Etude des modifications temporelles des otoémissions acoustiques provoquées lors d'une stimulation acoustique controlatérale, chez l'humain normo-entendant

Abstract
In 32 subjects, the medial olivo-cochlear efferent system was activated by a contralateral acoustic stimulation (CAS) which is able to mimic the inhibitory effects of electrical stimulation of the crossed olivo-cochlear bundle. A white noise CAS of 35dB SL induced temporal alterations in otoacoustic emissions evoked by clicks of 63dB SPL, called phase shift effect (PSE). The PSE appeared as an advance of signals in 80% of cases and occurred after a latency of about 8ms. Two different signal processing methods (in time and frequency domains), showed that the phase shift was mainly located on lower frequencies with a maximum around 1.5kHz and a lack around 4kHz. When contralateral stimulation intensity was varying from 25 to 45 dB SPL, the PSE, increased linearly ; the shape of the curve allowed to rule out a middle ear reflex. On the contrary, when ipsilateral stimulation intensity was varying from 57 to 69 dB SPL, the PSE decreased linearly, indicating that PSE originated in inner ear mechanisms. Lastly, a significant correlation had been evidenced between the amplitude of the suppressive (inhibitory) effect of CAS, and the amplitude of the phase shift effect, allowing one to suggest that both effects may have a common physiological origin.