Variability and the development of skilled actions.

Consistency and invariance in movements have been seen as the essential features of motor skill development. This emphasis on the stabilisation of action has led to the neglect of the processes whereby skills are modified and reorganised into new and more complex acts, that is the process of adaptation. It is argued that variability of motor behaviour has a major role to play in this process and hence in the development of skilled actions. The significance of variability for open systems and its implications for development are examined. A distinction is made between error variability and functional variability, the latter being used in the solution of motor problems. Two experiments on the acquisition of a skilled action by children are reported. A sequential coincident timing task which permitted an operational distinction between the macrostructure and microstructure of the task was used. The results support the argument that with development the action becomes increasingly consistent at the macrostructure level and that this is achieved by maintaining variability at the microstructure level.