  Zero-shot action recognition is the task of recognizing action classes
without visual examples, only with a semantic embedding which relates unseen to
seen classes. The problem can be seen as learning a function which generalizes
well to instances of unseen classes without losing discrimination between
classes. Neural networks can model the complex boundaries between visual
classes, which explains their success as supervised models. However, in
zero-shot learning, these highly specialized class boundaries may not transfer
well from seen to unseen classes. In this paper, we propose a clustering-based
model, which considers all training samples at once, instead of optimizing for
each instance individually. We optimize the clustering using Reinforcement
Learning which we show is critical for our approach to work. We call the
proposed method CLASTER and observe that it consistently improves over the
state-of-the-art in all standard datasets, UCF101, HMDB51, and Olympic Sports;
both in the standard zero-shot evaluation and the generalized zero-shot
learning.
