A study of the acoustic reflex using fast-rate otoacoustic emissions.

Fast-rate otoacoustic emissions (OAEs) were used to determine the inward and outward transmission change produced by the stapedial muscle reflex. The subjects were otologically normal adult volunteers. Satisfactory recordings were obtained from a total of 16 ears. Runs of 16 click-evoked OAEs were recorded at a rate of 4282 clicks/s using the maximum length sequence (MLS) technique, with a contralateral tone presented at 10 dB above the contralateral acoustic reflex threshold during the recording of OAEs 5-12 in each run. The OAEs recorded with the contralateral tone were compared with those recorded without the tone to determine the effect of the acoustic reflex. An analysis of the OAEs in 0.5 kHz frequency bands suggested that the reflex produced significant attenuation of low frequency sound with smaller effects at high frequencies, which included amplification for some subjects. For eight of the 16 ears there was an increase in OAE amplitude with the acoustic reflex for at least one frequency band. At low frequencies (1, 1.5 kHz) the inward transmission change produced by the acoustic reflex appeared to be similar in magnitude to the outward transmission change.