A phenomenological model explains critical periods in learning

An intriguing feature of learning in animals is the existence of critical periods, windows of time in which learning is easy, and after which the ability to learn is dramatically diminished. Classic experiments in barn owls and songbirds showed that juveniles can adapt to perturbed sensory feedback, such as a shift in the visual field or in the pitch of a song, and this experience shapes their susceptibility to adapting to shifts as an adult. Recent work from our group has shown that certain aspects of adult learning in a pitch-shift experiment is described well by the Bayesian integration of feedback. Building on the Langevin dynamics formulation of this model for the dynamics of Bayesian learning, we develop a general approach to find conditions under which critical periods naturally appear as a result of Bayes-optimal learning. Our results suggest that two factors, the distribution of feedback signals and coupling to latent dynamical variables, can account for a range of critical period observations, including rapid learning as a juvenile and experience-dependent learning dynamics for adults. We discuss testable predictions for other systems.