Transient evoked otoacoustic emissions recorder using maximum length sequences as a function of stimulus rate and level.

Objective: The recently developed technique of recording transient evoked otoacoustic emissions (TEOAEs) using clicks presented according to maximum length sequences (MLSs) enables very high stimulation rates to be used. The aim of this study was to provide normative data on the relationship between TEOAEs recorded conventionally (at 40 clicks/sec) and those recorded using the MLS technique (at 11 maximum rates between 100 and 5000 clicks/sec) to establish a baseline for future clinical studies.

Design: TEOAEs were recorded at 12 rates from 12 normally hearing adult ears at click levels decreasing in 5 dB steps from 68 dB peSPL.

Results: The morphology of the waveforms and the pattern of the input/output functions with latency were similar for conventional and MLS TEOAEs. The only major difference between TEOAEs recorded at the different rates was in their absolute amplitude. As the click rate was increased from 40 clicks/sec there was a reduction in amplitude that reached a near asymptote at approximately 1500 clicks/sec. When expressed as a percentage reduction in amplitude compared with that recorded at 40 clicks/sec, this MLS "rate effect" was independent of stimulus level over all but the lowest test level (38 dB peSPL SPL).

Conclusion: Over a wide range of amplitudes of conventionally recorded TEOAEs (21 to 450 microPa for the 9 to 13 msec section of the otoacoustic emission), the mechanism involved in the MLS rate effect seems to act in a way that reduces the amplitude by an almost constant proportion, whatever its original size.