Data Shapes What, Scale Shapes How: Lexical Learning Dynamics in LLMs

Nazanin Shafiabadi, Guillaume Wisniewski


Abstract
We investigate how model scale shapes lexical acquisition in LLMs, introducing trajectory comparison as a methodological tool and three new convergence metrics. Tracking surprisal dynamics across four Pythia model sizes and 153 training checkpoints, we report two main findings. First, scale drives a global rise in inter-word surprisal coherence: synonym curves become more correlated at larger scales, but baseline correction reveals that the advantage of semantic relatedness over random pairs is invariant with scale, indicating that what scales is broad inter-word coherence rather than semantic abstraction specifically. Second, learning dynamics are shaped primarily by training data rather than by model capacity: surprisal trajectories are highly similar across model sizes, and our new metrics confirm that larger models converge faster but not along qualitatively different paths. Together, these results call for baseline-corrected analyses and longitudinal evaluation when assessing lexical competence in LLMs.
Anthology ID:
2026.findings-emnlp.1812
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
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SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
38703–38716
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URL:
https://aclanthology.org/2026.findings-emnlp.1812/
DOI:
Bibkey:
Cite (ACL):
Nazanin Shafiabadi and Guillaume Wisniewski. 2026. Data Shapes What, Scale Shapes How: Lexical Learning Dynamics in LLMs. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 38703–38716, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Data Shapes What, Scale Shapes How: Lexical Learning Dynamics in LLMs (Shafiabadi & Wisniewski, Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.1812.pdf