Results using the OPAL strategy in Mandarin speaking cochlear implant recipients

Abstract

Objective: To evaluate the effectiveness of an experimental pitch-coding strategy for improving recognition of Mandarin lexical tone in cochlear implant (CI) recipients. Design: Adult CI recipients were tested on recognition of Mandarin tones in quiet and speech-shaped noise at a signal-to-noise ratio of +10 dB; Mandarin sentence speech-reception threshold (SRT) in speech-shaped noise; and pitch discrimination of synthetic complex-harmonic tones in quiet. Two versions of the experimental strategy were examined: (OPAL) linear (1:1) mapping of fundamental frequency (F0) to the coded modulation rate; and (OPAL+) transposed mapping of high F0s to a lower coded rate. Outcomes were compared to results using the clinical ACE™ strategy. Study sample: Five Mandarin speaking users of Nucleus® cochlear implants. Results: A small but significant benefit in recognition of lexical tones was observed using OPAL compared to ACE in noise, but not in quiet, and not for OPAL+ compared to ACE or OPAL in quiet or noise. Sentence SRTs were significantly better using OPAL+ and comparable using OPAL to those using ACE. No differences in pitch discrimination thresholds were observed across strategies. Conclusions: OPAL can provide benefits to Mandarin lexical tone recognition in moderately noisy conditions and preserve perception of Mandarin sentences in challenging noise conditions.

Key Words:

• cochlear implant
• pitch coding
• Mandarin perception
• lexical tone

Acknowledgements

This research was supported by the Commonwealth of Australia through the establishment and operations of the Hearing CRC. In addition, we acknowledge the support that the Bionics Institute receives from the Victorian Government through its Operational Infrastructure Support Program and Cochlear Ltd for use of laboratory test equipment. Thanks also to Chris James for proposing the F0 transposition algorithm applied to OPAL+ in this research; to John Heasman, Adam Hersbach, and Stefan Mauger for their help in implementing the OPAL strategy in Cochlear’s real-time system; and to Yanyou Yu for his help as an interpreter and in scoring the Mandarin test responses.

Declaration of interest

The authors report no conflicts of interest.