Trends in the refinement and optimization of fine-motor trajectories.

Digitally recorded handwriting movements of primary school children exhibiting good or poor writing quality were examined from two perspectives. The first approach ascertained the extent to which differences existed in the refinement of individual pen movements, in terms of Hay's (1979) movement categories of "ballistic," "step," and "ramp." A second analysis explored the extent to which good writers appear to minimize the physical costs of such movements, in terms of impulse, force, power, and jerk estimates, calculated from kinematic data. The results provide a qualification of an earlier analysis of the data using crosscorrelation techniques, and the relevance of each approach as a description of the development of movement control is discussed. It is concluded that poorer writers tend to use less mature patterns of movement that allow greater visual control during execution, and they also appear to have less control over both normal force and effective planar force levels.