The effect of the stapedius reflex on attenuation and poststimulatory auditory fatigue at different frequencies.

The effect of the stapedius reflex on attenuation was measured in patients with unilateral facial palsy (Bell's palsy) and stapedius muscle paralysis. Poststimulatory auditory fatigue was determined in the same patients and in a group of normal test subjects with a normal bilateral stapedius muscle function. The attenuation for a 0.5 kHz tone was found to begin at the reflex threshold, to increase about 7 dB per a 10 dB increase in the stimulus tone and to reach a maximum in the vicinity of 20 dB. When a 2.0 kHz tone was used, no attenuation of note appeared until the sound had risen to about 10 dB above reflex threshold. The attenuation reached a maximum at a little less than 10 dB. A properly functioning stapedius muscle significantly reduced poststimulatory auditory fatigue at 0.75 kHz while at 3.0 kHz, it could do so only if it was stimulated into action by low-frequency noise.