How Much Noise Can BERT Handle? Insights from Multilingual Sentence Difficulty Detection

Nouran Khallaf, Serge Sharoff


Abstract
Noisy training data can significantly degrade the performance of language-model-based classifiers, particularly in non-topical classification tasks. This study explores a range of denoising strategies for sentence-level difficulty detection, using training data derived from document-level difficulty annotations obtained through noisy crowdsourcing. Beyond monolingual settings, we also address cross-lingual transfer, where a multilingual language model is trained in one language and tested in another. We evaluate several noise reduction techniques, including Gaussian Mixture Models (GMM), Co-Teaching, Noise Transition Matrices, and Label Smoothing. Our results indicate that while BERT-based models exhibit inherent robustness to noise, incorporating explicit noise detection can further enhance performance. For our smaller dataset, GMM-based noise filtering proves particularly effective in improving prediction quality by raising the AUC score from 0.52 to 0.86, or to 0.92 when two de-noising methods are combined (GMM and Co-Teaching). However, for our larger dataset, the intrinsic regularisation of pre-trained language models provides a strong baseline, with denoising methods yielding only marginal gains (from 0.8948 to 0.8984, or to 0.9061 when two denoising methods are combined). Nonetheless, removing noisy sentences (about 20% of the dataset) helps in producing a cleaner corpus with fewer infelicities. As a result we have released the largest available multilingual corpus for sentence difficulty prediction.
Anthology ID:
2026.lrec-1.485
Volume:
Proceedings of the Fifteenth Language Resources and Evaluation Conference
Month:
May
Year:
2026
Address:
Palma de Mallorca, Spain
Editors:
Stelios Piperidis, Núria Bel, Henk van den Heuvel, Nancy Ide, Simon Krek, Antonio Toral
Venue:
LREC
SIG:
Publisher:
ELRA Language Resource Association
Note:
Pages:
6132–6143
Language:
External URL:
https://lrec.elra.info/lrec2026-main-485
DOI:
10.63317/3996hxsmfa2k
Bibkey:
Cite (ACL):
Nouran Khallaf and Serge Sharoff. 2026. How Much Noise Can BERT Handle? Insights from Multilingual Sentence Difficulty Detection. In Proceedings of the Fifteenth Language Resources and Evaluation Conference, pages 6132–6143, Palma de Mallorca, Spain. ELRA Language Resource Association.
Cite (Informal):
How Much Noise Can BERT Handle? Insights from Multilingual Sentence Difficulty Detection (Khallaf & Sharoff, LREC 2026)
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