Global Metric Properties and Preparatory Processes in Drawing Movements
1 Instituto di Fisiologia dei Centri Nervosi, CNR, Milano, Italy 2Laboratory of Neurophysiology, University of Minnesota, Minneapolis, U.S.A.
3Laboratoire de Physiologie Neurosensorielle, CNRS, Paris
On the basis of previous work on the relation between kinematic and geometrical properties of drawing movements, it is argued that a multiplicative gain factor K enters in the specification of the instantaneous velocity of execution. We also argue that this gain factor pertains to the preparatory processes which specify the general properties of the movement before its inception. In the case of periodic movements, whereby a simple closed pattern is traced repeatedly, the gain factor depends in a highly consistent fashion on the perimeter of the pattern, being insensitive to the area. In the case of aperiodic movements, producing long and complex trajectories, the factor K is correlated with the surface encompassed by the movement. An attempt is made to unify these findings on the basis of a general scaling principle.
It has often been proposed ( Schmidt, 1982) that the planning of voluntary movements can be logically divided in at least two phases: one in which the topological and figural properties of the movement are defined, and a second one in which the general plan is specified by assigning appropriate values to some of its parameters. There are reasons for suggesting that the second--or preparatory phase--is involved mostly in the specification of the kinematic parameters, and in particular of the velocity. In general, however, the velocity is also modulated by some of the movement parameters during its execution. Thus, the notion of a preparatory phase would be strengthened if one were able to decompose the