New cochlear implant coding strategy for tonal language speakers

Abstract

Accurate pitch perception on the basis of fundamental frequency patterns is essential for the processing of lexical tones in tonal languages such as Cantonese. Speech intelligibility in Cantonese-speaking CI recipients was compared using current signal processing strategies, which typically result in poor pitch perception, and a new strategy, known as the multi-channel envelope modulation (MEM) strategy, was designed to enhance temporal periodicity cues to the fundamental frequency. Performance of nine postlingually hearing-impaired adult cochlear implant users was measured twice using each strategy, initially after a four week trial, and again after two weeks of use with each strategy. Speech intelligibility in speech-spectrum shaped noise was measured using the Cantonese hearing in noise test. A fixed noise level of 65 dB A was used and the signal-to-noise ratios were fixed at either +10, +15, or +20 dB, depending on the baseline performance of individual subjects using the clinical processor. Self-reported benefit in 18 listening situations and overall preference for strategies were obtained at the end of these trial periods. Results showed poorer speech intelligibility with CIS while results obtained using ACE and MEM were comparable. Unfamiliar place coding might have contributed to poorer performance using CIS. Self-reported benefit across strategies did not differ in most listening situations. Participants preferred ACE for listening overall in daily situations, and a few preferred MEM in noise. Whilst the results did not demonstrate any advantages for speech recognition in noise when using MEM compared to ACE, no degradation in performance was observed. This implies that the form of processing employed by MEM retains similar segmental information to that provided by ACE and that potentially, future variations/optimizations of MEM may lead to some improvement in tone perception.