Fig 3. Experimental paradigm.

The duration of single imagery trials (T _i) was 10 s. At t = 0 s, a cross was presented in the middle of the screen. Participants were asked to relax and fixate the cross to avoid eye movements. At t = 3 s, a beep was sounded to get the participant’s attention. The cue indicating the requested imagery task, one out of five graphical symbols, was presented from t = 3 s to t = 4.25 s. At t = 10 s, a second beep was sounded and the fixation-cross disappeared, which indicated the end of the trial. A variable break (inter-trial-interval, ITI) lasting between 2.5 s and 3.5 s occurred before the start of the next trial. Participants were asked to avoid movements during the imagery period, and to move and blink during the ITI. Experimental runs began and ended with a blank screen (duration 4 s). Modified from [38].