Abstract
Goal-directed aiming movements are organized to be fast, accurate and energy optimal. Whereas the speed and accuracy components of these movements are constrained by the target width and amplitude (Fitts, 1954), energy optimization is strategic and used by performers to bias against errors associated with greater energy expenditure (Oliviera et al., 2005). In order to determine how energy and accuracy requirements jointly mediate the performance and kinematic characteristics of aiming movements, participants performed reciprocal aiming trials between sets of three target widths located either at the same level as, or at a 4cm distance above, the surface of a table. Because target misses in the latter would require a corrective movement against gravity, it was hypothesized that these movements would be both slower and described by higher trajectories than those to targets at table level. Results revealed that movement times were greater to the small targets when they were located above the surface of the table, a finding attributed to greater time spent after peak velocity. A decrease in proportional time to, and an increase in the trajectory height of, the primary sub-movement to the higher targets presumably allowed more space and time for an accurate approach to the target. The results are consistent with a Multiple Process of Model of limb control (Elliott et al., 2010), which suggests that the accuracy and energy requirements of a task shape how behaviour is organized.Acknowledgments: NSERC, Queen Elizabeth II Science & Technology, Anne Poucher Scholarship