Viability of cochlear travelling wave signal processing for cochlear implants

Abstract

English: The travelling wave encodes acoustic information by stimulating the auditory nerve fibres. Understanding the travelling wave and its process is important for the development of cochlear implants speech processors. The development of a normal hearing auditory model, using a hydrodynamic model of the travelling wave to predict the nerve fibre spiking diagrams, marked the first stage of this study. This study then proceeded to look at the development of a travelling wave speech processing algorithm and model the electrical response due to the stimulation from the vocoder speech processor, and the travelling wave speech processor. The final stage was to predict whether temporal encoding occurred during cochlear implant stimulation for the vocoder speech processor and the travelling wave speech processor. The results showed that the travelling wave normal hearing model was able to predict the nerve fibre characteristics seen in measurements from literature. This showed that the mechanical encoding performed by the travelling wave is vital to the encoding of information in auditory nerve fibres. The travelling wave speech processor was able to encode temporal cues for pitch up to 1060 Hz, where the results for the vocoder speech processor showed the 300 Hz limit seen in other literature of phase locking. Mimicking the travelling wave in cochlear implant speech processors may potentially benefit the delivery of information to the auditory cortex for cochlear implant users. However, these results must be legitimised using animal models and psychoacoustic experiments.

Afrikaans: Die loopgolf enkodeer akoestiese inligting deur stimulasie van die gehoorsenuwees. 'n Begrip van die loopgolf is belangrik vir die ontwikkeling van kogleêre inplanting spraakverwerkers. Die eerste fase van hierdie studie was die ontwikkeling van 'n ouditiewe model van normale gehoor. Hierdie model maak gebruik van 'n hidrodinamiese model van die loopgolf om senuweevuurpatrone te voorspel. Verder het die studie die ontwikkeling van 'n loopgolf spraakverwerkingsalgoritme ondersoek, en het die elektriese respons in reaksie op stimulasie van vokoder- en loopgolfspraakverwerkers gemodelleer. Die finale fase was om te voorspel of temporale enkodering ontlok is tydens kogleêre inplanting stimulasie met die vokoder- en loopgolfspraakverwerkers. Die resultate toon dat die loopgolfmodel vir normale gehoor in staat is om die senuweeeienskappe van gepubliseerde metings te voorspel. Dit wys dat meganiese enkodering deur die loopgolf van kardinale belang is in die enkodering van inligting in die gehoorsenuwee. Die loopgolfspraakverwerker is in staat om temporale leidrade vir toonhoogte te enkodeer tot en met 1060 Hz, terwyl die vokoderspraakverwerker die 300 Hz limiet gedemonstreer het wat ook in ander literatuur oor fasesluiting gevind word. Om die loopgolf na te boots in kogleêre inplanting spraakverwerkers mag potensieel voordele inhou vir die aanbied van inligting aan die ouditiewe korteks van kogleêre inplantinggebruikers. Hierdie resultate moet wel bevestig word deur gebruik van diermodelle en psigo-akoestiese eksperimente.