A STUDY OF THE ACOUSTIC REFLEX USING FAST-RATE OTOACOUSTIC EMISSIONS

Fast-rate otoacoustic emissions (OAEs) were used to determine the inwa rd and outward transmission change produced by the stapedial muscle re flex. The subjects were otologically normal adult volunteers, Satisfac tory recordings were obtained from a total of 16 ears. Runs of 16 clic k-evoked OAEs were recorded at a rate of 4282 clicks/s using the maxim um length sequence (MLS) technique, with a contralateral tone presente d at 10 dB above the contralateral acoustic reflex threshold during th e recording of OAEs 5-12 in each run. The OAEs recorded with the contr alateral tone were compared with those recorded without the tone to de termine 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 frequ encies, which included amplification for some subjects. For eight of t he 16 ears there was an increase in OAE amplitude with the acoustic re flex for at least one frequency band. At low frequencies (1, 1.5 kHz) the inward transmission change produced by the acoustic reflex appeare d to be similar in magnitude to the outward transmission change.