Effects of handedness and arm position on stroke-direction preferences in drawing

Abstract

Summary. In the present experiment we study the degree to which movements in graphic workspace are dictated by the geometrical features of that workspace, and by the anatomical features of the effector system that performs the movements. We investigate the effects of handedness and arm position on stroke-direction preferences in a drawing task. The subjects, 10 righthanders, 7 lefthanded inverters, and 7 lefthanded non-inverters, repeatedly produced small back-and-forth drawing movements in many directions. The position of their writing arm was varied at two levels. An analysis of polar frequency distributions derived from the digitally recorded drawing movements revealed different group effects and arm-position effects. The results indicate that multiple reference systems are involved in the control of movement direction. Whereas anatomical features of the effector system induce preferences for diagonal movement directions in graphic work space, non-anatomical factors are shown to be responsible for preferences for horizontal and vertical movement directions. Moreover, the present results support the view that the inverted hand position adopted by many lefthanders in writing tasks is probably used for biomechanical rather than for neurological reasons. This posture allows lefthanders to increase the relative contribution of wrist abduction and adduction in producing rightward-slanted script.