Loudness normalization for cochlear implant using pulse-rate modulation to convey Mandarin tonal information: A model-based study

Cochlear implant (CI) devices employ electrical pulsatile stimulation of the auditory nerves (AN) to restore partial hearing to a profoundly deafened person. In order to improve the speech perception for CI users speaking tonal language, such as Mandarin, the pulse-rate has been suggested to be modulated according to the Mandarin tonal patterns to convey the Mandarin tonal information. However, recent psychological experiments have found that the pulse-rate modulation will produce accompanying variation of perceived loudness. The purpose of this paper is to introduce an amplitude compensation scheme to normalize the loudness perception when the pulse-rate is modulated to convey the Mandarin tonal information. Based on an integrate-and-fire AN model, a loudness perception model and a pitch perception were implemented. Result of model-based simulation showed that using the proposed amplitude compensation scheme, the estimated loudness was normalized while the Mandarin tonal information could still be efficiently transmitted. It is believed that, when the proposed electrical pulsatile stimulation incorporating both pulse-rate modulation and amplitude compensation is integrated with present CI devices, it would more efficiently enhance the speech identification for cochlear implantee speaking tonal languages, such as Mandarin.