Studies measuring ERPs during phonetic and tonal oddball tasks have provided direct evidence of the contribution of lateralized neurocognitive processes to N2 and P3 asymmetries.10,33,35,36 Both healthy adults and schizophrenic patients showed task-related asymmetries of N2 and P3 in the expected direction, with larger amplitudes over right hemisphere sites for the tonal task, but over left hemisphere sites for the phonetic task. If abnormal N2 and P3 asymmetries in schizophrenia reflect a left-sided deficit in temporal lobe regions,17,18 one might expect such abnormalities to be particularly evident in the phonetic oddball task. Contrary to expectations, Kayser et al.10 did not find evidence of a specific left-sided reduction of N2 or P3 in schizophrenic patients in either the tonal or phonetic task. However, it should be noted that a silent-counting condition was not included in this study and the schizophrenic patients did not show an overall reduction of P3 amplitude, which may have contributed to the absence of a difference in P3 asymmetry between patients and controls.37 Although task-related asymmetries of N2 and P3 were modulated by response hand, evaluation of response hand effects was limited because right versus left button press was only compared across subjects.
