Influence of visual distractors on movement trajectory

In the present study, we explored the influence of a visual distractor on the trajectory of movements made to join two dots. The two dots could be unconnected (D) or connected by a straight (L) or curved line, convex either to the left (LL) or to the right (RL). The connecting line constituted the visual distractor. In Experiment 1, subjects were asked to perform the joining movement as straight as possible. The results showed that hand trajectory moved to the left of the midsagittal axis in LL and to the right in RL, while it was almost straight both in L and D. In Experiment 2, subjects were explicitly required to follow the connecting line during their movements to verify whether, in the previous experiment, they had used curved lines as guide for their movements. An increase of movement time and different hand paths showed that this was not the case. In Experiment 3, subjects were asked to move as straight as possible without vision of their hand. Hand trajectories were shifted to the left in all experimental conditions, but the leftward shift was greater in LL than in all other conditions, and also greater in D and L than in RL. These findings suggest that the visual distractor influenced hand trajectory by attracting subject's attention and competing with target for motor response. It is hypothesized that the attracting influence operated by the distractor was sustained by involuntary attentional mechanisms.