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Towards Optical Cochlear Implants

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This thesis focuses on the development of a cochlear implant (CI) that uses photons to stimulate surviving auditory neurons in severe-to-profoundly deaf individuals. The benefit of optical over electrical stimulation is its spatial selectivity with the potential to create significantly more independent channels to encode acoustic information and likely enhances the CI users’ performance in challenging listening environments. Towards the development of an optical cochlear implant, there are two challenges that we addressed in the dissertation: firstly, the development of the light delivery system that can be implanted into the cochlea and evoke auditory responses; secondly, the creation of a coding strategy with temporal periodic cues to accommodate for the low rate of infrared neural stimulation (INS). INS has demonstrated superior potential in more selective stimulation of the cochlea using single flat polished optical fibers. To enable the delivery of photons to the cochlea for future clinical applications, more sophisticated light delivery systems are required. Aim 1 of the thesis is to develop and test such systems. In this dissertation, we have developed a light delivery system using small light sources that evoked auditory responses in vivo. INS is limited by the rate of stimulation. A low rate speech coding strategy is needed to enable this technology for cochlear implants. A novel speech coding strategy has been developed in our lab that fits such requirements, which elicited speech perception in CI users. Such coding strategy encoded the temporal cues of speech (F0 and its harmonics). Aim 2 of the thesis is to examine the functional role of speech temporal cues and their neural representations to give guidance for proper representations of speech temporal cues in CIs. This dissertation demonstrated that the temporal cues within 500 Hz are essential for speech perception in normal hearing listeners under both quiet and noisy listening environment. The dissertation also uncovered the neural processing of temporal cues of speech.

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