Accurate binaural mirroring of spontaneous otoacoustic
emissions suggests influence of time-locking in medial efferents
Martin Braun
Hear Res 1998, Apr, 118:1-2, 129-38
Abstract
Spontaneous otoacoustic emissions (SOAEs) of nearly identical acoustic
frequency in both ears are a common observation, but it is unknown if
this binaural mirroring effect is random, artefactual, genetic, developmental,
or of other origin. The available raw data of all human SOAE surveys were
pooled, and the intervals of all possible binaural emission pairs (N =
9555) were listed according to size on the Cent-scale (1 Cent = 1/100
semitone = 1/1200 octave). Statistical analysis showed (1) a slight broad-band
mirroring in the 0-100 Cent range (P < 0.05), and (2) a strong narrow-band
mirroring (NBM) in the 0-20 Cent range (P < 0.001). Negative results
in a detailed SOAE cluster detection program excluded experimental artefacts
as causes of NBM. Analysis of the large subgroup of twin data excluded
genetic and intrauterine developmental causes. Systemic developmental
causes are unrealistic, as 20 Cent corresponds to only approximately 80
microm on the cochlear map. Analysis of infant data indicated that the
effect may be introduced after birth by secondary factors. Interaural
crosstalk was examined but had to be rejected. It is suggested that bilaterally
spreading period information in the medial olivocochlear system influences
outer hair cells of the same best frequency in both ears very similarly.
Evidence concerning possible effects on electromotility is discussed,
and experimental tests are proposed.
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