CausalPC: Improving the Robustness of Point Cloud Classification by Causal Effect Identification

Deep neural networks have demonstrated remarkable performance in point cloud classification. However, previous works show they are vulnerable to adversarial perturbations that can manipulate their predictions. Given the distinctive modality of point clouds, various attack strategies have emerged, posing challenges for existing defenses to achieve effective generalization. In this study, we for the first time introduce causal modeling to enhance the robustness of point cloud classification models. Our insight is from the observation that adversarial examples closely resemble benign point clouds from the human perspective. In our causal modeling, we incorporate two critical variables, the structural information, (standing for the key feature leading to the classification) and the hidden confounders, (standing for the noise interfering with the classification). The resulting overall framework CausalPC consists of three sub-modules to identify the causal effect for robust classification. The framework is model-agnostic and adaptable for integration with various point cloud classifiers. Our approach significantly improves the adversarial robustness of three mainstream point cloud classification models on two benchmark datasets. For instance, the classification accuracy for DGCNN on ModelNet40 increases from 29.2% to 72.0% with CausalPC, whereas the best-performing baseline achieves only 42.4%.