Cited by 897Topic ModelingNatural Language Processing TechniquesExplainable Artificial Intelligence (XAI)

How Contextual are Contextualized Word Representations? Comparing the Geometry of BERT, ELMo, and GPT-2 Embeddings

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Ethayarajh, Kawin·2019·Proceedings of the 2019 Conference on Empirical Methods in Natural Language Processing and the 9th International Joint Conference on Natural Language Processing (EMNLP-IJCNLP)

Abstract

Replacing static word embeddings with contextualized word representations has yielded significant improvements on many NLP tasks.However, just how contextual are the contextualized representations produced by models such as ELMo and BERT?Are there infinitely many context-specific representations for each word, or are words essentially assigned one of a finite number of word-sense representations?For one, we find that the contextualized representations of all words are not isotropic in any layer of the contextualizing model.While representations of the same word in different contexts still have a greater cosine similarity than those of two different words, this self-similarity is much lower in upper layers.This suggests that upper layers of contextualizing models produce more context-specific representations, much like how upper layers of LSTMs produce more task-specific representations.In all layers of ELMo, BERT, and GPT-2, on average, less than 5% of the variance in a word's contextualized representations can be explained by a static embedding for that word, providing some justification for the success of contextualized representations.

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  • Precedent exists for using PCA to extract network-level patterns from high-dimensional neural data, including fMRI, EEG, and LLM embeddings.

    “Precedent exists for using PCA to extract network-level patterns from high-dimensional neural data, including fMRI (Smith et al., 2015), EEG (Blankertz et al., 2011), and even LLM embeddings (Ethayarajh, 2019).”

    From Can "consciousness" be observed from large language model (LLM) internal states? Dissecting LLM representations obtained from Theory of Mind test with Integrated Information Theory and Span Representation analysis (2025) · cites this paper as Ethayarajh, 2019

    Section 4.3 (page not available in our copy) uses the first principal component of contextualized BERT, ELMo, and GPT-2 word representations to create static embeddings. This supports a precedent for applying PCA to language-model embeddings, but the paper does not describe extracting network-level patterns. The fMRI and EEG examples are attributed to other citations in the sentence. (LLM, conf=0.86)

    Experimental — accuracy not yet measured
  • Ethayarajh (2019) notes that unidirectional models produce embeddings that vary smoothly across tokens, implying that the difference operation can still capture meaningful transitions within a span.

    “Ethayarajh (2019) notes that unidirectional models produce embeddings that vary smoothly across tokens, implying that the difference operation can still capture meaningful transitions within a span.”

    From Can "consciousness" be observed from large language model (LLM) internal states? Dissecting LLM representations obtained from Theory of Mind test with Integrated Information Theory and Span Representation analysis (2025) · cites this paper as Ethayarajh, 2019

    Section 4.2 measures similarity among words in the same sentence, but does not examine whether embeddings change smoothly between successive tokens. Neither that section nor the passages found on vector geometry address whether subtracting embeddings captures meaningful transitions within a span (searched for unidirectional models, neighboring tokens, smooth variation, and differences). (LLM, conf=0.72)

    Experimental — accuracy not yet measured
  • BERT embeddings capture rich semantic information and are widely recognized as effective for sentence similarity tasks.

    “Previous literature showed the BERT embeddings54 capture rich semantic information and are widely recognized as effective for sentence similarity tasks55–57.”

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1 of the 27 references couldn’t be matched to a known paper.

Research works printed but not linked: 5

  1. Eneko Agirre, Daniel Cer, Mona Diab, Aitor Gonzalez- Agirre, and Weiwei Guo. 2013. Sem 2013 shared task: Semantic textual similarity, including a pilot on typed-similarity. In SEM 2013: The Second Joint Conference on Lexical and Computational Seman- tics. Association for Computational Linguistics.
  2. John Hewitt and Christopher D. Manning. 2019. A structural probe for finding syntax in word represen- tations. In North American Chapter of the Associ- ation for Computational Linguistics: Human Lan- guage Technologies. Association for Computational Linguistics.
  3. Tomas Mikolov, Ilya Sutskever, Kai Chen, Greg S Cor- rado, and Jeff Dean. 2013a. Distributed representa- tions of words and phrases and their compositional- ity. In Advances in Neural Information Processing Systems. pages 3111-3119.
  4. Matthew Peters, Mark Neumann, Mohit Iyyer, Matt Gardner, Christopher Clark, Kenton Lee, and Luke Zettlemoyer. 2018. Deep contextualized word rep- resentations. In Proceedings of the 2018 Confer- ence of the North American Chapter of the Associ- ation for Computational Linguistics: Human Lan- guage Technologies, Volume 1 (Long Papers). pages 2227-2237.
  5. Ian Tenney, Patrick Xia, Berlin Chen, Alex Wang, Adam Poliak, R. Thomas McCoy, Najoung Kim, Benjamin Van Durme, Samuel R. Bowman, Dipan- jan Das, and Ellie Pavlick. 2019. What do you learn from context? probing for sentence structure in contextualized word representations. In Inter- national Conference on Learning Representations. https://openreview.net/forum?id=SJzSgnRcKX.

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Authors
Ethayarajh, K.
Affiliations
Stanford University (US)
Corresponding author
Ethayarajh, Kawin
Venue
Proceedings of the 2019 Conference on Empirical Methods in Natural Language Processing and the 9th International Joint Conference on Natural Language Processing (EMNLP-IJCNLP)
Published
2019
Pages
55-65
OpenAlex
W2971569798
Cited by
841
References
27
Citations by year
2026: 93 · 2025: 92 · 2024: 115 · 2023: 160 · 2022: 158 · 2021: 157 · 2020: 64 · 2013: 1 · 2012: 1
FWCI
36.26
Type
conference paper
Language
en
Open access
Licence
cc-by
Locations
  • Conference on Empirical Methods in Natural Language Processing (EMNLP) (publishedVersion, cc-by)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Funders
Natural Sciences and Engineering Research Council of Canada
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Topic Modeling
  • Physical Sciences › Computer Science › Artificial Intelligence › Natural Language Processing Techniques
  • Physical Sciences › Computer Science › Artificial Intelligence › Explainable Artificial Intelligence (XAI)
Keywords
contextualized word representations, word embeddings, BERT, ELMo, GPT-2, embedding geometry, cosine similarity, static embeddings, layer-wise analysis

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