Figure 1. Schematic of the trial events for a grip trial with the right hand.

In trials requesting gripping with the left hand, the image of the hand would be displayed to the left of the traffic light. The initial cue was displayed as yellow traffic light, which served as GO cue when it turned green, on average 1.5 ± 0.4 s after its onset. The gripping movement had to occur within two seconds of the GO cue onset to count as valid trial. Upon gripping, a white bar representing the grip force would move up (see bottom right corner in the rightmost plot). Visual feedback was presented according to whether the movement was performed at least for 100 ms and within the correct window. Trial onsets were on average separated by 4.7s ± 1.2s.