Out-of-equilibrium disordered systems may form memories of external driving
in a remarkable fashion. The system "remembers" multiple values from a series
of training inputs yet "forgets" nearly all of them at long times despite the
inputs being continually repeated. Here, learning and forgetting are
inseparable aspects of a single process. The memory loss may be prevented by
the addition of noise. We identify a class of systems with this behavior,
giving as an example a model of non-brownian suspensions under cyclic shear.Comment: 4 pages, 3 figure
