Bimodal Hearing or Bilateral Cochlear Implants: A Review of the Research Literature

Carol A. Sammeth, Ph.D.,1,2 Sean M. Bundy,1 and Douglas A. Miller, M.S.E.E.3

ABSTRACT

Over the past 10 years, there have been an increasing number of patients fitted with either bimodal hearing devices (unilateral cochlear implant [CI], and hearing aid on the other ear) or bilateral cochlear implants. Concurrently, there has been an increasing interest in and number of publications on these topics. This article reviews the now fairly voluminous research literature on bimodal hearing and bilateral cochlear implantation in both children and adults. The emphasis of this review is on more recent clinical studies that represent current technology and that evaluated speech recognition in quiet and noise, localization ability, and perceived benefit. A vast majority of bilaterally deaf subjects in these studies showed benefit in one or more areas from bilateral CIs compared with listening with only a unilateral CI. For patients who have sufficient residual low-frequency hearing sensitivity for the provision of amplification in the nonimplanted ear, bimodal hearing appears to provide a good nonsurgical alternative to bilateral CIs or to unilateral listening for many patients.

KEYWORDS: Bimodal hearing, bimodal devices, bilateral cochlear Downloaded by: SASLHA. Copyrighted material. implants, binaural hearing

Learning Outcomes: As a result of this activity, the participant will be able to (1) compare possible benefits of bimodal hearing versus bilateral cochlear implantation based on current research, and (2) identify when to consider fitting of bimodal hearing devices or bilateral cochlear implants.

Multichannel cochlear implants (CIs) tion for persons with hearing loss that is too have proven to be a highly successful interven- severe for good performance with conventional

1Cochlear Americas, Centennial, Colorado; 2Division of Centennial, CO 80111 (e-mail: [email protected]). Speech, Language, and Hearing Sciences, University of Bimodal Hearing and Bilateral Implantation; Guest Colorado, Boulder, Colorado; 3Department of Electrical Editor, Teresa Y.C. Ching, Ph.D. and Computer Engineering, University of Denver, Semin Hear 2011;32:3–31. Copyright # 2011 by Denver, Colorado. Thieme Medical Publishers, Inc., 333 Seventh Avenue, Address for correspondence and reprint requests: Carol New York, NY 10001, USA. Tel: +1(212) 584-4662. A. Sammeth, Ph.D., Senior Regulatory/Clinical Specialist, DOI: http://dx.doi.org/10.1055/s-0031-1271945. Cochlear Americas, 13059 East Peakview Avenue, ISSN 0734-0451. 3 4 SEMINARS IN HEARING/VOLUME 32, NUMBER 1 2011

amplification.1 As CI technology has evolved Although most individuals with bilateral over the past 25 years, outcomes for implant deafness are still only fitted with one CI, more recipients also have significantly improved.2 CI recipients are now wearing a hearing aid This has resulted in an expanding candidacy (HA) in the opposite ear (bimodal hearing) criteria in terms of how severe the hearing loss because they have sufficient low-frequency must be for a patient to be approved for residual hearing sensitivity to benefit from implantation. For example, in the United acoustic amplification. In addition, an increas- States the Nucleus multichannel CI (Cochlear ing number of patients are receiving bilateral Ltd, Sydney, Australia) was initially approved CIs, either in sequential (one ear at a time) or by the Food and Drug Administration for use simultaneous (both ears at the same time) in the 1980s only for adults with bilaterally surgeries. profound hearing loss (thresholds 90 dB HL) There is good reason for the increase in across the frequency range. Today, however bimodal fittings and bilateral cochlear implan- (see Fig. 1), hearing loss in the low frequencies tation. The psychoacoustics and HA literature (below 1000 Hz) can be of only a moderate speaks to the benefits of having two-eared degree in adults (40 dB HL) or only a severe rather than one-eared input.3–8 Bilateral listen- degree in children aged 2 and older (70-dB ing benefits can range from improved speech HL). recognition ability for separated sound sources Downloaded by: SASLHA. Copyrighted material.

Figure 1 Current U.S. Food and Drug Administration-approved audiometric and speech recognition candidacy criteria by age group for the Nucleus 5 (Cochlear Ltd, Sydney, Australia) cochlear implant. HL, hearing loss; ANSI, American National Standards Institute; MLNT, Multisyllable Lexical Neighborhood Test; LNT, Lexical Neighborhood Test. BIMODAL HEARING OR BILATERAL COCHLEAR IMPLANTS/SAMMETH ET AL 5 and listening in noise, to better sound local- ization ability, to a more satisfactory and ‘‘nat- ural’’ sound perception, and even to a better perceived quality of life. There are three main areas in which benefits are ascribed to bilateral listening: the head shadow effect, binaural summation and redundancy effects, and the binaural squelch effect.3

HEAD SHADOW (OR HEAD DIFFRACTION) EFFECT This effect results from the fact that the head blocks transmission of higher-frequency sounds due to their small wavelength. Persons fitted with only a unilateral CI often must turn their implanted ear toward whomever they want to hear and may miss important sounds on the other side. With two-eared listening (bimodal hearing or bilateral CIs), the ear with the more favorable signal-to-noise ratio (SNR) in the particular listening situation is always available. In the research literature, the head shadow effect is commonly tested by presenting speech from a frontal loudspeaker (0 degrees azimuth) and noise from a side loudspeaker (often 90 degrees right or left, also referred to as either 90 degrees or 90 and 270 degrees azimuths). Performance is compared for unilateral listening with the ear ipsilateral to the noise source to that for the bilateral listening condition (adding

the ear contralateral to the noise source). Any Downloaded by: SASLHA. Copyrighted material. measured performance increase with addition of the second ear represents benefit primarily from Figure 2 Schematic illustration of the loudspea- overcoming the head shadow effect. This is ker configurations commonly used to measure the three binaural/bilateral listening effects. illustrated in Fig. 2A. Shown is a patient whose unilateral listening condition is a right ear cochlear implant (CI), with the left CI added for the bilateral listening condi- BINAURAL SUMMATION tion. (A) Speech emanates from the front and AND REDUNDANCY EFFECTS noise from the unilateral CI side. Head shadow When both ears are listening rather than only benefit occurs when the CI for the ear opposite one, sound is perceived as louder due to binaural the noise is added for bilateral listening. (B) Both summation. This is evidenced by the fact that speech and noise emanate from a single frontal clinicians often have to adjust comfort levels loudspeaker to measure binaural summation and/ down for mapping of bilateral CIs compared or redundancy benefits of listening with both CIs with the patient listening with a unilateral CI. compared with only one. (C) Speech emanates from the front and noise from the side opposite Binaural redundancy refers to the fact that there the unilateral CI. Binaural squelch benefit occurs are cues that can be picked up when both ears when the CI on the side of the noise is added for are participatory (redundancies or overlapping bilateral listening. information) that result in improved sensitivity to fine differences in the intensity and frequency 6 SEMINARS IN HEARING/VOLUME 32, NUMBER 1 2011

domains. This may translate into improved trated in Fig. 2C. Even though the ear added speech perception ability in more difficult lis- actually has a poorer SNR, it also is receiving tening situations. The binaural redundancy ef- timing and intensity cues from the frontal loud- fect is typically measured in research studies by speaker that the central auditory nervous system presenting either speech alone or both speech can use to help ‘‘separate’’ the desired speech and noise from a single frontal loudspeaker. signal from the undesired noise signal. Performance is compared for unilateral listening versus bilateral listening. Any measured per- formance increase with addition of the second LOCALIZATION (DIRECTIONALITY) ear is assumed to represent primarily benefit In addition to the possibility for improved from binaural redundancy (and also binaural speech recognition with bilateral inputs, there summation if loudness balancing between the is another practical benefit of having two func- conditions was not done). This is illustrated in tional ears: improvement in the ability to deter- Fig. 2B. Unlike the head shadow effect, which mine the direction that a sound is coming from. is purely an external physical phenomenon, Persons with input from only one ear can attest binaural summation and redundancy effects to the frustration of hearing their name spoken are the result of binaural processing via central but not knowing which direction to turn to find auditory system integration of information ar- the person calling them. Localization ability also riving at each ear. can be a safety consideration; for example, when crossing a busy street, it is important to know the direction that a car is coming from. Localization BINAURAL SQUELCH (OR ability depends on the auditory system’s percep- UNMASKING) EFFECT tion of interaural differences in time and inten- When both ears participate for listening to sity. Interaural timing differences provide the spatially separated speech and noise sources, information necessary to locate the direction of binaural squelch can occur, providing a better low-frequency sounds below 1500 Hz.5,9 For representation of the signal than would be sounds that are higher in frequency, the main obtained with unilateral listening. This results cue for horizontal plane localization is the in- from binaural signal processing wherein the teraural intensity difference that occurs because brain stem nuclei process timing, amplitude, of the head shadow effect. and spectral differences in the signal arriving Some researchers have done studies to

at each ear.* In the literature, this effect is directly examine bilateral implant recipients’ Downloaded by: SASLHA. Copyrighted material. usually measured by presenting speech from 0 sensitivity to interaural level and timing differ- degrees azimuth, and noise from one side (often ences. However, most localization research has 90 or 270 degrees azimuth). Performance for focused on measurements of performance in unilateral listening with the ear contralateral to the horizontal azimuth, either as a simple left- the noise source is compared with that for the right lateralization task (i.e., 90 degrees azi- bilateral listening condition (adding the ear muth) or using a more complex setup with ipsilateral to the noise source). Any measured multiple loudspeakers. In a typical localization performance increase with addition of the sec- study, arrays of numbered loudspeakers are ond ear is assumed to represent benefit primarily placed in a frontal arc in the horizontal plane. from binaural squelch. This test setup is illus- The subject’s head is faced forward and kept

