The Sequential Organization of Movement is Critical to the Development of Reaching: A Neural Dynamics Account

Abstract — We present a neuro-dynamic model of looking, reaching, and grasping movements in infants in three pre-reaching phases. We attribute the evolution from pre-reaches to their suppression and subsequent re-emergence reported in a longitudinal study of von Hofsten [1] to the development of the sequential organization of movements, through which a set of elementary movements (visual fixation, reaching, opening the hand) are coordinated in time. The spatial precision hypothesis, which has emerged from work on spatial, visual, and action working memory, characterizes developmental changes as a change from strongly input-driven to more strongly interaction-dominated neural dynamics. Applying this hypothesis to reach-ing, we propose that the intention to reach is increasingly able to suppress competing movement behaviors, enabling object-oriented reaches. We evaluate three versions of the model that capture the three phases reported by von Hofsten and illustrate the properties of the movement model in simulations and in demonstration on a NAO robot. I