Post-hoc Concept Bottleneck Models

Concept Bottleneck Models (CBMs) map the inputs onto a set of interpretable concepts (``the bottleneck'') and use the concepts to make predictions. A concept bottleneck enhances interpretability since it can be investigated to understand what concepts the model "sees" in an input and which of these concepts are deemed important. However, CBMs are restrictive in practice as they require concept labels in the training data to learn the bottleneck and do not leverage strong pretrained models. Moreover, CBMs often do not match the accuracy of an unrestricted neural network, reducing the incentive to deploy them in practice. In this work, we address the limitations of CBMs by introducing Post-hoc Concept Bottleneck models (PCBMs). We show that we can turn any neural network into a PCBM without sacrificing model performance while still retaining interpretability benefits. When concept annotation is not available on the training data, we show that PCBM can transfer concepts from other datasets or from natural language descriptions of concepts. PCBM also enables users to quickly debug and update the model to reduce spurious correlations and improve generalization to new (potentially different) data. Through a model-editing user study, we show that editing PCBMs via concept-level feedback can provide significant performance gains without using any data from the target domain or model retraining.