Two separate codes for missing-fundamental pitch in the human auditory cortex.

Two auditory event-related potential components, the supratemporal N1 and the mismatch negativity (MMN), index traces encoding the missing-fundamental pitch. The present results suggest that these two codes derive from separate pitch extraction processes. Frequent 300-Hz and infrequent 600-Hz missing-fundamental tones were presented, in some stimulus blocks with short (150 ms), in others, with long (500 ms) stimulus durations. MMN, reflecting a preattentive change detection process, was elicited by infrequent missing-fundamental tones only in the long-duration condition. Correspondingly, subjects were able to detect these high-pitch missing-fundamental tones amongst similar low-pitch ones only when the stimulus duration was long. In addition, the MMN response peaked ca. 120 ms later for missing-fundamental tones than for pure tones of the fundamental frequency suggesting that missing-fundamental pitch resolving took substantially longer than extracting the spectral pitch. In contrast, a differential N1 response to the missing-fundamental pitch was found for both stimulus durations, with no substantial difference in peak latency between the pure and missing-fundamental tones. The contrasting features found for the two auditory cortical missing-fundamental pitch codes support the notion of two separate missing-fundamental pitch resolving mechanisms.