*However, Christopher Long, Ph.D., of Cochlear Americas, notes that such binaural effects are not necessarily indicative of particular mechanisms (personal communication, 2009). For example, dichotic speech cue summation (i.e., processors using interleaved frequency bands on the two sides) would not be expected to give binaural decorrelation benefit, but could still give benefits beyond head shadow and binaural redundancy effects. Also, a listener with patchy nerve survival may hear different cues in each ear across SNRs, but this would not be detected by a simple binaural redundancy test. Thus, it is still debatable whether ‘‘true’’ binaural processing effects are being measured with today’s CIs, especially because ITD (interaural timing difference) sensitivity is likely the source of binaural ‘‘unmasking’’ yet these cues are often blurred by the sound processing. Although this is an important academic discussion, for purposes of this article, the focus will not be on the source of bilateral benefits, but simply whether or not they are reported using traditional measurements. BIMODAL HEARING OR BILATERAL COCHLEAR IMPLANTS/SAMMETH ET AL 7 stationary, and stimuli are presented from one optimal central auditory system development. of the loudspeaker locations. The subject is Despite this, however, there also have been asked to identify the loudspeaker he or she reports of benefit from bilateral implantation believes the sound came from, or in the case even in adults with long-standing deafness in of young children, an observer may identify the second implanted ear.13 direction of head movement for right-/left-side discrimination. Multiple presentations and an adaptive procedure are used to determine the BIMODAL HEARING DEVICES degree of accuracy in localizing the sounds (for There were a couple publications in 1992 de- example, minimum audible angle for a certain scribing patients in which a power acoustic HA percent correct, or mean root-mean-squared was placed on the opposite ear of a unilateral CI [RMS] error). In some studies, the intensity to obtain bilateral input to the ears.14,15 This level of the presentations is roved around a approach to providing bilateral hearing is now central value in an effort to reduce monaural commonly called ‘‘bimodal hearing’’ or ‘‘bimodal level cue comparisons at the two ears. devices.’’y Subsequently, more extensive studies began to be reported in the research literature that used larger numbers of subjects and further AUDITORY DEPRIVATION EFFECTS explored binaural processing with an HA and One of the strongest arguments that has been CI on opposite ears.16,17 used in the HA literature for binaural rather A concern sometimes expressed has been than monaural HA fittings is the known impact that sound via the two different methods of of auditory deprivation. If only one ear is aided signal delivery, electric and acoustic, will some- when there is significant hearing impairment in how interact in a negative manner in the central both ears, the speech recognition ability of the auditory nervous system so that there will be unaided ear significantly deteriorates over time poorer performance than if a CI is worn alone— in both adults and children.8,10 It is now widely that is, that some kind of ‘‘binaural interference’’ accepted that it is important not only to provide will occur. For example, Mok et al18 observed a binaural amplification for bilateral hearing loss, trend toward bimodal subjects in their study but also as soon as possible, to retain the ability with the poorest aided mid-frequency hearing of the brain to efficiently use inputs from each thresholds performing better, and thus sug- ear. Given the fact that CI recipients who have gested the possibility of mid-frequency hearing

longer duration of hearing loss prior to implan- interference with the CI stimulation. Some Downloaded by: SASLHA. Copyrighted material. tation tend to have poorer absolute postoper- investigations have shown differences in percep- ative performance,11 it seems reasonable to tion of acoustically versus electrically processed assume that a similar argument can be made sound in terms of pitch across the HA and in support of bilateral CIs. Whether via bimodal CI ear19 and dynamic range and shape of hearing or bilateral CIs, both auditory pathways iso-loudness curves.20 Despite these concerns, should be stimulated as well and as early as however, the literature overall has shown benefit possible to produce the best chance for optimal from the use of bimodal hearing devices for most utilization of binaural processing cues. Research patients who have sufficient hearing to benefit by Sharma et al12 examining the morphology from acoustic amplification in one ear.z Ching and latency of P1 of cortical auditory evoked and colleagues21 hypothesized that bimodal potentials in children receiving CIs at various hearing benefit may arise from a combination ages supports the concept of a critical period for of the head shadow effect, binaural redundancy, yAlthough occasionally authors have referred to the bimodal hearing configuration as ‘‘electric-acoustic hearing,’’ that term will not be used herein because it can also mean stimulation with investigational hybrid devices currently in development but not yet approved for marketing. In hybrid devices, like in bimodal hearing, both electric (CI) and acoustic (HA) hearing are provided; however, in the case of hybrid devices, both are provided to the same ear, rather than opposite ears as in bimodal hearing. zNote that studies that directly compared performance of a group of subjects with bimodal hearing with a group subjects with bilateral CIs are reviewed later in this article. 8 SEMINARS IN HEARING/VOLUME 32, NUMBER 1 2011

and squelch effects, and possibly even ‘‘comple- with three subjects showing no difference in mentary cues’’ provided by the two different performance bimodally compared with either types of hearing prostheses. A demographic unilateral condition. study by Cowan and Chin-Lenn22 indicated Ching et al (see Table 1)23 evaluated local- that 50% of adults with an unaided threshold ization abilities of 29 children and 21 adults of 90 dB HL at 500 Hz in the ear opposite the when listening with only the CI compared with CI chose to wear an HA in that ear for at least listening using bimodal hearing. In terms of 4 hours a day. RMS error across 11 loudspeakers in a 180- degree frontal arc, results were significantly better for bimodal listening compared with Speech Recognition in Adults and unilateral. In contrast, however, Beijen et al31 Children with Bimodal Hearing recently reported that localization acuity in So, what does the research literature reveal children with bimodal hearing in their study about the efficacy of bimodal hearing for speech was as poor as unilateral listening, except for a recognition? As an example, Table 1 lists key slight benefit for bimodal hearing in the most findings from clinical research studies located in complicated stimulus condition, which in- a PubMed search that were published in Eng- volved a roved amplitude and spectrum. lish over about the past 5 years (between 2006 and early 2010) and that examined speech recognition performance in adults and children Subjective Outcomes with Bimodal using bimodal hearing devices.18,23–30 There are Hearing also several earlier publications on the topic, but Finally, a few studies published from 2006 to this time period was chosen both to reduce the the present reported subjective outcome data size of the literature for the current brief review with bimodal hearing device users.28,29,32,33 and because more contemporary studies are Berrettini et al28 notedthatmostsubjectsin likely to better represent modern CI and HA their study anecdotally reported that bimodal technology, current patient candidacy, and the hearing provided a more natural sound quality newest test methods. There have been largely than listening with the CI alone. In the Potts positive findings across the studies, indicating et al29 study, responses to the Speech, Spatial, that speech recognition is enhanced with bimo- and Qualities of Hearing (SSQ) questionnaire dal devices compared with listening unilaterally and a custom questionnaire also were col-

with either the HA alone or the CI alone for lected. Results on the SSQ corresponded Downloaded by: SASLHA. Copyrighted material. most patients who have aidable hearing in the well to objective performance on speech and ear opposite the CI. However, patients who localization tasks, and subjects indicated a receive little benefit from the HA alone also, as strong preference for bimodal compared with expected, do not show benefit from bimodal unilateral stimulation. hearing. Fitzpatrick et al32 did a retrospective chart review to compare 93 adult unilateral CI users who did not use an HA in the nonimplant ear Localization in Adults and Children (many of whom had amplifiable residual hear- with Bimodal Hearing ing) to 31 adult unilateral CI users who used an A few clinical research studies published from HA in the nonimplant ear. The bimodal hear- 2006 to the present examined localization per- ing group did not differ from the nonbimodal formance using bimodal hearing devices.23,29,31 group in terms of age of implantation or For example, Potts et al (see Table 1)29 re- duration of deafness, but they did have less ported a significantly reduced RMS error in severe hearing loss on average and were more localization ability across 15 loudspeakers recently implanted than those not using an placed in a frontal 140-degree arc for 19 adults HA. Custom questionnaire data collected using bimodal hearing compared with when on 24 of the patients using bimodal hearing they used either the HA or CI alone. There indicated that 15 used the HA more than was, however, significant individual variability, 50% of the time. These 15 subjects reported a Table 1 Summary of Speech Recognition Studies of Adults or Children Using Bimodal Hearing Devices Published from 2006 to Early 2010 Authors/ Year Subjects/CIs Method/Statistics Stimuli and Loudspeaker Setup Key Findings

