Figure 2

Experimental procedure. Concept and time course of the auditory stimulation with respect to the constant sequencing and random sequencing conditions. Pass-bands and stop-bands of the band-eliminated noises (BENs) are represented by the light gray and white areas, respectively. The notch-bandwidth of a BEN (white area) is either 1/4, 1/2, or 1 critical band. Target and non-target test stimuli (TS) are represented as red lines with gap (target TS, requiring a button press) and black lines without gap (non-target TS), respectively. During the constant sequencing condition (constant frequency: upper graph), TS has identical frequency, whereas during the random sequencing condition (random frequency: lower graph) TS has different frequencies (e.g., 250, 350, 450, 570, 700, 840, 1000, 1170, 1370, 1600, 1850, 2150, 2500, 2900, 3400, or 4000 Hz). The TS frequencies differed between constant sequencing blocks. In total, identical bottom-up auditory inputs are provided during the constant sequencing and random sequencing conditions. Exemplary sound files corresponding to constant sequencing and random sequencing conditions are available in Additional file 1.