How to Plant Trees in Language Models: Data and Architectural Effects on the Emergence of Syntactic Inductive Biases
Paper · 2023 · Aaron Mueller and Tal Linzen
Summary
Language models that read text as flat word sequences may rely on positional shortcuts, such as "the first noun is the subject," instead of syntactic structure, which limits robust generalization. Mueller and Linzen ask which parts of pre-training give encoder-decoder Transformers a preference for hierarchical rules. They fine-tune T5-style models, using both public "efficient" checkpoints from Tay et al. (2022) and models they pre-train themselves on corpora of different genres and sizes. The fine-tuning tasks are two English syntactic transformations: question formation and passivization. The training examples fit both a structural rule and a linear heuristic. Test sentences with an inserted relative clause or prepositional phrase then reveal which rule the model actually learned. Raw parameter count does not predict hierarchical generalization, and adding layers helps more than widening them. Pre-training on child-directed speech produces the hierarchical bias with roughly an order of magnitude less text than Wikipedia or web data. These results inform data curation for pre-training and suggest Transformers can be credible models of human language acquisition.
Key points
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Paradigm: The study uses a poverty-of-the-stimulus design.
- In question formation, MOVE-MAIN (the correct rule) is pitted against MOVE-FIRST.
- In passivization, MOVE-MAIN is pitted against MOVE-SECOND.
- The data are taken from the English-language datasets released by Mueller et al. (2022), which themselves extend McCoy et al. (2020).
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Metrics: Models are scored with exact sequence accuracy plus a targeted measure for each task: main auxiliary accuracy for questions and object accuracy for passives.
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Architectures: The T5 variants from Tay et al. (2022) are:
Variant Parameters Layers per encoder/decoder Tiny 16M 4 Mini 31M 4 Small 60M 6 Base 220M 12 Across these variants, depth outweighs width for hierarchical generalization.
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Data efficiency: Simpler input, such as child-directed speech, yields the hierarchical bias with far less data than Wikipedia or C4-type web text. The authors propose a two-phase "starting small" pre-training scheme based on this finding.
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Limitations and resources: The study covers only T5-like models with a span denoising objective, only English, and only two transformations. Code is available at github.com/aaronmueller/emergent-syntax.
Institutions
Fields, topics and concepts
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 19,503 worksArtificial Intelligence · 18,805 worksArts and Humanities · 17,959 worksLanguage and Linguistics · 17,789 works
🧭 Topics 1Research subjects and languages the work is about.Language models & pretraining · 4,145 works
Cite
Cite as Aaron Mueller and Tal Linzen. 2023. How to Plant Trees in Language Models: Data and Architectural Effects on the Emergence of Syntactic Inductive Biases. arXiv:2305.19905.
@misc{mueller2023how,
title = {{How to Plant Trees in Language Models: Data and Architectural Effects on the Emergence of Syntactic Inductive Biases}},
author = {Aaron Mueller and Tal Linzen},
year = {2023},
doi = {10.48550/arxiv.2305.19905},
eprint = {2305.19905},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2305.19905}
}References
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