Click-evoked otoacoustic emissions: new techniques and applications.

There are practical, clinical circumstances in which a decrease in test time for evoked otoacoustic emissions would be of economic or practical value. In addition, there are circumstances in which it is desirable to obtain more diagnostic information from the evoked emission. This preliminary report concerns predominantly one of these aspects but considers both of them. It is not possible to reduce the test time by simply increasing the stimulation rate because responses and stimuli will overlap and give rise to contaminated responses. However, these limitations can be overcome if a maximum length sequence of clicks is used. These sequences of clicks and silences enable responses of a duration greater than the time between stimuli to be recorded and deconvolved to produce an uncontaminated response. Conventional recordings at stimulus rates of 33/s and 50/s have been taken together with maximum length sequence recordings at rates up to 840/s and the waveforms correlate very well. Although the emission shows some adaptation at the highest stimulation rate this does not prevent a significant reduction in test time.