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Hearing, Balance and Communication

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Performance differences between electroacousticand electric alone cochlear stimulation usingcomplex tests in noise. A pilot study

Italo Cantore, Carmen De Nicola, Alessandro Santandrea, Gabriella Carelli,Paola Valente, Lorenzo Santandrea & Rocco Cantore

To cite this article: Italo Cantore, Carmen De Nicola, Alessandro Santandrea, GabriellaCarelli, Paola Valente, Lorenzo Santandrea & Rocco Cantore (2016) Performance differencesbetween electroacoustic and electric alone cochlear stimulation using complex testsin noise. A pilot study, Hearing, Balance and Communication, 14:4, 194-200, DOI:10.1080/21695717.2016.1236596

To link to this article: http://dx.doi.org/10.1080/21695717.2016.1236596

Published online: 15 Dec 2016.

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ORIGINAL ARTICLE

Performance differences between electroacoustic and electric alone cochlearstimulation using complex tests in noise. A pilot study

Italo Cantorea, Carmen De Nicolaa, Alessandro Santandreaa, Gabriella Carellia, Paola Valenteb,Lorenzo Santandreaa and Rocco Cantorea

aOtolaryngology, Head and Neck Surgery Unit, Regional Reference Center for Cochlear Implants, San Carlo Regional Hospital, Potenza,Italy; bOphthalmology Unit, Bambino Ges�u Paediatric Hospital, Potenza, Italy

ABSTRACTObjectives: Hybrid cochlear implants enable very interesting performances in bisyllabic wordsrecognition, mainly in noisy conditions. In this paper, we studied patients with implants perform-ing some very difficult timbric tasks in quiet and noisy conditions.Methods: We studied three adult patients with hybrid implants (group A-hybrid implants) andthree adult patients with traditional ones (group B-traditional implants). We made the followingtests (in quiet and noise): bisyllabic words recognition; voice kind recognition; common melodiesidentification and recognition; musical instrument identification and recognition.Results: Mean results in quiet: test 1: 35% A, 47% B; test 2: 92% A, 42% B; test 3: identificationscores 88% A, 100% B, recognition scores: 37.5% A, 50% B; test 4 identification scores 50% A,20% B, recognition scores 30% A, 20% B. As for tests in noise: test 1: 28% A, 46% B; test 2: 75%A, 25% B; test 3: identification 81% A, 87.5% B and recognition 56% A, 50% B; test 4: identifica-tion 60% A, 30% B and recognition 50% A, 20% B.Conclusion: Patients with hybrid implants seem to have better results, mainly in noisy timbrictasks. This could be explained by the better quality of low frequency stimulation and could bean encouragement for further studies and a larger diffusion of this kind of implant in the future.

KEYWORDSHybrid cochlear implants;residual hearing; speechrecognition; voice kindrecognition; melodiesrecognition; musicalinstruments recognition

Introduction

Cochlear implants represent a real innovation for oto-laryngology in the last 20 years. Recent improvementsin cochlear implantation have enhanced performanceand expectations for patients and their families. Oneof the new major topics is the possibility to preserveand use the residual hearing in low frequencies in orderto obtain better results than those with electric stimula-tion alone. Hybrid cochlear implants are indicated forslight to moderate hearing loss in frequencies less than500Hz and severe to profound hearing loss for frequen-cies over 1500Hz.[1] As reported in previous stud-ies,[1–5] electroacoustic stimulation on the same earallows better results in terms of speech recognition andin musical tests, mainly in the presence of noise, thanthose achievable with electric stimulation alone. This ispossible through a soft surgical procedure [2,6,7] thatenhances the possibility of residual hearing preservationand the opportunity to use some particular kinds ofdevice such as CochlearTM Hybrid Implant (CochlearCorp., Australia) or Med-ElVR Duet (Med-El AG,

Austria), characterized by the integration, in the sameexternal device, of an electric stimulation traditionalcomponent and an endomeatal hearing-device acousticstimulation component, under the control of the samespeech processor. A special procedure is needed for acti-vation and fitting that includes the selection of a cut fre-quency between the electric stimulation and the acousticstimulation and the modulation of qualitatively differentparameters in order to obtain homogeneous thresholds,a slightly more difficult procedure than electric-onlystimulation. The aim of this study is to report and com-pare results obtained on six cochlear implant patients,three with traditional electric-only stimulation implantsand three with electroacoustic stimulation implants.Patients were submitted to various tests, with and with-out background noise: bisyllabic words recognition,voice-type recognition, common melodies identificationand recognition, musical instrument identification andrecognition. To our knowledge, no previous studieshave been reported with these kinds of mainly timbrictasks, in quiet and noisy modes, comparing electroa-coustic stimulation results with electric-only results.

