  Deep learning has recently seen rapid development and received significant
attention due to its state-of-the-art performance on previously-thought hard
problems. However, because of the internal complexity and nonlinear structure
of deep neural networks, the underlying decision making processes for why these
models are achieving such performance are challenging and sometimes mystifying
to interpret. As deep learning spreads across domains, it is of paramount
importance that we equip users of deep learning with tools for understanding
when a model works correctly, when it fails, and ultimately how to improve its
performance. Standardized toolkits for building neural networks have helped
democratize deep learning; visual analytics systems have now been developed to
support model explanation, interpretation, debugging, and improvement. We
present a survey of the role of visual analytics in deep learning research,
which highlights its short yet impactful history and thoroughly summarizes the
state-of-the-art using a human-centered interrogative framework, focusing on
the Five W's and How (Why, Who, What, How, When, and Where). We conclude by
highlighting research directions and open research problems. This survey helps
researchers and practitioners in both visual analytics and deep learning to
quickly learn key aspects of this young and rapidly growing body of research,
whose impact spans a diverse range of domains.
