Inferior colliculus as candidate for pitch extraction: multiple support from statistics of bilateral spontaneous otoacoustic emissions.

The fibrodendritic laminae of the central nucleus of the inferior colliculus (ICC) constitute a frequency map in stacked sheets that are consistently related to the psychoacoustic critical bandwidth (CB) [Schreiner and Langner, 1997. Nature 388, 383-386]. The recently observed co-occurrence of the CB and the double CB (2CB) suggested an adaptation of the ICC frequency map to the extraction of the fundamental frequency f(0) [Braun, 1999. Hear. Res. 129, 71-82]. The present study examined a possible influence of this frequency map upon efferent signaling towards the cochlea. The f(0) distribution of 2890 monaural and 2604 binaural pairs of human spontaneous otoacoustic emissions was analyzed by three statistical methods and in each case showed non-random behavior in the CB-2CB range. Single results were (1) a bias of right ear f(0) (mode at 349 Hz) and left ear f(0) (mode at 262 Hz) towards different ranges of speech f(0) (P<0.02); (2) a bias of binaural, but not monaural, f(0) towards five of 12 semitone bins, C-G-D-A-E, representing the most frequent tones in music (P<0.003); (3) a bias of binaural, but not monaural, f(0) fine-distribution towards the exact pitch frequencies used in music, according to the international standard A4=440 Hz (P=0.03). The results support a model of lamina-based f(0) extraction in the ICC and suggest a specific colliculo-cochlear feedback for f(0) enhancement.