Benefits of Bilateral Electrical Stimulation with the Nucleus Cochlear Implant in Adults: 6-Month Postoperative Results

Abstract

Objective: To evaluate the benefits of bilateral electrical stimulation for hearing-impaired adult subjects using the Nucleus 24 cochlear implant in a multicenter study, and to compare and quantify performance on speech perception measures in quiet and in noise and localization ability for unilateral and bilateral cochlear implant use. Design: Repeated single subject measures were carried out for each subject, with each subject serving as their own control. Assessment of unilateral and bilateral listening conditions for performance on tests of speech comprehension and sound localization were performed. Speech comprehension measures were performed in quiet at 0 degree azimuth and in the presence of background noise simultaneously presented from the same speaker and spatially separated by 90 degrees, at S+45°N45°and at S−45°N+45°. Test materials included Freiburger monosyllabic words, Oldenburger sentences, and the Hochmair-Schulz-Moser sentences. Tests of localization were performed in the horizontal plane with 12 speaker locations 30 degrees apart using a shortened sentence stimulus from the Hochmair-Schulz-Moser sentences at two possible presentation levels of 55 and 70 dB sound pressure level for assessment of directionality. The binaural advantage provided by bilateral stimulation was calculated with respect to each ear separately, classified as either the better or poorer performing ear for each speech material in quiet and in noise test conditions. For localization of sound, the binaural advantage was compared with left and right ears separately. Paired comparisons for performance data in all conditions were carried out by considering measurements for each subject in different conditions as paired observations and applying the Student's t test to determine the statistical difference between the data sets. Setting: Tertiary referral centers with a cochlear implant program. Patients: Thirty-seven profoundly hearing-impaired adults were enrolled in the study, 22 simultaneously and 15 sequentially bilaterally implanted. All patients received the Nucleus 24 cochlear implant and used the Nucleus SPrint or ESPrit 3G speech processor, with the vast majority using the ACE speech coding strategy. Results: For spatially separated speech in noise conditions, an interaural performance advantage for the ear closest to the speech source (i.e., with a superior signal to noise ratio) compared with that for the ear closest to the noise source (i.e., with an inferior signal to noise ratio) is consistently demonstrated regardless of whether it is the better or poorer performing ear closest to the speech signal. This is referred to as a significant binaural head-shadow benefit, resulting in a mean improvement between −10 dB and −11.4 dB in the critical signal to noise ratio required for 50% speech comprehension for the Oldenburger sentences and a mean improvement in the maximum score of 42% to 55% for the ear closest to the speech signal over the ear farthest away for the Hochmair-Schulz-Moser sentences. Bilateral stimulation i...

Restoring hearing symmetry with two cochlear implants or one cochlear implant and a contralateral hearing aid

“…Performance was similar for speech and pink noise bursts. Laszig et al used shortened sentence stimuli and a 12-speaker array forming a circle around the subject [85]. In the unilateral condition, subjects responded toward the side of stimulation, and 15 of 16 subjects who participated in this study had better localization with bilateral device use.…”

“…In general and compared with unilateral implant conditions, adult recipients of bilateral implants perform fairly well in localization tasks in the horizontal plane [75,78,[84][85][86][87][88][89][90][91][92][93]. For example, in five subjects using pink noise bursts presented from eight loudspeakers that spanned 108°, unilateral conditions resulted in 20° to 60°R MS errors, but only 10° RMS errors were noted for bilateral conditions [93].…”

Cochlear implants: A remarkable past and a brilliant future

“…In particular, bilateral stimulation can provide a substantial benefit in recognizing difficult speech materials such as monosyllabic words and in recognizing speech presented in competition with spatially distinct noise, in comparison to scores obtained with either unilateral implant alone (e.g., Gantz et al, 2002;Müller et al, 2002;Laszig et al, 2004;Ramsden et al, 2005;Litovsky et al, 2006;Ricketts et al, 2006). In addition, use of both implants supports an improved ability to lateralize or localize sounds (depending on which was measured in a particular study), again compared with either unilateral implant (e.g., van Hoesel and Tyler, 2003;Nopp et al, 2004;Senn et al, 2005;Grantham et al, 2007;Tyler et al, 2007).…”

Binaural Unmasking of Multi-channel Stimuli in Bilateral Cochlear Implant Users

“…This benefit results from an improvement in signal-to-noise ratio at one ear (better-ear effect) and from noise suppression that can occur when speech and noise have different interaural phase and level relationships (binaural unmasking). In CI users, most bilateral benefits seem to arise from better-ear effects, whereas limited true binaural hearing abilities have been established with clinical speech processors (e.g., Buss et al 2008;Laszig et al 2004;Litovsky et al 2006;Schleich et al 2004;Van Deun et al 2010b). It is unknown how much of these limitations originate from technical aspects, related to the independent functioning of left and right speech processors.…”