Evidence for Pitch Chroma Mapping in Human Auditory Cortex

Some areas in auditory cortex respond preferentially to sounds that elicit pitch, such as musical sounds or voiced speech. This study used human electroencephalography (EEG) with an adaptation paradigm to investigate how pitch is represented within these areas and, in particular, whether the representation reflects the physical or perceptual dimensions of pitch. Physically, pitch corresponds to a single monotonic dimension: the repetition rate of the stimulus waveform. Perceptually, however, pitch has to be described with 2 dimensions, a monotonic, "pitch height," and a cyclical, "pitch chroma," dimension, to account for the similarity of the cycle of notes (c, d, e, etc.) across different octaves. The EEG adaptation effect mirrored the cyclicality of the pitch chroma dimension, suggesting that auditory cortex contains a representation of pitch chroma. Source analysis indicated that the centroid of this pitch chroma representation lies somewhat anterior and lateral to primary auditory cortex.