The dynamics of walking acquisition: a tutorial

Tracking for developmental changes is at the heart of developmental psychology. The qualitative features of the variation of the center of mass (CoM) acceleration during a sequence of steps are revealed by first return maps, a tool taken from differential dynamics. The focus is put on the acceleration of the CoM along the antero-posterior and medio-lateral axes. Application is shown on data recorded from one infant followed up repeatedly during the first year of learning to walk. At a given experience in walking, the gait dynamics is exhaustively characterized by a specific enchainment of pendula and quasi-equilibria. The developmental process is revealed by the succession of dynamical structures, each determined at each walking experience. It shows a drift toward increasingly regular gait patterns, together with a clear asymmetry between an impulse foot and a regulatory foot.