  What are the functions of curiosity? What are the mechanisms of
curiosity-driven learning? We approach these questions about the living using
concepts and tools from machine learning and developmental robotics. We argue
that curiosity-driven learning enables organisms to make discoveries to solve
complex problems with rare or deceptive rewards. By fostering exploration and
discovery of a diversity of behavioural skills, and ignoring these rewards,
curiosity can be efficient to bootstrap learning when there is no information,
or deceptive information, about local improvement towards these problems. We
also explain the key role of curiosity for efficient learning of world models.
We review both normative and heuristic computational frameworks used to
understand the mechanisms of curiosity in humans, conceptualizing the child as
a sense-making organism. These frameworks enable us to discuss the
bi-directional causal links between curiosity and learning, and to provide new
hypotheses about the fundamental role of curiosity in self-organizing
developmental structures through curriculum learning. We present various
developmental robotics experiments that study these mechanisms in action, both
supporting these hypotheses to understand better curiosity in humans and
opening new research avenues in machine learning and artificial intelligence.
Finally, we discuss challenges for the design of experimental paradigms for
studying curiosity in psychology and cognitive neuroscience.
  Keywords: Curiosity, intrinsic motivation, lifelong learning, predictions,
world model, rewards, free-energy principle, learning progress, machine
learning, AI, developmental robotics, development, curriculum learning,
self-organization.
