Subjects performed in a tone discrimination task at two levels of difficulty, and a reaction time response was required on half of the trials. Four prominent components of the event-related potential waveform (N1, P2, N2, and P3) were analyzed. The results suggested that P2 represents the beginning of a central process responsible for stimulus identification and the initiation of decision making, while N2 and possibly P3 represent the end of this process. The notion that the P3 component is an unusually important sign of central processing is questioned, and the notion that P3 represents a central process of memorial update is also questioned. It seems more likely that N2 or p3 represent the end of a central process started at the time of P2.