  Glass-forming materials are characterized by an intermittent motion at the
microscopic scale. Particles spend most of their time rattling within the cages
formed by their neighbors, and seldom jump to a different cage. In molecular
glass formers the temperature dependence of the jump features, such as the
average caging time and jump length, characterizes the relaxation processes and
allows for a short-time prediction of the diffusivity. Here we experimentally
investigate the cage-jump motion of a two-dimensional hard-sphere-like
colloidal suspension, where the volume fraction is the relevant parameter
controlling the slowing down of the dynamics. We characterize the volume
fraction dependence of the cage-jump features and show that, as in molecular
systems, they allow for a short time prediction of the diffusivity.
