  The disorder function formalism [Gunaratne et.al., Phys. Rev. E, {\bf 57},
5146 (1998)]^M is used to show that pattern relaxation in an experiment on a
vibrated layer of brass beads^M occurs in three distinct stages. During stage
I, all lengthscales associated with ^M moments of the disorder grow at a single
universal rate, given by $L(t) \sim t^{0.5}$. In stage II, pattern evolution is
non-universal and includes a range of growth indices. Relaxation in the final
stage is characterized by a single, non-universal index. We use analysis of
patterns from the Swift-Hohenberg equation to argue that mechanisms that
underlie the observed pattern evolution are linear spatio-temporal dynamics
(stage I), non-linear saturation (stage II), and stochasticity (stage III)