Mok et al, 200618 14 adults with bimodal hearing; Within-subject comparison: CNC words at 65 dB SPL; CUNY sentences 6 of 14 subjects showed significant thresholds 90 dB in the low CI alone, HA alone, and at 65 dB SPL with noise at 75 dB SPL bimodal benefit on the open frequencies in the HA ear; bimodal; arcsine-transformed (þ10 SNR); selected spondees with an set CNC and CUNY measures, CIs: Nucleus 24 percent correct scores adaptive SNR; speech frontal (0 degrees and 5 subjects showed subjected to ANOVA and t tests azimuth), with three noise loudspeaker benefit on spondee testing; conditions: 0 degrees, and 90 degrees however, 2 subjects showed (90 and 270 degrees azimuths) poorer speech perception with the HA added on at least one speech test; more subjects

demonstrated improvement in IMPLANTS COCHLEAR BILATERAL OR HEARING BIMODAL noise than in quiet; information transmission analyses of CNC results suggested that bimodal benefit is likely based on improved perception of low-frequency speech components Ching et al, 200623 29 children with bimodal Within-subject comparison: CI BKB sentences in 8-talker babble Significant bilateral advantages (also tested hearing (age range not alone versus bimodal; ANOVA at þ10 dB SNR were both were demonstrated in all test localization; see text) reported in article) and 21 presented from 0 degrees conditions when comparing adults with bimodal hearing; azimuth (to evaluate binaural the unilateral CI condition with CIs: Nucleus 22 and 24 redundancy); speech was also bimodal hearing; no significant presented on the HA side and relationship could be noise on the CI side from two demonstrated between degree loudspeakers at 60 degrees (60 of loss or duration of and 300 degrees azimuths) amplification use and the amount of binaural advantage found in testing / AMT TAL ET SAMMETH 9

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Table 1 (Continued ) 2011 1 NUMBER 32, HEARING/VOLUME IN SEMINARS Authors/ Year Subjects/CIs Method/Statistics Stimuli and Loudspeaker Setup Key Findings

Gifford et al, 200724 11 adults with bimodal hearing; Within-subject comparison: CNCs in quiet at 70 dB SPL; AzBio Scores for bimodal hearing were significant levels of residual preoperative HA(s), sentences at 70 dB SPL in quiet and significantly better than for all other low-frequency hearing (e.g., postoperative HA alone, in noise at þ5 and þ10 dB SNR; all conditions for CNCs and AzBio <65 dB HL thresholds at CI alone, and bimodal; ANOVA stimuli presented from a single sentences in noise at both SNRs; mean 500 Hz) in both ears at the with Bonferroni adjustments loudspeaker at 0 degrees azimuth bimodal performance on AzBio time of surgery; CIs: Nucleus sentences in quiet was also superior Freedom, Advanced Bionics to the CI alone, but the difference did not reach statistical significance Luntz et al, 200725 13 adults with bimodal hearing; Within-subject comparison: CI alone CUNY and CID sentences in noise at Bimodal scores were consistently CIs: Nucleus 24, Advanced versus bimodal; testing at 6, 12, 55 dB and a þ10 dB SNR; both superior to CI alone but differences Bionics Clarion, Med-El 18, 24, and 36 mo postactivation; speech and noise from a single did not reach statistical significance; mixed linear regression model to loudspeaker at 0 degrees azimuth both the CI alone and bimodal evaluate progression of scores hearing scores improved over over time and value of HA addition the 36 mo follow-up period Beijen et al, 200826 22 children/adults (aged 5 to Within-subject comparison: Dutch PB monosyllabic word lists Bimodal scores in quiet and noise were (also tested 20 y at testing, but implanted CI alone, bimodal; Wilcoxon in quiet at 65 dB SPL presented significantly better than CI alone localization; see text) between ages 1.5 and 15 y), signed-rank test for phoneme from 0 degrees azimuth; also scores; preoperative unaided and with bimodal hearing; mean scores; multiple linear regression speech at 0 degrees azimuth aided thresholds or phoneme test threshold at 250 and 500 Hz in for predictive factors and speech noise at 90 degrees scores were not found to be adequate HA ear of 89 dB HL; CIs: azimuth on the CI side at predictors of postoperative bimodal not specified þ5 dB SNR benefit Lee et al, 200827 14 children (aged 4.6 to 13.8 y), Within-subject comparison: Korean words in noise, both Significant performance benefits for with bimodal hearing; CIs: HA alone, CI alone, bimodal; presented from the same bimodal hearing over the CI Nucleus 24 or Freedom t tests loudspeaker at 0 degrees azimuth alone condition Berrettini et al., 201028 10 adults, prelingually deafened, Within-subject comparison: Italian disyllabic word test at 65 dB One subject chose to stop wearing the (also obtained with bimodal hearing; thresholds HA alone, CI alone, bimodal; in quiet at 0 degrees azimuth; contralateral HA during the study and questionnaire data; at 500 Hz in HA ear of testing at initial activation and also in babble noise at þ10 dB had tested more poorly initially with see text) 85 to 100 dB HL; CI: Nucleus 24, 6 mo postactivation; t tests SNR with speech at 0 degrees addition of the HA; for the other Freedom Contour, and Freedom azimuth with 3 noise loudspeaker 9 subjects, bimodal hearing resulted Contour Advance conditions: 90, 180, and in significantly improved performance 270 degrees azimuths in quiet and noise compared with the CI alone condition, with performance improvements from initial activation to 6 mo postactivation

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Potts et al., 200929 19 adults with bimodal hearing; Within-subject comparison: CNC words at 60 dB SPL (roved 3 dB) Mean bimodal performance significantly (also did localization average unaided threshold HA only, CI alone, bimodal; were presented from various better than HA alone or CI alone; testing and obtained in HA ear of 80 dB HL at ANOVA, regression analyses locations in an array of 15 loudspeakers performance was poorer in both uni- questionnaire data; 500 Hz; CIs: Nucleus 24 placed 10 degrees apart in the frontal lateral listening conditions when the see text) plane (comprising a 140 degree arc) speech was presented from the opposite side of the HA or CI (head shadow effect), but no difference in bimodal performance regardless of loudspeaker location; two subjects with little benefit from the HA alone IOA ERN RBLTRLCCLA IMPLANTS COCHLEAR BILATERAL OR HEARING BIMODAL performed the same for CI alone and bimodal; unaided thresholds and speech performance in the HA ear were significantly related to bimodal hearing performance Yuen et al, 200930 20 Mandarin-speaking children, Within-subject comparison: Mandarin lexical tones in monosyllables, No significant bimodal benefit shown aged 5 to14 y, with bimodal CI alone, bimodal; subjects and disyllabic word picture identification; from binaural redundancy with hearing; CIs: Nucleus 24 were split into two groups to SNR individually optimized to avoid speech and noise both from the assess head shadow and binaural ceiling or floor effects; speech from front; significant bimodal benefit redundancy effects; t tests 0 degrees azimuth, with 2 noise from the head shadow effect loudspeaker conditions: demonstrated with spatially 0 degrees, and 90 degrees or separated speech and noise 270 degrees (depending on CI ear) CI, cochlear implant; HA, hearing aid; HL, hearing loss; ANOVA, analysis of variance; CNC, consonant-nucleus-consonant test; SPL, sound pressure level; CUNY, City University of New York sentences; SNR, signal-to- noise ratio; BKB, Bamford-Kowal-Bench sentences test; AzBio speech test; CID, Central Institute for the Deaf sentence test; PB, phonetically balanced words. / AMT TAL ET SAMMETH 11

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preference for listening bimodally across a va- to localize the direction of sounds when using riety of listening environments, including mu- bimodal devices than have others. One factor sic, noise, and reverberation, and reported that may explain differences in findings across improved sound quality and clarity with addi- patients and studies is how the HA was fit and tion of the HA. Most reported, however, little whether loudness was balanced between the or no improvement in localization ability. For HA and the CI. Recommendations for fitting the nine bimodal users who wore the contrala- approaches with bimodal hearing devices can teral HA less often, complaints were that the be found in Ching et al34 and Huart and HA did not improve speech understanding, Sammeth.37 Another possible factor, suggested was uncomfortable or produced feedback, or by Ching et al,21 is that a failure to show amplified noise excessively. improvement for some children in the bimodal Finally, Sucher and McDermott33 eval- hearing condition may be due to their relative uated whether bimodal hearing benefitted mu- lack of experience in using binaural processing sic perception or sound quality for music and cues. Similarly, prelingually deafened adults or nonspeech sounds in nine adult implantees those who have not previously used HAs could compared with the HA-alone and CI-alone be expected to show deficits in binaural proc- conditions. On average, bimodal stimulation essing ability. Studies that have followed pa- provided better results for music and perceptual tients over time have generally shown sound quality than did listening unilaterally. continued performance improvements.25 The biggest factor in individual perform- ance differences across patients with bimodal Summary of the Bimodal Hearing hearing devices may be that the ability to use the Literature acoustic stimulation effectively depends on As shown in the above brief review of the past the degree of residual low-frequency hearing 5 years of published literature on this topic, and in the nonimplant ear, and possibly also the consistent with other published reviews of the degree of midfrequency loss.18 It is reasonable full bimodal hearing literature,34–36 some to conclude that with an increasing degree of degree of bimodal advantage in speech recog- hearing loss, there will be a diminishing benefit nition has been consistently demonstrated for a from an HA in the non-implant ear. There are majority of patients, and across different lan- not yet sufficient data, however, to recommend guages and test setups, despite the fact that the a specific cutoff frequency or degree of loss for

