Abstract
The purpose of the present study is to assess the influence of AR on the sound transmission in the middle ear. Reduction of TTS at 0. 5, 1, 1. 5, 2, 4, and 8kHz has been used as the index of attenuation effect of the AR. The test ear of each of ten subjects with normal hearing acuity was exposed to one of six pure tones for three minutes, during which an octave band noise(f_c=4000Hz) of 110dB SPL was presented to the contralateral ear in order to activate AR. Three reflex activating conditions were used; (1)no exposure(control), (2)continuous exposure(noise steady), (3)intermittent exposure with 50ms on- and 50ms off-time(noise 50/50). The largest value of TTS was observed in the control condition. TTS was reduced when a reflex activating noise was presented to the contralateral ear. The reduction of TTS was remarkable in the lower frequency region, but not so large in the higher frequency region. The noise 50/50 condition resulted in greater reduction of TTS compared with the noise steady condition. However large individual difference were observed. These differences in the reduction of TTS can be explained from the dynamic properties of AR. Magnitude of AR activated by noise 50/50 was maintained almost constant during three minutes exposure, but large adaptation was observed in the noise steady condition. The increase of transmission loss induced by AR was estimated from the reduction of TTS at 2kHz.
