|Year : 2017 | Volume
| Issue : 1 | Page : 27-31
Sound localization performance in children with cochlear implants using bimodal stimulation
Poonam Raj, Sachin Saini, AK Mishra
Department of ENT and HNS, Army Hospital (R and R), New Delhi, India
|Date of Web Publication||6-Feb-2017|
Dr. Poonam Raj
Department of ENT and HNS, Army Hospital (R and R), Delhi Cantt., New Delhi - 110 010
Source of Support: None, Conflict of Interest: None
Introduction: There are clear benefits of having bilateral inputs to the auditory nervous system. Hearing-impaired children are, therefore, generally fitted with two hearing aids so that they can benefit from hearing binaurally. Children who use a cochlear implant in one ear and no amplification in the opposite ear are, however, deprived of these advantages. The current study was undertaken to determine the benefits of bimodal stimulation in pediatric population. Methods and Materials: This study comprised of 20 children between 6-11 years of age with profound bilateral sensorineural hearing loss with cochlear implant in one ear and fitted with digital hearing aid in non-implanted ear. Mean sound localization score was compared in children with cochlear implant only and those with both cochlear implant and hearing aid. Result: A statistically significant difference was found between mean sound localization in both test condition under quiet surrounding. Conclusion: Hence it is suggested that the use of bimodal fitting can be considered as an effective management option in order to obtain binaural hearing benefits in children who undergo unilateral cochlear implantation.
Keywords: Auditory deprivation, bimodal stimulation, binaural hearing, cochlear implantee
|How to cite this article:|
Raj P, Saini S, Mishra A K. Sound localization performance in children with cochlear implants using bimodal stimulation. Indian J Otol 2017;23:27-31
| Introduction|| |
Sound localization is a very important function of the auditory system. It is directly linked to the binaural information of sound received by both the ears and allows the listener to quickly orient toward the sound source. Binaural hearing uses auditory inputs from both ears and helps localize sounds in adverse listening situations such as in the presence of noise or when there are many speakers at the same time. While binaural fittings have been traditionally applied to hearing aids, monaural stimulation has commonly persisted in cochlear implants.
Children with profound bilateral sensorineural hearing loss with a unilateral cochlear implant are unable to localize sound because of lack of balance between acoustic inputs of the two ears. This shows the importance of bilateral amplification to gain binaural information. Binaural hearing for these children can be provided through bilateral cochlear implantation and/or bimodal stimulation.
When an individual is stimulated by two different modes of hearing (i.e., hearing through electrical stimulation in one ear and acoustic stimulation in the other ear), it is known as bimodal stimulation. In this study, it means a cochlear implant in one ear which gives electrical stimulation and a hearing aid in the other which gives acoustic stimulation. The problem with this bimodal stimulation is an atypical interaural difference due to two different stimuli resulted in asymmetry hearing in two ears. However, still benefit is seen in terms of improvement in the ability to localize sound as compared to one cochlear implant only.
Till date, very few studies have been performed on the benefits of bimodal hearing particularly in India. From the available literature, it was found that most of the studies on benefits of bimodal hearing in the past have targeted mainly adult population and studies on pediatric population are very limited. The majority of these studies showed a benefit in speech recognition and sound localization although the magnitude of benefit and the testing procedures used differ greatly among these studies. Hence, this present study was conducted with an aim to determine the effects of bimodal hearing in terms of sound localization in pediatric population.
| Materials and Methods|| |
The aim of this study was to compare sound localization ability in children with profound bilateral hearing loss with unilateral cochlear implant with and without bimodal hearing as measured by sound localization score.
Twenty children between 6 and 11 years of age with profound bilateral sensorineural hearing loss and cochlear implant of uniform type in one ear were selected. A detailed history and routine ENT examination of all the children were done to rule out any middle ear pathology of recent onset or any congenital external ear malformation or acquired external ear defect. The duration of cochlear implant usage ranged from 12 to 54 months [Figure 1] and the onset of bimodal stimulation ranged from 3 to 13 months after cochlear implantation. The duration of bimodal stimulation ranged from 08 to 38 months [Figure 2]. All participant children underwent sound localization tests first with cochlear implant in one ear and then with bimodal hearing. Hearing aids used for bimodal stimulation were of the same brand and were optimized. It was ensured that all the children have attained a stable cochlear implant map.
Sound localization score was measured on same set of children first without hearing aid and then with a hearing aid in the contralateral ear. The scoring system used was a modification of method used by Potts et al. 2009.
Speech stimulus was presented in a sound-treated laboratory where 08 specialized speakers were arranged at 45° in the horizontal planes (0°, 45°, 90°, 135°, 180, 225°, 270°, 315°) which were numbered from 1 to 8 and all speakers were connected with a STUDIO ONE Software (Setron India Pvt Ltd, New Delhi, Delhi, India). The distance of the patient's head was 1 m from each loudspeaker and height of speakers was adjusted to be at ear level. A total of five attempts were given to each child first with cochlear implant only and then with cochlear implant in one ear and hearing aid in other ear. The child was asked to point at the speaker through which sound was heard.
