Benefits of bilateral cochlear implants- sound localization, speech perception in noise and self-reported hearing ability

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Örebro University School of Medicine Degree project, 30 ECTS June 1st 2017

Benefits of bilateral cochlear implants

- sound localization, speech perception in noise and self-reported hearing ability

Version 2

Author: Linnéa Hinz, Bachelor of Medicine Supervisors: Prof. Claes Möller, MD, PhD Jonas Ekeroot, PhD Örebro, Sweden

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Abstract

Introduction

Patients with bilateral hearing loss traditionally receive a unilateral cochlear implant (UCI), but the number of patients with bilateral cochlear implants (BCI) increases. UCI patients perform poorly on binaural hearing tasks. This study aimed to explore the benefits of BCI in the binaural tasks sound localization, speech perception in noise, and self-reported hearing ability. The study was performed at the Örebro University Hospital.

Methods

Seventeen BCI patients completed Sound Localization Test (SLT), Hearing in Noise Test (HINT) and Speech, Spatial, Quality of Hearing questionnaire (SSQ). Data was analyzed using descriptive statistics. Spearman correlation analyses compared SLT with SSQ2 and HINT with SSQ1 respectively.

Results

The HINT signal-to-noise ratio ranged from 0 to 26 decibel. Four patients were unable to complete HINT due to profound hearing loss. In the SLT bilateral condition all but one patient performed better than chance, range 0.46 to 0.94. Most patients performed worse than chance when listening monaurally. SSQ1 ranged from 1.70 to 9.36, SSQ2 0.85 to 8.88, SSQ3 2.49 to 9.78 and total SSQ 1.81 to 9.34. A significant correlation was found between SLT and SSQ2 (rs = -0.68, p < 0.05), but not between HINT and SSQ1 (rs = -0.37, p > 0.05).

Conclusions

Binaural benefits were provided for some BCI patients in terms of sound localization and speech perception in noise. Better sound localization performance was related to increased self-reported spatial hearing. SLT was better using two rather than one CI. Mode of communication and etiology influenced HINT results.

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List of abbreviations

BCI – bilateral cochlear implants CI – cochlear implant

dB – decibel EI – Error Index

HINT – Hearing in Noise Test HL – hearing loss

ILD – interaural level difference ITD – interaural time difference mEI – mean Error Index

SD – standard deviation SLT – sound localization test SNR – Signal-to-Noise Ratio

SSQ – Speech, Spatial, Quality of Hearing questionnaire

SSQ1 – speech section on Speech, Spatial, Quality of Hearing questionnaire SSQ2 – spatial section on Speech, Spatial, Quality of Hearing questionnaire

SSQ3 – quality of hearing section on Speech, Spatial, Quality of Hearing questionnaire UCI – unilateral cochlear implant

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Table of content

Introduction ... 4

Material and Methods ... 6

Sound localization test ... 7

Hearing in Noise Test ... 8

Speech, Spatial, Quality of Hearing questionnaire ... 8

Ethical considerations ... 8

Results ... 9

Discussion ... 12

Strengths and limitations ... 15

Conclusions ... 15

Acknowledgements ... 16

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Introduction

Individuals with profound hearing loss (HL) that do not benefit from hearing aids may be evaluated for cochlear implantation to restore hearing. Traditionally in Sweden a single cochlear implant (CI) has been provided. In recent years however, the number of patients obtaining bilateral cochlear implants (BCI) has increased [1].

In the normal hearing population, the ear receives airborne sound waves that set parts of the middle and inner ear into motion, ultimately producing nerve signals. The signals from the two ears are integrated in the central auditory pathways of the brain. About 30% of the input from one ear goes directly to the ipsilateral cortex for interpretation, but the majority of the signal crosses over to the contralateral hemisphere [2].

Figure 1. Hearing with a cochlear implant. (With permission from Cochlear®).

In a CI, sound is picked up by an external microphone and converted into digitally processed signals that are sent through an electrode inserted into the patient’s cochlea (figure 1). The signal bypasses the external, middle and parts of the inner ear and directly stimulate the spiral ganglion cells in the cochlea, sending electrical impulses to the cochlear nerve [3]. The

signals are then processed in the central auditory system [4].

