Fig. 1

Stimuli and experimental procedure. ‘C’ and ‘IC’ are the abbreviation for congruent and incongruent, respectively. A1, A2 show the stimuli of the two experiment paradigms, and B1, B2 demonstrate the experimental procedure of the two paradigms. A1, B1 represent the stimuli and procedure of semantic congruent paradigm, A2, B2 represent the stimuli and procedure of the semantic incongruent paradigm. The coordinate axis in (B1), (B2) represent time. The first character means the target character in the following block and 2 s means the time interval between the target prompting and the block onset in (B1), (B2). Note that the four different random stimuli sequence consisted of blocks repeated 10 times. The visual stimuli and the auditory stimuli were presented simultaneously