Cortical differences in tonal versus vowel processing as revealed by an ERP component called mismatch negativity (MMN).

Event-related potentials were recorded from four aphasic subjects in order to study if discrimination of synthetic vowels is impaired by left posterior brain damage. A component called the mismatch negativity (MMN) which is assumed to reflect basic discriminatory processes of auditory stimuli was measured. In accordance with the hypothesis, two patients with posterior lesions failed to show any MMN response to synthetic vowels, whereas two patients with predominantly anterior lesions produced the response. The fact that all four patients produced an MMN response to sine wave stimuli indicates that the result does not reflect an across-the-board effect.