Abstract
Event-related potentials (ERPs) were recorded while two tones (1000Hz ; 80%, 1100Hz ; 20%) were presented in random order. ERPs were compared in three conditions : choice reaction time (CRT) condition, in which subjects were required to respond to two tones discriminatively ; simple reaction time (SRT) condition, in which they were required to respond to the tones in the same manner regardless of the pitches ; and reading (READ) condition, in which they were required to read a comic book and to ignore the tones.
NA for the CRT condition was larger in amplitude than that for the SRT condition, while NA was not observed for the READ condition. The amplitude of MMN (mismatch negativity) for the three conditions did not differ among them. N2b of equal amplitude was observed for the CRT and SRT conditions, whereas it was not observed in the READ condition. These differences together with latency differences suggested that NA, MMN and N2b reflect different psychological processes.
