The effectiveness of sound‐processing strategies on tonal language cochlear implant users: A systematic review

IMPORTANCE: Contemporary cochlear implants (CIs) are well established as a technology for people with severe‐to‐profound sensorineural hearing loss, with their effectiveness having been widely reported. However, for tonal language CI recipients, speech perception remains a challenge: Conventional signal processing strategies have been demonstrated to possibly provide insufficient information to encode tonal cues, and CI recipients have exhibited considerable deficits in tone perception. Thus, some tonal language–oriented sound‐processing strategies have been introduced. The effects of available tonal language–oriented strategies on tone perception are reviewed and evaluated in this study. The results may aid in designing and improving tonal language–appropriate sound‐processing strategies for CI recipients. OBJECTIVE: The objective of this systematic review was to investigate the effects of tonal‐language‐oriented signal processing strategies on tone perception, music perception, word and sentence recognition. METHODS: To evaluate the effects of tonal language–oriented strategies on tone perception, we conducted a systematic review. We searched for relevant reports dated from January 1979 to July 2017 using PubMed, Cochrane Library, EBSCO, Web of Science, EMBASE, and 4 Chinese periodical databases (CBMdisc, CNKI, VIP, and Wanfang Data). RESULTS: According to our search strategy, 672 potentially eligible studies were retrieved from the databases, with 12 of these studies included in the final review after a 4‐stage selection process. The majority of sound‐processing strategies designed for tonal language were HiResolution(®) with Fidelity 120 (HiRes 120), fine structure processing, temporal fine structure (TFS), and C‐tone. Generally, acute or short‐term comparisons between the tonal language–oriented strategies and the conventional strategy did not reveal statistically significant differences in speech perception (or show a small improvement). However, a tendency toward improved tone perception and subjectively reported overall preferred sound quality was observed with the tonal language–oriented strategies. INTERPRETATION: Conventional signal processing strategies typically provided very limited F0 information via temporal envelopes delivered to the stimulating electrodes. In contrast, tonal language–oriented coding strategies attempted to present more spectral information and TFS cues required for tone perception. Thus, a tendency of improved performance in tonal language perception in CI users was shown.