Effects of multi-channel compression on speech intelligibility at the patients with loudness-recruitment

Objective: In this study, the effects of different limiting methods on speech discrimination at the patients with recruitment had been investigated. For this purpose, audiologic, impedansmetric and speech discrimination tests were carried out on 43 ears with cochlear pathology. Materials and Methods: The patients aged between 30 and 70 years (average 53.43±13.41). The sound pressure level at which the maximum speech discrimination score obtained was determined for each patient. A digital behind-the-ear four-channel hearing aid in which compression settings can be programmed independently in each channel was used for all listeners. The hearing aid was fitted to the test ear of the subjects and programmed according to WDRC, PC, CL, BILL and TILL limiting methods. Then speech discrimination scores with hearing aid were examined. This examination was done for the situations the speech noise is absent and S/N ratios of 0dB and +5dB. Results: Although for noiseless situations there was no significant difference between CL and TILL, it has been found that with TILL method statistically better speech discrimination scores were obtained for both 0dB and +5dB S/N ratios. No any significant differences have been marked among the scores obtained with WDRC, PC and BILL methods both in noise and noiseless situations. Any statistically significant correlation was not found between the determined speech discrimination scores and the sound pressure level that rollover occurred. Conclusion: Examination of the results statistically shows that, the highest speech recognition performance obtained with TILL limiting method. The results obtained with CL method were worse than TILL but better than WDRC, BILL and PC. It can be stated that, it is better to adjust the hearing aids used for the patients with recruitment phenomenon for TILL type operation. The CL limiting method could be second choice for limiting but PC, WDRC and BILL methods may not be good candidates for these patients.