Efficacy of non-linear frequency compression in Individuals with and without cochlear dead regions

Abstract

There have been reports about different frequency lowering strategies like Non-linear Frequency Compression (NLFC) in individuals with a sloping hearing loss (Simpson, Hersbach, and McDermott, 2005, 2006). The present study investigated the usefulness of NLFC in individuals with and without cochlear dead regions. Two groups (Group I without cochlear dead region and Group II with cochlear dead region) formed the basis of the study. The hearing aid testing was done for three aided conditions- without NLFC, with NLFC initial fit settings and with NLFC fine-tuned settings. The parameters assessed were speech identification scores, Ling’s six sound identification and quality judgment. The results revealed that there was a significant difference in the mean SIS scores for words only for the pair without NLFC and NLFC fine-tuned settings for Group I with no significant difference in Group II for any pair. The performance was similar for all the aided conditions for SIS for sentences in both the groups. Ling’s six sound identification revealed a slight improvement in fricative identification among participants in Group I with no improvement in the Group II. The results of quality ratings showed that the mean ratings of quality were higher for the Group I compared to Group II and there was a significant difference in the quality rating between both the groups. In conclusion, the amplification needs of individuals with and without cochlear dead region are different and frequency lowering strategies like NLC may be of limited usefulness to individuals with cochlear dead region.