Figure 1.

Experimental set-up and procedure. (a) Participants sat in front of a table where two LEDs were positioned, one providing the fixation point (FIX. LED, red) and the other delivering the visual stimulus (STIM. LED, yellow). Participants kept their right index finger on a small button laying on a rigid support below the table. The auditory tones were delivered by two loudspeakers placed in front of the participants. (b) Trial started with the FIX. LED being lit. Four auditory tones (800 Hz, 50 ms) were then played at 1 Hz (inter-sound interval: 1 000 ms; marked in blue). Participants were asked to continue the sequence of tones by pressing the button four times with their right index finger at the same rate as the sound presentation. At random times between the 3rd and the 4th button press (marked in orange), two visual flashes (5 ms each) were presented separated by a variable temporal interval centred on 150 ms (probe; marked in yellow). Participants were required to report verbally whether the probe interval was shorter or longer compared with the standard interval (150 ms, presented at the beginning of each block; not shown).