Mind the Gap: How BabyLMs Learn Filler-Gap Dependencies

Chi-Yun Chang, Xueyang Huang, Humaira Nasir, Shane Storks, Olawale Akingbade, Huteng Dai


Abstract
Humans acquire syntactic constructions like filler-gap dependencies from limited and often noisy input. Can neural language models do the same? We investigate this question by evaluating GPT-2 models trained on child-oriented input from the BabyLM Challenge. Our experiments focus on whether these “baby” language models acquire filler-gap dependencies, generalize across constructions, and respect structural constraints such as island effects. We apply a suite of syntactic constructions to four models trained on child language, including two base models (trained on 10M and 100M tokens) and two well-performing models from the BabyLM Challenge (ConcreteGPT and BabbleGPT). We evaluate model behavior using wh-licensing scores, flip tests, and grammaticality contrasts across four constructions. Results show that BabyLM-scale models partially acquire filler-gap dependencies but often fail to generalize or fully capture island constraints.
Anthology ID:
2025.emnlp-main.761
Volume:
Proceedings of the 2025 Conference on Empirical Methods in Natural Language Processing
Month:
November
Year:
2025
Address:
Suzhou, China
Editors:
Christos Christodoulopoulos, Tanmoy Chakraborty, Carolyn Rose, Violet Peng
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EMNLP
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Publisher:
Association for Computational Linguistics
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Pages:
15060–15076
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URL:
https://preview.aclanthology.org/ingest-emnlp/2025.emnlp-main.761/
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Cite (ACL):
Chi-Yun Chang, Xueyang Huang, Humaira Nasir, Shane Storks, Olawale Akingbade, and Huteng Dai. 2025. Mind the Gap: How BabyLMs Learn Filler-Gap Dependencies. In Proceedings of the 2025 Conference on Empirical Methods in Natural Language Processing, pages 15060–15076, Suzhou, China. Association for Computational Linguistics.
Cite (Informal):
Mind the Gap: How BabyLMs Learn Filler-Gap Dependencies (Chang et al., EMNLP 2025)
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