Auditory behaviors and vocalization in children using cochlear implants were evaluated using MAIS and MUSS in the preoperative phase and during twenty-four months of CI use. Thirty-two children who received cochlear implants before the age of four years were enrolled and the following results were obtained.
1) The average scores on MAIS and MUSS showed rapid improvement by three months after the start of CI use. The MAIS scores exceeded the MUSS scores at all the evaluation time-points and the scores on the two scales were highly correlated.
2) The rate of improvement of the MAIS score was the highest after one month of CI use, while that of the MUSS score was highest at three months after the start of CI use (initial improvement period). Individual differences of MAIS scores became minimal by twenty-four months, while those of MUSS increased during the same period.
3) In the initial improvement period, the MAIS scores were higher in the children in whom the language development was better preoperatively and who underwent CI at an older age. Preoperative language development influenced the MUSS scores in the initial improvement period, but no longer exerted influence in the middle improvement period.
4) To predict cochlear implant performance, the middle improvement period is notable the most suitable, at which time the effect of the preoperative status is eliminated, and careful observation is needed.
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