Atypical Change Detection in Sound Sequences: A Behavioral and Magnetoencephalography Study in Congenital Amusia

Pitch change detection and pitch memory are behaviorally impaired in congenital amusia. Yet rather preserved mismatch negativity (MMN) to unexpected pitch changes has previously been reported using EEG, suggesting a discrepancy between conscious and preattentive pitch perception in this population. Coupling MEG with EEG, our study re-examined MMN in congenital amusia in light of two factors: stimulus onset asynchrony (SOA) and change size of the deviant. Individuals with and without congenital amusia passively listened to oddball sequences with either frequency (pitch) or intensity (loudness) deviants, using short (500 ms) or long (1500 ms) SOAs and small or large changes (0.25 or 2 semitones; -5 or -15 dB). In a subsequent active change detection task, participants with amusia had impaired detection of small frequency changes, while a smaller group difference was found for small intensity changes. Long SOAs increased amusics' behavioral response times more than those of controls for frequency and intensity deviants. Time courses of source data in MEG revealed decreased amplitude and increased latency of MMNs to frequency deviants in right temporal and right frontal cortices in amusia, across all the tested SOAs and change sizes. Some MMN abnormalities were found in amusic participants also for intensity deviants, across all the tested SOAs and change sizes. Thanks to the sensitivity of MEG, this study pinpoints that the right-sided fronto-temporal anomalies characterizing amusia are linked to modifications in the processing of sounds in sequences, most particularly for the pitch dimension, already at the preattentive level.