On your mark: Examining the self-selection of starting positions during the control of goal-directed aiming


Individual differences in the planning and control of rapid goal-directed actions have been observed under various visual and sensory conditions. However, explanations and causes of these differences have yet to be identified beyond socio-cultural and evolutionary explanations. The purpose of the current experiment was to examine potential differences in movement planning strategies. Participants completed a rapid aiming task, first used by Augustyn and Rosenbaum (2005), where individuals self-selected a start position anywhere on a line between two potential target locations that were equally likely to become the target. Individuals should have bisected the line when the potential targets were of equal size and biased their start position toward the smaller target if the targets differed in size in order to equalize the information processing and potential movement time (Fitts, 1954). Participants spent significantly less time selecting their start position when the targets were the same size rather than different sizes for the line of longer length, F(1,62)=11.58, p=0.001, µ2=0.157. Participants failed to adjust their start position toward the smaller of two targets regardless of the length of the line between the targets, F(1,62)=336.99, p=0.001, µ2=0.845. Males reacted to the target significantly faster than females, F(1,62)=5.76, p=0.019, µ2=0.085. Males also completed their movements in a shorter time than females except for when the line was shorter with two small targets, F(1,62)=4.13, p=0.046, µ2=0.063. Results are discussed in the context of modern models of goal-directed aiming and the potential contribution of endogenous hormone levels to the functioning of the human sensory-motor system.

Acknowledgments: Nipissing University Internal Research Grant (S. Hansen).