Pitch and tonal language perception in cochlear implant users

Abstract

Pitch ranking and tonal language perception was investigated with nine native Cantonese-speaking postlingually deaf adults who were users of the Nucleus CI24 implant system. All subjects were experienced users of the Advanced Combinational Encoding (ACE) strategy. The subject’s use of three sound coding strategies was evaluated. Two of these were the ACE and the Continuous Interleaved Sampling (CIS) strategy which are widely used in current clinical practice. The third was a novel experimental strategy termed Multi-channel Envelope Modulation (MEM) that was specifically designed to enhance F0 periodicity cues in the stimulus envelope. All three strategies were implemented in an experimental body-worn research processor (SPEAR3). A repeated ABC-ABC experimental design was adopted, in which each strategy was taken home by subjects and used for a period of 4 weeks (for each strategy) in the first stage of evaluation and then subsequently for a further 2 weeks in the second stage (providing a total of 6 weeks use with each strategy over a period of 18 weeks in total, excluding follow-up tests). Tonal language perception was measured using the Cantonese HINT (CHINT) sentence test (presented in speech-spectrum shaped noise) and a Cantonese tone minimal-pair identification test. Pitch perception through the processor/strategy was measured using a 3-harmonic complex-tone pitch ranking test. There were no significant differences in perception scores for use of the MEM strategy as compared to ACE for the Cantonese speech perception tests. However, scores using the CIS strategy were significantly lower than either ACE or MEM strategies for the CHINT sentence test in noise. Results for the pitch ranking tests provided lower F0 difference limens (DLs) for three of the subjects, comparable DLs for five of the subjects, and a poorer DL in one subject, when using the MEM strategy compared to the clinical strategies. Previous studies had demonstrated that enhancement of F0 periodicity cues in the stimulus envelope can provide improvement to pitch perception, at least for pitch ranking of sung vowel stimuli. It may be that lack of experience and/or training in use of temporal periodicity cues exclusively for tone perception in tonal language may be important, and that this contributed to the findings of the current study. In addition, differences in central processing of pitch in music and language tasks may be partly responsible for these outcomes. Support provided by the CRC for Cochlear Implant and Hearing Aid Innovation, the University of Hong Kong, and Cochlear Limited, Australia and Hong Kong.