[Rate discrimination and tone recognition in mandarin-speaking cochlear-implant listeners]

To explore the relationship between the rate discrimination and the tone recognition with psychophysical method, and provide a basis for evaluating the results from mandarin-speaking cochlear implantees who used multi-channel cochlear implant and designing new speech coding strategies of the speech processor.

Four postlingually-deafened adults with cochlear implant participated in this study. We used the method of constant stimuli to measure the rate discrimination as a function of the standard rate at 50, 100, 200, 400 Hz on electrode pairs (E1, E3), (E7, E9), (E14, E16), and (E20, E22), respectively. We also measured tone recognition in 25 consonant-vowel syllables, each of which has four tonal variations, resulting in a total of 100 words. These words were recorded by a male talker and were presented five times each to the implant users via their speech processors. The tone recognition results were scored in overall percent correct and analyzed by error patterns in the confusion matrix and fundamental frequency.

The rate discrimination thresholds, defined at the 75% correct level, varied greatly among individuals and ranged from several Hz to hundreds of Hz. A three-way ANOVA indicated significant effect (P < 0.05) on rate discrimination for the standard rate, electrode position, and patient variable. The tone recognition ranged from 40% to 80% and tones 1 and 3 were more easily identified than tones 2 and 4. Preliminary analysis using linear regression revealed highly significant correlation between rate discrimination and tone recognition.

These results suggest that identification of tones relies on good rate discrimination in cochlear implant listeners. Clinical rehabilitation strategies in improving rate discrimination were discussed.