CONTACT Italo Cantore i.cantore@ospedalesancarlo.it Referent for Regional Reference Center for Cochlear Implants, Otorhinolaryngology, Headand Neck Surgery Unit, affiliated to Rienzi Foundation – New York University, San Carlo Regional Hospital, Via Potito Petrone, 85100 Potenza, Italy� 2016 International Association of Physicians in Audiology

HEARING, BALANCE AND COMMUNICATION, 2016VOL. 14, NO. 4, 194–200http://dx.doi.org/10.1080/21695717.2016.1236596

Methods and materials

Subjects

We studied six adult patients, three males and threefemales, with age range of 57–75 years. Three werefitted with Hybrid Cochlear Implants based upon aCochlearTM freedom processor with integrated endo-meatal device and CI 422 arrays (group A), anotherthree underwent traditional cochlear implantationwith CochlearTM CP-810 processors and CI24RE(CA)arrays (group B). As shown in Table 1, all patientswere adults, at 12–18 months from the time of firstactivation. They all used implants every day. Nobodyused bimodal stimulation on the contralateral side.Patients’ candidacy and preparation was the same forthe two groups and included computed tomography(CT) and magnetic resonance imaging (MRI), audio-logical tests, speech therapist evaluations and, only forgroup A, outer ear stamp collection for the acousticdevice.

Surgical procedures

Two different surgical techniques were used. For thetraditional cochlear implant group (group B), we per-formed mastoidectomy, posterior tympanotomy, coch-leostomy anteroinferiorly to the round window niche,receiver niche drilling, electrode array insertion. Forgroup A, the hybrid implant patients, we employedthe same surgical steps, except that cochleostomy wasnot executed. Instead, a slight round window incisionwas made followed by 0.5mL of 0.1 mg of bethameta-sone 1:10 and 0.5mL of Healon injection, gentle elec-trode insertion and small muscular tissue flappositioning across the round window. In all six cases,activation was performed 3 weeks after surgery.

Audiology assessment

We had tried to select, from among our traditionalcochlear implant patients, those with similar preopera-tive audiological characteristics to those in group A.The preoperative mean auditory abilities of allpatients are summarized in Figure 1.

Patients were submitted to two kinds of verbal testsand two kinds of musical tests, both with and withoutbackground noise. Tests were executed inside a MercuryNG-3 enlarged (Mercury-GN Hearing Srl, Italy) silentroom, with an Interacoustics AC-40 (Interacoustics AS,Denmark) audiometer, using Telephonics 296d000-1(Telephonics Corp., NY) headphones, and amplaid 335a(Amplifon Biomedica, Italy) speakers. For musical tests,a keyboard ROLAND BK-5 (Roland Corporation, CA) Ta

ble1.

Patientscomparativetables

forgrou

pAandB.

Patient

Age

Work

Etiology

Hearin

gaids

perio

dPure

tonespre-op

.threshold

lipreader

Preoperastiveauditory

abilities

with

H.A.

HHEI

A1 male

75Retired

Prog

ressive,un

know

n8years

60-60-60-65-65-70-80

dBhl

from

125

to8000

Hzon

leftside,n

othresh-

oldon

therig

hton

e

Yes

Detectio

n100%

,identificatio

n90%;d

isyllabicwords

recogn

i-tio

n30%;com

prehension

25%

Mild-severehand

icap

(situ

ational¼

20em

otional¼

15,total

score35)

A2 female

72Retired

Prog

ressive,un

know

n,youn

gageon

set

35years

40,4

5,80,1

00,1

10dB

Hlfrom

125

to2000

Hzon

therig

htside,1

00,

110,

110from

500to

2000

Hzon

theop

posite

one

not

Discrimination90%,d

isyllabic

words

recogn

ition

35%,com

-prehension

75%

Severe

hanicap(situ

ational¼

26em

o-tio

nal¼

18totalscore

¼44)

A3 male

68Retired

Unkno

wn

6years

35,40,75,85,100,115dB

Hlfrom

125

to8000

Hzandno

useful

residu

alon

theop

posite

side

Yes

Identification65%,d

isyllabic

words

recogn

ition

15%;com

-prehension

60%

Mild

tosevere

hand

icap

(situ

ational

¼25em

otional¼

13,totalscore

¼38)

B1 female

67Hou

sewife

Unkno

wn

6years

80,85,90,100,110

dBHlfrom

125to

4000

Hz,bo

thsides

not

Identification40%,recog

nitio

n10%,com

prehension

5%Sign

ificant

hand

icap

with

situational

¼30,

emotional¼

20,total

score

¼50

B2 female

57Hou

sewife

Otosclerosis

11years

85,9

0,110,

120,

100,

95,1

10dB

Hl

from

125to

8000

Hzon

theleft

side.N

ouseful

residu

alson

the

contralateralo

ne.