A randomized clinical trial by Smulders et al found that adults with BCI performed significantly better than those with UCI in tests evaluating speech perception and sound

1. Microphones on the sound processor pick up sounds and the processor converts them into digital information.

2. The information is transferred through the coil to the implant just under the skin.

3. The implant sends electrical signals down the electrode into the cochlea.

4. The hearing nerve fibers in the cochlea pick up the signals and send them to the brain, giving the

sensation of sound.

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localization [5]. The results remained stable during follow-up two years later [6]. BCI supposedly provides the listener with a binaural advantage, to receive sound input from two ears, as opposed to monaural listening using only one ear [7-10]. Swedish guidelines for unilateral cochlear implant (UCI) candidacy exist [11], but there are no guidelines for BCI. There are three main binaural mechanisms; the head shadow, squelch, and summation effects [2]. The first is a purely physical mechanism [12]. A sound originating from one side of the head must travel farther to the most distant ear, creating an interaural time difference (ITD). The head provides a shadow effect, reducing the intensity of the sound at the most distant ear, resulting in an interaural level difference (ILD) [7]. The binaural squelch and summation effects are not mainly physical mechanisms; they depend on processes in the central auditory pathways. The squelch effect occurs when two sounds are spatially separated so that the ears receive different sound input. The signals are integrated in the central pathways, ultimately refining them so that the best possible signal reaches the auditory cortex for interpretation. The summation effect occurs when one and the same signal arrives at the two ears. The signals complement each other and take advantage of the best parts of the signals from each ear [2, 12]. Both the squelch and summation effects seem less important than the head shadow effect in BCI recipients, but all are associated with binaural hearing benefits [13], specifically regarding sound localization and speech perception in noise [5, 13, 14]. Some studies have tried to restore binaural hearing in UCI patients by using one microphone at each ear, both sending signals to the electrode in the unilaterally implanted ear [15, 16]. However, this means bypassing parts of the auditory pathways, as only some of the information from the stimulated cochlea will go directly to the same side of the brain and some will cross over [17]. The risk of losing vital information is high using input from only one ear, and BCI have been indicated to be a better option [15, 16].

In Sweden, 182 adults had received BCI at the end of 2016 [1]. They are mainly younger adults with congenital progressive HL or have additional disabilities such as visual

impairment or dual sensory loss (personal communication, C. Moller, May 2017). There is little research in Sweden exploring the benefits of BCI, and international research on BCI is limited to small samples.

The aims of this study were to explore possible benefits of BCI regarding sound localization and speech perception in noise, and how this related to self-reported hearing ability.

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Material and Methods

This exploratory cross-sectional study assessed data from the CIRi-study, which is an ongoing research project regarding sound localization in CI-recipients at the Audiological Research Centre at Örebro University Hospital. Patients with CI are continuously recruited during clinical visits. Seventeen patients were included in this study (table 1), all of whom completed testing between February 2015 and April 2017.

Inclusion criteria: 1) age ≥ 18 years at testing, 2) bilateral profound HL, 3) minimum 6

months experience using BCI, 4) in contact with the Audiological Clinic at Örebro University Hospital, 5) completed one or more of the Hearing in Noise Test (HINT), sound localization test (SLT) and Speech, Spatial and Quality of Hearing questionnaire v5.6 (SSQ).

Table 1. Basic characteristics of patients included in study.

1_{CI1: first cochlear implant.}2_{CI2: second cochlear implant.}

Number of patients 17

Age (years)

At CI11, mean ± SD (range) 35 ± 13.3 (9-57)

At testing, mean ± SD (range) 43 ± 12.5 (23-68)

Gender

Women (n) 9

Men (n) 8

Cochlear implant use (months)

Time with CI11, mean ± SD (range) 89.4 ± 62.2 (15-229) Time with CI22, mean ± SD (range) 39.8 ± 36.6 (6-122) Inter-implant time, mean ± SD (range) 49.9 ± 46.7 (0-178) Primary mode of communication

Spoken language n (%) 9 (53)

Sign language n (%) 8 (47)

Etiologies of HL were difficult to obtain from the patients’ medical records. In 11 patients there was information regarding sensorineural HL, which only tells us that the patient is hearing impaired, but not the cause of deafness. There were 2 patients with deaf-blindness, 2 patients with hereditary HL and one patient whose cause of deafness was not recorded.

