Limitations of Autoregressive Models and Their Alternatives

Chu-Cheng Lin, Aaron Jaech, Xin Li, Matthew R. Gormley, Jason Eisner


Abstract
Standard autoregressive language models perform only polynomial-time computation to compute the probability of the next symbol. While this is attractive, it means they cannot model distributions whose next-symbol probability is hard to compute. Indeed, they cannot even model them well enough to solve associated easy decision problems for which an engineer might want to consult a language model. These limitations apply no matter how much computation and data are used to train the model, unless the model is given access to oracle parameters that grow superpolynomially in sequence length. Thus, simply training larger autoregressive language models is not a panacea for NLP. Alternatives include energy-based models (which give up efficient sampling) and latent-variable autoregressive models (which give up efficient scoring of a given string). Both are powerful enough to escape the above limitations.
Anthology ID:
2021.naacl-main.405
Original:
2021.naacl-main.405v1
Version 2:
2021.naacl-main.405v2
Volume:
Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies
Month:
June
Year:
2021
Address:
Online
Editors:
Kristina Toutanova, Anna Rumshisky, Luke Zettlemoyer, Dilek Hakkani-Tur, Iz Beltagy, Steven Bethard, Ryan Cotterell, Tanmoy Chakraborty, Yichao Zhou
Venue:
NAACL
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
5147–5173
Language:
URL:
https://aclanthology.org/2021.naacl-main.405
DOI:
10.18653/v1/2021.naacl-main.405
Bibkey:
Cite (ACL):
Chu-Cheng Lin, Aaron Jaech, Xin Li, Matthew R. Gormley, and Jason Eisner. 2021. Limitations of Autoregressive Models and Their Alternatives. In Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies, pages 5147–5173, Online. Association for Computational Linguistics.
Cite (Informal):
Limitations of Autoregressive Models and Their Alternatives (Lin et al., NAACL 2021)
Copy Citation:
PDF:
https://aclanthology.org/2021.naacl-main.405.pdf
Video:
 https://aclanthology.org/2021.naacl-main.405.mp4