UCSC NLP at SemEval-2026 Task 10: Boundary-Aware Span Extraction and RoBERTa Classification for Conspiracy Detection

Dom Marhoefer, Milos Suvakovic, Glenn Grant-Richards, Aidan Pinero, Ryan King


Abstract
We present our systems for SemEval-2026 Task10 (PsyCoMark), addressing conspiracy markerextraction (Subtask 1) and document-level con-spiracy detection (Subtask 2). For marker ex-traction, we formulate the task as multi-labelspan classification over enumerated candidatespans, using IoU≥0.95 positive labeling, hard-negative sampling, and containment-based non-maximum suppression (NMS) with boundary-aware span representations. Document classi-fication is modeled independently using a se-quence classifier with label smoothing and astratified train–validation split. Analysis showsthat entity-like roles (Actor, Victim) are de-tected robustly, while abstract roles (Action,Effect, Evidence) remain sensitive to boundarycriteria. On the official test set, our systemsrank 7th in Subtask 1 (0.2251 macro F1) and12th in Subtask 2 (0.7694 weighted F1).
Anthology ID:
2026.semeval-1.194
Volume:
Proceedings of the 20th International Workshop on Semantic Evaluation (2026)
Month:
July
Year:
2026
Address:
San Diego, California, USA
Editors:
Ekaterina Kochmar, Debanjan Ghosh, Kai North, Mamoru Komachi
Venues:
SemEval | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
1495–1500
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URL:
https://preview.aclanthology.org/ingest-acl-workshops/2026.semeval-1.194/
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Cite (ACL):
Dom Marhoefer, Milos Suvakovic, Glenn Grant-Richards, Aidan Pinero, and Ryan King. 2026. UCSC NLP at SemEval-2026 Task 10: Boundary-Aware Span Extraction and RoBERTa Classification for Conspiracy Detection. In Proceedings of the 20th International Workshop on Semantic Evaluation (2026), pages 1495–1500, San Diego, California, USA. Association for Computational Linguistics.
Cite (Informal):
UCSC NLP at SemEval-2026 Task 10: Boundary-Aware Span Extraction and RoBERTa Classification for Conspiracy Detection (Marhoefer et al., SemEval 2026)
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 2026.semeval-1.194.SupplementaryMaterial.zip