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.

Figure 1.

Hearing threshold levels of the nonimplanted ear of subjects S1 and S2.

Figure 2.

Localization performance of subject S1 with the first implant alone (CI alone), with the first implant and a hearing aid (CI + HA), and with bilateral implants (CI + CI) at two intervals after activation of the second implant.

Figure 3.

Localization performance of subject S2 with the first implant alone (CI alone), with the first implant and a hearing aid (CI + HA), and with bilateral implants (CI + CI) at two intervals after activation of the second implant.

Figure 4.

Binaural speech perception with speech from the front and noise from left and right simultaneously. The left panel shows the speech reception threshold (SRT) in terms of dB signal-to-noise ratio (SNR). The right panel shows the percentage of correct scores for consonants. Filled circles represent results from subject S1, and open squares represent results from subject S2.

Figure 5.

Binaural intelligibility level difference (BILD) expressed as the difference in speech reception threshold (SRT) between the condition with no interaural delay and the condition when an interaural delay of 700 microseconds was introduced in the noise in dB signal-to-noise ratio (SNR). Filled circles represent the results for subject S1, and open squares represent results from subject S2.

Figure 6.

Functional performance of subject S1 when using his first implant with a hearing aid (CI + HA) and his two cochlear implants at two months (CI + CI, 2m), 6 months (CI + CI, 6m), and 12 months (CI + CI, 12m) after activation of the second implant. The left panel shows results of the National Acoustics Laboratory Functional Performance Questionnaire (NAL-FQ). The subscale scores of listening in “Quiet,” listening in “Noise,” awareness of environmental sounds (“Env”), and the “Total” overall scores are shown. The right panel shows results from the Speech, Spatial, and Quality of Hearing Questionnaire (SSQ), with the subscale scores for “Speech,” “Spatial,” and “Quality” and the “Total” overall scores. SSQ scores are available for only the bilateral implant conditions.

Figure 7.

Functional performance of subject S2 when using his first implant with a hearing aid (CI + HA) and using his two implants at two months (CI + CI, 2m) and 6 months (CI + CI, 6m) after activation of the second implant. The left panel shows subscale and total scores based on the National Acoustic Laboratory Functional Performance Questionnaire (NAL-FQ), and the right panel shows subscale and total scores for the Speech, Spatial, and Quality of Hearing Questionnaire (SSQ).