Yes

Recogn

ition

30%

comprehension

50%

Sign

ificant

hand

icap

with

atotalscore

of98

B3 male

66Retired

Prog

ressiveon

left

side,sud

denon

contralateral

3years

95,9

0,95,9

5,100,

110dB

Hlfrom

125to

4000

Hzon

right

side

and

95,1

00,1

10dB

Hlfrom

125to

500Hzon

theop

posite

one

Yes

Identification20%,recog

nitio

nandcomprehension

5%Sign

ificant,w

ithsituational¼

26,

emotional¼

19,total

score¼4

5

HEARING, BALANCE AND COMMUNICATION 195

was used with a MIDI synthesizer and a SONY cdp-395CD player (SONY Corporation, NY). Backgroundnoise was a 65dB SPL cocktail party noise introducedon the contralateral side. All tests were conducted twicewith and without background noise.

The first test was bisyllabic words recognition. Inorder to measure the intensity, a sound level meter(Extech mod. 407355, Extech Inc., NH) was placedinside the test room each time the test was performed.

In the second test, patients were asked to recognizedifferent kinds of voices. The Italian phrase ‘il pap�aha un paio di pipe ma non fuma’ (the dad has twopipes but he does not smoke) was used and the fol-lowing voices: male child (about 275Hz), female child(about 290Hz), adult man (about 175Hz), adultwoman (about 225Hz), elderly man (about 150Hz)and elderly woman (about 190Hz). The same phrasewas presented in a random order pronounced by adifferent voice, asking the patient to recognize it.

The third test concerned identification and recogni-tion of musical melodies. Selected melodies are thefollowings: Adriano Celentano ‘chi non lavora non fal’amore’, the Italian National Anthem ‘Inno di Mameli’,Gino Paoli ‘Sapore di Sale’, Orietta Berti ‘Finch�e labarca va’, Mina ‘Tintarella di luna’, Nilla Pizzi ‘Papaverie papere’, the war song ‘Bella ciao’ and DomenicoModugno ‘Nel blu dipinto di blu’. All are well-knownand very famous Italian songs. A single melody eachtime was proposed to the patient, with the patient dis-posed in front of the speaker, at 65dB Hl, asking thepatient to try to recognize it (open set). The

identification task (closed set) was conducted in thesame way, as for all the tests, with and without back-ground noise.

The last test was musical instrument recognitionand identification. A well-known melody named ‘Framartino, campanaro’ was introduced to the patient,with the same tonalities, time and musical beats,repeated 5 times, each one synthesized with a differentmusical instrument, by means of a random sequence.The musical instruments list included violin, guitar,piano, flute and accordion. The test frequency rangewas 392–880Hz. Patients had to recognize the instru-ment each time (open set) and, after that, to identify(closed set) the instrument among all the ones usedduring the test.

Due to the small number of recipients, it was notpossible to apply statistical analysis concerning thesignificance of the test results.

Results

Group A patients had good residual hearing preserva-tion at 1 month after surgery. On the implant side,patient A1 had a 10 dB Hl threshold switch for125Hz, 5 dB Hl for 250, 1000 and 2000Hz; patientA2 a 5 dB Hl switch for 125, 250 and 500Hz and lostresidual hearing for 2000Hz; as for patient A3, histhreshold was 15 dB Hl lower for 125 and 250Hz,without any variation for other frequencies. All hybridimplant patients reported good residuals thresholds,useful for acoustic combined stimulation.

Figure 1. Comparison of pre- and post-operative auditory abilities.

196 I. CANTORE ET AL.

Auditory abilities for patient A1 were 90% foridentification, 92% for recognition and 95% for com-prehension. Hearing handicap of the elderly inventory(HHEI) test documented a mild–moderate handicapwith a total score of 18.

