Effect of carrier bandwidth on understanding mandarin sentences in simulated electric-acoustic hearing

For patients suffering with high-frequency hearing loss and preserving low-frequency hearing, combined electric-acoustic stimulation (EAS) may significantly improve their speech perception compared with cochlear implants (CIs). In combined EAS, a hearing aid provides low-frequency information via acoustic (A) stimulation and a CI evokes highfrequency sound sensation via electrical (E) stimulation. The present work investigated the EAS advantage when only a small number (i.e., 1 or 2) of channels were provided for electrical stimulation in a CI, and the effect of carrier bandwidth on understanding Mandarin sentences in a simulation of combined EAS experiment. The A-portion was extracted via low-pass filtering processing and the E-portion was generated with a vocoder model preserving multi-channel temporal envelope waveforms, whereas a noise-vocoder and a tone-vocoder were used to simulate the effect of carrier bandwidth. The synthesized stimuli were presented to normalhearing listeners to recognize. Experimental results showed that while low-pass filtered Mandarin speech was not very intelligible, adding one or two E channels could significantly improve the intelligibility score to above 86.0%. Under the condition with one E channel, using a large carrier bandwidth in noise-vocoder processing provided a better intelligibility performance than using a narrow carrier bandwidth in tonevocoder processing.