The variability of pointing orientation, as expressed by the standard
deviation of the pointing angle displayed in Fig. 3 (top row of
radar charts), differs across devices. The gamepad and mouse give
rise to higher variability than is the case when using the other four
devices. For the mouse, the average variability for pointing at the
vertical (90, 90) orientations is higher than the average variability
for pointing at the horizontal (180, 0) orientations. As
shown by Lee and Bang (2013), the execution of horizontal and
vertical mouse movements is associated with different completion
times and levels of variability: movements take longer and the amplitudes
of movements are more variable in the vertical than in the
horizontal orientations. The finding of Lee and Bang (2013)therefore
indicate that the execution of vertical movements is more difficult
than the execution of horizontal movements, which is in agreement
with our findings. In contrast to the experiment of Lee and Bang
(2013), vision was not used to control the execution of the movement
in our experiment. We therefore conclude that differences in
the difficulty of executing horizontal and vertical movements with a
mouse are generated partially in the motor system. A major cause for
the difference is due to the different motor systems involved in
horizontal and vertical movements (Lee and Bang, 2013): horizontal
movements of the mouse are generated by wrist-joint rotations
whereas vertical movements are produced by finger-joint rotations.
The latter type of movement is more difficult to control.
When