A score of “2” was given if the child pointed to the correct speaker. If the child pointed to the speaker at 45° left or right to the speaker in which sound was pulsed, he/she was given a score of 1. A score of “0” was given if the response was other than the above two conditions. The same test was done on same set of children with Cochlear implant in one ear and a hearing aid in nonimplanted ear. The maximum possible sound localization score for each test condition was ten. All results were compiled for each listening condition. In this study, the sound localization benefits were tested in the horizontal plane only.
| Results|| |
Data from twenty patients were collected and analyzed using paired t-test and significance value was derived. Mean sound localization score with cochlear implant only and with both cochlear implant and hearing aid were 5.05 and 6.45, respectively. A statistically significant difference was found between mean sound localization score with use of cochlear implants only and with use of both cochlear implant and hearing aid (P < 0.001) [Figure 3] and [Figure 4].
|Figure 3: Comparison of sound localization score with use of cochlear implant alone and with use of both cochlear implant and hearing aid.|
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|Figure 4: Sound localization score of each patient with use of unilateral cochlear implant only and with use of both cochlear implant and hearing aid.|
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The sound localization test results showed improvement in sound localization score in majority of patients when hearing aid was used with cochlear implant. With the addition of a hearing aid with cochlear implant, individual sound localization score showed an improvement of 0%–40% in majority of patients. However, two patients showed a slight decrease in scores after addition of the hearing aid. The mean score showed an improvement of 14%, which was statistically significant (P < 0.001).
| Discussion|| |
Children with profound bilateral sensorineural hearing loss with unilateral cochlear implant lack binaural information and thus have impaired speech recognition and are unable to localize sound. Bilateral amplification provides significant benefits in two ways; it ensures better sense of balance in terms of speech perception and also preserves some of the benefits that persons with normal binaural hearing experience, including localization ability and improved speech recognition. Nowadays, bilateral amplification is gaining importance in clinical practice in cochlear implant recipients. Various studies have shown the benefits of bilateral implantation over unilateral implantation. However, there are debates on efficacy and cost-effectiveness of unilateral vis-a-vis bilateral cochlear implantation.
Recently, a new concept of bimodal hearing has been introduced to deal with a lack of sound localization and impaired speech recognition in unilateral cochlear implant recipients with bilateral sensorineural hearing loss.
Recent studies have described the effects of bilateral inputs in terms of sound localization and speech recognition in patients with bilateral hearing impairment fitted with cochlear implant. In most of the studies on localization, the sound is presented to the patient in free field or in a closed room by speakers located around the patients head and the listener locating the sound by pointing at the source or by azimuth and elevation coordinate.
Blamey et al. demonstrated that different pitches might be elicited when processed by a cochlear implant and hearing aid in opposite ear. Despite these concerns, patients with residual hearing in nonimplanted ear preferred to wear hearing aid in nonimplanted ear compared to wearing only a unilateral cochlear implant.
Tyler et al. evaluated three patients who wore a cochlear implant on one ear and a hearing aid on the other ear using word and sentence recognition and localization tasks. Speech stimuli were presented from the front in quiet and in noise, and noise was presented from the front, right, or left. Localization was tested with noise bursts presented at ±45° azimuth's right or left. Results indicated a bimodal advantage in quiet for only one of the three patients for words and none for sentences.
Ching et al. in 2005 reported that horizontal localization in children with cochlear implant and hearing aid was significantly better than in children with cochlear implant alone. The results of our study, however, were consistent with the majority of available literature in that bimodal hearing provides a significantly better sound localization than with cochlear implant alone. Ching et al. and Litovsky et al. reported that cochlear implant and hearing aid group localized sound better than cochlear implant group and the duration of bimodal devices use and degree of hearing loss were not found to be related to binaural benefits.,
Phanindra et al. conducted a study on ten children in the age range of 5–10 years (7.8 years) who used cochlear implant in one ear for at least 8 months and used hearing aid for about 2 years binaurally before the cochlear implantation. Speech identification scores were obtained in both the aided conditions (cochlear implant alone and cochlear implant + hearing aid) using “Speech Identification Test for Children Speaking Telugu” in three situations, i.e., in quiet, +10 dB signal-to-noise ratio (SNR), and +5 dB SNR. They concluded that the use of hearing aid and cochlear implant in opposite ear results in binaural advantages in speech perception, and therefore, bimodal hearing may be considered as one of the better option in aural rehabilitation approach for the children with unilateral cochlear implant.
However, Dunn et al. in 2005 found that only a few listeners (2 out of 12) showed an improvement in localization despite wearing a cochlear implant and hearing aid in opposite ears. It is possible that timing and level differences between the cochlear implant and hearing aid explains why binaural advantages have not been observed across all studies or across all patients with cochlear implant and hearing aid.
From the above-mentioned studies, it is apparent that almost all studies consistently showing a binaural advantage for majority of patients and for various test conditions. However, very few patients in few studies are also showing a detrimental performance with the addition of hearing aid in other nonimplanted ear and are considered as exceptions. Studies done in children are fewer and show less positive results as compare to adults.
| Conclusion|| |
Although the test conditions cannot fully match real life situations, reasonable conclusions may be drawn from this study. This study concludes that despite the difference in mode of auditory stimulus the pediatric cochlear implant recipients achieved statistically significant difference in sound localization under bimodal condition in quiet environment. Hence, the use of bimodal fitting device can be considered as an effective management option to obtain binaural hearing and it is also beneficial to prevent the effect of auditory deprivation in children with unilateral cochlear implants.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]