Figure 1.

Example of four trials in the N-back task. Every trial appeared every 2 s and lasted 1 s each. Participants were instructed to press left mouse button when “yes” and the right one if “no.” For 0-back (A), targets were letter X; for 1-back (B), the target was when the letter matched the previous letter; and for 2-back (C) and 3-back (D) when it was identical to the one presented 2 or 3 trials before, respectively.