We evaluated the long-term development of categorical auditory performance and speech intelligibility rating of Mandarin-speaking prelingually deaf children within 5 years after early cochlear implantation. The categorical auditory performance increased after cochlear implantation, the median categorical auditory performance after 1 year of implantation was 4 and became 7 three years after implantation. The median categorical auditory performance remained to be 7 till 5 years after implantation. There was significant difference in categorical auditory performance category between 'before implantation' and '1 year after implantation', also between '1 year after implantation' and '3 years after implantation'. But no significant difference was found between 3 years and 5 years after implantation. The median speech intelligibility rating before implantation was 1. After 2 years of implantation, the median speech intelligibility rating became 4. Significant difference was found between these two time points. Three years after implantation, the median speech intelligibility rating improved to 5 and maintained at that level till 5 years after implantation. Eighty-one per cent (17/21) of our subjects reached the maximal category (7) of categorical auditory performance 5 years after implantation. Eighty-one percent (17/21) of our subjects achieved the highest category (5) of speech intelligibility rating 5 years after implantation.

This paper discusses a single-channel speech enhancement method for cochlear implant listeners. It is assumed that the Fourier Transform coefficients of speech and background noise have different statistical distributions. A statistical-model-based method is adopted to update the signal-to-noise ratio and estimate the background noise so that the musical noise and speech distortion induced by traditional spectral subtraction method can be effectively reduced. This enhancement method was evaluated on seven postlingually deaf Chinese cochlear implant listeners in comparison with other two speech enhancement methods. Test materials were Mandarin sentences corrupted by three different types of background noise. Experimental results showed that the proposed speech enhancement method could benefit the speech intelligibility of Chinese cochlear implant listeners. The results suggest that different noise types may affect the performance of different speech enhancement algorithms.