Binaural interaction of stapedius reflex.

It is known that stapedius reflex (SR) shows bilateral interaction and that its center is located in the brainstem. In the present study, the pattern of SR was compared in two different conditions, either with binaural acoustic stimuli or with monaural stimuli using the impedance measurement method. When the sound source was placed in front of the head model, the amplitude of impedance change was higher in the binaural hearing condition than in the monaural condition, suggesting bilateral superposition. When the sound source was placed laterally to the head model, the amplitude of impedance change was higher in the ipsilateral ear than in the contralateral ear in the binaural condition. In the monaural condition, the amplitude of impedance change in the ipsilateral ear was as high as that obtained in the ipsilateral ear in the binaural condition, whereas it was markedly low in the contralateral ear. It is assumed that sense of sound direction cannot be well maintained without binaural interaction of SR.