Properties of maximum length sequence and nonlinear volterra slice otoacoustic emissions


Ismail-Koch, Hasnaa (2008) Properties of maximum length sequence and nonlinear volterra slice otoacoustic emissions. University of Southampton, School of Medicine, Doctoral Thesis , 282pp.

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Description/Abstract

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.

Item Type: Thesis (Doctoral)
Subjects: R Medicine > RF Otorhinolaryngology
T Technology > TA Engineering (General). Civil engineering (General)
Q Science > QP Physiology
Divisions: University Structure - Pre August 2011 > School of Medicine > Clinical Neurosciences
ePrint ID: 67632
Date Deposited: 28 Aug 2009
Last Modified: 27 Mar 2014 18:48
URI: http://eprints.soton.ac.uk/id/eprint/67632

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