  We show that the dynamics between inherent structures in glass forming
systems can be understood in purely dynamical terms, without any reference to
``topographic'' features of the potential energy landscape. This
``non-topographic'' interpretation is based instead on the existence of
dynamical heterogeneities and on their statistical properties. Our view is
supported by the study of simple dynamically facilitated models of glass
formers. These models also allow for the formulation of quantitative
theoretical predictions which are successfully compared to published data
obtained in numerical and experimental studies of local dynamics of supercooled
liquids.
