Abstract
Current cochlear implants (CIs) are semi-implantable devices with an externally worn sound processor that hosts the microphone and sound processor. A fully implantable device, however, would ultimately be desirable as it would be of great benefit to recipients. While some prototypes have been designed and used in a few select cases, one main stumbling block is the sound input. Specifically, subdermal implantable microphone technology has been poised with physiologic issues such as sound distortion and signal attenuation under the skin. Here we propose an alternative method that utilizes a physiologic response composed of an electrical field generated by the sensory cells of the inner ear to serve as a sound source microphone for fully implantable hearing technology such as CIs. Electrophysiological results obtained from 14 participants (adult and pediatric) document the feasibility of capturing speech properties within the electrocochleography (ECochG) response. Degradation of formant properties of the stimuli /da/ and /ba/ are evaluated across various degrees of hearing loss. Preliminary results suggest proof-of-concept of using the ECochG response as a microphone is feasible to capture vital properties of speech. However, further signal processing refinement is needed in addition to utilization of an intracochlear recording location to likely improve signal fidelity.
Highlights
To date, it is estimated that as many as 466 million individuals worldwide have hearing loss as defined as an average hearing level of ≥35 dB HL by pure-tone audiometry[1]
Since the cochlear microphonic (CM) response is dominated by hair cell activity[17], sensorineural hearing loss (SNHL) would likely cause degradation of how well the incoming signal is represented by the CM
Base-to-peak amplitudes of the non-normalized ECochGdiff response, measured as the region of the ECochGdiff response after stimulus onset that produced the maximal amplitude deflection, were calculated and for those evoked by /da/ presented at 108 dB peak equivalent www.nature.com/scientificreports
Summary
It is estimated that as many as 466 million individuals worldwide have hearing loss as defined as an average hearing level of ≥35 dB HL by pure-tone audiometry[1]. Cochlear implants (CI) have long been a treatment option for individuals with severe-to-profound hearing loss; with advancements in technology, candidacy criteria have expanded to include individuals with greater amounts of residual hearing With this trend, the focus has shifted toward developing techniques and technology to allow for the preservation of residual hearing, as this has been shown to be important in obtaining optimal outcomes through the use of electric-acoustic stimulation. First described by Weaver and Bray[16], it was termed the ‘microphone’ potential as the response typically mimics the acoustic waveform generated from an external source that is transferred from the external ear canal and middle ear Owing to this property, the CM response could serve as an internal microphone for a hearing device such as a CI.
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