CIFS: Improving Adversarial Robustness of CNNs via Channel-wise Importance-based Feature Selection
This work addresses adversarial robustness for CNNs, which is critical for security in AI applications, but it is incremental as it builds on existing adversarial training methods.
The paper tackles the problem of improving adversarial robustness in CNNs by analyzing channel-wise activations, finding that adversarial training aligns some channels but leaves negatively-relevant channels over-activated, and proposes CIFS to suppress these channels and align positively-relevant ones, resulting in enhanced robustness as verified on datasets like CIFAR10 and SVHN.
We investigate the adversarial robustness of CNNs from the perspective of channel-wise activations. By comparing \textit{non-robust} (normally trained) and \textit{robustified} (adversarially trained) models, we observe that adversarial training (AT) robustifies CNNs by aligning the channel-wise activations of adversarial data with those of their natural counterparts. However, the channels that are \textit{negatively-relevant} (NR) to predictions are still over-activated when processing adversarial data. Besides, we also observe that AT does not result in similar robustness for all classes. For the robust classes, channels with larger activation magnitudes are usually more \textit{positively-relevant} (PR) to predictions, but this alignment does not hold for the non-robust classes. Given these observations, we hypothesize that suppressing NR channels and aligning PR ones with their relevances further enhances the robustness of CNNs under AT. To examine this hypothesis, we introduce a novel mechanism, i.e., \underline{C}hannel-wise \underline{I}mportance-based \underline{F}eature \underline{S}election (CIFS). The CIFS manipulates channels' activations of certain layers by generating non-negative multipliers to these channels based on their relevances to predictions. Extensive experiments on benchmark datasets including CIFAR10 and SVHN clearly verify the hypothesis and CIFS's effectiveness of robustifying CNNs. \url{https://github.com/HanshuYAN/CIFS}