Sparse MoE as a New Treatment: Addressing Forgetting, Fitting, Learning Issues in Multi-Modal Multi-Task Learning

Jie Peng, Sukwon Yun, Kaixiong Zhou, Ruida Zhou, Thomas Hartvigsen, Yanyong Zhang, Zhangyang Wang, Tianlong Chen

Keywords: transformer, sparse mixture-of-experts, multi-modal learning, multi-task learning

TL;DR: We propose a systematic approach addressing the forgetting, fitting, and learning issues in multi-modal multi-task learning via Sparse MoE.

Abstract:

Sparse Mixture-of-Experts (SMoE) is a promising paradigm that can be easily tailored for multi-task learning. Its conditional computing nature allows us to organically allocate relevant parts of a model for performant and efficient predictions. However, several under-explored pain points persist, especially when considering scenarios with both multiple modalities and tasks: 1. $\textit{{Modality Forgetting Issue.}}$ Diverse modalities may prefer conflicting optimization directions, resulting in ineffective learning or knowledge forgetting; 2. $\textit{{Modality Fitting Issue.}}$ Current SMoE pipelines select a fixed number of experts for all modalities, which can end up over-fitting to simpler modalities or under-fitting complex modalities; 3. $\textit{{Heterogeneous Learning Pace.}}$ The varied modality attributes, task resources, and objectives usually lead to distinct optimization difficulties and convergence. Given these issues, there is a clear need for a systematic approach to harmonizing multi-modal and multi-task objectives when using SMoE. We aim to address these pain points and propose a new $\underline{S}$parse $\underline{M}$oE for $\underline{M}$ulti-$\underline{M}$odal $\underline{M}$ulti-task learning, $\textit{a.k.a.}$, $\texttt{SM$^4$}$, which ($1$) disentangles model spaces for different modalities to mitigate their optimization conflicts;
($2$) automatically determines the modality-specific model size to improve fitting; and ($3$) synchronizes the learning paces of disparate modalities and tasks based on training dynamics in SMoE like the entropy of routing decisions. Comprehensive experiments validate the effectiveness of $\texttt{SM$^4$}$, which outperforms previous state-of-the-art across $3$ task groups and $11$ different modalities with a clear performance margin ($\textit{e.g.}$, $\ge 1.37\%$) and a substantial computation reduction ($46.49\% \sim 98.62\%$). Codes are in supplement.

Submission Number: 2