Modelling the cochlear origins of distortion product otoacoustic emissions

Distortion product otoacoustic emissions (DPOAEs) arise within the cochlea in response to two<br/>stimulus tones (f1 and f2) at frequencies such as 2f1 ? f2 and 2f2 ? f1. Each DPOAE derives from two<br/>contributing mechanisms within the cochlea: a distributed distortion source and a reflection source.<br/>They are used for hearing screening, but a better understanding of their cochlear origin and<br/>transmission could potentially extend their clinical application to facilitate objective hearing loss<br/>assessment, differential diagnosis of sensorineural hearing losses and improved auditory<br/>rehabilitation using hearing aids.<br/><br/>In this thesis a numerical model of the human cochlea is developed to study the generation<br/>of DPOAEs. It is based on a pre-existing active nonlinear model, the micromechanics of which are<br/>carefully re-tuned to simulate the response of the human cochlea to single- and two- tone<br/>stimulation. Particular attention is paid to the form and position of the nonlinearity within the<br/>model to best match experimental results. The model is also reformulated to verify its stability and<br/>ensure computational convergence of the iterative frequency domain solution method. Its<br/>predictions are validated against estimated time domain simulations and documented experimental<br/>DPOAE measurements. Additionally a novel method is developed for decomposing each<br/>frequency component of the cochlear response into forward and backward travelling waves, which<br/>is applied to investigate the multiple sources of both the 2f1 ? f2 and 2f2 ? f1 DPOAEs.<br/><br/>The model is used to explain and predict a variety of phenomena observed in experimental<br/>DPOAE studies. It also confirms for the 2f1 ? f2 emission, that the two source mechanisms are<br/>spatially separated and that the only significant reflection contribution is associated with the 2f1 ? f2<br/>travelling wave. In contrast, it predicts that the two source mechanisms will overlap in the case of<br/>the 2f2 ? f1 DPOAE, which can be influenced by reflection of both the primary and 2f2 ? f1<br/>travelling waves.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2011

Author dc:creator

• Young, Jacqueline Ann

Advisor dc:contributor.advisor

• Elliott, S.J.