Introduction

As technology advances, what was once termed science fiction begins to look increasingly plausible—even, at times, realistic. Artificial intelligence has beaten shogi, chess, and even igo champions. Smartphones can understand human speech, and video calls can provide real-time machine interpretation. "No-crash cars" with built-in cameras protect human lives, and automatic vehicles are getting closer to practical use. When we look around, we find that artificial intelligence flawlessly performs what we once thought exclusively human tasks—even, at times, surpassing us. The development of artificial intelligence is changing our world, making it anew.

"Deep learning" technology plays an important role in such remarkable developments. Researchers around the world praise deep learning as an innovative technology, even calling it a once-in-decade breakthrough. The term is now as familiar to the general public as it is to researchers...