Modulation of postural sway during manual aiming

We examined the modulation of postural sway during performance of a supra-postural aiming task. Participants aimed a laser pointer at a large, medium, or small target located 1.5 m away. There were two aiming conditions: (1) participants held the laser pointer, or (2) the laser pointer was attached to the body using a belt. Participants stood either directly facing the target or facing the target with the head, but with the body facing the side. Postural sway variability was measured. Sway variability decreased with decreasing target size, but the decrease depended upon whether the pointer was held or attached, the direction participants faced, and on the direction of postural motion. The results showed that postural variability was modulated in order to meet the precision, manual, and directional constraints imposed by the aiming task. Implications for human-computer interaction via aiming are discussed.