Binaural-Bimodal Fitting or Bilateral Implantation for Managing Severe to Profound Deafness: A Review

Abstract

There are now many recipients of unilateral cochlear implants who have usable residual hearing in the non-implanted ear. To avoid auditory deprivation and to provide binaural hearing, a hearing aid or a second cochlear implant can be fitted to that ear. This article addresses the question of whether better binaural hearing can be achieved with binaural/bimodal fitting (combining a cochlear implant and a hearing aid in opposite ears) or bilateral implantation. In the first part of this article, the rationale for providing binaural hearing is examined. In the second part, the literature on the relative efficacy of binaural/bimodal fitting and bilateral implantation is reviewed. Most studies on comparing either mode of bilateral stimulation with unilateral implantation reported some binaural benefits in some test conditions on average but revealed that some individuals benefited, whereas others did not. There were no controlled comparisons between binaural/bimodal fitting and bilateral implantation and no evidence to support the efficacy of one mode over the other. In the third part of the article, a crossover trial of two adults who had binaural/bimodal fitting and who subsequently received a second implant is reported. The findings at 6 and 12 months after they received their second implant indicated that binaural function developed over time, and the extent of benefit depended on which abilities were assessed for the individual. In the fourth and final parts of the article, clinical issues relating to candidacy for binaural/ bimodal fitting and strategies for bimodal fitting are discussed with implications for future research.

The Contribution of a Frequency-Compression Hearing Aid to Contralateral Cochlear Implant Performance

“…In addition, processing time differences between devices or the use of directional microphones on one or both devices may also be factors. For CI+HA users, digital processing delays (or 'group' delay; e.g., Dillon et al, 2003) and different compression and microphone characteristics (e.g., Ching et al, 2007;Musa-Shufani et al, 2006) can result in time delays and have the potential to negatively affect speech understanding and localization.…”

Modulation Enhancement in the Electrical Signal Improves Perception of Interaural Time Differences with Bimodal Stimulation

“…With clinical devices, it has been demonstrated that adding a hearing aid in the nonimplanted ear improves sound source localization and speech perception, as illustrated in a review by Ching et al (2007). However, with their clinical devices, most bimodal listeners are unable to use interaural timing cues which, for normal hearing (NH) listeners, are important for sound source localization and related to binaural unmasking of speech in the presence of spatially separated interfering sounds (Akeroyd 2006;Bronkhorst 2000;Colburn et al 2006).…”

Sensitivity to Interaural Time Differences with Combined Cochlear Implant and Acoustic Stimulation

“…With clinical devices, it has been demonstrated that a contralateral hearing aid improves sound source localization and speech perception performance, as illustrated in a recent review by Ching et al (2007). While performance improves by adding a contralateral hearing aid (HA), it is still poor compared to NH listeners.…”