Abstract
Three cochlear implant (CI) sound coding strategies were combined in the same signal processing path and compared for speech intelligibility with vocoded Mandarin sentences. The three CI coding strategies, biologically-inspired hearing aid algorithm (BioAid), envelope enhancement (EE), and fundamental frequency modulation (F0mod), were combined with the advanced combination encoder (ACE) strategy. Hence, four singular coding strategies and four combinational coding strategies were derived. Mandarin sentences with speech-shape noise were processed using these coding strategies. Speech understanding of vocoded Mandarin sentences was evaluated using short-time objective intelligibility (STOI) and subjective sentence recognition tests with normal-hearing listeners. For signal-to-noise ratios at 5 dB or above, the EE strategy had slightly higher average scores in both STOI and listening tests compared to ACE. The addition of EE to BioAid slightly increased the mean scores for BioAid+EE, which was the combination strategy with the highest scores in both objective and subjective speech intelligibility. The benefits of BioAid, F0mod, and the four combinational coding strategies were not observed in CI simulation. The findings of this study may be useful for the future design of coding strategies and related studies with Mandarin.
Highlights
T HE cochlear implant (CI) is a successful neural prosthetic device that restores the sense of hearing for hundreds of thousands of hearing-impaired listeners
The Tukey post-hoc test showed that biologically-inspired hearing aid algorithm (BioAid), F0mod, BioAid+EE, BioAid+F0mod, EE+F0mod, and BioAid+EE+F0mod were significantly different to advanced combination encoder (ACE) (p < 0.001)
The addition of the EE processing stage to ACE, BioAid, F0mod, and BioAid+F0mod did not affect the statistical significance of the short-time objective intelligibility (STOI) scores
Summary
T HE cochlear implant (CI) is a successful neural prosthetic device that restores the sense of hearing for hundreds of thousands of hearing-impaired listeners. With an external sound processor and an internal implant, a CI bypasses a malfunctioning cochlea [1]–[3] and transmits sound signals through the electro-to-neural interface to stimulate auditory nerves [4], [5]. The coding strategy in a CI sound processor plays an important role in defining the stimulation patterns achievable and recognizable by the auditory brain. Huang is with the Department of Electrical Engineering, National Central University, Taoyuan, Taiwan
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