Simultaneous bilateral cochlear implantation in adults: a multicenter clinical study

Abstract

Objective: To determine the efficacy of "simultaneous" bilateral cochlear implantation (both implants placed during a single surgical procedure) by comparing bilateral and unilateral implant use in a large number of adult subjects tested at multiple sites.

Design: Prospective study of 37 adults with postlinguistic onset of bilateral, severe to profound sensorineural hearing loss. Performance with the bilateral cochlear implants, using the same speech processor type and speech processing strategy, was compared with performance using the left implant alone and the right implant alone. Speech understanding in quiet (CNCs and HINT sentences) and in noise (BKB-SIN Test) were evaluated at several postactivation time intervals, with speech presented at 0 degrees azimuth, and noise at either 0 degrees , 90 degrees right, or 90 degrees left in the horizontal plane. APHAB questionnaire data were collected after each subject underwent a 3-wk "bilateral deprivation" period, during which they wore only the speech processor that produced the best score during unilateral testing, and also after a period of listening again with the bilateral implants.

Results: By 6-mo postactivation, a significant advantage for speech understanding in quiet was found in the bilateral listening mode compared with either unilateral listening modes. For speech understanding in noise, the largest and most robust bilateral benefit was when the subject was able to take advantage of the head shadow effect; i.e., results were significantly better for bilateral listening compared with the unilateral condition when the ear opposite to the side of the noise was added to create the bilateral condition. This bilateral benefit was seen on at least one of the two unilateral ear comparisons for nearly all (32/34) subjects. Bilateral benefit was also found for a few subjects in spatial configurations that evaluated binaural redundancy and binaural squelch effects. A subgroup of subjects who had asymmetrical unilateral implant performances were, overall, similar in performance to subjects with symmetrical hearing. The questionnaire data indicated that bilateral users perceive their own performance to be better with bilateral cochlear implants than when using a single device.

Conclusions: Findings with a large patient group are in agreement with previous reports on smaller groups, showing that, overall, bilateral implantation offers the majority of patients advantages when listening in simulated adverse conditions.

Figures

Figure 1

Mean (+1 SE) percent correct CNC word scores in quiet in the left ear alone, right ear alone, and bilateral listening conditions for the 33 subjects with complete data across the preoperative (hearing aids), and 1-, 3-, and 6-mo postactivation intervals.

Figure 2

Mean (+1 SE) percent correct HINT sentences-in-quiet scores in the left ear alone, right ear alone, and bilateral listening conditions for the 33 subjects with complete data across the preoperative (hearing aids), and 1-, 3-, and 6-mo postactivation intervals.

Figure 3

Individual (N = 34) and group mean (+1 S.E.) dB SNRs needed for SRT on the BKB-SIN Test at 6-mo postactivation for the condition in which speech and noise were both at 0° azimuth (to assess the “binaural redundancy effect”). Note that a lower number indicates better performance on this task. Results are sorted by bilateral scores, with an asterisk indicating an individual significant benefit for bilateral versus unilateral. A circumflex symbol represents an individual significant bilateral decrement. The double asterisk indicates significance of the bilateral versus left implant alone comparison.

Figure 4

Individual (N = 34) and group mean (+1 S.E.) results on the BKB-SIN test at 6 mo postactivation for the condition in which speech was at 0° azimuth, noise was at 90° azimuth, and the ear with the better SNR (i.e., that opposite the noise) was added for the bilateral condition (to assess the “head shadow effect”). Results in this figure are shown as difference scores between the bilateral and unilateral results, sorted from worst to best. Note that a larger difference indicates greater bilateral benefit. The light-shaded bars represent the amount of bilateral benefit when the bilateral score (in dB SNR) with noise to the left was subtracted from the left-implant alone score (in dB SNR). The darker bars represent the amount of bilateral benefit in dB SNR when the bilateral score with noise to the right was subtracted from the right-implant alone score. A single asterisk indicates an individual significant benefit for bilateral versus unilateral. The double asterisks indicate significant mean differences for the comparisons between the bilateral condition and the unilateral ear conditions.

Figure 5

Individual (N = 34) and group mean (+1 S.E.) results on the BKB-SIN test at 6 mo postactivation for the condition in which speech was at 0° azimuth, noise was at 90° azimuth, and the ear with the poorer SNR (i.e., same side as noise) was added for the bilateral condition (to assess the “binaural squelch effect”). Results in this figure are shown as difference scores between the bilateral and unilateral results, sorted from worst to best. Note that a larger difference indicates greater bilateral benefit. The light-shaded bars represent the amount of bilateral benefit when the bilateral score (in dB SNR) with noise to the left was subtracted from the right-implant alone score (in dB SNR). The darker bars represent the amount of bilateral benefit in dB SNR when the bilateral score with noise to the right was subtracted from the left-implant alone score (in dB SNR). A single asterisk represents an individual significant advantage for the bilateral versus unilateral condition. A circumflex symbol represents an individual significant bilateral decrement. The double asterisks indicate significant mean differences for the comparisons between the bilateral condition and the unilateral ear conditions.

Figure 6

Results for the Ear Asymmetry Group (N = 10 subjects with significant unilateral performance differences between the ears) in the same format as Figure 3 to assess the “binaural redundancy effect”, except that results are shown here for better ear and poorer ear based on unilateral condition performance on this task. Asterisk symbols indicate an individual significant benefit for bilateral versus unilateral. A cross symbol represents an individual significant bilateral decrement (subject #17 in the better-ear condition). On the right side of the graph are means and standard errors for the Ear Asymmetry Group and for the Ear Symmetry Group (N = 24).

Figure 7

Results for the Ear Asymmetry Group (N = 10) in the same format as Figure 4 to assess the “head shadow effect”, except that results are shown here for better ear and poorer ear(based on unilateral implant performances for frontal noise). Individual results are sorted in order from worst to best scores for noise on the poorer ear side. Individual bilateral advantage values above the horizontal bar are statistically significant. On the right side of the graph are means and standard errors for the Ear Asymmetry Group and for the Ear Symmetry Group (N = 24).

Figure 8

Results for the Ear Asymmetry Group (N = 10) in the same format as Figure 5 to assess the “binaural squelch effect”, except that results are shown here for better ear and poorer ear (based on unilateral implant performances for frontal noise). Individual results are sorted in order from worst to best scores for noise on the better ear side. Individual bilateral advantage values above the horizontal bar are statistically significant. On the right side of the graph are means and standard errors for the Ear Asymmetry Group and for the Ear Symmetry Group (N = 24).

Figure 9

Mean (+1 S.E.) scores on the Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire results, by sub-scale, for the 30 subjects with data for both wearing only the best unilateral implant, and for wearing bilateral implants. A higher value (towards “always”) indicates better perceived performance. An asterisk indicates significant bilateral benefit compared with the unilateral condition.

Figure 10

BKB-SIN Test Performance-Intensity (PI) function (±1 S.E.) for data collected from 19 unilateral cochlear implant recipients listening with both speech and noise from a single loudspeaker placed at 0° azimuth.