Stapedius reflex decay in normal hearing subjects.

The fatigue of the stapedius reflex was studied in 100 normal ears. Stimulus frequencies 500 and 1000 Hz were used,and the decrement of the stapedius reflex at 5, 10, and 15 dB above the reflex threshold was estimated. No decrement at all (less than 10% decay 10 sec after the onset of a stimulus 10 dB above the reflex threshold) was present in a majority of the ears. Between 27 and 58% of the ears showed reflex decay depending on variations of different factors such as stimulus frequency, intensity of the stimulus, and the method to register the reflex. Reflex decay was more often seen at 1000 Hz than at 500 Hz stimulus frequency. Reflex decay was also more often seen 5 dB above the reflex threshold than at higher intensity levels. The reflex decay thus observed in normal ears was generally small and did only very occasionally reach values which can be regarded as pathological.