提出自归一化重置机制,缓解持续学习中的可塑性衰减问题。
Self-Normalized Resets for Plasticity in Continual Learning
- 基于神经元激活率的假设检验,动态重置不活跃神经元权重。
- 在多种任务与模型上均优于现有算法,且对超参数不敏感。
- 理论证明理想化版本可学习单个ReLU,而正则化方法可能失败。
可塑性损失是神经网络在持续学习多个变化任务时,适应新任务能力随时间下降的常见现象。本文提出自归一化重置(SNR),一种简单自适应算法:当证据表明神经元激活率已趋近于零时,自动重置其权重。在一系列持续学习任务与网络架构中,SNR始终优于对比算法。同时,SNR对唯一超参数——拒绝百分位阈值具有鲁棒性,而对比算法对此高度敏感。该阈值重置机制基于我们推导的简单假设检验。从该视角看,现有重置方法错误检测不活跃神经元的误差率较高,或可解释实验结果。此外,我们对学习单个ReLU的优化景观进行理论分析,发现即使初始化不利,理想化版本的SNR仍能学习目标ReLU,而基于正则化的方案可能失败。
原文摘要 · Abstract (English)
Plasticity Loss is an increasingly important phenomenon that refers to the empirical observation that as a neural network is continually trained on a sequence of changing tasks, its ability to adapt to a new task diminishes over time. We introduce Self-Normalized Resets (SNR), a simple adaptive algorithm that mitigates plasticity loss by resetting a neuron's weights when evidence suggests its firing rate has effectively dropped to zero. Across a battery of continual learning problems and network architectures, we demonstrate that SNR consistently attains superior performance compared to its competitor algorithms. We also demonstrate that SNR is robust to its sole hyperparameter, its rejection percentile threshold, while competitor algorithms show significant sensitivity. SNR's threshold-based reset mechanism is motivated by a simple hypothesis test that we derive. Seen through the lens of this hypothesis test, competing reset proposals yield suboptimal error rates in correctly detecting inactive neurons, potentially explaining our experimental observations. We also conduct a theoretical investigation of the optimization landscape for the problem of learning a single ReLU. We show that even when initialized adversarially, an idealized version of SNR learns the target ReLU, while regularization based approaches can fail to learn.
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