Patient A2 obtained 95% of identification, 92% ofrecognition and 100% of comprehension with nohearing handicap reported on the elderly inventory(HHEI) test (total score of 6).

For patient A3, we had 80% of identification, 90%of recognition and 85% of comprehension.

Hearing handicap on the elderly inventory (HHEI)test showed no handicap with a total score of 10.

Patient B1 achieved 100% for identification, recog-nition and comprehension with a hearing handicap ofthe elderly inventory (HHEI) test total score of 15 (nohandicap).

Patient B2 auditory abilities were 90% of identifica-tion and recognition, 95% of comprehension. Hearinghandicap of the elderly inventory (HHEI) test reportwas no handicap (total score¼0).

As for the last patient, B3, he achieved 95% foridentification, 95% for recognition and comprehen-sion with a hearing handicap on the elderly inventory(HHEI) test showing no handicap, summarizing atotal score of 10.

The mean auditory abilities comparisons are sum-marized in Figure 1. As it can be seen, improvementsare evident for all patients, with no substantial detect-able differences.

Despite auditory abilities results, as for other tests,it can be appreciated that there are differences

between the two groups, with and without back-ground noise. Without background noise, it can beseen that there are better results for group A patientsconcerning voice-kind recognition and musical instru-ment identification. In contrast, with backgroundnoise, percentages of correct responses are higher forhybrid implant patients in musical instrument identi-fication and recognition and voice kind recognition(Figure 2).

Comparing the two groups, mean results in quietwere the following: test 1 (bisyllabic words recogni-tion): 35% group A, 47% group B; test 2 (kinds ofvoices test): 92% group A, 42% group B; test 3 (melo-dies): identification scores 88% group A, 100% groupB, recognition scores: 37.5% group A, 50% group B;test 4 (musical instruments): identification scores 50%group A, 20% group B, recognition scores 30% groupA, 20% group B. Mean differences without back-ground noise are reported in Figure 3.

As for tests in noise: test 1: 28% group A, 46%group B; test 2: 75% group A, 25% group B; test 3:identification 81% group A, 87.5% group B and rec-ognition 56% group A, 50% group B; test 4: identifi-cation 60% group A, 30% group B and recognition50% group A, 20% group B. Graphical representationof mean differences with background noise are shownin Figure 4.

Despite the differences detected between the twogroups with higher results mainly in noise for groupA patients and for timbric tasks, due to the smallnumber of patients, it was not possible to reliably testfor significance.

Figure 2. Comparison of tests scores with and without background scores.

HEARING, BALANCE AND COMMUNICATION 197

Discussion

In the literature, there are papers showing that, interms of auditory abilities and global auditory patientperformances with electroacoustic stimulation, it ispossible to obtain better results with hybrid implantsthan with electric-only stimulation, mainly innoise[1,2,4,5,8]. Furthermore, other studies haveexamined the audiological aspects of musical abilitiesfor traditional cochlear implants and electroacousticimplants.[3,9–13] However, the verbal and musicaltests reported do not include some timbric aspects,

such as different kind of voice recognition and musicalinstrument recognition, with and without backgroundnoise, as those proposed as the main aim of this pilotstudy.

Turner et al. and Stickney et al. [8,14] reported thelowering of cochlear implant patients’ performancesin the presence of background noise was mainlyattributed to the inadequate possibility of pitch com-ponent extraction in the presence of multiple irregularfrequencies of the noise.

As shown in previous studies,[1,3,4] hybrid cochlearimplants allow for obtaining a higher performance interms of auditory abilities with background noise thanelectric-only stimulation implants. With hybrid coch-lear implants, a lower signal-to-noise ratio is sufficientto obtain 50% of words recognition compared to thehigher S/N ratio needed with traditional cochlearimplants to obtain the same percentage. These reportscould be explained as due to the better quality ofstimulation for lower frequencies for these patients, fre-quencies so well known as fundamental for the verbalmessage.[8,15,16] The Polish group of Skarzynski et al.,which could be considered a pioneer research group inEurope in this field, confirm the encouraging perform-ances of electroacoustically stimulated patients in back-ground noise.[17,18] Having few available channels,even with codify strategy implementation, should beconsidered one of the most limiting factors in terms ofpitch for electric-alone stimulation systems. Furthermore,this limited number of channels often stimulatesinappropriately some apical portions of the cochlea withconsequently inadequate low frequency stimulation. Forexample, an apical electrode with software assigned fre-quency band of 210–360Hz, not only stimulates mainlythe same cochlear region for each frequency included inthis range, but can stimulate an apical region that evokedeffective frequency can be lower or higher than the soft-ware assigned one. These pitch-mismatch effects weredemonstrated by means of comparison of pitches evokedby acoustic stimulation of residual hearing and thoseobtained with electric stimulation.[19] Furthermore, elec-trical stimulation cannot evoke frequencies lower than150–180Hz.[19,20] However, with hybrid cochlearimplants, it is reasonable to anticipate better results forcochlear apical turn stimulation, as we and othersauthors have reported, due to the higher quality and fre-quency matching of acoustic stimulation on lowerfrequencies,.

