On the Origin of Delayed Evoked Otoacoustic Emissios

Abstract

The impulse response of the ear was measured in the closed external ear canal by a probe with a sensitive microphone. The spectrum of the impulse response showed a ripple of about 100Hz periods around 1kHz region. The frequency response of the same ear to pure tone stimulations was also measured and it was shown to have fluctuations of almost the same frequency structure as the ripple on the spectrum of the impulse response. The coincidence of them was interpreted as coming from the linear nature of the ear at the stimulus level below saturation. The ripple on the spectrum of the impulse response was mathematically proved to correspond to the delayed evoked otoacoustic emission (e-OAE) which showed up with a latency of about 10msec. It was also proved that the ripple was composed of the frequency components which delayed by 2π in phase every 100Hz frequency increase. It was presumed that the e-OAE was a beat phenomenon which would appear about 10msec after the click stimulation because all the frequency components were in phase after 10msec.