Anaoysis of latency and frequency component of evoked otoacoustic emission

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In order to investigate the properties of otoacoustic emissions(EOAEs)in detail, we introduced a new method for frequency analysis of EOAEs, (100 Hz harrow-band EOAEs analysis) : a series of ten echo responses to click stimuli, filtered by a 100 Hz step of pass-band width in the frequencyregions from 1.0 to 2.0 kHz with the use of a dual channel variable filter. In the present study, we investigate the properties of EOAEs from normal ears and from ears with sudden deafness and Meniere's disease. The results were as follows :1)EOAEs from normal ears were composed of two main echo trains and several subechoes. The main echo trains were divided into fast components with short latency below 10 msec and slow components with long latency over 10 msec. The fast component was detected clearly in the higher frequency ranges than 1.5 kHz, the slow component in the lower frequency ranges than 1.4 kHz. Although both fast and slow components showed nonlinear properties, the slow component had a relatively low detection threshold, usually below O dB nHL and saturated around 20 - 30 dB nHL.2)In an early stage of sudden deafness or Meniere's disease, 100 Hz narrow-band EOAEs could often be detected from ears with a severe hearing loss greater than 5O dB HL. But slow component of EOAEs from ears with these lesions was usually small in amplitude or absent, because slow component was more vulnerable than fast component.3)In Meniere's disease or early of sudden deafness, the persistence of slow component indicated a good prognosis of hearing loss.4)Nonlinear property of EOAES, marked in normal ears, was lost in lesioned ears. Therefore, EOAEs could not be detected from a pathologic ears with use of nonlinear click sequence.