  Recent years have produced great advances in training large, deep neural
networks (DNNs), including notable successes in training convolutional neural
networks (convnets) to recognize natural images. However, our understanding of
how these models work, especially what computations they perform at
intermediate layers, has lagged behind. Progress in the field will be further
accelerated by the development of better tools for visualizing and interpreting
neural nets. We introduce two such tools here. The first is a tool that
visualizes the activations produced on each layer of a trained convnet as it
processes an image or video (e.g. a live webcam stream). We have found that
looking at live activations that change in response to user input helps build
valuable intuitions about how convnets work. The second tool enables
visualizing features at each layer of a DNN via regularized optimization in
image space. Because previous versions of this idea produced less recognizable
images, here we introduce several new regularization methods that combine to
produce qualitatively clearer, more interpretable visualizations. Both tools
are open source and work on a pre-trained convnet with minimal setup.

Computer Vision and Pattern Recognition;Machine Learning;Neural and Evolutionary Computing