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The Effect of Instantaneous Input Dynamic Range Setting on the Speech Perception of Children with the Nucleus 24 Implant

Davidson, Lisa S.1; Skinner, Margaret W.1; Holstad, Beth A.2; Fears, Beverly T.3; Richter, Marie K.4; Matusofsky, Margaret4; Brenner, Christine2; Holden, Timothy1; Birath, Amy2; Kettel, Jerrica L.4; Scollie, Susan5

doi: 10.1097/AUD.0b013e31819ec93a
Research Articles
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Objective: The purpose of this study was to examine the effects of a wider instantaneous input dynamic range (IIDR) setting on speech perception and comfort in quiet and noise for children wearing the Nucleus 24™ implant system and the Freedom™ speech processor. In addition, children's ability to understand soft and conversational level speech in relation to aided sound-field thresholds was examined.

Design: Thirty children (age, 7 to 17 years) with the Nucleus 24 cochlear implant system and the Freedom speech processor with two different IIDR settings (30 versus 40 dB) were tested on the Consonant Nucleus Consonant (CNC) word test at 50 and 60 dB SPL, the Bamford-Kowal-Bench Speech in Noise Test, and a loudness rating task for four-talker speech noise. Aided thresholds for frequency-modulated tones, narrowband noise, and recorded Ling sounds were obtained with the two IIDRs and examined in relation to CNC scores at 50 dB SPL. Speech Intelligibility Indices were calculated using the long-term average speech spectrum of the CNC words at 50 dB SPL measured at each test site and aided thresholds.

Results: Group mean CNC scores at 50 dB SPL with the 40 IIDR were significantly higher (p < 0.001) than with the 30 IIDR. Group mean CNC scores at 60 dB SPL, loudness ratings, and the signal to noise ratios-50 for Bamford-Kowal-Bench Speech in Noise Test were not significantly different for the two IIDRs. Significantly improved aided thresholds at 250 to 6000 Hz as well as higher Speech Intelligibility Indices afforded improved audibility for speech presented at soft levels (50 dB SPL).

Conclusion: These results indicate that an increased IIDR provides improved word recognition for soft levels of speech without compromising comfort of higher levels of speech sounds or sentence recognition in noise.

The ability of children to understand speech at soft and conversational levels with two instantaneous input dynamic range (IIDR) settings (30 & 40) on the Freedom Cochlear Implant Processor™ was examined for thirty children (age 7-17). Aided threshold and recorded speech perception testing was conducted using FM tones, noise-bands, Ling 6 sounds, loudness scaling, CNC words at 50 & 60 dB SPL and the BKB-SIN. Results revealed that mean group thresholds were 6-8 dB better with the 40 IIDR. Group mean CNC word scores at 50 dB SPL were significantly better with the 40 IIDR (59.2% vs. 47.8%) while the CNC word scores at 60 dB SPL and BKB-SIN scores at 65 dB SPL were not significantly different. It was concluded that an IIDR of 40 provided significantly better sound-field thresholds and this enabled the children to achieve significantly better CNC word scores at 50 dB SPL by making more sounds audible and recognizable. The BKB-SIN SNR-50 and loudness ratings results were not significantly different between the two IIDR settings, thus improved aided thresholds and recognition of soft speech does not compromise recognition of speech in noise or comfort of higher level sounds.

1Department of Otolaryngology-Head and Neck Surgery, Washington University School of Medicine, St. Louis, Missouri; 2Department of Audiology, The Moog Center for Deaf Education, St. Louis, Missouri; 3St. Joseph Institute for the Deaf, St. Louis, Missouri; 4Department of Audiology, Central Institute for the Deaf, St. Louis, Missouri; and 5School of Communication Sciences and Disorders, University of Western Ontario, Ontario, Canada.

This research was supported by grant RO1 DC000581 from the National Institute on Deafness and Other Communication Disorders. Freedom speech processors for all subjects were provided by Cochlear America's.

This research was approved by the Human Studies Committee at Washington University School of Medicine (06-0211).

Address for correspondence: Lisa S. Davidson, PhD, Washington University School of Medicine, 4560 Clayton Avenue, St. Louis, MO 63110. E-mail: davidsonl@ent.wustl.edu.

Received February 4, 2008; accepted January 16, 2009.

© 2009 Lippincott Williams & Wilkins, Inc.