Fast Hierarchical Games for Image Explanations

As modern neural networks keep breaking records and solving harder problems, their predictions also become less intelligible. The current lack of interpretability undermines the deployment of accurate machine learning tools in sensitive settings. In this work, we present a model-agnostic explanation method for image classification based on a hierarchical extension of Shapley coefficients --Hierarchical Shap (h-Shap)-- that resolves some limitations of current approaches. Unlike other Shapley-based explanation methods, h-Shap is scalable and it does not need approximation. Under certain distributional assumptions, which are common in multiple instance learning, h-Shap retrieves the exact Shapley coefficients with an exponential improvement in computational complexity. We compare our hierarchical approach with popular Shapley-based and non-Shapley-based methods on a synthetic dataset, a medical imaging scenario, and a general computer vision problem. We show that h-Shap outperforms the state of the art in both accuracy and runtime.