ON KNOWING HOW TO DO THINGS - A THEORY OF MOTOR IMAGERY

The distinction between 'knowing how' and 'knowing that' is fundamenta l to current theories of cognition. Two distinct encodings or represen tations are implied, one conscious and verbalisable and the other norm ally unconscious yet demonstrable in behaviour. The paper discusses th e nature of these two kinds of representation and relations between th em. It is shown that imagery forms an essential mediating link between the two encodings and a theoretical model - the Action-Language-Imagi nation or ALI model - is presented. An important feature of the model is the role attributed to the motor system in generating imagery and p rincipal features of motor imagery are reviewed in the context of the ALI model and with reference to recent experimental findings. Problems in mapping conscious representations of action onto physical brain me chanisms are briefly discussed. It is proposed that the physical basis of imaginal representations of actions is best understood in terms of the mechanisms of motor control. A two stage theory of motor imagery is proposed in which the first stage, the generation of a prototypical action is virtually identical to that involved in overt actions whils t the second stage depends on the retrieval of sensory impressions fro m memory.