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

Martin Braun

Hear Res 2000, 145, 130-140

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 f0 (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 f0 distribution of 2890 monaural and 2604 binaural pairs of human spontaneous otoacoustic emissions (SOAEs) 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 f0 (mode at 349 Hz) and left ear f0 (mode at 262 Hz) towards different ranges of speech f0 (P < 0.02); (2) a bias of binaural - but not monaural - f0 towards 5 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 - f0 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 f0 extraction in the ICC and suggest a specific colliculo-cochlear feedback for f0 enhancement.

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