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7 Sound localization test

A live end dead end semi-anechoic room, with a 26 decibel (dB) background sound pressure level, was used for SLT. Twelve speakers arranged in a circle, situated 1.45 m from a chair in the center, presented sounds at 0º (straight ahead), ±30º, ±60º ±90º, ±120º, ±150º and 180º. The patient was seated in the chair and asked to face the speaker straight ahead (figure 2).

Figure 2. Sound localization test set-up with patient and surrounding speakers.

The SLT tests localization ability of three different sound stimuli (car horn, bicycle bell and pink noise) under three separate listening conditions using the right, left or both CI. Listening to the sound bicycle bell with the left ear represented one round, in which the 12 speakers presented the sound 3 times each for a total of 36 sound presentations. The sound was never presented twice in a row from the same speaker. Each loudspeaker in the circle was

represented by a button in a circle on a hand-held device. The patient was instructed to press the button corresponding to the loudspeaker from which the sound was perceived. An Error Index (EI) was calculated, which is the sum of errors for one round divided by the average random error 108 (all possible errors from all speakers x number of presentations per

speaker/the number of speakers). One error equals pushing the button representing the sound next to the correct speaker, two errors equal pushing the button two speakers away, and so forth. The result was presented as a mean Error Index (mEI), calculated as the mean value of EI for all sounds during one listening condition. EI possible scoring range is from 0 to 2, with 0 representing a perfect score and 2 maximum error. EI has been described in detail by Asp et al [18]. A Monte Carlo simulation established the level of random guessing for our set-up at 0.8, so that all values above that would equal pure chance, meaning a lower number

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8 Hearing in Noise Test

HINT consists of 20 phonemically balanced Swedish sentences presented from straight ahead with a speech weighted masking noise, starting at 64 dB speech volume [19]. The patient was instructed to repeat the phrase after each sentence. A correct answer generated a 2 dB noise level increase before the next sentence was presented, while the noise level was decreased by 2 dB if the answer was incorrect. Results were presented as a signal-to-noise ratio (SNR), calculated as the initial speech volume minus the average noise level in dB.

Speech, Spatial, Quality of Hearing questionnaire

SSQ was developed by Gatehouse and Noble [20] with the purpose of investigating how reported hearing deficits in complex auditory environments relate to the patient’s experience of handicap. It consists of 14 questions on speech hearing (SSQ1), 17 questions regarding spatial hearing (SSQ2) and 18 questions on quality of hearing (SSQ3), such as listening effort and clarity of sound. Questions were answered using a visual analogue scale from 0 representing greater deficit, to 10 signifying greater ability. The patient could mark a box labelled “Not applicable” if the situation described did not apply to the patient’s experiences [20]. Results were presented as the patient’s mean value for each section, and as a total mean for the entire questionnaire.

The SLT, HINT and SSQ were analyzed using descriptive statistics in Microsoft Excel 2010. Additional information was gathered in a medical chart review regarding age, time using the implants, mode of communication and etiology of hearing loss. Correlation analyses were performed using IBM SPSS Statistics, version 22 to analyze HINT and SSQ1, as well as SLT and SSQ2.Due to small sample sizes the non-parametric Spearman’s rank correlation test was chosen. Results with values of p < 0.05 were considered significant.

Ethical considerations

The CIRi-study was approved by the Regional Ethical Review Board in Uppsala, registered as Dnr 2014/533. Informed written consent was obtained from each participant. Test results were saved in medical charts according to ordinary clinical practice, and on the county server using an anonymous code. The tests were non-invasive with sound levels equal to normal

conversation (64dB), and should not be discomforting. It is important for the field of clinical audiology to research localization and speech perception in noise to evaluate patient

performance. Results will likely be part of a longitudinal study, using the same tests and patients, which may be of use for the study patients as well as future patients eligible for BCI.

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Results

Sound localization test

All 17 patients completed the sound localization test. One patient received a bilateral mEI of 0.94, above the level of random error at 0.8, which means the patient scored worse than chance. That patient was implanted at the youngest age, 9 years, and had the longest experience using two CI. The remaining patients ranged bilateral mEI from 0.46 to 0.79. Altogether the group had a mean of 0.61 (SD 0.12) for the bilateral listening condition. The mEI in the monaural right ear condition ranged from 0.66 to 1.04, mean mEI 0.87 (SD 0.11). mEI in the left ear condition ranged from 0.68 to 1.09, mean mEI 0.87 (SD 0.10). SLT results are presented in medians and quartiles in figure 3.

