Journal of Neuroscience, Vol 7, 819-828, Copyright © 1987 by Society for Neuroscience
Changes in spatial scale in drawing and handwriting: kinematic contributions by proximal and distal joints
F Lacquaniti, G Ferrigno, A Pedotti, JF Soechting and C Terzuolo
The coordination of arm and hand motions was studied in tasks involving
drawing and handwriting movements of different amplitudes. To this end, pen
motion was recorded by means of a digitizing table, while the positions of
different markers on the limb were monitored by the ELITE system. It was
found that the amplitude of shoulder and elbow angular motions scales
roughly with the size of the figure drawn or of the script, whereas the
amplitude of wrist and finger motions is small, independent of size.
Consequently, the larger the limb movement, the smaller the magnitude of
the contributions by motions at distal joints relative to that at proximal
joints. Furthermore, while shoulder and elbow motions are tightly coupled
(constant phase relation), motions at distal joints are loosely coupled to
those at the proximal joints (variable phase relation). On the other hand,
motion at distal joints increases the accuracy of the movement, as
indicated by the smaller variability of pen trajectories compared to that
of wrist trajectories.