Figure 2.

The axes of both graphs are measured in mm. Depicted are hand trajectories (the marker is placed on the knuckle of the middle finger) for the first 5 strikes of a 214 days old infant a) and a 408 days old infant b). All strikes were standardized to begin at the Cartesian origin. The figure illustrates the curved hand trajectories seen at younger ages and the straighter up-and-down trajectories typical of older infants.