Figure 3. Differences in mean Error Index depending on listening condition during sound localization test in patients with bilateral cochlear implants.

All patients scored lower (better) in the bilateral condition than when listening with one ear at a time. Only one patient achieved a monaural mEI below the level of random error for both ears respectively, with an mEI for the right as well as the left ear at 0.72. That patient also scored the lowest in the bilateral condition. One patient turned out to be using mainly one CI, despite being equipped with two. This patient performed better than chance in the bilateral and the right ear condition, and worse than chance for the left ear.

0 0,2 0,4 0,6 0,8 1 1,2

Mean bilateral Mean right ear Mean left ear

M e an E rr o r In d e x Listening condition 1.2 1.0 0.8 0.6 0.4 0.2 0.0

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10 Hearing in Noise Test

Thirteen patients successfully completed HINT, with an SNR ranging from 0 to 26 dB, mean 7.05 (SD 7.52). Four patients attempted but could not complete HINT as their HL was too severe. They, together with the patients with an SNR at or above 7.29 dB, were deaf-blind or mostly dependent on sign language and/or working in deaf environments. One patient also did not have Swedish as a first language. Among the patients with an SNR of 6.47 dB or less no one used sign language (figure 4). They received implants due to sensorineural HL, trauma or for unknown reasons.

Figure 4. Hearing in Noise Test. Results from 13 patients with bilateral cochlear implants. 1)

Signal to Noise Ratio = 0 for one patient.

The worst SNR was recorded by the two patients with the highest and lowest age at implantation, at 57 and 9 years respectively. The patient with the worst SNR also suffered from cochlear otosclerosis, resulting in surgical difficulties as the implant electrodes could not be inserted correctly. One of the patients with best SNR received a malfunctioning second implant that had to be replaced shortly after initial surgery, but had no hearing rehabilitation complications thereafter. The two patients with best SNR had the longest experience of using CI1 at 209 and 229 months, as well as the longest inter-implant time at 178 and 132 months respectively. 0 5 10 15 20 25 30 Si gn al to N o ise R atio Patients Spoken language Sign language or deaf-blind 1)

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Table 2. Results on Speech, Spatial, Quality of Hearing questionnaire in 16 patients with bilateral cochlear implants. Presented as range, mean and standard deviation (SD).

SSQ1 – speech section, SSQ2 – spatial section, SSQ3 – quality of hearing section.

SSQ1 SSQ2 SSQ3 SSQ Total

Range 1.70-9.36 0.85-8.88 2.49-9.78 1.81-9.34

Mean (SD) 4.76 (2.24) 4.06 (2.34) 6.30 (2.02) 5.21 (2.05)

The SSQ questionnaire was completed by 16 patients (table 2). All patients scored higher individually on SSQ3 than the speech and spatial hearing sections. Patients with the highest (best) total SSQ mean score all used spoken communication. Most of the patients with a lower total SSQ mean score were either sign language users, patients with deaf-blindness or had severe tinnitus or complications during the hearing rehabilitation process.

Associations between SLT and SSQ2 was investigated using the Spearman rank correlation analysis, which revealed a statistically significant correlation (rs = -0.68, p < 0.05). The relationship between HINT and SSQ1 was also analyzed using Spearman rank correlations. There was no correlation between the two tests (rs = -0.37, p > 0.05).

The two patients with the highest (worst) bilateral mEI were either unable to perform HINT or had the second highest (worst) SNR. One of the patients unable to complete HINT had the lowest total score on SSQ. The three patients with the highest total SSQ score also had the lowest bilateral mEI and were among the lowest scorers on HINT. They received implants due to sensorineural HL or trauma, and had no complications during hearing rehabilitation, apart from one patient whose second CI had to be replaced due to a malfunctioning implant before rehabilitation began. Their primary mode of communication was spoken language.

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Discussion

This study aimed to explore benefits of BCI at Örebro University Hospital regarding speech perception in noise, sound localization and self-reported hearing ability. The most important findings were:

1. Horizontal sound localization performance was better using BCI compared to UCI. 2. Results on HINT were diverse and possibly influenced by mode of communication. 3. The SLT showed a statistically significant correlation to the spatial section on SSQ. Sound localization

Sound localization puts high demands on binaural hearing [13, 14]. The patients in this study all but one performed bilaterally better than chance, but generally worse than chance for monaural conditions, indicating that binaural hearing benefits were provided for most patients. This concurs with previous studies in which localization performance significantly improved using BCI [5, 6, 14, 16, 21].

