Experimental setup.

<p>Examples of photographs of the setup presented to the subjects during the a. motor imagery (MI), and b. visual imagery (VI) tasks. Both photographs show a whiteboard with circle targets in the middle and a black line with the red dot from the laser (highlighted here) in between. During MI trials, a balance board is present in front of the whiteboard. During VI trials, a blue carpet replaces the balance board. In these examples, the trajectory length is long (80% of subjects' maximal sway) and the target size is large (8 cm of diameter); c. Time course of motor imagery trials. During each trial, after a short inspection of the photo on display, the subjects closed their eyes and imagined standing on the balance board. The subjects were asked to press a button with the index finger of their right hand to signal that they had started imagining swaying on the balance board. The subjects were asked to press the button again when they imagined the balance board was back to the starting position, after having aimed the laser dot at both targets. Following the second button press, a fixation cross was presented on the screen and the subjects could open their eyes. The duration of the inter-trial interval (ITI) was 3–6 s.