A retrospective study of the spectral probability
of spontaneous otoacoustic emissions: Rise of octave shifted second mode
Hear Res 2006, 215, 39-46
The recording of otoacoustic emissions (OAEs) is today a widely used tool
in medical diagnosis. The mechanisms of OAE generation in the cochlea
and their transmission to the external ear canal, however, are not well
understood and a matter of long-standing debates. Here, the frequency
distribution of 1660 spontaneous otoacoustic emissions (SOAEs) from three
surveys, covering 296 human subjects, is analyzed. Neonates show a monomodal
distribution with a peak at 4 kHz, but both children (5-11y) and adults
show an identical bimodal distribution, with two peaks in an octave distance
(1.5 and 3 kHz). For the combined children and adult data, distribution
density at the two peak tops is 2.8 and 2.7 times as high as at the low
between them. Mean SOAE amplitudes are unrelated to the two peaks, but
show a significant narrow-band dip precisely at the low in between at
2140 Hz (P < 0.008). External ear canal resonance can explain
the single 4 kHz mode at birth and the 3 kHz mode in children and adults.
The octave shifted 1.5 kHz mode remains without mechanical explanation.
It may reflect descending neural influence from central octave band processing.
The results are relevant for the interpretation of OAE levels in medical
Keywords: Spontaneous otoacoustic emission; Medial olivocochlear system;
Abbreviations: CEOAE, click evoked otoacoustic emission; DPOAE, distortion
product otoacoustic emission; OAE, otoacoustic emission; OHC, outer hair
cell; SOAE, spontaneous otoacoustic emission; ST, semitone