PathFinder: Discovering Decision Pathways in Deep Neural Networks
This provides a method for improving interpretability in deep learning, particularly for fully-connected layers, but it is incremental as it builds on existing clustering and visualization techniques.
The paper tackles the problem of explainability in deep neural networks by identifying decision pathways through clustering activation patterns across layers, revealing that instances of the same class follow a small number of cluster sequences, which helps explain classification decisions and detect outliers.
Explainability is becoming an increasingly important topic for deep neural networks. Though the operation in convolutional layers is easier to understand, processing becomes opaque in fully-connected layers. The basic idea in our work is that each instance, as it flows through the layers, causes a different activation pattern in the hidden layers and in our Paths methodology, we cluster these activation vectors for each hidden layer and then see how the clusters in successive layers connect to one another as activation flows from the input layer to the output. We find that instances of the same class follow a small number of cluster sequences over the layers, which we name ``decision paths." Such paths explain how classification decisions are typically made, and also help us determine outliers that follow unusual paths. We also propose using the Sankey diagram to visualize such pathways. We validate our method with experiments on two feed-forward networks trained on MNIST and CELEB data sets, and one recurrent network trained on PenDigits.