One of the problems in continual learning, where models are trained sequentially on tasks, is a sudden drop in performance after switching to a new task, called stability gap. The presence of stability gap likely indicates that training is not done optimally. In this work we aim to address stability gap problem by using sharpness-aware optimization that biases convergence to flat minima. While flat minima are known to mitigate forgetting, their role in ensuring stable learning during task transitions remains unexplored. Through systematic analysis of two Entropy-SGD and C-Flat, we demonstrate that sharpness-aware optimizers produce smoother learning trajectories with reduced instability after task switch. Furthermore, we show that C-Flat’s second-order curvature approximation provides additional stabilization, suggesting that efficient Hessian-aware methods offer advantages for continual learning. The source code is available at Stability-Gap-SAM. ... Read more

Continual learning aims to enable neural networks to acquire new knowledge sequentially without forgetting what they have already learned. While many strategies have been developed to address catastrophic forgetting, a subtler challenge known as the stability gap—a temporary drop in performance immediately after switching tasks—remains insufficiently understood. Recent work suggests that the learning rate may influence this phenomenon by shaping the model’s optimization trajectory. This paper systematically investigates how different constant learning rates affect the stability gap and whether dynamic learning rate scheduling can mitigate it. Experiments on Rotated MNIST with perfect replay show that smaller constant learning rates reduce the immediate drop but slow down recovery and convergence, while larger rates yield higher final accuracy but at the cost of a more severe gap. Scheduling methods, including CyclicLR and our custom IncreaseLROnPlateau, demonstrate potential for balancing this trade-off, but also introduce new challenges such as intra-task fluctuations. Overall, a carefully tuned constant learning rate provides the most robust trade-off in this setting. By isolating and quantifying these effects, this work offers insights for selecting and tuning learning rates in continual learning and lays the groundwork for future studies on more effective scheduling strategies. All code and experiments are publicly available at: https://github.com/wjssk/learning-rate-in-stability-gap. ... Read more

In the context of continual learning, recent work has identified a significant and recurring perfor- mance drop, followed by a gradual recovery, upon the introduction of a new task. This phenomenon is referred to as the stability gap. Investigating it and the potential solutions is essential, as such findings can reduce both the energy consumption and computational time required to prepare a high- performing agent. Given the strong influence of training procedures on model performance and sta- bility, we analyze how various optimizers –SGD, NAG, AdaGrad, RMSprop, Adam– and momentum values affect the stability gap. We expose a deep neural network to a sequence of digit-identification tasks with varying rotations, and track several met- rics to capture the components of the stability gap and the overall performance. Our results reveal that increasing momentum amplifies the steepness and depth of the gap, while shortening its duration. Within this simplified setup, RMSprop proves most effective in reducing the magnitude and duration of the drop while maintaining high overall perfor- mance. ... Read more

Continual learning aims to train models that can incrementally acquire new knowledge over a sequence of tasks while retaining previously learned information, even in the absence of access to past data. A key challenge in this setting is maintaining stability at task transitions, where even methods like experience replay can suffer from temporary performance degradation known as the stability gap. In this work, we evaluate Layerwise Proximal Replay (LPR), a recently proposed optimisation strategy that constrains updates at the layer level to preserve internal representations of past data. We implement LPR on a simple multi-layer perceptron and benchmark it against an incremental joint training baseline on a domain-incremental variant of Rotated MNIST. To quantify the stability gap, we track accuracy drops immediately following task switches and compute local minima after transitions. Our results show that LPR consistently reduces the stability gap across a range of learning rates, with statistically significant improvements at higher values. However, this improvement comes at the cost of reduced performance on later tasks. These findings demonstrate that LPR significantly mitigates short-term performance degradation at task boundaries while maintaining high learning rates, offering a practical solution for increased stability in continual learning. ... Read more

Task-based continual learning setups suffer from temporary dips in performance shortly after switching to new tasks, a phenomenon referred to as stability gap. State-of-the-art methods that considerably mitigate catastrophic forgetting do not necessarily decrease the stability gap well. One notable continual learning regularization approach, neuronal decay, attempts to encourage learning solutions that have small activations in the hidden layers. It previously showed improvement in terms of catastrophic forgetting but was not assessed in the context of stability gap. In this study, we compare neuronal decay with a baseline model to see if it can reduce the stability gap. Qualitative analysis with plots and quantitative analysis with metrics, such as gap depth, time-to-recover and average accuracy, both give strong evidence that this simple regularization method can reduce the stability gap with no substantial sacrifice of performance or training time.
The source code is available at https://github.com/zkkv/neuronal-decay. ... Read more