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The Influence of Audibility on Speech Recognition With Nonlinear Frequency Compression for Children and Adults With Hearing Loss

McCreery, Ryan W.1; Alexander, Joshua2; Brennan, Marc A.1; Hoover, Brenda1; Kopun, Judy1; Stelmachowicz, Patricia G.1

doi: 10.1097/AUD.0000000000000027
Research Articles

Objective: The primary goal of nonlinear frequency compression (NFC) and other frequency-lowering strategies is to increase the audibility of high-frequency sounds that are not otherwise audible with conventional hearing aid (HA) processing due to the degree of hearing loss, limited HA bandwidth, or a combination of both factors. The aim of the present study was to compare estimates of speech audibility processed by NFC with improvements in speech recognition for a group of children and adults with high-frequency hearing loss.

Design: Monosyllabic word recognition was measured in noise for 24 adults and 12 children with mild to severe sensorineural hearing loss. Stimuli were amplified based on each listener’s audiogram with conventional processing (CP) with amplitude compression or with NFC and presented under headphones using a software-based HA simulator. A modification of the speech intelligibility index (SII) was used to estimate audibility of information in frequency-lowered bands. The mean improvement in SII was compared with the mean improvement in speech recognition.

Results: All but 2 listeners experienced improvements in speech recognition with NFC compared with CP, consistent with the small increase in audibility that was estimated using the modification of the SII. Children and adults had similar improvements in speech recognition with NFC.

Conclusion: Word recognition with NFC was higher than CP for children and adults with mild to severe hearing loss. The average improvement in speech recognition with NFC (7%) was consistent with the modified SII, which indicated that listeners experienced an increase in audibility with NFC compared with CP. Further studies are necessary to determine whether changes in audibility with NFC are related to speech recognition with NFC for listeners with greater degrees of hearing loss, with a greater variety of compression settings, and using auditory training.

Listeners with hearing loss may experience limited high-frequency audibility through conventional amplification. Nonlinear frequency compression (NFC) increases high-frequency audibility, but the magnitude of improvements in speech recognition in previous studies has varied. The purpose of the present study was to determine if improvements in speech recognition occurred with improvements in audibility with NFC. Twentyfour adults and 12 children with hearing loss completed word recognition in noise with conventional processing (CP) and NFC. Improvements in word recognition were consistent with estimates of audibility modified to account for the location of frequency bands after lowering.

1Hearing and Amplification Research Laboratory, Boys Town National Research Hospital, Omaha, Nebraska, USA; and 2Department of Speech, Language, & Hearing Sciences, Purdue University, West Lafayette, Indiana, USA.

This research was supported by National Institutes of Health grants to Dr. Stelmachowicz (R01 DC04300), Dr. McCreery (R03 DC012635), Dr. Brennan (F32 DC012709), Dr. Alexander (RC1 DC010601), and the Post-doctoral training (T32 DC00013) and Human Research Subjects Core (P30-DC004662) grants to Boys Town National Research Hospital.

The authors declare no other conflict of interest.

Address for correspondence: Ryan McCreery, Boys Town National Research Hospital, Omaha, NE 68131, USA. E-mail: Ryan.McCreery@boystown.org

Received December 5, 2012; accepted December 3, 2013.

© 2014 by Lippincott Williams & Wilkins