Cochlear Implant and Hearing Aid: Objective Measures of Binaural Benefit

Abstract

Cochlear implants (CI) improve hearing for the severely hearing impaired. With an extension of implantation candidacy, today many CI listeners use a hearing aid on their contralateral ear, referred to as bimodal listening. It is uncertain, however, whether the brains of bimodal listeners can combine the electrical and acoustical sound information and how much CI experience is needed to achieve an improved performance with bimodal listening. Patients with bilateral sensorineural hearing loss undergoing implant surgery were tested in their ability to understand speech in quiet and in noise, before and again 3 and 6 months after provision of a CI. Results of these bimodal listeners were compared to age-matched, normal hearing controls (NH). The benefit of adding a contralateral hearing aid was calculated in terms of head shadow, binaural summation, binaural squelch, and spatial release from masking from the results of a sentence recognition test. Beyond that, bimodal benefit was estimated from the difference in amplitudes and latencies of the N1, P2, and N2 potentials of the brains’ auditory evoked response (AEP) toward speech. Data of fifteen participants contributed to the results. CI provision resulted in significant improvement of speech recognition with the CI ear, and in taking advantage of the head shadow effect for understanding speech in noise. Some amount of binaural processing was suggested by a positive binaural summation effect 6 month post-implantation that correlated significantly with symmetry of pure tone thresholds. Moreover, a significant negative correlation existed between binaural summation and latency of the P2 potential. With CI experience, morphology of the N1 and P2 potentials in the AEP response approximated that of NH, whereas, N2 remained different. Significant AEP differences between monaural and binaural processing were shown for NH and for bimodal listeners 6 month post-implantation. Although the grand-averaged difference in N1 amplitude between monaural and binaural listening was similar for NH and the bimodal group, source localization showed group-dependent differences in auditory and speech-relevant cortex, suggesting different processing in the bimodal listeners.

Modelling speech reception thresholds and their improvements due to spatial noise reduction algorithms in bimodal cochlear implant users

“…Only with both poor and similar speech-in-noise performance across ears, significant benefits beyond better-ear-listening can be expected ( Jürgens, Wesarg, Oetting, Jung, Williges, 2021 , Yoon, Shin, Gho, Fu, 2015 ). The difference between NH and bimodal CI users in behavioural studies is further supported by Balkenhol et al. (2020) , who found differences in cortical processing between bimodal CI users and NH listeners using objective methods.…”

“…Evidence for that is predominantly found in carefully controlled laboratory measurements ( Francart et al., 2008 ). However, studies employing less controlled commercial speech processors, couldn’t replicate these benefits for speech processing ( Balkenhol, Wallhusser-Franke, Rotter, Servais, 2020 , Dieudonn, Francart, 2020 , Williges, Wesarg, Jung, Geven, Radeloff, Jürgens, 2019 ). Introducing and validating a binaural processing strategy in a normal-hearing setting for FADE may offer an insight into possible missing binaural processing in bimodal CI users.…”

Considerations for Fitting Cochlear Implants Bimodally and to the Single-Sided Deaf

“…Various behavioral and evoked-response based measurements have been suggested to derive the interaural level mismatch in CI users ( Balkenhol et al, 2020 ). Most commonly “loudness balancing” is the reported fitting goal and as such also the mismatch measurement technique ( van Eeckhoutte et al, 2018 ; Veugen et al, 2016a ).…”

Study protocol for a randomised controlled trial evaluating the benefits from bimodal solution with cochlear implant and hearing aid versus bilateral hearing aids in patients with asymmetric speech identification scores

“… 15 Many bimodal CI and HA users are missing these benefits because the devices are unsynchronised. 16 …”