Binaural hearing likely provides benefits regarding working performance and quality of life [22]. BCI would enable the patient to follow a group conversation as improved sound localization makes it possible to turn the head in the direction of a new speaker, instead of first having to visually determine who is speaking. Another example of an important benefit is determining from which direction a vehicle approaches. BCI patients may become less

dependent on sign language interpretation and more secure in both work environments and at home.

Deaf-blind patients already have an impaired sound localization due to dual sensory loss [23]. Still, the patients in our study performed better than chance, indicating the importance of BCI for deaf-blind patients to preserve at least one of their two impaired senses. Two implants might also reduce the cognitive load being a result of dual sensory loss. A person with deaf-blindness has great difficulties to see expressions and body language. Receiving equally strong signals to both auditory and visual cortex might improve cognitive spare capacity. Despite the heterogenic group of patients, their performance on a group level was fairly similar. One patient used one CI more regularly than both at the same time. Bilateral

localization performance in a patient that has not actively trained using BCI would likely give results closer to a UCI patient. Several studies show that BCI users localize sounds more accurately using both devices rather than having one turned off [6, 16, 21]. In this particular

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patient there was no greater difference between ears than for other patients, indicating that sound localization, in contrast to previous research, is not always dependent on binaural hearing. The one patient with poor bilateral result was implanted at the youngest age; a surprising finding considering studies showing that longer CI experience increases overall CI performance [24, 25]. The only patient with low monaural mEI also had the lowest bilateral mEI, indicating that certain individuals might be better at locating sounds in general. The plasticity of the brain and the fact that the auditory neural pathways and its individual differences are not yet completely understood probably contributes to this possibility. Hearing in Noise Test

HINT results indicate a great heterogeneity in the patient sample with all but two patients achieving an SNR comparable to other BCI studies [5], and some unable to even complete testing. A few patients were close to the normal hearing SNR found during the development of the HINT material [19]. For reference, the normal hearing in the CIRi-study have an SNR ranging from -5.06 to -2.12.

HINT results divided patients into two groups. Patients with deaf-blindness or sign language users performed worse than other patients. HL etiology [24] and main mode of

communication [26] are known to influence speech perception in CI users. The deaf-blind patients in our material were either unable to perform HINT or achieved a comparably high SNR. CI may be beneficial for deaf-blind patients for sound localization purposes, but not necessarily to improve spoken communication [27, 28], which seems to be true for our patients as well. Communication mode is assumed to influence cognition in CI recipients; phonological sensitivity decreases with length of hearing impairment [29, 30]. Further studies regarding speech perception, cognitive ability and mode of communication may be important for future candidate selection.

Time using CI also affects speech perception [24], as seen in the two patients with best SNR. They had the longest inter-implant time; which in part concurs with previous findings in where a second implant improved hearing independent of inter-implant time [31], although a shorter interval increased the benefits [32].

The patients implanted at the highest and lowest age displayed the worst SNR. Some studies claim age at implantation influences CI outcome, but not as much as duration of HL [24] which was not studied here. Other studies have found that age does not affect speech perception [33, 34]. The oldest patient was also had otosclerosis, likely affecting results

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negatively. Speech perception is influenced by a number of factors of which electrode placement is only one [35]. It may be interesting to wait a few years before testing binaural skills as the plasticity of the brain might further improve speech perception. CI requires extensive rehabilitation and time is likely to improve outcome.

HINT presents speech and noise together from the front. Studies comparing UCI and BCI under the same conditions, essentially comparing monaural and binaural hearing, have found there are no differences in speech perception between the groups, even after a two-year follow up [5, 6]. In a study by Laske et al the BCI group achieved better results than the UCI group, but with no statistical significance [32]. However, when testing speech and noise coming from spatially separate directions the BCI group showed a significant advantage [5, 32, 36]. There is no hard evidence that sound localization and speech perception in noise use the same pathways within the auditory system but it would be of interest to perform similar tests on our sample to further evaluate the benefits of binaural hearing.