signals to each ear are different. The largest and use of bimodal devices, and further research is Downloaded by: SASLHA. Copyrighted material. most consistent benefits, not surprisingly, have needed in this area. been from head shadow effects,18,23,26,28–30 but in some studies there also have appeared to be binaural redundancy effects for at least some BILATERAL COCHLEAR IMPLANTS subjects listening bimodally.18,23–28 Across lo- For patients who have little or no low-fre- calization studies, the general finding has been quency residual hearing in either ear, or who that patients are usually unable to localize with receive very limited or no benefit from an any consistency when wearing only a unilateral acoustic amplification trial in the nonimplanted CI or HA. When listening bimodally however, ear, bimodal devices will not be an effective some, albeit not all, individual patients are treatment. These patients are, however, good reported to achieve at least some directional candidates for bilateral cochlear implantation. hearing ability. There are several reasons why having bilateral It is notable that a few individual subjects CIs may be beneficial to bilaterally deaf pa- have been reported to show a decrement in tients. First, this will ensure that the ear with performance on some speech tasks with the the best postoperative performance always will addition of the contralateral HA,18,23,28 be implanted, an important factor given that although this appears to be the exception rather preoperative predictions of which ear will have than the rule. Additionally, some individual the best postoperative performance are not al- patients have certainly shown a greater ability ways correct. In addition, there will still be a BIMODAL HEARING OR BILATERAL COCHLEAR IMPLANTS/SAMMETH ET AL 13 functional ear should a problem or malfunction Consistent with the bimodal hearing liter- occur with one implant or sound processor. As ature, it can be seen that the studies produced with bilateral HAs and bimodal hearing, bilat- mostly positive findings for bilateral listening eral stimulation with CIs may allow preserva- compared with unilateral listening. Across stud- tion of some bilateral/binaural listening ies, listening with bilateral CIs consistently benefits experienced by persons with normal showed substantial and significant advantages hearing. Finally, bilateral implantation may over listening with only a unilateral CI in a vast help prevent the neural degeneration that can majority of recipients. As with bimodal hearing, occur over time due to auditory deprivation. the primary and strongest speech recognition Reports of bilateral CIs in adults first benefit from bilateral CIs is from the head started appearing in the literature in the late shadow effect,44,48,53,55,65,73 although there is 1980s to early 1990s.38,39 A primary reason for also evidence that true binaural signal processing bilateral implantation at that time was either in the form of binaural redundancy and squelch that there was a need for a technology upgrade effects do occur for some patients.44,48,53,55,61,65 for the patient (e.g., where one ear had a As with bimodal device studies, a potential functioning but older single-channel device so problem in comparing results across speech the contralateral ear was fitted with a newer, recognition studies with bilateral CIs has multichannel device), or that the device in one been the use of different test materials and ear produced inadequate performance but was SNRs (with some studies having shown ceiling still functional. It really was not until the late effects from too easy a fixed level task) and 1990s that bilateral CIs began to be provided adaptive versus nonadaptive test paradigms. In solely with the hope and intention of providing addition, there have been differences in exper- binaural benefits.40 Vermiere and colleagues41 imental design factors such as the amount of appear, in 2002, to have been the first to publish time given for acclimatization to the bilateral a report of a child receiving bilateral CIs. Since CIs, the loudspeaker azimuths chosen, and the that time, the number of articles published on type of sound processing or electrode array used the topic of bilateral CIs has exploded—for by the CI system. Finally, there have been example, see reviews by Brown and Balkany42 differences across subjects in the age at which and Papsin and Gordon.43 As time went on, deafness occurred, duration of deafness prior to published studies started to report on greater implantation, relative symmetry between the numbers of subjects and to show results that ears in the degree and duration of hearing loss,

were progressively more positive. whether they were implanted simultaneously or Downloaded by: SASLHA. Copyrighted material. sequentially (and the length of the intersurgical interval), and whether they previously wore Speech Recognition in Adults HAs binaurally or bimodal hearing devices. and Children with Bilateral CIs The astonishing finding is that, across the When a PubMed search was done for research studies to date, despite subject, implant system, studies that examined speech performance and methodological differences, the results using bilateral CIs that were published in have consistently and strongly supported bene- English between 2006 and early 2010, a large fit of bilateral CIs for speech recognition, number of publications were located.44–73 To particularly for spatially separated speech and reduce the number summarized, Table 2 lists noise sources, a situation that is likely to occur key findings for only those nine clinical studies frequently in everyday listening situations. that evaluated larger groups (n 20) of chil- Although only studies with English language dren or adults and performed statistical anal- speech materials were chosen for tabling, sim- yses of the data.44,48,53,55,58,59,61,65,73 Repeat ilar results have been reported from studies publications by the same author were not using test materials in other languages, includ- included to reduce the chance of overlap of ing German,57 French,67 and Spanish47. subjects. Note that the data in the table The number of research studies evaluating represent studies that used CIs from all three speech perception in pediatric bilateral patients major manufacturers. has increased in the last few years and overall is 14 EIASI ERN/OUE3,NME 2011 1 NUMBER 32, HEARING/VOLUME IN SEMINARS Table 2 Summary of Speech Recognition Studies of Adults or Children Using Bilateral Cochlear Implants Published from 2006 to Early 2010* Authors/ Year Subjects/CIs Method/Statistics Stimuli and Loudspeaker Setup Key Findings

Litovsky et al, 200644 37 postlingually deafened adults with Within-subject comparison; unilateral CNCs and HINT sentences in quiet at By 6 mo postactivation, significant (also obtained bilateral CIs (all simultaneously CI versus bilateral CIs; arcsine-transformed 65 dB SPL from a loudspeaker at bilateral listening advantage in questionnaire implanted); CIs: Nucleus 24 Contour percent correct in quiet; adaptive noise level 0 degrees azimuth; BKB-SIN test quiet (binaural redundancy); for data; see Table 4) testing to determine SNR for 50% correct; with speech at 65 dB SPL; both testing in noise, large and robust ANOVA; binomial comparisons speech and noise from 0 degrees bilateral benefit when the head azimuth, or speech at 0 degrees and shadow effect utilized; a few noise at 90 or 270 degrees azimuths subjects also showed binaural squelch benefits Peters et al, 200748 30 children (aged 3 to 13 y), with Within-subjects comparison; unilateral MLNT, LNT, HINT-C test, as age- Children < 8 y at 2nd implantation bilateral CIs (sequentially implanted CI versus bilateral CIs; percent-correct appropriate, at 70 dB SPL in quiet; acquire 2nd CI speech recognition with first surgery before age 5); CIs: scores; for testing in noise, SNR fixed but CRISP spondees with both target and more quickly than those implanted Nucleus 22, Nucleus 24 individually set to avoid ceiling or floor competing speech (‘‘noise’’) from later, and achieve higher scores effects; ANOVA 0 degrees azimuth, or speech at at 12 mo postactivation; speech 0 degrees and ‘‘noise’’ at 90 or scores in quiet did not differ 270 degrees azimuths significantly for unilateral versus bilateral CIs, but mean performance in noise was significantly better bilaterally than with either CI alone, and improved over time; greatest bilateral benefit for head shadow effect, but also shown for binaural redundancy and squelch Buss et al, 200853 26 adults with bilateral CIs (postlingually Within-subject comparison: unilateral CNC words in quiet from 0 degrees Bilateral listening benefits from deafened, all but one simultaneously CI versus bilateral CIs; arcsine-transformed azimuth (simulated using head-related head shadow were shown implanted); CIs: Med-El Combi 40þ percent correct scores; ANOVA transfer function processing, and immediately, but consistent delivered via direct audio input); CUNY benefits across subjects from sentences from simulated 0 degrees binaural squelch did not appear with noise from simulated 0, 90, or until 1 y postimplantation 270 degrees azimuths

Downloaded by: SASLHA. Copyrighted material. Table 2 (Continued ) Authors/ Year Subjects/CIs Method/Statistics Stimuli and Loudspeaker Setup Key Findings

Dunn et al, 200855 32 adults with bilateral CIs (some Between-groups comparison; for bilateral CNC and HINT sentences at 70 dB in quiet Significantly better performance for (also tested simultaneously, some sequentially CIs group, also within-subject comparison: from 0 degrees azimuth; not all subjects bilateral CI group than for unilateral localization; implanted); 32 adults with unilateral unilateral CI versus bilateral CIs; t tests on completed all testing CI group on both words and see Table 3) CIs; CIs: Advanced Bionics Clarion arcsine-transformed percent correct scores sentences; for bilateral CIs group, CII and HiRes 90K, Nucleus 24, Ineraid significantly better performance with both CIs than for either CI used alone Zeitler et al, 200858 22 adults; 43 children (mean age at 2nd Within-subject comparison: unilateral Adults: CNCs and HINT sentences in quiet; Adults: mean performance with implant ¼ 7.8 y); (all sequentially CI versus bilateral CIs (retrospective BKB-SIN with speech at 65 dB SPL; bilateral CIs was better than implanted; all wore bimodal analysis); adaptive noise level speech at 0 degrees azimuth and three performance with either CI alone, IOA ERN RBLTRLCCLA IMPLANTS COCHLEAR BILATERAL OR HEARING BIMODAL devices prior to receiving 2nd testing to determine SNR for 50% noise loudspeaker conditions: 0, 90, and but only the comparison with implant); CIs: Advanced Bionics, correct in noise; t tests 270 degrees azimuths; children: GASP, the 2nd implant ear reached Med-El, Nucleus PBK, LNT or MLNT, HINT-C tests significance; children: performance (according to age) with bilateral CIs for both quiet and noise tests was significantly better than preoperative performance with bimodal hearing; significant negative correlation on MLNT and HINT-C between performance and length of deafness in the first ear before receipt of 1st implant Budenz et al, 200959 20 adults (sequentially implanted); Within-subject comparison: unilateral CNC words at 65 dB SPL in quiet All patients were consistent users CIs: Advanced Bionics, Med-El, CI versus bilateral CIs (retrospective after 1 y of both CIs; differing Nucleus (subjects had different CI chart review for data collected CIs in each ear did not prevent models and processing strategies 1 y postimplantation); nonparametric bilateral benefit each ear) Mann-Whitney U test Gordon and Papsin, 58 children with bilateral CIs (all early Within-subject comparison: unilateral Age-appropriate closed or open-set Performance significantly better

