What Brain Data Adds to Language Model Training
Summary
Earlier studies reported that fine-tuning language models to predict fMRI responses ("brain-tuning") improves some downstream tasks. However, those baselines usually also saw less of the stimulus text, so the gains could come from extra exposure to that text. The authors set up a controlled comparison of three regimes on bert-base-cased and gpt2-small:
- Brain-Tuned: trained only to predict brain recordings through a brain mapping head.
- Stimulus-Tuned: trained only on the matching stimulus text.
- Jointly-Tuned: trained on both signals together.
Training uses two public fMRI reading datasets: Harry Potter and The Moth Radio Hour. Each model is then probed for linguistic competence with the Holmes benchmark, which has over 200 tasks covering syntax, semantics, discourse, morphology and reasoning.
Joint tuning beats the pretrained models in every subfield, and Brain-Tuned models beat their Stimulus-Tuned counterparts. Single-signal tuning, however, usually falls below the pretrained baseline. The study shows that neural recordings carry useful signal beyond the text itself and offers a general way to measure such non-textual information gain.
Key points
- Datasets:
- Wehbe et al. (2014a): 8 participants reading Chapter 9 of Harry Potter and the Sorcerer's Stone, word by word at 500 ms each, TR=2s, 1211 images per participant.
- Deniz et al. (2019): 6 participants, 11 Moth Radio Hour stories, 4028 images, reading condition used.
- Evaluation: Holmes (Waldis et al., 2024) with more than 200 probing datasets grouped by linguistic subfield.
- Jointly-Tuned results: these were the only models that consistently surpassed the pretrained baselines, with the clearest gains in syntax, morphology and discourse.
- Brain-Tuned vs. Stimulus-Tuned: Brain-Tuned models outperformed Stimulus-Tuned ones. Both were generally worse than pretrained models, and Brain-Tuned exceeded pretrained only on morphology.
- Code: github.com/bridge-ai-neuro/lm-brain-tuning. Stated limitations are incomplete benchmark coverage (e.g., few discourse datasets), only two fMRI datasets, and a single stimulus genre.
Cite
@inproceedings{merlin2026what,
title = {{What Brain Data Adds to Language Model Training}},
author = {Merlin, Gabriele and Moussa, Omer and Toneva, Mariya},
booktitle = {Proceedings of the 30th Conference on Computational Natural Language Learning},
year = {2026},
doi = {10.18653/v1/2026.conll-main.12},
url = {https://doi.org/10.18653/v1/2026.conll-main.12}
}References
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