The fact that such functional presetting was not found for the earliest monosynaptic response confirms that was previously shown by studying changes in the reactivity of reflex pathways during preparation. These changes influence a large set of spinal motor structures and appear to make the motoneuron pools less accessible to peripheral inputs. However, with adequate procedures, the reactivity of spinal reflex pathways was found sensitive to the force of the movement to be performed.
These results, together with other data collected in the field, are discussed in the frame of the hierarchical three-stage model proposed for motor organization, each stage being the target for specific preparatory processes.
As is often the case when concepts are drawn from the colloquial vocabulary before being introduced into the scientific field, precise definitions remain to be found. This is the case with "preparation." As the concept is used in experimental psychology, it does not refer to a particular class of behavioral activities, but to a permanent component of any adaptative behavior. A large body of experimental studies has shown that providing advance information to an individual about what he will have to do results in an increase in the performance level of the actual action. From the analysis of this relationship, inferences can be drawn about the changes that advance information triggers in the functional state of processing systems which are presumably responsible for this intended action. From the neurophysiological point of view, preparation generally refers, in a more extensive sense, to the changes which are observed in neuronal structures before they are activated to perform an action, these changes being either experimentally induced or spontaneously and considered as some early stages of the activation process. The psychobiological perspective, which we adopt, implies an attempt to combine psychological and neurophysiological approaches. We propose to use the concept of preparation in a restricted operational sense. Preparatory processes refer to physiological changes which not only anticipate the action that they are supposed to prepare for, but can be experimentally manipulated and have a predictive value for performance efficiency ( Requin, 1980a, 1980b).
Since such a definition of preparation may refer not only to motor output processes but also to all the intermediate processes that culminate in behavior (sensory input, memory, perceptual, and cognitive processes), we consider the concept of preparation as it applies to motor behavior only. Considering the various experimentally induced effects on motor performance that have been labeled as "preparatory" by psychologists, as well as the number of neuronal structures in which neurophysiologists have observed activity changes anticipating motor actions, the taxonomy and study of these processes must be closely