61 /

2009 onset deafness); 4 groups: (1) CI versus bilateral CIs; ANOVA tests, including ESP, WIPI, GASP, bilateral CIs versus unilateral CI, AL ET SAMMETH simultaneous CIs at < 3 y old, (2) MLNT/LNT, and PBK words; speech except for group with the 1st CI < 3 y old and < 1 y to 2nd at 55 and 65 dB SPL in quiet from longest preimplant deafness implant, (3) 1st implant < 3 y old, 0 degrees azimuth; speech and noise and interimplant delay; greatest but > 2 y delay to 2nd implant, (4) 1st both from 0 degrees azimuth with benefit seen for those implanted implant delayed > 3 y old and long speech at 65 dB SPL and þ10 dB SNR earlier and with shorter interimplant interval to 2nd implant; interstimulus intervals

CIs: Nucleus 15

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Table 2 (Continued ) 2011 1 NUMBER 32, HEARING/VOLUME IN SEMINARS Authors/ Year Subjects/CIs Method/Statistics Stimuli and Loudspeaker Setup Key Findings

Litovsky et al, 200965 17 adults with bilateral CIs Within-subject comparison: unilateral BKB-SIN with speech at 65 dB SPL at Subjects showed better performance (also tested (simultaneous surgeries or CI versus bilateral CIs; adaptive 0 degrees azimuth, and three noise with bilateral CIs than with a localization; <1 mo apart with simultaneous noise level testing to determine SNR loudspeaker conditions: 0, 90, and unilateral CI for conditions see Table 3) activation); CIs: Nucleus 24 Contour for 50% correct in noise; t tests 270 degrees azimuths measuring head shadow, binaural redundancy and binaural squelch; bilateral benefit in noise was greater at 6 mo than at 3 mo postactivation for spatially separated speech and noise; greater bilateral benefit correlated positively with higher localization performance Lovett et al, 201073 30 children with bilateral CIs; 20 children Between-group comparisons; within-subject Recorded instructions presented in Not surprisingly the normal hearing (also tested localization with unilateral CIs; (age range 18 mo to calculation of SRM by comparing noise pink noise (observational study); group tended to perform better and obtained 16 y; mean age each group ¼ 7 y); to the side versus noise from the front speech from 0 degrees azimuth, than the bilateral group across questionnaire data; 56 normal hearing children (mean for the unilateral condition (1st implant) and three noise loudspeaker conditions: tests; the bilateral CIs group see Tables 3 and 4) age 4.5 as a match to the ‘‘hearing age’’ versus bilateral; nonparametric 0, 90, and 270 degrees azimuths displayed greater SRM compared of the groups with CIs); CIs: Advanced Mann-Whitney U test with the unilateral CI group for Bionics, Med-El, Nucleus the head shadow effect condition, with performance about the same for the binaural squelch condition

*To reduce the number of studies summarized, only those that used English language speech tests and statistical analysis of data from 20 subjects are included. Note that duplicate publications by the same authors were also excluded to avoid patient population overlap between studies. CI, cochlear implant; SNR, signal-to-noise ratio; ANOVA, analysis of variance; SRM, spatial release from masking; CNC, consonant-nucleus-consonant test; HINT, Hearing in Noise Test; SPL, sound pressure level; BKB-SIN, Bamford-Kowal-Bench sentences Speech in Noise test; MLNT, Multisyllabic Lexical Neighborhood Test; LNT, Lexical Neighborhood Test; HINT-C, Hearing in Noise Test – Children; CRISP, CUNY, City University of New York sentences; GASP, Glendonald Auditory Screening Procedure; PBK, Phonetically Balanced – Kindergarten words, ESP, Early Speech Perception test; WIPI, Word Intelligibility by Picture Identification test.

Downloaded by: SASLHA. Copyrighted material. BIMODAL HEARING OR BILATERAL COCHLEAR IMPLANTS/SAMMETH ET AL 17 similar to adult data, supporting bilateral CIs The data appear to be slightly less strong in for children with bilateral deafness. One prob- some studies using pediatric subjects compared lem can be if a study did not allow adequate with the adult data. It seems intuitive that rehabilitation time postactivation for learning children may need more training or experience to use the new form of processed sound, which with bilateral implants to show maximal benefit may be particularly important for prelingually on a localization task, as they have not had the deafened children to show maximum perform- previous localization experience many adventi- ance. It is also more difficult to find develop- tiously deafened adult patients have. Further- mentally and age-appropriate objective speech more, it may be that some children will never tests that these children can consistently per- develop localization skills to the same extent as form over time. The need for early implanta- normal children or adult CI recipients if their tion in children, however, is highlighted by the deafness occurred during the key time when fact that typically the highest performers are neural pathways for localization develop.84 those implanted at a younger age and either Also, it appears that localization ability is simultaneously or with shorter time periods stronger for persons who have had previous between sequential implant surgeries. auditory binaural listening experience and who have had longer periods of using their bilateral CIs. In some localization studies, there may Localization in Adults and Children have been an insufficient period postactivation with Bilateral CIs for this binaural processing ability to fully Many studies have examined localization abil- develop, because those studies that have fol- ities of recipients listening with bilateral CIs lowed patients longer term have shown con- compared with listening with only one implant. tinuing improvement in at least some subjects. Early on, in a series of experiments in the 1990s, In addition, there is a fairly consistent van Hoesel and his colleagues74,75 showed that finding across psychoacoustic studies85 that two adults with bilateral CIs could effectively adult recipients of bilateral CIs have much fuse the bilateral information to obtain good better sensitivity to interaural level differences sensitivity to interaural level differences (ILDs) (ILDs) than to differences in timing/arrival for localization. Subsequently, other researchers time of the stimuli between the ears (interaural started examining localization in larger numbers timing differences; ITDs). This finding is con- of subjects.76 sistent with the fact that speech testing shows

A PubMed search of the literature from greater benefit from the head shadow effect, Downloaded by: SASLHA. Copyrighted material. 2006 to early 2010 for localization and later- which is more dependent on ILDs, than from alization studies of groups of adult or children the binaural squelch effect, which also is de- who are recipients of bilateral CIs again re- pendent on ITDs. vealed a fairly large number of studies.44,50,55– 57,64,65,67,73,77–83 To reduce the number sum- marized,Table3listskeyfindingsfromthose Subjective Outcomes in Adults and six studies that used larger numbers of subjects Children with Bilateral CIs (n 15) and compared performance for uni- Finally, some recent research studies have ex- lateral versus bilateral listening.57,65,67,73,78,83 amined subjective outcome data using bilateral Across these studies, the test setups varied in CIs.44,46,51,56,64,72,73,83,86–88 Table 4 lists key terms of the number of loudspeakers and thus findings from those five studies that used the minimal audible angle, making direct standardized questionnaire data to evaluate comparisons difficult. However, across the perceived performance and benefit in larger studies as a whole, there appear to be fairly groups (n 10) of children or adults using striking results illustrating that even though bilateral CIs.44,46,64,73,83 Patients and parents patients with bilateral CIs still perform well perceive benefit from bilateral CIs compared below normal on localization tasks,64 they with listening with a unilateral CI that is perform much better with both CIs than generally consistent with that shown in the when listening with only a unilateral CI. objectively measured benefit studies. 18 EIASI ERN/OUE3,NME 2011 1 NUMBER 32, HEARING/VOLUME IN SEMINARS Table 3 Summary of Localization Studies of Adults or Children Using Bilateral Cochlear Implants Published from 2006 to Early 2010 Authors/ Year Subjects/CIs Method/Statistics Stimuli and Loudspeaker Setup Key Findings

