Beyond the Token: Correcting the Tokenization Bias in XAI via Morphologically-Aligned Projection

Muhammet Anil Yagiz, Fahrettin Horasan


Abstract
Current interpretability methods for Large Language Models (LLMs) operate on a fundamental yet flawed assumption: that subword tokens represent independent semantic units. We prove that this assumption creates a fidelity bottleneck in Morphologically Rich Languages (MRLs), where semantic meaning is densely encoded in sub-token morphemes. We term this phenomenon the Tokenization-Morphology Misalignment (TMM). To resolve TMM, we introduce MAFEX (Morpheme-Aligned Faithful Explanations), a theoretically grounded framework that redefines feature attribution as a linear projection from the computational (token) basis to the linguistic (morpheme) basis. We evaluate our method on a diverse suite of Turkish LLMs, including BERTurk, BERTurk-Sentiment, Cosmos-BERT, and Kumru-2B. On our embedded benchmark (N=20), MAFEX achieves an average F1@1 of 91.25% compared to 13.75% for standard token-level baselines (IG, SHAP, DeepLIFT), representing a +77.5% absolute improvement, establishing it as the new standard for faithful multilingual interpretability.
Anthology ID:
2026.sigturk-1.19
Volume:
Proceedings of the Second Workshop Natural Language Processing for Turkic Languages (SIGTURK 2026)
Month:
March
Year:
2026
Address:
Rabat, Morocco
Editors:
Kemal Oflazer, Abdullatif Köksal, Onur Varol
Venues:
SIGTURK | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
228–235
Language:
URL:
https://aclanthology.org/2026.sigturk-1.19/
DOI:
Bibkey:
Cite (ACL):
Muhammet Anil Yagiz and Fahrettin Horasan. 2026. Beyond the Token: Correcting the Tokenization Bias in XAI via Morphologically-Aligned Projection. In Proceedings of the Second Workshop Natural Language Processing for Turkic Languages (SIGTURK 2026), pages 228–235, Rabat, Morocco. Association for Computational Linguistics.
Cite (Informal):
Beyond the Token: Correcting the Tokenization Bias in XAI via Morphologically-Aligned Projection (Yagiz & Horasan, SIGTURK 2026)
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PDF:
https://aclanthology.org/2026.sigturk-1.19.pdf