Aim: 

Hand movement may be influenced by the presence of irrelevant objects (distractors) in the environment. Some studies reported the presence of a deviation of moving hand toward (Chieffi et al., 2001; Welsh et al., 1999) and others away from the distractor (Tipper et al., 1997). We examined whether a selective influence of distractor on movement trajectory was present when its position, with respect to that of target, varied both along the horizontal (left vs. right) and vertical (above vs. below) dimension.

Methods: 

16 subjects participated in the experiment. They were instructed to move at natural speed from a near dot (starting position) to a distal dot (target) placed along the midsagittal axis. A distractor was placed either to the right or to the left and either above or below the target. We measure the lateral deviation of movement trajectory from the midsagittal axis.

Results: 

Lateral deviation was significantly affected by Condition (p<0.001) and a significant interaction among Horizontal position, Vertical position and Distance (p<0.01) was present. Post-hoc comparisons showed that movement trajectory deviated (a) toward the distractor in both above conditions, and (b) away from the distractor in both below conditions.

Conclusions: 

The position of distractor affected selectively movement trajectory. The deviation of the trajectory toward the distractor placed above the target might depend on production of (a) a single response directed to an intermediate position between distractor and target or (b) separate responses directed to target and distractor. Conversely, when the distractor was placed below it might represent a potential obstacle to hand movement and produce a deviation of the trajectory away from its position.