We can approach the reason for the good resultsobtained for musical tasks through the higher qualityof pitch representation with hybrid implant patients.Reports in the literature with hybrid patients and

Figure 4. Comparison of the mean scores of group A andgroup B) in background noise.

Figure 3. Comparison of the mean scores of group A andgroup B without background noise.

198 I. CANTORE ET AL.

music melody tasks [21] show very interesting results.Golub et al. [22] reported data on musical tasks forhybrid implant patients’ spectral-ripple discriminationand clinical assessment of music perception. Pitchperformance was significantly better in hybrid userswhen compared with standard implant controls andthe spectral-ripple analysis test was significantly betterin the hybrid group. This confirms that residual low-frequency acoustic hearing is advantageous for pitchperception and that the clinical benefits enjoyed byhybrid implant recipients are mainly due to improvedspectral discrimination provided by the residual hear-ing. As for results of this study, we can confirm theimportance of residual hearing and its usage withelectroacoustic combined stimulation for music tasks,despite the small number of patients. Further studiesare needed with greater numbers, as with only fewpatients in the study it was not possible to performstatistical testing to determine the significance of thedifferences found. Further studies with a higher num-ber of patients and/or meta-analysis are necessary inthe future.

It is the authors’ opinion that the value of theimproved fidelity of pitch representation for lower fre-quencies can be appreciated mainly for the timbrictasks submitted to our patients: kind of voice andmusical instruments identification and recognition.These types of test are in our opinion among themost difficult ones for cochlear implants patients, asare all timbric trials. To our knowledge, there are nocomparable studies in the literature for hybrid implantpatients, with and without background noise. One ofthe main difficulties for these recipients is to distin-guish a voice from another or, even harder, onemusical instrument from another, without visual feed-back. The higher performance in these kinds of tim-bric test could be explained through the theoreticalcapability to exploit the better quality of stimulationand the higher number of different pitches detectablefor low frequencies by hybrid implant patients, withthe possibility of being able to manage and separatemultiple frequencies overlying the sound to be identi-fied or recognized. However, it has to be remarkedthat the better results obtained with electroacousticstimulation in background noise are often, as in thispaper, reported with only a small number of patients.Larger studies with meta-analysis should be awaitedin order to appropriately assess these points.

As for the surgical aspects, one of the main fearsconcerning electroacoustic stimulation is the possibil-ity of not preserving residual hearing. Various studiesreported percentages of between 70% and 90% of

hearing preservation with soft surgery techniques andthe possibility of preserving residual hearing evenafter re-implantation procedures.[6] The use of ashort electrode (as Cochlear L24 or 10 trial) despite alonger one (as Cochlear CI422) seems not to influencesignificantly better residual hearing preserva-tion.[2,5,17,21–23] So, in the event of the necessity toobtain a better low frequency electric stimulation inthe case of complete residual hearing loss after sur-gery, it would be better to consider the possibility ofusing a longer, slimmer and softer electrode array,such as Cochlear CI422, when approaching this kindof surgery.[4] These considerations concerning thesafety of the procedure, in addition to the good per-formances reported, should advance the use of elec-troacoustic stimulation even in countries where it isnot yet approved.

Conclusion

Hybrid cochlear implants patients seem to show betterperformances in terms of auditory abilities in back-ground noise than traditional cochlear implants. Betterresults can be obtained in musical tests with electroa-coustic stimulation mainly due to the higher qualitativeand quantitative pitch representation in lower frequen-cies. Furthermore, the higher performances of hybridpatients in timbric tasks with background noise shouldencourage the diffusion of residual hearing preservationsurgical procedures and arrays, even in children, inorder to allow a possible subsequent electroacousticcombined stimulation. However, further studies with alarger number of patients are necessary to validatethese encouraging results.

Disclosure statement

The authors report no conflicts of interest. The authors aloneare responsible for the content and writing of this article.

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