  Lifelong learning occurs on timescales ranging from minutes to decades.
People can lose themselves in a new skill, practicing for hours until
exhausted. And they can pursue mastery over days or decades, perhaps abandoning
old skills entirely to seek out new challenges. A full understanding of
learning requires an account that integrates these timescales. Here, we present
a minimal quantitative model that unifies the nested timescales of learning.
Our dynamical model recovers classic accounts of skill acquisition, and
describes how learning emerges from moment-to-moment dynamics of motivation,
fatigue, and work, while also situated within longer-term dynamics of skill
selection, mastery, and abandonment. We apply this model to explore the
benefits and pitfalls of a variety of training regimes and to characterize
individual differences in motivation and skill development. Our model connects
previously disparate timescales -- and the subdisciplines that typically study
each timescale in isolation -- to offer a unified account of the timecourse of
skill acquisition.
