A cochlear implant is a prosthetic device that can provide severe-to-profoundly deaf individuals with partially restored hearing. It emulates the function of a normal cochlea through combined functioning of externally situated electronics and an electrode array surgically implanted into the cochlea. Speech coding strategies implemented in speech processors aim to stimulate the auditory nerve in a way similar to that of a normal working cochlea by modelling the way the cochlea processes sound. Current speech processing strategies rely on the tonotopicity of the cochlea, i.e. the relation between distance from the base of the cochlea and the specific frequency that causes the highest amplitude of deflection at the specific point. The phenomenon of the travelling wave on the basilar membrane is thus reduced to its point or points of maximal deflection. In this study, the behaviour along the full length of the basilar membrane will be investigated in the time domain, i.e. the deflection along the whole membrane for any point in time, in order to evaluate the relevance of the travelling wave in coding sound in a cochlear implant system. The additional information acquired by emulating the motion of the fluid and the basilar membrane in the cochlea, will be transmitted to the recipient in electrical stimulus patterns, to assess whether it provides recipients of cochlear implants with better pitch perception. It will be shown that for the individuals that partook in the experiments, improvement of discrimination around 100 Hz were obtained when compared to current speech coding strategies like the advanced combination encoder (ACE) speech coding strategy in the same recipient.
Dissertation (MEng (Bio-Engineering))--University of Pretoria, 2007.