Figure 1: Learned hierarchical features from a deep learning algorithm. Each feature can be thought of as a filter, which filters the input image for that feature (a nose). If the feature is found, the responsible unit or units generate large activations, which can be picked up by the later classifier stages as a good indicator that the class is present. Image by Honglak Lee and colleagues (2011) as published in “Unsupervised Learning of Hierarchical Representations with Convolutional Deep Belief Networks”.