Grantham et al, 200778 22 postlingually deafened adults Within-subject comparison: unilateral 200 milliseconds noise burst or Substantial individual variability but with bilateral CIs (20 were CI versus bilateral CIs; modified speech sample, at an average performances better for speech than simultaneously implanted); source identification task without 70 dB SPL roved 10 dB; for noise; bilateral listening CIs: Med-El C40þ feedback or identification of the 43- loudspeaker horizontal performances better than the best active loudspeakers; results array from 90 to 270 degrees unilateral ear performance (mean characterized in terms of adjusted azimuth, with 17 speakers active, adjusted constant error bilateral constant error in an anechoic chamber ¼ 22.8 degrees, unilateral ¼ 47.9 degrees [just above chance]); some showed improvement when tested again 10 mo later; manipulation of spectral content and rise-decay time suggested that ILD rather than ITD cues contribute most to localization Steffens et al, 200857 19 children (aged 3 y and older; Within-subject comparison: unilateral 500 milliseconds pulsating white Mean lateralization ability with binaural (also tested speech sequentially implanted with 1st CI versus bilateral CIs; Wilcoxon, noise at 60 dB SPL; 10 stimuli implants was significantly better than recognition) implant prior to age 4); CIs: Nucleus binomial tests, Pearson correlations per speaker for a total of 30 per with either the 1st or 2nd CI alone; listening condition; 3-loudspeaker 18 of 19 subjects scored significantly setup: 0, þ90, and 90 degrees above chance level for bilateral azimuths listening; experience with bilateral implants was found to moderately correlate with lateralization ability Litovsky et al, 200965 17 adults with bilateral CIs Within-subject comparison: unilateral 4 bursts of 170 milliseconds pink Most received bilateral benefit for (also tested speech (simultaneous surgeries or <1mo CI versus bilateral CIs; lateralization noise; 20 times/speaker; roving lateralizing right/left, but only about recognition; see Table 2) apart with simultaneous activation); (hemifield source) and localization level 54 to 66 dB SPL; 8 half could localize well with bilateral CIs: Nucleus 24 Contour (multispeaker array) tasks; loudspeakers in frontal arc CIs at 3 mo postactivation; the nonparametric Kruskal-Wallis; Barnard’s spanning 70 degrees authors suggested they might do exact test; Spearman correlation better with longer experience; localization ability was positively correlated with speech recognition scores

Downloaded by: SASLHA. Copyrighted material. Table 3 (Continued ) Authors/ Year Subjects/CIs Method/Statistics Stimuli and Loudspeaker Setup Key Findings

Mosnier et al, 200967 27 adults (simultaneously implanted); Within-subject comparison: unilateral Multiple presentations of French Mean localization performance with (also tested speech based on speech scores at 12 mo CI versus bilateral CIs; results disyllabic words presented at an bilateral CIs was better than recognition) postactivation, 16 had symmetrical expressed as mean percentage intensity varying from 60 to 80 dB SPL, performance with a unilateral CI for all performance between ears, and correct responses per loudspeaker; with competing cocktail party noise loudspeakers for patients with 11 had asymmetrical performance measurements done at 12 mo emanating from all loudspeakers; symmetrical speech performances between ears; CIs: Med-El Combi postactivation 5-loudspeaker array from 90 to between ears; for the asymmetrical 40/40þ 270 degrees azimuths; SNR individually group, benefit of bilateral CIs adjusted for 50% SRT from central compared with a unilateral CI was loudspeaker observed for the 45 degree and 90 degree side speakers for either IOA ERN RBLTRLCCLA IMPLANTS COCHLEAR BILATERAL OR HEARING BIMODAL ear, but for the loudspeaker at 0 degrees, there was bilateral benefit only compared with the poorer ear; speech scores did not correspond well to localization performance Lovett et al, 201073 30 children with bilateral CIs; 20 children Between-group comparisons; Spoken phrase for right/left On average, although they did not (also tested speech with unilateral CIs; age range 18 mo to lateralization response lateralization task with perform as well as normal controls, recognition and obtained 16 y; mean age each group ¼ 7y;56 through observation; localization loudspeakers at 60 degrees and the bilaterally implanted children were questionnaire data; see normal hearing children (mean age task response was picking up a 30 degrees; localization with a able to lateralize and localize Tables 2 and 4) 4.5 as a match to the ‘‘hearing age’’ block off the correct loudspeaker; 3-loudspeaker array each significantly better than the of the groups with CIs); CIs: Advanced Mann-Whitney U test separated by 60 degrees (for unilaterally implanted children; Bionics, Med-El, Nucleus children aged 4 and older) children with a unilateral CI often performed at chance level on either task / AMT TAL ET SAMMETH 19

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In addition, Veekmans et al88demonstrated that recipients of bilateral CIs show an im- proved music perception ability compared with unilateral CI users, although not performing to the same level as normal-hearing listeners.

Summary of Research on Bilateral CIs Given the still relatively small number of recip-

significantly better than chance; mean absolute error scores averaged across the loudspeakers varied from 9 todegrees 51 for individual children, with RMS error varying from 13 todegrees; 63 the best scores were obtained by: (1) children who received their second implant before the age of 2 y, (2) those whoaids used prior hearing to implantation for aof period 18 mo or more, (3)attended those a who mainstream school rather than a school for the deaf ients of bilateral CIs compared with unilateral 63% of the children could localize implant recipients,§ there is a surprising num- ber of publications available on the topic to date, and a notable increase in recent publications and numbers of subjects evaluated compared with the early studies. The overall evidence is com-

60 pelling that, just like has been demonstrated

TD, interaural timing difference; RMS, root-mean-squared. with HAs and bimodal hearing devices, patients 60 to

þ with bilateral deafness do best with bilateral CIs rather than unilateral stimulation. This appears to be true even when there is a difference in

array in the frontal horizontal plane from degrees azimuth duration of deafness and differing etiologies Broadband bell ring; 9-loudspeaker between ears, or different implant or electrode models in each ear,89 and potentially even after a long duration of deafness.13 Benefits are seen in terms of speech recog- nition in quiet and in background noise across several listening configurations, in lateralization and localization abilities, and in perceived ben- efit and satisfaction with bilateral CIs versus using only a unilateral CI. Across the studies, the vast majority of patients show benefits on at Downloaded by: SASLHA. Copyrighted material.

identification task, with feedback given following a correct response; data characterized as mean absolute error in degrees least one measure, with a few showing no Bilateral mode testing only; loudspeaker difference or poorer performance with the sec- ond implant than with the first, but no reports of a clear deficit in performance with addition of a second ear implant. The continued daily use of bimodal hearing or bilateral CIs that has been reported for most patients in recent studies seems to indicate that any added cosmetic or practical hindrance of wearing a device on each ear is overcome by the patient’s perception that they are receiving binaural benefit in their

sequential bilateral CIs; CIs: Nucleus CIs ability to function in the real world. 30 children, aged 4–15 y, with There has been much discussion about the ) fact that not all subjects receive bilateral benefits 83 in the form of integration by the brain (binaural squelch and redundancy effects), with the pri- Continued (

§Internal Cochlear estimates are that, of the more than 140,000 recipients of Nucleus CIs worldwide, less than 10% are currently (also obtained questionnaire data; see Table 4)

Table 3 Authors/ YearVan Deun et al, 2010 Subjects/CIs Method/StatisticsCI, cochlear implant; SPL, sound pressure level; SNR, signal-to-noise ratio;implanted SRT, speech reception threshold; ILD, interaural level Stimuli difference; I and Loudspeaker Setup bilaterally. Key Findings Table 4 Summary of Studies Using Standardized Questionnaires in Adults or Children Using Bilateral Cochlear Implants Published From 2006 to Early 2010 Authors/ Year Subjects/CIs Method/Statistics Questionnaire Key Findings

Litovsky et al, 200644 30 postlingually deafened adults Within-subject comparison of bilateral APHAB questionnaire (given after Results indicated significantly better (also tested speech with bilateral CIs; all simultaneously use versus unilateral CI use; 3-wk deprivation period in which perceived performance on the three recognition and implanted; CIs: Nucleus 24 Contour nonparametric Wilcoxon signed-ranks only the better ear CI was worn, communication subscales (EC, BN, and localization; see test for matched pairs (2-tailed) then again after another period RV), with no difference on the Tables 2 and 3) of bilateral CIs use) aversiveness to sound (AV) subscale Galvin et al, 200746 10 children, aged 4 to 15, with bilateral Perception of performance preoperative Modified SSQ for parents to fill 8 of 10 children were perceived as having (also tested speech CIs (sequentially implanted); CIs: (with unilateral implant) versus out re: perception of child’s higher performance with bilateral recognition and Nucleus 24 postoperative (with bilateral implants) performance CIs than preoperatively with a unilateral localization) after 6 to 13 mo of use CI; the parents of the other 2 perceived

no change, but ceiling effects IMPLANTS COCHLEAR BILATERAL OR HEARING BIMODAL (excellent performance with the first CI) may have limited the outcome; biggest perceived bilateral benefits were in the spatial hearing measure, and communication in a group with no visual cues; these results were consistent with the objectively measured speech recognition and localization results Laske et al, 200964 15 adults with bilateral CIs; 15 matched Between-group comparison; paired SSQ All sections of SSQ had better results (also tested speech adults with unilateral CIs; CIs: Nucleus t tests; multiple linear regression, for the bilateral CIs group compared recognition and localization) ANOVA with the unilateral CI group, although the difference did not reach statistical significance; also, there was a significant correlation for spatial hearing results and objectively measured localization results; and for hearing quality results and speech / in quiet test results AL ET SAMMETH 21

