Sparse Autoencoders, Again?

TL;DR

This paper identifies limitations in traditional sparse autoencoders and variational autoencoders, proposing a hybrid model that better captures data structure, yields sparser representations, and outperforms existing models in various domains.

Contribution

The authors introduce a hybrid autoencoder model that overcomes weaknesses of canonical SAEs and VAEs, with theoretical guarantees and improved empirical performance.

Findings

The hybrid model recovers structured data across multiple manifolds.

It produces sparser latent representations without losing reconstruction quality.

It outperforms traditional SAEs, VAEs, and recent diffusion models in experiments.

Abstract

Is there really much more to say about sparse autoencoders (SAEs)? Autoencoders in general, and SAEs in particular, represent deep architectures that are capable of modeling low-dimensional latent structure in data. Such structure could reflect, among other things, correlation patterns in large language model activations, or complex natural image manifolds. And yet despite the wide-ranging applicability, there have been relatively few changes to SAEs beyond the original recipe from decades ago, namely, standard deep encoder/decoder layers trained with a classical/deterministic sparse regularizer applied within the latent space. One possible exception is the variational autoencoder (VAE), which adopts a stochastic encoder module capable of producing sparse representations when applied to manifold data. In this work we formalize underappreciated weaknesses with both canonical SAEs, as well as analogous VAEs applied to similar tasks, and propose a hybrid alternative model that circumvents these prior limitations. In terms of theoretical support, we prove that global minima of our proposed model recover certain forms of structured data spread across a union of manifolds. Meanwhile, empirical evaluations on synthetic and real-world datasets substantiate the efficacy of our approach in accurately estimating underlying manifold dimensions and producing sparser latent representations without compromising reconstruction error. In general, we are able to exceed the performance of equivalent-capacity SAEs and VAEs, as well as recent diffusion models where applicable, within domains such as images and language model activation patterns.