  A bouncing drop and its associated accompanying wave forms a walker. Based on
previous works, we show in this article that it is possible to formulate a
simple theoretical framework for the walker dynamics. It relies on a time scale
decomposition corresponding to the effects successively generated when the
memory effects increase. While the short time scale effect is simply
responsible for the walker's propulsion, the intermediate scale generates
spontaneously pivotal structures endowed with angular momentum. At an even
larger memory scale, if the walker is spatially confined, the pivots become the
building blocks of a self-organization into a global structure. This new
theoretical framework is applied in the presence of an external harmonic
potential, and reveals the underlying mechanisms leading to the emergence of
the macroscopic spatial organization reported by Perrard et al. (2014, Nature
Commun. 5, 3219)
