Recent Progress in Cochlear Implant

Abstract

In modern cochlear implants, the electrode array has a small volume, is less stiff, and is positioned to prevent traumatic contact with the fine structure of the cochlea. With these improvements, the electrode array causes less trauma, and preservation of residual inner ear function is possible. Newly developed speech coding strategies are based on the psychology of hearing. The fine structure of speech is reproduced by mimicking the temporal excitatory patterns of inner hair cells. The role of the virtual channel is to excite the spiral ganglion neurons located between two electrode contacts by controlling the current spread from two neighboring electrodes. The psychoacoustic masking model is also utilized in channel selection. This model considers the physiological masking effect and reduces the number of stimulated channels without deteriorating the speech understanding. Due to the development of atraumatic electrode arrays, residual hearing at low frequencies can be preserved after cochlear implantation. The remaining hearing can be utilized to transmit low-frequency sounds, and the spiral ganglion neurons in the basal turn, which transmit high-frequency sounds, can be electrically stimulated (electric acoustic stimulation). Bilateral cochlear implantation is also a new trend. The use of two implants improves sound source localization and speech understanding in noisy environments.