and O2 (see Figure 2). The data were sampled at 256 Hz. Signals were recorded for 120 s during each task. Each task was repeated for three sessions. Each session contained 40 trials with a 1 : 1 target/nontarget relation. Namely, the total number of targets was 60, the same as that of nontargets. The hit rate and the reaction time were measured, as shown in Figure 3.
