The Temporal Fine Structure of Background Noise Determines the Benefit of Bimodal Hearing for Recognizing Speech
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JARO (2020) DOI: 10.1007/s10162-020-00772-1 D 2020 The Author(s)
Research Article
Journal of the Association for Research in Otolaryngology
The Temporal Fine Structure of Background Noise Determines the Benefit of Bimodal Hearing for Recognizing Speech H. C. STRONKS,1
J. J. BRIAIRE,1
AND
J. H. M. FRIJNS1,2
1
Department of Otorhinolaryngology, Leiden University Medical Center, PO Box 96002300 RC, Leiden, The Netherlands
2
Leiden Institute for Brain and Cognition, Leiden University, Leiden, The Netherlands
Received: 4 June 2019; Accepted: 14 October 2020
ABSTRACT Cochlear implant (CI) users have more difficulty understanding speech in temporally modulated noise than in steady-state (SS) noise. This is thought to be caused by the limited low-frequency information that CIs provide, as well as by the envelope coding in CIs that discards the temporal fine structure (TFS). Contralateral amplification with a hearing aid, referred to as bimodal hearing, can potentially provide CI users with TFS cues to complement the envelope cues provided by the CI signal. In this study, we investigated whether the use of a CI alone provides access to only envelope cues and whether acoustic amplification can provide additional access to TFS cues. To this end, we evaluated speech recognition in bimodal listeners, using SS noise and two amplitudemodulated noise types, namely babble noise and amplitude-modulated steady-state (AMSS) noise. We hypothesized that speech recognition in noise depends on the envelope of the noise, but not on its TFS when listening with a CI. Secondly, we hypothesized that the amount of benefit gained by the addition of a contralateral hearing aid depends on both the envelope and TFS of the noise. The two amplitudemodulated noise types decreased speech recognition more effectively than SS noise. Against expectations, however, we found that babble noise decreased speech recognition more effectively than AMSS noise in the CI-only condition. Therefore, we rejected our hypothesis that TFS is not available to CI users. In line with expectations, we found that the bimodal benefit was highest in babble noise. However, there was no Correspondence to: H. C. Stronks & Department of Otorhinolaryngology & Leiden University Medical Center & PO Box 96002300 RC, Leiden, The Netherlands. email: [email protected]
significant difference between the bimodal benefit obtained in SS and AMSS noise. Our results suggest that a CI alone can provide TFS cues and that bimodal benefits in noise depend on TFS, but not on the envelope of the noise. Keywords: cochlear implants, sensorineural hearing loss, hearing aids, speech intelligibility, speech perception, bimodal hearing
INTRODUCTION Cochlear implants (CIs) are auditory prostheses offered to individuals who are severe-to-profoundly deaf. CIs can partly restore hearing by electrically stimulating auditory-nerve cells directly, thereby bypassing the degenerated hair cells in the cochlea. The performance of CIs has greatly improved since their inception by the advent of ongoing
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