Electrophysiological evidence for the hierarchical organization of auditory change detection in the human brain.

Auditory change detection has been associated with mismatch negativity (MMN), an event-related potential (ERP) occurring at 100-250 ms after the onset of an acoustic change. Yet, single-unit recordings in animals suggest much faster novelty-specific responses in the auditory system. To investigate change detection in a corresponding early time range in humans, we measured the Middle Latency Response (MLR) and MMN during a controlled frequency oddball paradigm. In addition to MMN, an early effect of change detection was observed at about 40 ms after change onset reflected in an enhancement of the Nb component of the MLR. Both MMN and the Nb effect were shown to be free from confounding influences such as differences in refractoriness. This finding implies that early change detection processes exist in humans upstream of MMN generation, which supports the emerging view of a hierarchical organization of change detection expanding along multiple levels of the auditory pathway.