Deviations from auditory regularities elicit electric potentials distributed over the frontal regions of the scalp. The mismatch negativity (MMN) is elicited by change in repetitive auditory input, whereas the early right anterior negativity (ERAN) is elicited when sounds deviate from a hierarchically organized musical regularity. In this study we wished to disentangle the functional roles of these two brain processes associated with the detection of sequential vs. hierarchical musical violations by studying the localization of their neural generators. Subjects listened to musical cadences constituted by seven chords, each containing either harmonically congruous chords, harmonically incongruous chords (Neapolitan subdominant), or harmonically congruous but mistuned chords (5th raised 50 cents). Electroencephalography (EEG) was recorded and source analysis was performed. Incongruous chords violating the rules of harmony elicited a bilateral ERAN, whereas mistuned chords within chord sequences elicited a right-lateralized MMN. We found that the dominant neural sources for the ERAN were localized in Broca’s area and its right homologue, whereas the MMN generators were localized in auditorycortex. These findings demonstrate the predominant role of theudauditory cortices in detecting sequential scale regularities and of the prefrontal cortex in parsing hierarchical regularities in music.
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