Figure 1. Reaction time tasks and stimulus timings. A, For the SRTT in experiment 1, participants performed the task with their right wrist, and median nerve stimulus (MNS) and TMS stimulus timings were limited to WS and IS time points. B, For the CRTT in experiment 2, a noninformative visual WS (left and right LEDs lit for 150 ms) preceded a left or right IS (75 ms duration), which cued a response with either the left or right index, respectively. C, In experiment 3, participants performed separate blocks of the SRTT with their left and right index fingers. They received a visual WS (150 ms duration) before a visual IS (75 ms duration). D, For the Go/No Go task in experiment 4, an auditory WS (500 Hz tone, 150 ms duration) preceded either a green (Go) or red (No Go) visual stimulus (75 ms duration), which cued the execution of a right index response and the withholding of a response, respectively. Within each experiment, stimuli were delivered at one of several time points in a trial: at the WS, in the warning period (WP) 0.25 s after the WS and before the IS (B, C) at the IS and after the IS at 35% and 70% of the mean baseline reaction time (35%RT, 70%RT). TMS was delivered with the coil positioned to induce PA currents (see A) only in experiment 1, and both PA and AP currents (position coil handle rotated 180° around the intersection of coil windings) in experiments 2–4. Note that for trials cueing a right-hand response, MEPs were recorded from the (right) responding hand; and for trials cueing a left-hand response, MEPs were recorded from the (right) nonresponding hand. An example raw EMG trace is shown at the bottom to illustrate the MEP against the background voluntary muscle activity during experiments 2–5.