Flow AM: Generating Point Cloud Global Explanations by Latent Alignment

TL;DR

This paper introduces Flow AM, a novel activation flow-based method for generating global explanations of point cloud models without relying on generative models, improving interpretability and fidelity.

Contribution

It proposes a new activation flow-based Activation Maximization method for point clouds that avoids the use of generative models, enhancing explanation clarity and fidelity.

Findings

Flow AM produces more perceptible explanations than existing methods.

Generative model-based AM methods fail sanity checks and lack fidelity.

Extensive experiments validate the effectiveness of Flow AM.

Abstract

Although point cloud models have gained significant improvements in prediction accuracy over recent years, their trustworthiness is still not sufficiently investigated. In terms of global explainability, Activation Maximization (AM) techniques in the image domain are not directly transplantable due to the special structure of the point cloud models. Existing studies exploit generative models to yield global explanations that can be perceived by humans. However, the opacity of the generative models themselves and the introduction of additional priors call into question the plausibility and fidelity of the explanations. In this work, we demonstrate that when the classifier predicts different types of instances, the intermediate layer activations are differently activated, known as activation flows. Based on this property, we propose an activation flow-based AM method that generates global explanations that can be perceived without incorporating any generative model. Furthermore, we reveal that AM based on generative models fails the sanity checks and thus lack of fidelity. Extensive experiments show that our approach dramatically enhances the perceptibility of explanations compared to other AM methods that are not based on generative models. Our code is available at: https://github.com/Explain3D/FlowAM