The patient heterogeneity is seen also in the SSQ answers, which ranged almost the entire scale. Patients with spoken communication scored generally higher than patients with sign language or deaf-blindness, who in many cases also use signed communication. A possible explanation is that the SSQ was most likely developed to evaluate spoken communication. The statistically significant correlation between SLT and SSQ2 concurs with previous studies. They also found connections between speech perception and SSQ1, which was not seen here [5, 6]. The correlation shows that BCI patients not only perform well on SLT but also that they share that experience subjectively as well, which might be important for how they function in daily life.

Patient heterogeneity is again apparent in some finale outliers. Two patients with poor SLT results had poor or no HINT results. Both tests measure hearing and the results may reflect their severe HL in general. Most adults receive CI for improved spoken communication [11], and expectations are likely formed accordingly. The inability to complete HINT was reflected in one patient as the lowest total SSQ score, perhaps because the expected speech perception outcome was not achieved. The three patients with the best total SSQ score, whose results clearly indicate that patients who perform well on objective tests also report a better self-reported hearing ability are perhaps our most interesting findings. They only had spoken language in common, and one patient was even re-operated. Many factors influence CI

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outcome and we did not investigate all of them, but this indicates that patients with diverse backgrounds might still benefit from BCI.

Strengths and limitations

There is no standardized sound localization test, which makes SLT impossible to compare to other studies. Most studies use a half-circle set up, but the circular arrangement with sounds from all directions in SLT is closer to everyday listening situations. Adding competing background noise would make it even more binaurally demanding [37].

A strength in our study is the use of HINT to evaluate speech perception in noise. It is standard procedure in CI research in Sweden and a validated tool to compare with HINT in other languages as well [19]. It should be noted that patients were tested at different times during the day, and hearing impaired are known to become increasingly tired after a work day due to strenuous listening. HINT is an effort-demanding test, and not timing best performance may influence results.

Small patient samples lead to statistical difficulties, but results are presented on both group and individual levels and outliers are discussed in detail. An important strength is that this study includes 17 of 28 BCI patients in total at Örebro University Hospital, out of which only 20 would have been able to participate in the study as the rest have been too recently

implanted. Considering that Örebro has the highest surgical rate regarding CI in Sweden [1], the CIRi-study is expected to grow in numbers and will provide an important basis for BCI research in the future.

Conclusions

This study has demonstrated that BCI provide benefits to most patients in terms of better sound localization, which was correlated to a greater self-reported spatial hearing ability. Patients with a spoken language demonstrate a better speech perception than patients who are deaf-blind or use sign language. There is great heterogeneity in the BCI sample from Örebro University Hospital, both in patient characteristics and performance on tests, and further studies should be performed as the group increases.

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Acknowledgements

I would like to express my gratitude towards the entire staff at the Audiological Research Centre at Örebro University Hospital, with Claes Möller and Jonas Ekeroot as my guides from confusion to clarity. Thank you for your time, expertise and warm welcoming into the world of audiological research. I extend a special thank you to Åsa Skagerstrand, for invaluable help and daily laughs in the office.

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28. Hoshino AC, Echegoyen A, Goffi-Gomez MV, Tsuji RK, Bento RF. Outcomes of Late Implantation in Usher Syndrome Patients. International archives of otorhinolaryngology. 2017;21(2):140-3.

29. Moberly AC, Harris MS, Boyce L, Nittrouer S. Speech Recognition in Adults With Cochlear Implants: The Effects of Working Memory, Phonological Sensitivity, and Aging. Journal of speech, language, and hearing research : JSLHR. 2017;60(4):1046-61.

30. Hua H. Employees with Aided Hearing Impairment : An Interdisciplinary Perspective [Doctoral thesis, comprehensive summary]. Linköping: Linköping University Electronic Press; 2014.

31. Ohta Y, Kawano A, Kawaguchi S, Shirai K, Tsukahara K. Speech recognition in bilaterally cochlear implanted adults in Tokyo, Japan. Acta oto-laryngologica. 2017:1-5. 32. Laske RD, Veraguth D, Dillier N, Binkert A, Holzmann D, Huber AM. Subjective and objective results after bilateral cochlear implantation in adults. Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology. 2009;30(3):313-8.

