The one-target advantage: a test of the movement integration hypothesis.

Two experiments were conducted to compare the temporal structure of single aiming movements to two-component movements involving either a reversal in direction or an extension. For reversal movements, there was no cost associated with the movement time for the first segment of the movement. However, regardless of movement direction, initiation instructions, handedness or effector, two-component extension movements were always associated with a longer movement time for the first movement segment. This disadvantage for extension movements, but not reversal movements, is consistent with the notion that there is interference between the execution of the first movement and implementation of the second movement. By contrast, because the muscular force used to break the first movement is also used to propel the second movement, reversal movements are organised as an integrated unit.