languages/en/33-implicature-and-presupposition.md. Measure: the EMD-style shift between ambiguous and unambiguous pairs, run twice, with a shuffled-verb negative control that should show no shift.
Library summary
Written for the Research library (claude-opus-5-5) from the paper text. Original — aclanthology.org/2023.findings-eacl.75.pdf
Summary
Coreference systems typically assign every pronoun to an antecedent, even when people would find the reference unclear and ask for clarification. The authors test whether current models notice such ambiguity. They built AmbiCoref, a synthetic English diagnostic corpus of minimal sentence pairs. In each pair, swapping only the verb phrase turns a pronoun with a clear antecedent into one with an unclear antecedent. The templates draw on psycholinguistic findings about experiencer verbs, implicit causality and transfer of possession. Verbs were chosen manually from VerbNet classes, and the templates were filled with names and noun phrases.
Crowdworkers resolved the unambiguous items as intended and were noticeably less confident on the ambiguous ones. Five coreference systems trained on CoNLL 2012 mostly produced the same output for both versions. Only SpanBERT changed its predictions to any measurable degree. The results suggest that models need finer-grained annotation or better calibration to respond to ambiguity the way humans do.
Key points
- AmbiCoref contains more than 96 thousand sentences. They come from four template families (ECO, ECS, IC, TOP), which make up six ambiguous/unambiguous template pairs.
- Template slots were filled as follows:
- Verbs come from VerbNet classes 31 (psych verbs), 13 (change of possession) and 37 (communication).
- Names were sampled from US popular-name lists.
- Gendered noun phrases come from WinoBias.
- In the Mechanical Turk study, each instance received 3 judgments. On unambiguous items, annotators picked the intended referent 83.2% (ECO), 91.9% (ECS), 85.8% (IC) and 68.3% (TOP) of the time. Ambiguous items shifted toward low-confidence or "ambiguous" answers.
- Five models were evaluated: SpanBERT, NeuralCoref 4.0, and the deterministic, statistical and neural CoreNLP systems. A template was excluded for a model if the model resolved fewer than 40% of its unambiguous cases correctly. TOP was frequently excluded under this rule.
- The authors measured how much each model's output distribution changed between ambiguous and unambiguous versions, using mean Earth Mover's Distance:
| Model | Mean EMD |
|---|---|
| SpanBERT | 11.7% |
| NeuralCoref 4.0 | 4.0% |
| CoreNLP Neural | 3.5% |
| CoreNLP Statistical | 1.2% |
| CoreNLP Deterministic | 0.6% |
Cite
@inproceedings{yuan2023ambicoref,
title = {{AmbiCoref: Evaluating Human and Model Sensitivity to Ambiguous Coreference}},
author = {Yuan, Yuewei and Malaviya, Chaitanya and Yatskar, Mark},
booktitle = {Findings of the Association for Computational Linguistics: EACL 2023},
year = {2023},
doi = {10.18653/v1/2023.findings-eacl.75},
eprint = {2302.00762},
archivePrefix = {arXiv},
url = {https://doi.org/10.18653/v1/2023.findings-eacl.75}
}References
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