Electromyographic pattern in fast goal-directed arm movements

The one-target advantage refers to the fact that a rapid aimed hand movement is executed faster when it is performed as a single, isolated movement than when it is performed as a member of a series. According to a recent account of this phenomenon, that is the movement integration hypothesis, the first movement in a series is slowed because implementation of the second movement may overlap with execution of the first. In this study, we tested the movement integration hypothesis by recording electromyographic (EMG) activity of six muscles acting at the shoulder in nine participants performing 1-tap and 2-tap aiming movements. Movement time results showed a reliable one-target advantage. EMG data indicated a pattern of differential EMG-activity for the first movement that was strongly contingent upon the movement context. In particular, EMG results indicated that, in the 2-tap conditions, implementation of the second movement started during execution of the first. This outcome is consistent with the movement integration hypothesis.