Comparing Two Hearing Aid Fitting Algorithms for Bimodal Cochlear Implant Users

Objectives: To investigate the possible advantage of the use of a dedicated bimodal hearing aid fitting formula, the Adaptive Phonak Digital Bimodal (APDB), compared with a frequently used standard hearing aid fitting formula, the NAL-NL2. We evaluated the effects of bimodal hearing aid fitting on provided hearing aid gain and on bimodal auditory functioning in a group of experienced bimodal cochlear implant (CI) users. A second aim of our study was to determine the effect of broadband loudness balancing on the prescribed gain of those two fitting formulas. Design: This prospective study used a crossover design in which two fitting methods were compared varying in basic prescription formula (NAL-NL2 or APDB fitting formula). The study consisted of a three-visit crossover design with 3 weeks between sessions. Nineteen postlingually deafened experienced bimodal CI users participated in this study. Auditory functioning was evaluated by a speech in quiet test, a speech in noise test, and a questionnaire on auditory performance. Results: Significant differences between the two fitting formulas were found for frequencies of 2000 Hz and above. For these frequencies, less gain was provided by the APDB fitting formula compared with NAL-NL2. For the APDB fitting formula, a higher compression ratio for frequencies of 1000 Hz and above was found compared with the NAL-NL2 fitting formula. Loudness balancing did not result in large deviations from the prescribed gain by the initial fitting formula. Bimodal benefit was found for speech perception in quiet and for speech perception in noise. No differences in auditory performance were found between the two fitting formulas for any of the auditory performance tests. Conclusions: The results of this study show that CI users with residual hearing at the contralateral ear can benefit from bimodal stimulation, regardless of the fitting method that was applied. Although significant differences between the output and compression ratio of the NAL-NL2 and the APDB fitting formula existed, no differences in bimodal auditory performance were observed. Therefore, NAL-NL2 or the APDB fitting prescription both seem suited for bimodal fitting purposes. Additional loudness balancing has a marginal effect on the provided hearing aid output.

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