Event-related potentials (ERPs) in the Go/Nogo task. A Shown are the ERPs in Go (dashed lines) and Nogo trials (solid lines) at frontal (Fz) and posterior (Pz) sites, separately for 50% (left side) and 72% go blocks (right side) and for the easy (upper half) and hard condition (lower half). Marked are the time windows that were analyzed for the N2 and P3a effects. B Average difference values (Nogo - Go) with the respective standard error bars at frontal sites (Fz) for the time window 200 - 400 ms (N2). Results are shown separately for the two groups (grey: 4rep and black: 7rep), for 50% (left side) and 72% go blocks (right side) and further separated for the two conditions.