title: A neural-based vocoder implementation for evaluating cochlear implant coding strategies.
abstract: Most simulations of cochlear implant (CI) coding strategies rely on standard vocoders that are based on purely signal processing techniques. However, these models neither account for various biophysical phenomena, such as neural stochasticity and refractoriness, nor for effects of electrical stimulation, such as spectral smearing as a function of stimulus intensity. In this paper, a neural model that accounts for stochastic firing, parasitic spread of excitation across neuron populations, and neuronal refractoriness, was developed and augmented as a preprocessing stage for a standard 22-channel noise-band vocoder. This model was used to subjectively and objectively assess consonant discrimination in commercial and experimental coding strategies. Stimuli consisting of consonant-vowel (CV) and vowel-consonant-vowel (VCV) tokens were processed by either the Advanced Combination Encoder (ACE) or the Excitability Controlled Coding (ECC) strategies, and later resynthesized to audio using the aforementioned vocoder model. Baseline performance was measured using unprocessed versions of the speech tokens. Behavioural responses were collected from seven normal hearing (NH) volunteers, while EEG data were recorded from five NH participants. Psychophysical results indicate that while there may be a difference in consonant perception between the two tested coding strategies, mismatch negativity (MMN) waveforms do not show any marked trends in CV or VCV contrast discrimination.
authors.affiliation: Institute for Neuroinformatics (INI), Universität Zürich (UZH)/ ETH Zürich (ETHZ), Zürich, Switzerland. Electronic address: n.el.boghdady@umcg.nl.
authors.forename: Nawal
authors.initials: N
authors.lastname: El Boghdady
authors.affiliation: Laboratory of Experimental Audiology, ENT Department, Universitätsspital Zürich (USZ), Zürich, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kegel
authors.affiliation: Laboratory of Experimental Audiology, ENT Department, Universitätsspital Zürich (USZ), Zürich, Switzerland.
authors.forename: Wai Kong
authors.initials: WK
authors.lastname: Lai
authors.affiliation: Laboratory of Experimental Audiology, ENT Department, Universitätsspital Zürich (USZ), Zürich, Switzerland.
authors.forename: Norbert
authors.initials: N
authors.lastname: Dillier
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D001306:Auditory Pathways / Q000503:physiopathology*; D001309:Auditory Threshold; D019929:Cochlear Implantation / Q000295:instrumentation*; D003054:Cochlear Implants; D003198:Computer Simulation; D004558:Electric Stimulation; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008144:Loudness Perception; D008297:Male; D008875:Middle Aged; D016571:Neural Networks, Computer; D019986:Persons with Hearing Disabilities / Q000523:psychology / Q000534:rehabilitation*; D011474:Prosthesis Design; D011571:Psychoacoustics; D012815:Signal Processing, Computer-Assisted; D013061:Speech Acoustics; D013067:Speech Perception; D013269:Stochastic Processes; D013997:Time Factors; D014833:Voice Quality
keywords: ACE; ECC; EEG; MMN; Neural vocoder; Objective measures