Coordination dynamics of elliptic shape drawing: effects of orientation and eccentricity

The aim of the present study was to show the effect of orientation on producing ellipses of various eccentricities. Ten right-handed adults were required to reproduce eight series of 84 ellipses on a graphic tablet at spontaneous speed. The ellipses displayed seven eccentricities, corresponding to the Lissajous plot produced by two orthogonal harmonic oscillators whose relative phase (RP) varied from 0° (a line) to 90° (a circle), and twelve orientations, the long axis of the ellipses aligned in a direction ranging from three to nine o'clock with respect to the body transverse plane. Results confirmed the participant's preference for two eccentricities, 0° and 45°, that is, a line and an ellipse of intermediate eccentricity, respectively. Except for the circle, insensitive to orientation by definition, orientation became a cogent constraint: In the 10:30 o'clock direction, line drawing (0° RP) increased in variability and the intermediate ellipse (45° RP) was attracted towards a circle (90° RP). These findings suggest an interaction between orientation effects, putatively due to differences in the motion of the wrist and fingers, and eccentricity effects, which may pertain to preferences arising from the non-linear coupling between the effectors.