High-multiple spontaneous otoacoustic emissions confirm theory of local tuned oscillators

Abstract

Understanding the origin of spontaneous otoacoustic emissions (SOAEs) in mammals has been a challenge for more than three decades. Right from the beginning two mutually exclusive concepts were explored. After 30 years this has now resulted in two well established but incompatible theories, the global standing-wave theory and the local oscillator theory. The outcome of this controversy will be important for our understanding of inner ear functions, because local tuned oscillators in the cochlea would indicate the possibility of frequency analysis via local resonance also in mammals. A previously unexploited opportunity to gain further information on this matter lies in the occasional cases of high-multiple SOAEs in human ears, which present a large number of adjacent small frequency intervals. Here, eight healthy ears of four subjects (12 to 32 SOAEs per ear) are compared with individually simulated ears where frequency spacing was random-generated by two different techniques. Further, a group of 1000 ears was simulated presenting a mean of 21.3 SOAEs per ear. The simulations indicate that the typical frequency spacing of human SOAEs may be due to random distribution of emitters along the cochlea plus a graded probability of mutual close-range suppression between adjacent emitters. It was found that the distribution of frequency intervals of SOAEs shows no above-chance probability of multiples of the preferred minimum distance (PMD) between SOAEs and that the size of PMD is related to SOAE density. The variation in size between adjacent small intervals is not significantly different in random-generated than in measured data. These three results are not in agreement with the global standing-wave theory but are in line with the local oscillator theory. In conclusion, the results are consistent with intrinsic tuning of cochlear outer hair cells.

Low-frequency sound affects active micromechanics in the human inner ear

“…Pre-exposure SOAE frequencies showed a bimodal distribution ( figure 4 b , dip statistic test for unimodality, dip=0.1, p =0) with maxima around 1.5 and 3 kHz, in line with previous studies [ 16 , 17 ]. A similar distribution was seen after the presentation of LF sound for permanent, bouncing SOAEs ( figure 4 c , dip statistic test for unimodality, dip=0.1, p =0).…”

The vibrating reed frequency meter: digital investigation of an early cochlear model

“…Both the secondary peak and the ripples are of interest because sometimes fine-grained and periodic structure is observed in the cochlea, seen in the audiogram ( Elliott, 1958 ), basilar membrane measurements ( Olson, 2001 ; Rhode, 1971 ), and otoacoustic emissions ( Braun, 1997 ; Braun, 2013 ; Fruth, Jülicher & Lindner, 2014 ; Kemp & Chum, 1980 ; Lineton & Lutman, 2003 ).…”

The 1.06 frequency ratio in the cochlea: evidence and outlook for a natural musical semitone

“…Confining ourselves to Western music for now, the semitone is equal to 2 (1/12) or 1.059 on the equal tempered scale or 16/15 (1.067) in Just intonation. The presence in the cochlea of an approximation to a semitone has been pointed out by several researchers ( Bell, 2002 ; Blinowska et al, 2012 ; Braun, 1997 ; Braun, 2006 ; Braun, 2013 ), but in general the musical link has not been widely recognised. Perhaps the most-frequent ratio is merely coincidence ( D’Amato, 1988 ; Justus & Hutsler, 2005 )?…”