Beyond Clean Text: Evaluating Encoder and Decoder Robustness for Bangla Event Detection in Noisy Text

Tanvir Ahmed Sijan, S M Golam Rifat, Nayeemul Islam, Md Musfique Anwar


Abstract
Event detection (ED) systems are typically evaluated on clean, curated text, leaving their robustness to real-world noise largely unexplored, particularly for low-resource languages such as Bangla. We introduce a generalized Bangla news event ontology and a benchmark comprising 9,979 annotated sentences across 40 event subtypes, spanning clean news text, real-world Automatic Speech Recognition (ASR) transcripts, and orthographically corrupted text. We systematically evaluate fine-tuned encoder-only models (BanglaBERT and XLM-R) alongside instruction-tuned decoder-only large language models (Llama 3 and Gemma 3). Our results reveal a clear architectural trade-off: encoder models achieve higher performance on clean text but degrade substantially under noise, whereas decoder-only LLMs are markedly more robust, particularly when event triggers are corrupted. We further show that embedding annotation guidelines during instruction tuning establishes a higher performance baseline on noisy text but yields inconsistent reductions in performance degradation across noisy conditions. Finally, model scaling consistently improves the robustness of decoder-only LLMs, while combined training on clean and noisy data serves as an effective regularization strategy that disproportionately benefits encoder architectures, significantly narrowing the robustness gap.
Anthology ID:
2026.wnut-1.3
Volume:
Proceedings of the 11th Workshop on Natural User-generated Text
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
JinYeong Bak, Rob van der Goot, Hyeju Jang, Weerayut Buaphet, Alan Ramponi, Wei Xu, Alan Ritter
Venues:
WNUT | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
26–48
Language:
URL:
https://aclanthology.org/2026.wnut-1.3/
DOI:
Bibkey:
Cite (ACL):
Tanvir Ahmed Sijan, S M Golam Rifat, Nayeemul Islam, and Md Musfique Anwar. 2026. Beyond Clean Text: Evaluating Encoder and Decoder Robustness for Bangla Event Detection in Noisy Text. In Proceedings of the 11th Workshop on Natural User-generated Text, pages 26–48, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Beyond Clean Text: Evaluating Encoder and Decoder Robustness for Bangla Event Detection in Noisy Text (Sijan et al., WNUT 2026)
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PDF:
https://aclanthology.org/2026.wnut-1.3.pdf