Common vs. independent limb control in sequential vertical aiming: Extending or reversing target-aiming movements


In discrete aiming, adult performers optimize their movement to maximize speed and accuracy, and to minimize energy expenditure.  This research was designed to examine trajectory regulation in sequential vertical aiming.  In Experiment 1, participants performed single up and down aiming movements, as well as sequential aiming movements that involved extending the initial movement to a second target. Of interest was how the first aiming movement was organized to accommodate the second aiming movement.  Overall, participants exhibited shorter movement times and times to peak acceleration and velocity when moving up. Peak acceleration was also greater for upward aims, but only for the single target trials.  Downward movements were spatially more variable. Analyses examining the relationship between kinematic events in the first and second aiming movements revealed positive r-values when moving up but little relationship when moving down.  These results suggest that sequential upward movements are planned together, while downward aiming involves more concurrent control and the independent regulation of the two movement components.  In Experiment 2, the experimental design was similar except that in the sequential aiming condition participants reversed the direction of their first movement, thus returning to the home position.  Consistent with previous research, participants exhibited shorter movement times and higher peak accelerations and velocities under two-target than one-target conditions.  Correlational analyses revealed positive relationships between movement one and two for both up and down initial movements.  For up movements, there was a stronger relationship between the peak acceleration in movement one and kinematic events in movement two, while for down movements, late markers co-varied with movement two. These findings are consistent with the notion that, in a reversal movement, the two components are organized together to optimize time and energy by using the same muscular forces to decelerate movement one and accelerate movement two.

Acknowledgments: This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).