Simultaneous pitches are encoded separately in auditory cortex: an MMNm study

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Abstract
This study examined whether two simultaneous pitches have separate memory representations or an integrated representation in preattentive auditory memory. Mismatch negativity fields were examined when a pitch change occurred in either the higher-pitched or the lower-pitched tone at 25% probability each, thus making the total deviation rate of the two-tone dyad 50%. Clear MMNm was obtained for deviants in both tones confirming separate memory traces for concurrent tones. At the same time, deviants to the lower-pitched, but not higher-pitched, tone within the two-tone dyad elicited a reduced MMNm compared to when each tone was presented alone, indicating that the representations of two pitches are not completely independent.