Abstract
Throughout the first year, infants are known to engage in repetitive motor behaviors. The current study examines the changes in the hand trajectory of one such behavior, banging, during the second half-year and the implications of these changes for tool use development. Fourteen (7- to 14-month-old) infants were seated at a table and presented with a small wooden cube. Kinematic measurements of their banging movements were recorded at 240 Hz. Analyses revealed stable temporal characteristics of the hand trajectories within and across infants. Results further indicated that as infants became older, their hands moved more efficiently in straighter up-and-down trajectories, with developmental changes especially pronounced for upward excursions of the hand: Younger infants' arm movements were less straight on the way up than down, but there was no difference in the straightness of the two movement phases for older infants. These changes with age may reflect improvements in overcoming constraints associated with gravity and/or in motor planning. Additionally, the angle at which infants hit the table became more perpendicular with age. Collectively, the reported changes lead to more efficient movements, better aim and improved force delivery, enabling spontaneous banging movements to become well suited for instrumental hammering and tool use, more generally, later in childhood.