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mary benefit due to the physical advantage of overcoming the head shadow. Frankly, this is somewhat of an academic argument,k because in terms of patient benefit, it does not matter to the user what the source of the advantage is, but only that his or her performance in real-world environments (where the head shadow effect is indeed a significant factor) is better with two implants than with one. Some factors that may predict whether or

higher for the bilateral group thanunilateral for group; the there were no significant differences between the groups on theor HUI VAS; the authors hypothesized thatreason one for this latter result mightbeen have the high ratings given onscales these for the unilateral CI grouplittle leaving room for improvement performance on a localization task—i.e., better perceived spatial performance corresponded to better objectively measured localization not an individual patient receives true binaural Parental ratings on the SSQ were significantly SSQ results significantly correlated with processing benefit appear to be duration of deafness prior to implantation, age at which

Background Noise], RV [Reverberation], AV [Aversiveness]; deafened, intersurgery interval for sequential implantations, and previous HA use.48,58,61,83 In any case, even when a relationship has been found between performance and one or more of these factors, a majority of the subjects in the study still received some degree of bilateral benefit on at least one measurement. Given questionnaires: SSQ, HUI, quality-of-life VAS section’’ of a modified version of the SSQ

Parent filled out three Parents filled out the ‘‘spatial the strength and fast-growing depth and breadth of the literature, it is difficult to argue that bilateral CIs should not be supplied to those patients who desire them and who meet candidacy criteria in both ears, unless an ear contralateral to the implanted ear has sufficient residual hearing to benefit from an HA (bimo- dal hearing). test

U There are now quite a few publications on pediatric bilateral implant users, and in studies

Whitney correlation in which the children were implanted bilaterally Between-group comparisons; Mann Bilateral mode testing only; Pearson

at an earlier age and tested after an adequate Downloaded by: SASLHA. Copyrighted material. acclimatization period, results do appear excel- lent. Some have argued against bilateral im- plantation in children based on the possibility of future treatments like gene therapy or hair-cell regeneration as treatments for hearing loss. The rationale is that if one cochlea remains intact, that ear could possibly still benefit from these therapies if they become viable within the life- time of the child (which, at present, is not a 7 y; 56 normal hearing children

with unilateral CIs; age range 18to mo 16 y; mean age each¼ group (mean age 4.5 as a match‘‘hearing to age’’ the of the groups withCIs: CIs); Advanced Bionics, Med-El, Nucleus bilateral CIs; CIs: Nucleus CIs certainty). This argument is certainly stronger 30 children with bilateral CIs; 20 children 26 children, aged 4–15 y, with sequential for those children who can successfully use a power HA to benefit in the ear contralateral to ) the implant, because they will still receive bi- 83 lateral stimulation and thus binaural develop- 73 Continued ( kAlthough from a future research perspective, it will be important to determine what cues provide benefits and which

(also tested speech recognition and localization; see Tables 2 and 3) (also tested localization; see Table 3) are lost, to assist in improving future outcomes with new Van Deun et al, 2010 Table 4 Authors/ YearLovett et al, 2010 Subjects/CIs Method/StatisticsCI, cochlear implant; ANOVA, analysis of variance; APHAB, Abbreviated Profile of Hearing Aid Benefit with subscales EC [Ease of Communication], BN [ Questionnaire Key Findings SSQ, Speech, Spatial and Qualities of Hearing questionnaire; HUI,sound Health Utilities Index Mark III; VAS, Visual Analogue Scale. processing approaches. BIMODAL HEARING OR BILATERAL COCHLEAR IMPLANTS/SAMMETH ET AL 23 ment of the auditory nervous system. However, sion of bimodal hearing if a patient shows for those children who receive little or no demonstrable advantage from the addition of benefit from amplification in either ear, an the HA, but there is also some evidence that alternative argument is that early bilateral patients with bilateral CIs may do better on implantation is needed to provide develop- some tasks than patients with bimodal hearing. ment of both auditory system pathways during Thus, the question of when and if a patient a critical period, if the child is to be able to with bimodal hearing should move to bilateral perform well in the future. Also, new, poten- CIs is still hard to answer. tially less damaging approaches such as the A problem with these studies is that not advance off-stylet technique with the Nucleus only have there been relatively few studies Contour Advance electrode array (Cochlear using larger groups of subjects evaluated on Ltd, Sydney, Australia), or the emerging con- the same tasks, but between-group compari- cept of partial insertions and possible hybrid sons are always difficult due to the fact that the technology in development for persons with groups can never be perfectly matched. In these residual low-frequency hearing sensitivity, studies, bimodal device users tend to be less may also partly mitigate the argument because hearing impaired and show higher speech these may potentially result in retention of the scores than bilateral CI users. Within-group residual hearing and more structural integrity standard deviations are also often large, making in the cochlea. it difficult to achieve a significant effect when comparing across groups. More research is needed in this area to BIMODAL HEARING VERSUS determine the relative benefits for patients BILATERAL CIs who obtain more limited results with acoustic amplification and to better delineate the impact of hearing thresholds and speech recognition Comparison Research performance with bimodal devices for an indi- For patients who receive some benefit from vidual patient to determine if they might do bimodal devices due to having aidable better with a second implant. Also see Firszt low-frequency hearing in the nonimplant ear, et al,98the meta-analysis of the literature by a question is obvious: Would they perform even Schafer et al,99 and the overview and discussion better if they received a second CI? Some of the potential benefits of bimodal hearing and 100 researchers have stated that for those patients bilateral implantation by Ching et al. Downloaded by: SASLHA. Copyrighted material. who have residual nonimplant ear hearing and thus can receive benefit from a contralateral HA, the benefits of bilateral implantation Recommendations would have to be clearly demonstrated because In 2005, Offeciers et al101 published a consensus bimodal devices are more cost-effective and statement on bimodal hearing device use and provide a noninvasive alternative.21 bilateral CIs. They noted that both bimodal Eight studies were found in a literature hearing and bilateral CIs are advantageous in search for the period 2006 to early 2010 that providing stimulation of both ears, and thus directly addressed the question of whether bilateral cortical stimulation and development bilateral CIs are better than bimodal hearing and the possibility of restoring binaural hearing for patients who could go either way, by functions. They also noted that it is important comparing performance of groups of patients to provide optimal results to balance the loud- with bimodal hearing to groups of patients ness between ears for either a bimodal or with bilateral CIs.90–97 These studies include bilateral CI fitting. For sequential implantation, measures of speech recognition, localization, they commented that long duration of deafness and subjective judgments and are summarized in the second ear is not a contraindication for in Table 5. bilateral implants, because a monaural input Looking across these comparative study may maintain some stimulation of the auditory results, there is certainly support for the provi- pathways given that there are both homolateral 24 EIASI ERN/OUE3,NME 2011 1 NUMBER 32, HEARING/VOLUME IN SEMINARS Table 5 Summary of Studies of Adults or Children Using Bimodal Hearing Devices Compared with Those Using Bilateral CIs Published from 2006 to Early 2010 Authors/Year Subjects/CIs Method/Statistics Stimuli and Loudspeaker Setup Key Findings

Shafer and Thibodeau, 12 children with bilateral CIs; Between-group comparison: individual SRT-in-noise task using simple No significant group mean bilateral versus 200692 10 children with bimodal binaural benefit calculated by phrases in simulated classroom unilateral performance difference, but hearing; aged 3 to 12 y; CIs: comparing bilateral condition to noise; noise level fixed at 60 dB(A) the authors stated this may have been Advanced Bionics HiRes 90K unilateral condition; ANOVA and speech varied to determine due to study limitations; individual data or HiFocus CII, Med-El Combi SNR for 50% correct; speech revealed that 8 of 12 bilateral CIs users 40þ, Nucleus 22 or 24 from 0 degrees azimuth, and had a significant binaural advantage noise from 135 and 225 degrees compared with only 2 of 10 bimodal users; azimuths advantages of using FM systems with either CIs or HAs was also demonstrated Litovsky et al, 2006a90 13 children with bilateral CIs; Between-group comparison: binaural Male-voice spondee words at 60 dB 9 of 13 children with bilateral CIs could aged 3 to 16; 6 children with benefit calculated within subject: SPL (roved 4 dB for some but lateralize for source separations of bimodal hearing (aged 4 to 14); bilateral condition versus unilateral not all subjects); 15-loudspeaker array <20 degrees, and 7 did better bilaterally CIs: Nucleus 22 or 24, Clarion II condition; localization task: MAA from 70 to þ70 degrees azimuths than with either CI alone; however, several HiFocus, Med-El Combi 40þ measurements; ANOVA children could perform the task when using a single cochlear implant under some conditions; some in the bimodal hearing group were also unable to perform the task, and the group as a whole did more poorly than the bilateral CIs group Litovsky et al, 200691 10 children with bilateral CIs; Between-group comparison: binaural CRISP test in quiet at 0 degrees; and in SRTs: significantly better mean performance (Note that this study 10 children with bimodal benefit calculated within subject: 2-talker competing speech with across conditions with bilateral CIs than may have used some hearing; all prelingually bilateral condition versus unilateral 3-loudspeaker conditions: 0, 90, when listening unilaterally, but of the same children as deafened; aged 3 to 14 y; condition; SRT task in quiet and noise; and 270 degrees azimuths; Localization: substantial individual variability; for Litovsky et al., 200690 ) CIs: Nucleus 22 or 24, Clarion noise fixed at 60 dB SPL and speech spondee words at 60 dB SPL roved bimodal group, some showed bilateral varied to determine SNR for SRT; 4 dB; 15-loudspeaker array from listening benefit in some conditions, localization: minimum audible angle 70 to þ70 degrees azimuths some showed no difference, and some (MAA); ANOVA showed poorer performance bimodally than with the unilateral CI; MAA testing: both groups showed bilateral benefit, but greater benefit with bilateral CIs than with bimodal hearing; of note is that the bimodal group performed better with the unilateral CI, leaving less room for bilateral improvement