33. Ghiselli S, Nedic S, Montino S, Astolfi L, Bovo R. Cochlear implantation in

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outcomes during the first year of use. Acta otorhinolaryngologica Italica : organo ufficiale della Societa italiana di otorinolaringologia e chirurgia cervico-facciale. 2016;36(6):513-9. 34. Friedmann DR, Green J, Fang Y, Ensor K, Roland JT, Waltzman SB. Sequential bilateral cochlear implantation in the adolescent population. The Laryngoscope. 2015;125(8):1952-8. 35. Holden LK, Finley CC, Firszt JB, Holden TA, Brenner C, Potts LG, et al. Factors

affecting open-set word recognition in adults with cochlear implants. Ear and hearing. 2013;34(3):342-60.

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Letter of intent

May 24th, 2017 Linnéa Hinz Bachelor of Medicine Örebro University Dear Editor,

Bilateral cochlear implantation is increasing among Swedish adults. Current medical

guidelines recommend a unilateral implant to restore hearing, even though studies show that bilateral implants are more beneficial in terms of binaural hearing skills. This study explores the binaural hearing tasks sound localization and speech perception in noise in post-lingually deafened individuals fitted with bilateral cochlear implants (BCI), and how they relate to self-reported hearing ability. Mode of communication and etiology of hearing loss seemed to influence speech perception results. The study showed that patients better locate sounds in binaural listening conditions than monaural conditions. Greater self-reported spatial hearing ability correlates to better performance on the sound localization test.

Explorative data of this kind are important as it provides a foundation to compose general guidelines for bilateral implantation. There are no previous studies on binaural performance or indications for implantation in this patient group. As the study sample comprises 85% of BCI patients in Örebro, the findings provide an overview of BCI performance at Örebro University Hospital of today that may be compared to other hospitals with similar patient groups.

This study has not been previously published.

Kind regards, Linnéa Hinz

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Populärvetenskaplig sammanfattning

Det blir allt vanligare att patienter med grav hörselnedsättning återfår hörseln med hjälp av kokleaimplantat. En elektrod förs in i hörselorganet och omvandlar ljudvågor till elektriska signaler. Efter en tids träning kan patienten uppfatta både tal och andra ljud i omgivningen. Barn som ännu inte lärt sig tala får alltid ett implantat på varje öra för att utveckla en så normal hörsel som möjligt, medan vuxna vanligen får ett ensidigt implantat trots en

dubbelsidig hörselnedsättning. På senare tid har även vuxna börjat få två implantat, eftersom man funnit att de med enbart ensidigt implantat presterar sämre på tester som kräver binaural hörsel, det vill säga ljudintryck från båda öronen. Ensidigt implanterade upplever även sin hörsel som sämre än de med två implantat.

I studien undersöktes vuxna patienter på Örebro Universitetssjukhus som fått två implantat. De utförde två test som ställer höga krav på binaural hörsel – taluppfattning i brus och ljudlokalisation. De fyllde även i ett självskattningsformulär som utvärderar hur patienten uppfattar sin hörsel i olika situationer.

Det fanns en stor spridning i hur god taluppfattning patienterna hade. Några kunde inte genomföra testet alls på grund av för dålig hörsel, medan andra uppnådde nästan

normalhörande nivåer. Patienter med talspråk presterade bättre på taluppfattningstestet än patienter som var dövblinda eller använde teckenspråk. Det gick bättre för patienterna på ljudlokalisationstestet när de hade båda implantat påslagna än när de testade ett öra i taget. De som hade bättre resultat på ljudlokalisationstestet skattade också sin riktnings- och

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Ethical considerations

All research is meant to contribute to extended knowledge in the field that is studied. Other patients may benefit from the research and tests performed on patients included in any study, and the expertise among medical personnel may deepen. But research cannot be pursued at any cost, and it is important to consider any discomfort or exposure of those included in the study as well as the reason for them to participate.

This study researched patients with hearing loss who have received bilateral cochlear

implants. They suffer from a chronical condition, and have gone through long and extensive rehabilitation and an expensive treatment. This means there is a possibility that patients in this and similar studies agree to participate due to gratitude and being in a position of dependence. We used non-invasive tests, already in clinical use, that take place during regular but extended control visits. They may be more time-consuming than a regular visit, but should not give rise to any discomfort. A written consent was obtained and patients were informed how data is presented to warrant there is no intrusion on patient integrity. Anonymity was ensured by coding and safe-keeping of records, which is vital to all research containing patient related material. In research using invasive tests the information to the patient should be extensive, and discomfort as limited as possible. Still, even invasive and uncomfortable research is sometimes of importance to reach new areas of knowledge, but requires careful preparation and consideration to ensure only the most necessary tests are performed.