New methods for analyzing high-multiple spontaneous otoacoustic emissions: no spectral periodicity but binaural mirroring

Three decades after their discovery, otoacoustic emissions (OAEs) are today widely used in medical diagnosis. Where, how, and why they are generated, however, is still fiercely debated, which severely impedes further medical applications. A previously unexploited opportunity to explore these questions are the occasionally found high-multiple spontaneous OAEs (SOAEs) in humans, because of their large number of adjacent small intervals. Here, the frequency distribution of 168 SOAEs from eight healthy ears of four subjects (12 to 32 SOAEs per ear) is analyzed by two newly developed methods: (a) statistical analysis of adjacent small intervals; (b) comparison of real vs. simulated, random-generated, interval data. Results: (a) The mean difference between adjacent small intervals is unexpectedly large, i.e. 26 % of the preferred minimum spacing. (b) The variation between adjacent small intervals is not significantly different between real and simulated, random-generated, data. (c) Binaural frequency mirroring occurs significantly more often in the real than in the simulated, random-generated, data (P < 0.0001) and ca 20 % of all SOAEs take part in above-chance binaural mirroring. In conclusion, there is no spectral periodicity of SOAEs, and thus no indication for spatial periodicity in the cochlea. The finding of binaural SOAE mirroring replicates earlier results derived by a different method and further emphasizes the strong role of neural influence on the formation of SOAE frequency loci.