Schematic of functional magnetic resonance imaging (fMRI) data acquisition using an event-related design.

We used an event-related design for the fMRI. Scans of 22 slices generated equal numbers of scan noises during a single repetition time (TR) of 2992 ms, and the same number of tones with a stimulus onset asynchrony (SOA) of 136 ms (TR/slice number = 2992/22) were presented. The presentation of tones was completely synchronized to scans by triggers generated by the MRI system in order to minimize the effect of scan noise on fMRI and electroencephalogram (EEG) raw data, which were also used to segregate and average EEG epochs in the ERP analysis. The SOA for event scans including the omission events and tones in the regular positions represent 7 or 8 scans (20,944 or 23,936 ms). Fifty-three event scans were assorted at random among the 247 baseline scans including baseline tones only, with no omission. Total scan time = 2992 ms x 300 scans = 897,600 ms. Event: scan including omission 53 times, indicated by red crossbars. Baseline: scan including only frequent stimuli 247 times, indicated by black crossbars. Frequent stimuli: 6547 trials, 3000 Hz, duration 35 ms, rise/fall 0/5 ms. Rare (omission) events: 53 trials (probability: 53/6600 = 0.00803).