Bifurcated P300 peaks: P3a and P3b revisited?

The P300 (P3) component of the event-related brain potential (ERP) was elicited with an auditory discrimination paradigm in a large group (n = 100) of undergraduates. Subjects who displayed bifurcated P3 peaks across trial blocks (n = 35) were classified into three groups based on the consistency of the replication of the two P3 subpeaks. Amplitude and latency measures for the first (P3a) and second (P3b) peaks from each subject demonstrated no statistically reliable differences between groups. Both subcomponents increased in amplitude from the frontal to parietal electrode sites, although the earlier peak was smaller at the frontal electrode site for the second compared to first trial block. The largest P3 peak for each trial block (P3MAX) from each subject was measured and produced amplitude and latency values that closely matched normative data from the same paradigm. The findings suggested that the P3a and P3b subcomponents from auditory stimuli may be distributed in the population in an asymmetric fashion, and that the P3MAX measurement technique provides a reasonable means of assessing amplitude and latency values from individuals with bifurcated peaks.