Effects of target size and symmetry on the structure of variability in precision aiming

The current experiment investigated the effects of target size and symmetry on the dynamics of precision aiming. Participants were asked to sit on a chair and point at the center of four different targets (a small and big square target, and a horizontal and vertical rectangular target). The aiming movements were assessed using linear (root mean square) and non-linear fractal statistics (DFA and MFDFA). We found that participants spontaneously exhibited more movement in target dimensions with less spatial constraint (i.e., larger target dimensions). These larger movements, however, were more deterministic than the movements accompanying the smaller targets, indicating that more variation in aiming does not necessarily mean more random. Finally, even though participants’ movements were multifractal, the different manipulations and task constraints had no effect on the width of the multifractal spectrum. These results suggest that human performance emerges from the complex relationship and interactions that exist between the perception and action capabilities of the human body and the physical environment.