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Effects of Nonlinear Frequency Compression on Speech Identification in Children With Hearing Loss

Hillock-Dunn, Andrea1; Buss, Emily2; Duncan, Nicole1; Roush, Patricia A.2; Leibold, Lori J.1

doi: 10.1097/AUD.0000000000000007
Research Articles

Objectives: This study evaluated effects of nonlinear frequency compression (NLFC) processing in children with hearing loss for consonant identification in quiet and for spondee identification in competing noise or speech. It was predicted that participants would benefit from NLFC for consonant identification in quiet when access to high-frequency information was critical, but that NLFC would be less beneficial, or even detrimental, when identification relied on mid-frequency cues. Further, it was hypothesized that NLFC could result in greater susceptibility to masking in the spondee task. The rationale for these predictions is that improved access to high-frequency information comes at the cost of decreased spectral resolution.

Design: A repeated-measures design compared speech-perception outcomes in 17 pediatric hearing aid users (9 to 17 years of age) wearing Naida V SP “laboratory” hearing aids with NLFC on and off. Data were also collected in an initial baseline session in which children wore their personal hearing aids. Children with a wide range of audiometric configurations were included, but all participants were full-time users of hearing aids with active NLFC. For each hearing aid condition, speech perception was assessed in the sound field by using a closed-set 12-alternative consonant–vowel identification measure in quiet, and a closed-set four-alternative spondee-identification measure in a speech-shaped noise or in a two-talker speech masker.

Results: No significant differences in performance were observed between laboratory hearing aid conditions with NLFC activated or deactivated for either speech-perception measure. An unexpected finding was that the majority of participants had no difficulty identifying the high-frequency consonant /s/ even when NLFC was deactivated. Investigation into individual differences revealed that subjects with a greater difference in audible bandwidth with NLFC on versus NLFC off were less likely to demonstrate improvements in high-frequency consonant identification in quiet, but were more likely to demonstrate improvements in spondee identification in speech-shaped noise. Group results observed in the initial baseline assessment using personal aids fitted with more aggressive NLFC settings than used in laboratory aids indicated better consonant identification accuracy in quiet. However, spondee identification in the two-talker masker was poorer with personal compared with laboratory hearing aids. Comparisons across personal and laboratory hearing aids are tempered, however, by the potential of an order effect.

Conclusions: The observation of comparable performance with NLFC on and NLFC off in the laboratory aids provides evidence that NLFC is neither detrimental nor advantageous when modest in strength. Results with personal hearing aids fitted with stronger compression settings than laboratory aids (NLFC on) highlight the critical need for further research to determine the impact of NLFC processing on speech perception for a wider range of speech-perception measures and compression settings.

The influence of nonlinear frequency compression (NLFC) processing was examined in children with hearing loss for phoneme identification in quiet and spondee identification in competing noise or speech. Outcomes were assessed using laboratory hearing aids with NLFC on and off and personal hearing aids with NLFC on. Results showed no consistent effect of NLFC on speech perception abilities for either measure, although performance differences were greater for children with stronger NLFC settings. Findings from measurements using personal and laboratory aids indicated a need for continued research on the influence of listening experience and NLFC settings on speech perception abilities.

1Department of Allied Health Sciences, The University of North Carolina at Chapel Hill, School of Medicine, Chapel Hill, North Carolina, USA; 2Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina at Chapel Hill, School of Medicine Chapel Hill, North Carolina, USA.

This work was supported by the March of Dimes Foundation (#5-FY10-28) and from the National Institute of Deafness and Other Communication Disorders (R01 DC011038).

The authors declare no other conflict of interest.

Address for correspondence: Lori Leibold, University of North Carolina, Allied Health Sciences, Division of Speech and Hearing Sciences, 301A South Columbia Street, 3105 Bondurant Hall, Chapel Hill, NC 27599, USA. E-mail:

© 2014 by Lippincott Williams & Wilkins