Downloaded by: SASLHA. Copyrighted material. Table 5 (Continued ) Authors/Year Subjects/CIs Method/Statistics Stimuli and Loudspeaker Setup Key Findings

Mok et al, 200793 9 children (aged 9 to 14 y) with Between-group comparisons: SNR for SDT in noise; 900-millisecond Both CI groups had significant spatial unmasking, bimodal hearing; 4 children ‘‘spatial unmasking’’ (SNR for duration male voice /baba/) from a but less than the normal controls; significant (aged 7 to 12 y) with bilateral binaural SDT noise front versus loudspeaker at 0 degrees, and benefit from head shadow effect, but bimodal CIs; CIs: Nucleus 24; also, noise side), ‘‘head shadow’’ 3-loudspeaker conditions for the users only showed benefit for the unilateral CI; 10 normal-hearing children (defined as SNR for monaural noise: 0, 90, or 270 degrees bilateral CIs group showed significant (aged 7 to 12 y) SDT noise front versus noise azimuths binaural advantage for noise near the contralateral to the active ear), 1st implant ear (binaural squelch) but not for ‘‘binaural advantage’’ (benefit noise at 0 degrees (binaural redundancy); for obtained by addition of the bimodal group, binaural advantage was found HA or 2nd CI) for noise from the front or CI side, but not the IOA ERN RBLTRLCCLA IMPLANTS COCHLEAR BILATERAL OR HEARING BIMODAL HA side; Note: the bimodal users had 8 to 14 y stimulation versus bilateral group’s 12 to 18 mo Mok et al, 201094 9 children (aged 9 to 14 y) with Between-group comparisons: CNCs for speech recognition; Bilateral listening was advantageous to both (same subjects bimodal hearing; 4 children bilateral condition versus examination of the relationship groups in at least some noise conditions; as in Mok et al., (aged 7 to 12 y) with bilateral unilateral condition within between aided thresholds in the within the bimodal group, those with better 200793 ) CIs; CIs: Nucleus 24 subjects; ANOVA, t tests HA ear and bimodal advantage aided thresholds at low frequencies and poorer aided thresholds at 4000 Hz demonstrated the greatest bilateral listening advantage Noble et al 200895 (Note: For questionnaires: 35 adult Retrospective between-group Questionnaires: HHIE and HHI; Questionnaires: highest perceived handicap scores Noble et al, 200896 : bilateral CIs users, 70 adult comparison; factor analysis; speech recognition: CNC for the bimodal group, and least perceived similar study and unilateral CI users, 39 adult ANOVA words at 70 dB (C) from handicap for the bilateral CIs group, including the results, with many bimodal devices users; small 0 degrees; Localization: everyday Emotional Distress and Social Restriction sub- of the same subjects) subsets of subjects also had sounds presented from 8 scores of the HHIE, and the Social Restriction preoperative versus loudspeakers forming an subscores of the HHQ; the difference in postoperative speech 108-degree frontal arc perceived handicap postoperatively between the recognition and localization bilateral CIs and bimodal group was also seen testing; CIs: not specified for a subset of subjects who had similar preoperative scores; speech: bimodal group had /

significantly higher scores preoperatively with AL ET SAMMETH bilateral HAs, but no significant differences postoperatively between the 3 groups; bimodal group had the smallest postoperative improvement; Localization: significant reduction in RMS error preoperatively to postoperatively for the bilateral CIs group, but no significant

change for the bimodal group 25

Downloaded by: SASLHA. Copyrighted material. 26 SEMINARS IN HEARING/VOLUME 32, NUMBER 1 2011

and contralateral projections.ô Finally, they noted that, with sequential surgeries, the first ear implant should be switched off for a time to obtain stable performance with the second im- plant before moving to bilateral stimulation. Specifically, Offeciers et al offered the following guidelines for determining candidacy. Bimodal stimulation should be recom- mended for: Patients with residual hearing in the non- implanted ear. postoperatively; no significant age-related differences in patients with a unilateralnor implant, in the bimodal group; ingroup, the the bilateral younger CIs cohort showed very substantial increases in both performance and self-rated abilities postoperatively versus preoperatively, but the older cohort had more mixed outcomes; the authors suggested that the latter finding mightdue be to individual differences in theaging impact on of the ability to use binaural cues

All 3 groups showed significant benefits Those with good HA performance in the nonimplanted ear. Those who want to restore binaural hearing. dicap Inventory; HHQ, Hearing Handicap Questionnaire; SSQ,

variance; CRISP, Children’s Realistic Index for Speech Perception All young children, because it is difficult to determine the hearing status of the nonim- planted ear. Notably, 5 years later this last recommen- dation may no longer represent the views of most researchers and surgeons given the good results appearing in the literature tied to earlier

speech recognition: CNC words at 70 dB (C) from 0Localization: degrees; everyday sounds presented from 8 loudspeakers forming an 108 degree frontal arc bilateral implantation. Questionnaires: HHIE, HHQ, SSQ; Bilateral implantation should be recom- mended for:

Patients in whom benefits obtained from a unilateral CI are poor. Those who are developing cochlear ossifica- tion from meningitis so that full insertion can still be achieved in both ears. Those who want, or need for their job, to Downloaded by: SASLHA. Copyrighted material.

correlation between age and benefit restore binaural hearing. Between-group comparisons; In children with permanent bilateral

60 y profound hearing loss, with consideration < of the speech and language acquisition period.

60 y old; CIs: not More recently in February 2008, an ad hoc > committee called the William House Cochlear Implant Group, which was composed of 10 leaders in the field (Balkany et al102) published 68 adults with unilateral CIs; 38 adults with bimodal hearing; evaluation of impact of age: old versus specified

36 adults with bilateral CIs; a consensus statement regarding bilateral im- ) ) ô (Note 95,96 Nevertheless, these researchers recommended an intersurgery

97 interval in postlingual adults of no more than 12 years and noted that in children a longer interval may result in the need Continued ( for additional rehabilitation to avoid refusal of the second implant. The value of 12 years may be arguable based on research showing benefit with even longer periods of auditory that this study used many of the same subjects as Noble et al. 2008 test; SDT, speech detectionSpeech, threshold; Spatial, CNC, and consonant-nucleus-consonant Qualities test; of HHIE, Hearing questionnaire; Hearing FM, Handicap frequency Inventory modulation; for RMS, the root-mean-squared. Elderly; HHI, Hearing Han Table 5 Authors/YearNoble et al, 2009 Subjects/CIs Method/StatisticsCI, cochlear implant; SNR, signal-to-noise ratio; SRT, speech reception threshold; HA, hearing aid; MAA, minimum audible angle; ANOVA, analysis of Stimuli anddeprivation. Loudspeaker Setup Key Findings BIMODAL HEARING OR BILATERAL COCHLEAR IMPLANTS/SAMMETH ET AL 27 plantation. These researchers and surgeons is more cost-effective than sequential implan- stated that they believed the body of literature tation for the same reason. that had been accumulated through that date was sufficient to demonstrate improved speech intelligibility and sound localization with two CONCLUSION CIs compared with only one and that it was Several other publications have reviewed the clear that both children and adults benefit from literature on bimodal hearing devices and bilat- bilateral CIs. Therefore, this committee eral CIs.42,43,104,105 Across these analyses, the strongly endorsed bilateral cochlear implanta- conclusion has been that there is much evidence tion in clinically appropriate adults and chil- and experience to support the efficacy and safety dren and stated that they considered it to have of bilateral implantation and that bilateral inputs become an accepted medical practice. obtained either with two CIs, or with one im- In the same year, several leading British plant and one HA, provide significant advan- researchers and clinicians, known as the Brit- tages for the patient compared with unilateral ish Cochlear Implant Group (Craddock et listening. This review, covering only the more al103), published a statement in which they recent literature from 2006 to early 2010, and also strongly recommended bilateral implan- the other articles in this special issue of Seminars tation. In their position statement, Craddock in Hearing provide additional support for that et al said that a review of the literature conclusion. The largest outstanding issue con- indicated that patients receiving bilateral im- tinues to be determination of the audiometric plantation can expect to benefit in terms of cutoff point or other key factor that indicates a improved localization and speech understand- patient could be expected to benefit more from ing in quiet and noise, and children can benefit bilateral CIs than from continued use of an HA in speech, language, and auditory development. in an ear contralateral to an implant. They also noted that there is evidence that the most benefit will be received from sequential implantation if the intersurgical interval is no REFERENCES more than 12 months. In conclusion, they stated that the indications for bilateral implan- 1. 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