U-shaped motor development emerges from Goal Babbling with intrinsic motor noise

The development of skills in human infants sometimes proceeds so-called U-shaped form, an sequence of disappearance and reappearance of a skill, which has been reported in [1] for pre-reaching to balls presented to infants of early age. We use Goal Babbling, a computational model for exploratory learning of motor skills, to model this U-shaped learning dynamics and furthermore also the qualitative differences caused by presentation modes of the goals. To this aim, we introduce developmentally plausible motor noise and adaptive learning rates in Goal Babbling and show through extensive simulation that U-shaped motor development emerges, thereby reproducing the findings of [1] in our computational model. The results suggest that the disappearance of the skill is caused by a combination of improving the skill and reducing the motor noise in the course of the maturing process, while the reappearance of the skill and its precision is directly reflecting the progress in learning the motor coordination.