The interaction between ear and sex differences and stimulus rate

Evoked otoacoustic emissions (EOAEs) are produced by the cochlea in response to acoustic stimuli and provide an objective and non-invasive measure of cochlear function. A new technique, based on maximum length sequences (MLSs), enables stimulus rates of up to 5000 clicks/s to be used. Conventional EOAE amplitude differs between ears and sexes, female subjects having responses of greater amplitude than male subjects and right ears larger responses than left ears. As a prerequisite to clinical use it is necessary to establish if these differences occur with the MLS OAE technique and whether they change with stimulus rate. Eighty ears of normally hearing adults between the ages of 18 and 40 years were tested. MLS OAEs were recorded at eight stimulus rates ranging from 40/s to 5000/s. Two stimulus levels and two recordings were made at each stimulus rate. Female subjects were found to have statistically significantly larger MLS OAEs than male subjects and gave larger amplitude responses in the right ears. The difference was not significant between male right and left ears. A rate effect was also demonstrated with the amplitude of the MLS OAEs decreasing with an increase in rate. The study provides normative data for MLS OAE testing and shows that females have MLS OAEs of larger amplitude than males and that as the click stimulus rate increases the significance of this difference decreases. Female right ears also have MLS OAEs of greater amplitude than female left ears.