Spherical Latent Spaces for Stable Variational Autoencoders

Jiacheng Xu, Greg Durrett


Abstract
A hallmark of variational autoencoders (VAEs) for text processing is their combination of powerful encoder-decoder models, such as LSTMs, with simple latent distributions, typically multivariate Gaussians. These models pose a difficult optimization problem: there is an especially bad local optimum where the variational posterior always equals the prior and the model does not use the latent variable at all, a kind of “collapse” which is encouraged by the KL divergence term of the objective. In this work, we experiment with another choice of latent distribution, namely the von Mises-Fisher (vMF) distribution, which places mass on the surface of the unit hypersphere. With this choice of prior and posterior, the KL divergence term now only depends on the variance of the vMF distribution, giving us the ability to treat it as a fixed hyperparameter. We show that doing so not only averts the KL collapse, but consistently gives better likelihoods than Gaussians across a range of modeling conditions, including recurrent language modeling and bag-of-words document modeling. An analysis of the properties of our vMF representations shows that they learn richer and more nuanced structures in their latent representations than their Gaussian counterparts.
Anthology ID:
D18-1480
Volume:
Proceedings of the 2018 Conference on Empirical Methods in Natural Language Processing
Month:
October-November
Year:
2018
Address:
Brussels, Belgium
Editors:
Ellen Riloff, David Chiang, Julia Hockenmaier, Jun’ichi Tsujii
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
4503–4513
Language:
URL:
https://aclanthology.org/D18-1480
DOI:
10.18653/v1/D18-1480
Bibkey:
Cite (ACL):
Jiacheng Xu and Greg Durrett. 2018. Spherical Latent Spaces for Stable Variational Autoencoders. In Proceedings of the 2018 Conference on Empirical Methods in Natural Language Processing, pages 4503–4513, Brussels, Belgium. Association for Computational Linguistics.
Cite (Informal):
Spherical Latent Spaces for Stable Variational Autoencoders (Xu & Durrett, EMNLP 2018)
Copy Citation:
PDF:
https://aclanthology.org/D18-1480.pdf
Code
 jiacheng-xu/vmf_vae_nlp
Data
20NewsGroupsAG NewsPenn Treebank