The acoustic reflex pattern studied by the averaging technique.

The acoustic reflex threshold and its pattern in response to stimuli of different intensities, were investigated by means of the signal-averaging technique in 20 normal, 20 sensorineural-impaired and 10 successfully stapedectomized ears. Trains of tone bursts between 110 and 0 dB HL were used. The frequencies tested were 500, 1 000, 2 000 and 4 000 Hz. In all normal subjects, the pattern of the acoustic reflex for stimuli between 110 and 100 dB HL was biphasic with an initial positive plateau followed by a longer negative one. For stimuli below 80 dB HL, the pattern of the reflex was monophasic with a single positive peak. In the sensorineural-impaired ears, the same double pattern of the waveform was obtained. In the stapedectomized ears, no compliance changes were observed for any sound stimuli. By the averaging technique, the difference between the acoustic reflex threshold and the auditory threshold was found to be between 7.5 and 32.5 dB, in normal and sensorineural-impaired ears.