TIME-WINDOWING OF CLICK-EVOKED OTOACOUSTIC EMISSIONS TO INCREASE SIGNAL-TO-NOISE RATIO

Objective: To investigate the effects of decreasing the response-windo w duration on the signal-to-noise ratio (S/N) of click-evoked otoacous tic emissions (CEOAEs). Design: The ILO88 (Otodynamics, Ltd.) was used to measure CEOAEs from 149 normal adult ears, and 75 adult ears with high-frequency sensorineural hearing loss. Data were collected using t he default response window of 2.5 to 20.5 msec post-click. Each respon se was rewindowed, post-hoc, from 2.5 to 7.5 msec, 2.5 to 9 msec, 7.75 to 14.25 msec, and 13 to 19.5 msec post-click. For each window, spect ra of the CEOAE and of the background noise were determined. The S/N w as estimated by subtracting the noise level from the CEOAE amplitude. Results: The 13- to 19.5-msec window contained little CEOAE energy rel ative to earlier windows. Relative to the 2.5- to 20.5-msec window, th e 2.5- to 7.5- and 2.5- to 9-msec windows reduced noise levels more th an CEOAE amplitudes, yielding increased S/N, and greater ''reproducibi lity'' values. The increased S/N of the 2.5- to 7.5- and 2.5- to 9-mse c windows allowed measurement of greater CEOAE-amplitude reductions in the impaired ears relative to the normal ears. With short-duration wi ndows, click-presentation rate could be increased, allowing more respo nses to be averaged in a given time, thus further decreasing noise lev els. Although click rate was not varied in the present study, the decr ease of noise levels is predictable. Accounting for this factor, it is expected that a specified S/N would be obtained about five times fast er using the 2.5- to 7.5-msec window with a 7.5-msec interstimulus int erval, than when using the default window. Conclusions: Decreasing the response-window duration substantially increases the measurement effi ciency of CEOAEs in adults, and thus may enhance clinical-test perform ance.