Properties of maximum length sequence and nonlinear volterra slice otoacoustic emissions

Evoked otoacoustic emissions (EOAEs) are produced by the cochlea 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, and gives increased speed and sensitivity of testing. Volterra slice otoacoustic emissions (VSOAEs) can be extracted from the response using this technique. These represent nonlinear temporal interaction components and are more sensitive to changes in cochlear pathology than the conventional response. 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 pre-requisite to clinical use it is necessary to establish if these differences occur with the Maximum length sequence otoacoustic (MLSOAE) technique and with VSOAEs and whether they change with stimulus rate, order or slice. The relationship between VSOAEs, Spontaneous otoacoustic emissions (SOAEs), Distortion product otoacoustic emissions (DPOAEs) and the input/output function (I/O) for click-evoked OAEs (CEOAEs) recorded at the conventional rate (40 clicks/s) was also investigated to assess if these measures of cochlear nonlinearity were related to one another. In the first set of experiments 80 ears of normally hearing adults were tested. MLSOAEs were recorded at eight stimulus rates and two stimulus levels. For the second and third experiments 45 ears of normally hearing adults were tested. SOAEs, DPOAEs, the input/output function (I/O) for CEOAEs at the conventional rate (40 clicks/s) and at four stimulus levels, and VSOAEs at three stimulus rates were recorded. Female subjects were found to have statistically significantly larger MLSOAEs than male subjects and gave larger amplitude responses in their right ears. This sex difference was observed with VSOAEs. A rate effect was also demonstrated with the amplitude of the MLSOAEs decreasing with an increase in rate. The VSOAE amplitude was greater for the second order compared with the third order response, and slice one had a greater amplitude than slice two. VSOAEs of higher amplitude were obtained in SOAE-positive ears. There was a significant relationship between the slope of the I/O function of the CEOAE and the VSOAEs. The study has provided normative data for MLSOAE testing and for VSOAEs. The data obtained suggest that the amplitude (CEOAE I/O function) and temporal (VSOAEs) nonlinearities arise from the same generators, whereas the frequency domain nonlinearities (SOAEs & DPOAEs) have different generators. MLSOAEs and VSOAEs have great potential for clinical use.EThOS - Electronic Theses Online ServiceMedical Research Council Institute of Hearing Research SouthamptonGBUnited Kingdo