Dynamical Decoupling of Generalization and Overfitting in Large Two-Layer Networks

Understanding the inductive bias and generalization properties of large overparametrized machine learning models requires to characterize the dynamics of the training algorithm. We study the learning dynamics of large two-layer neural networks via dynamical mean field theory, a well established technique of non-equilibrium statistical physics. We show that, for large network width $m$, and large number of samples per input dimension $n/d$, the training dynamics exhibits a separation of timescales which implies: $(i)$~The emergence of a slow time scale associated with the growth in Gaussian/Rademacher complexity of the network; $(ii)$~Inductive bias towards small complexity if the initialization has small enough complexity; $(iii)$~A dynamical decoupling between feature learning and overfitting regimes; $(iv)$~A non-monotone behavior of the test error, associated `feature unlearning' regime at large times.