Figure 1.

Level n = 2 of the dual n-back task. Each stimulus was composed by an auditory and a visual cue presented during 500 ms. This means the participants had to compare the third stimulus (S3) with the first one (S1), S4 with S2, S5 with S3, and so on. For the first correct response (R1), no stimuli matched those presented two trials back in time and no key press was requested. For R2, both auditory and visual stimuli matched the target (S4 identical to S2, green arrow)), such that both “A” and “L” key were pressed. For R3, only the auditory stimulus matched the target (red arrow) and only the “L” key was pressed. For R4, only the visual stimulus matched the target (blue arrow) and only the “A” key was pressed. Notice that in this example only correct responses are illustrated.