Aim: 

When normal subjects are asked to bisect a line flanked at one end by a distractor, they tend to misbisect the line in direction opposite to distractor location (Chieffi, 1999). It has been suggested that distractor interferes with line length representation and midpoint localization. However, misbisection might also depend on the deviation of movement trajectory produced by the presence of distractor in the environment (Chieffi et al., 2001; Tipper et al., 1997).

Methods: 

Subjects moved from the starting position to (a) a target (Reaching Experiment) or (b) the subjective midpoint of a horizontal line (Bisection Experiment). A distractor was placed either to the right or to the left and either above or below (a) the target (Reaching Experiment) or (b) one line-end (Bisection Experiment).

Results: 

In Reaching Experiment, distractor did not influence movement trajectory. In Bisection Experiment, movement trajectory (and subjective midpoint) deviated towards right when the distractor flanked the left end of line.

Conclusions: 

The data of the present study suggest that distractor influences line center localization. However, this effect was present only when the distractor flanked the left end of line. This finding probably is due to left-hemisphere superiority in right-handers in processing feedback information (Flowers, 1975) and solving distractor interference (Keulen et al., 2007) during goal-directed movements.