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° azimuth, and noise at either 0°, 90° right, or 90° 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. Persons with bilateral severe to profound sensorineural hearing loss have traditionally received a single cochlear implant. To date, health care professionals have recommended unilateral, rather than bilateral, cochlear implant fittings for these patients for several reasons, including: 1) cost/reimbursement issues, 2) preservation of one ear for future technologies, 3) additional risk of two, or extended, surgeries, and 4) lack of sufficient objective and/or subjective evidence documenting bilateral cochlear implant benefit. Although unilateral use of cochlear implants NIH-PA A...

Objective The abilities to localize sounds and segregate speech from interfering sounds in a complex auditory environment were studied in a group of adults who use bilateral cochlear implants. The first aim of the study was to investigate the change in speech intelligibility under bilateral and unilateral listening modes as a function of bilateral experience during the first 6 mo of activation. The second aim was to look at whether localization and speech intelligibility in the presence of interfering speech are correlated and if the relationship is specific to the bilateral listening mode. The third aim was to examine whether sound lateralization (right versus left) emerges before sound localization within a hemifield. Design Participants were 17 native English speaking adults with postlingual deafness. All subjects received the Nucleus 24 Contour implant in both ears, either during the same surgery or during two separate surgeries that were no more than 1 mo apart. Both devices for each subject were activated at the same time, regardless of surgical approach. Speech intelligibility was measured at 3 and 6 mo after activation. Target speech was presented at 0° in front. Testing was conducted in quiet and in the presence of four-talker babble. The babble was located on the right, on the left, or in front (colocated with the target). Sound localization abilities were measured at the 3 mo interval. All testing was conducted under three listening modes: left ear alone, right ear alone, or bilateral. Results On the speech-in-babble task, benefit of listening with two ears compared with one was greater when going from 3 to 6 mo of experience. This was evident when the target speech and interfering speech were spatially separated, but not when they were presented from the same location. At 3 mo postactivation of bilateral hearing, 82% of subjects demonstrated bilateral benefit when right/left discrimination was evaluated. In contrast, 47% of subjects showed a bilateral benefit when sound localization was evaluated, suggesting that directional hearing might emerge in a two-step process beginning with discrimination and converging on more fine-grained localization. The bilateral speech intelligibility scores were positively correlated with sound localization abilities, so that listeners who were better able to hear speech in babble were generally better able to identify source locations. Conclusions During the early stages of bilateral hearing through cochlear implants in postlingually deafened adults, there is an early emergence of spatial hearing skills. Although nearly all subjects can discriminate source locations to the right versus left, less than half are able to perform the more difficult task of identifying source locations in a multispeaker array. Benefits for speech intelligibility with one versus two implants improve with time, in particular when spatial cues are used to segregate speech and competing noise. Localization and speech-in-noise abilities in this group of patients are somewhat correlated.

Children with sequential BI cochlear implants represent a unique population of individuals who have undergone variable amounts of auditory deprivation in each ear. Our findings suggest that many but not all of these children perform better on measures of localization acuity with two cochlear implants compared with one and are better at the task than children using the cochlear implant + hearing aid. These results must be interpreted with caution, because benefits on other tasks as well as the long-term benefits of BI cochlear implants are yet to be fully understood. The factors that might contribute to such benefits must be carefully evaluated in large populations of children using a variety of measures.