Automatic measuring system of synchronous evoked otoacoustic emissions (se-OAE) was developed, and sound pressure level and phase of the output components, which had the same frequency as the stimulus, in normal subjects were measured precisely. Then, the extraction of se-OAE components from the measurement results was attempted by applying vector analysis to the measurement results, and the characteristics of se-OAE were evaluated by the aid of Nyquist plot of the se-OAE components. The following conclusions were obtained.
(1) Periodical fluctuation of the measured sound pressure level and phase were dominant in the lower frequency region (f<1.2kHz).
(2) Sound pressure level and phase fluctuated on a large scale in the frequency regions where spontaneous OAEs (s-OAEs) were detected, but in some frequency regions where s-OAEs were not detected, their large fluctuation was also observed.
(3) Nyquist plot clarified that the rotational velocity of the se-OAE components (dφ
se/dt or d
Δφ/dt) was proportional to the amplitude of the se-OAE components.
(4) Frequency interval when Nyquist plot drew a circle was nearly 70Hz, and this value was independent of the amplitude of the se-OAE components and of the existence of s-OAE.
(5) The basic characteristics of the measured sound pressure level, which revealed both dip and peak, only peak and only dip, were almost the same as each other, with the exception of the phases of the se-OAE components.
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