ABSTRACT
Human motor behaviour is characterised by an extreme flexibility. We can pick up a cup with the right hand or with the left hand, while the arm is positioned in all sorts of angles. We can even pick it up by using our feet as the main effector organs. We can walk forward and backward, we can jump, dance, run, shuffle, and produce all sorts of silly walks. We seem to be able to produce an almost infinite stream of movements in order to reach goals in the environment. Motor behaviour can be seen as problem solving. We are forced to find solutions for the problems which appear in the continuously changing environment. These solutions, however, are never static but are always tailored to current requirements. Since the environmental constraints are never the same, the solutions can never be the same. This is an important point since it indicates that motor control cannot be the result of a rigid, hierarchically organised system generating efferent commands to individual muscles and joints on the basis of motor programs stored in some neural warehouse. Control is largely non-hierarchical, self-organising, and driven by multisensory input. Furthermore, the organism never functions in vacuo, disconnected from its history and without any knowledge. On the contrary, almost all actions are influenced by knowledge and experience. We have learned how to handle a cup, to ride a bicycle, to write, to play the violin, to dance. Even the simplest actions such as opening a door are influenced by learning. We know, for example, when to push and when to pull on the basis of knowledge derived from experience. Hence, motor processes continuously interact with cognitive and perceptual processes. This interaction between perception, action, and knowledge forms the basis for human motor behaviour and enables us cope with environmental instability.
