Variability of pen-tip displacements and joint excursions in spatially and temporally constrained drawing

Abstract

The variability of pen-tip displacements and joint excursions in temporally constrained ellipse drawing and loop writing was studied using a new 3D recording and analysis technique. Twelve subjects were asked to copy loop patterns varying in height between 3 and 15 mm. The patterns were projected onto the writing surface together with a moving cursor. Additionally, an acoustic pacing signal accompanied the moving cursor. These signals varied in frequency between 1 and 5 Hz. Subjects were instructed to synchronize their pen-tip displacements with both the moving cursor and the acoustic pacing signal. Although subjects generally were capable of producing pen-tip displacements at movement frequencies up to 5 Hz, externally-paced loop writing was shown to be most stable at 3 Hz, particularly at the level of the wrist joint.