Kapadia, Sarosh, Thomas, Nathan, Lutman, Mark and Thornton, Roger
Toneburst-evoked otoacoustic emissions at high stimulus rates using maximum length sequences
At 27th Midwinter Meeting f the Association for Research in Otolaryngology.
01 Jan 2003.
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The application of the maximum length sequence (MLS) technique to recording click-evoked otoacoustic emissions (CEOAEs) allows for a reduction in test time by up to two orders of magnitude. This is because the technique permits the use of extremely high click rates, as inter-click intervals need not be greater than the response duration. The MLS technique also provides novel tools for studying CEOAE and cochlear nonlinearity, as, for example, the amplitude of the response progressively reduces with stimulus rate (rate suppression). However, the MLS technique has thus far only been applied to CEOAEs this study attempts to extend it to toneburst-evoked OAEs (TBOAEs). Our primary aims were to determine whether TBOAEs can be recorded using the MLS technique and whether they demonstrate rate suppression similar to MLS-recorded CEOAEs.
CEOAEs and TBOAEs at 0.5, 1, 2 and 4 kHz were measured in 21 normal adult ears at different stimulus levels and stimulus rates up to 2500/s, using both the conventional and MLS recording techniques. Reliable MLS TBOAEs were obtained for tonebursts at 1 and 2 kHz, while TBOAEs at 0.5 and 4 kHz were generally close to the noise floor. TBOAEs also exhibited rate suppression as stimulus rate increased, in a manner broadly comparable with the corresponding CEOAEs. However, system nonlinear artifacts were more problematic in recording TBOAEs than CEOAEs.
This study demonstrates that the MLS technique can be extended to TBOAEs. Rate suppression occurs in TBOAEs with a magnitude comparable to that in CEOAEs. The findings suggest new possibilities for (a) investigating cochlear nonlinearity, and (b) clinical assessment of cochlear function, using frequency-specific stimuli.
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