ERP topographies for 30 scalp electrodes were examined
in 26 healthy right-handed volunteers during oddball tasks
(20% targets) using binaurally presented consonant-vowel
syllables or complex tones. Response hand was counterbalanced
across participants. Both window averages and a principal
components analysis (PCA) with Varimax rotation revealed
task-related (tonal/phonetic) hemispheric asymmetries for
N2, early P3, and particularly for N2-P3 amplitude. In
the tonal task, N2 was maximal over right lateral-temporal
regions, and early P3 over right medial-parietal regions.
For the phonetic task, N2 was maximal over the left lateral-parietal
regions, and late P3/N3 over left medial-parietal regions.
A response-related frontal negativity (N3) interacted with
task-related asymmetries in an unbalanced fashion. The
distinct, asymmetric N2 and P3 topographies for tonal and
phonetic tasks presumably reflect differential involvement
of cortical structures in pitch (right frontotemporal)
and phoneme (left parietotemporal) discrimination.