Figure 1.

Experimental setup, countermanding task, and analysis. A, Participants held a robotic manipulandum with the right hand. Surface and intramuscular EMG recordings were made from the clavicular head of the pectoralis muscle, and from the posterior deltoid muscle. Stimuli and virtual hand position were viewed via a mirror. B, Each trial started by fixating a central starting position. After 1–2 s, a target appeared either to the left or right. Subjects moved their hands so that the cursor representing hand position intersected the target stimulus as quickly as possible. In 30% of the trials, the target jumped back to the starting position after an SSD, instructing the participant to try to withhold the planned movement. If the hand remained within 0.01 m of the start location, the stop trial was classified as successfully canceled; otherwise, it was classified as noncanceled. C, Depiction of the integration method for estimating SSRT. D, Overview of the kinematic and EMG measures. Movement RT is defined as the time at which the hand crosses the 0.01 m radius around the starting location, relative to the time of target presentation. The antagonist latency is the time from presentation of the stop signal to the onset of antagonist muscle activation.