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Hearing with two ears is better than with one - Dr. Dr. h. c. Monika Lehnhardt
- 1. Hearing with two ears is better than with one Dr. Dr. hc. Monika Lehnhardt May 2008
- 2. Glossary Bilateral: Both sides Bilateral cochlear implantation.(CI): CI placed in the two cochleae of an individual patient. Bimodal: Two different modes. Bimodal Hearing: CI in one ear, Hearing Aid (HA) on the non-implanted side. Binaural Hearing: Integration of input along the auditory pathway following sound/stimulation from both ears. A CI and an optimally fitted HA on the non- implanted ear also provide binaural hearing input to the auditory cortex.
- 3. How many bilateral Nucleus cochlear implant recipients are there currently worldwide? More than 5’500 of whom approximately 80% are under the age of 18. As of March 2008
- 4. Why is Binaural Hearing important? The ability to localise sound as well the ability to detect speech in complex acoustical environments is achieved by the central auditory system’s ability to calculate minute differences in the characteristics of sound arriving at each ear. Sound arrives later and softer Sound arrives earlier and louder
- 5. Improved sound localisation With a second CI, precision to localise sound more than doubles! Mean angular 67° C I: error: ral ° late 24 Uni I: lC ra at e Bil Verschuur, CA, Lutman, ME, Ramsden, R, Greehan, P, O’Driscoll, M., Auditory, localization abilities in bilateral cochlear implant recipients. Otology and Neurology, 26:965-971. 2005
- 6. Improved speech understanding in noise With a second CI, speech understanding in noise can increase by a factor of 9 % correct scores for HSM at 10dB SNR 100 90 80 CI closest to noise 70 60 Factor of 9 50 CI closest to speech 40 30 20 10 Bilateral 0 N=23 Speech +45 Noise -45 Laszig, R. et.al., Benefits of bilateral electrical stimulation with the nucleus cochlear implant in adults: 6-Month postoperative results, Otology and Neurotology, 25[6], 958-968. 2004.
- 7. What are the functional benefits of binaural hearing with CI? • Feel safer – Better sound localisation – Being more aware of the sound environment • Join in – Better speech understanding in noise – Socially more interactive in conversations • Relax – Listening becomes easier – Enjoying more balanced sound – “Incidental learning” – Confidence that the better ear is implanted
- 8. What are the objective benefits of binaural hearing with CI? a. Head shadow effect (a physical phenomenon): the benefit from adding the ear with the more favourable Signal-to-Noise Ratio when listening in spatially separated speech and noise. Speech Noise Mean improvement of 10dB in Critical SNR for 50% speech recognition * for Oldenburger sentences Laszig, R. et.al., Benefits of bilateral electrical stimulation with the nucleus cochlear implant in adults: 6- Month postoperative results, Otology and Neurotology, 25[6], 958-968. 2004.
- 9. What are the objective benefits of binaural hearing with CI? (cont.) b. Binaural squelch – the benefit of adding the ear with the less favourable signal to noise ratio Speech Up to 3 dB improvement in SNR for speech recognition * Noise Cochlear White paper B. Robert Peters et al., Rationale for Bilateral Cochlear Implantation in Children and Adults. 2006
- 10. What are the objective benefits of binaural hearing with CI? (cont.) c. Binaural Redundancy - two ears are better than one when listening to speech in quiet or in noise presented from the same location Speech and Noise 1 – 2 dB increase in perceived loudness Speec and Noise Cochlear White Paper. B. Robert Peters et al., Rationale for Bilateral Cochlear Implantation in Children and Adults. 2006
- 11. Are two ears better than one? The Evidence Says, YES • 37 of more than 300 studies selected • Evidence indicates specially sound localisation and understanding in noise benefits – + 21% sentences score (in noise) – 24° instead of 67° localisation error
- 12. Bimodal Options: Candidacy Considerations Adults: Greatest binaural benefit (CI + contralateral HA) for improved speech understanding in quiet and in noise was observed for subjects who scored at least 20% correct on bisyllabic word lists pre-operatively with their contralateral HA. Morera et al., Advantages of Binaural Hearing Provided through Bimodal Stimulation via a Cochlear Implant and a Conventional Hearing Aid.: A 6 month Comparative Study. Acta Otolaryngologica, 2005; 125: 596-606.
- 13. Bimodal Options: Candidacy Considerations (cont.) Children: Degree of benefit from contralateral HA is related to: • Amount of residual hearing • Optimal HA fitting • Experience with bimodal hearing “Assuming consideration of the above, binaural gains are seen to be superior to the monaural condition and optimise academic and social functioning for the child”. Cochlear White Paper . B. Robert Peters et al., Rationale for Bilateral Cochlear Implantation in Children and Adults. 2006
- 14. When to progress from bimodal to bilateral CI stimulation? Adults: Contralateral Aided Only condition: Two-thirds of polled clinical experts suggest further consideration of sequential CI if the subject scores 45% or less on open set word tests. Best Aided Bimodal listening condition: Experts suggest further consideration of sequential CI if the subject scores 55% or less on open set word tests. Wyss, J (Ed.) Bilateral Expert Survey Consensus 2008 (in progress)
- 15. Bilateral CI candidacy considerations Children: An optimally fitted HA in the non-implanted ear will enable some maturation of the auditory pathways. This will occur, however, only to the degree related to the amount of residual hearing. 1 The effectiveness of a hearing aid for this purpose can be monitored with CAEP.2 In children whose CAEP (P1 latency) fails to show a time course of development, CI implantation is the only way to achieve central binaural development. 1 1. B. Robert Peters et al., Rationale for Bilateral Cochlear Implantation in Children and Adults. 2006 2. Sharma et al., P1 Latency as a Bio-Marker for Central Auditory Development in Children with Hearing Impairment. J Am Acad Audiol 2005; 16: 568-577.
- 16. When to prefer simultaneous, when sequential bilateral cochlear implantation? Studies demonstrate a critical time period for binaural auditory development, more conducive to early simultaneous implantation. “Our data suggest a high degree of plasticity of the central auditory pathways seen only after early implantation (of bilateral implants)”. (Bauer PW, Sharma A et al. Central Auditory development in children with bilateral cochlear implants. Arch Otolaryngol Head Neck Surg. 2006 Oct;132(10) “Clear differences in auditory brainstem responses were seen in sequentially implanted children, even when the delay of the second implant was under one year”. (Gordon KA et al. Bilateral Best Practices Symposium, Charlotte, North Carolina, Apr 2007 re: Binaural processing in children using bilateral cochlear implants.Neuroreport. 2007 Apr 16)
- 17. Should the second ear be “saved” for future CI technologies? “Given that binaural hearing depends on bilateral input during a critical development period, if the second ear does not receive auditory input during the critical period of cortical development, later technology, no matter how advanced, will only provide input to a cortex incapable of receiving it” B. Robert Peters et al., Rationale for Bilateral Cochlear Implantation in Children and Adults. 2006
- 18. Is there an age effect for bilateral CI implantation in children? Older children benefit, but less so compared to younger children In children under 8 yrs: the “gap” in speech perception for 1st vs. 2nd ears is closed within the first 6 -12 months. This gap closure was generally not seen for children 8-13 yrs. Moreover, this gap persists even after 2 or 3 years, (except in isolated cases) Peters BR, Litovsky R,Parkinson A, Lake J.Otol Neurotol.2007 May. Importance of Age and Postimplantation Experience on Speech Perception Measures in Children with Sequential Bilateral Cochlear Implants.
- 19. Age and Inter Implant Interval P1 Latency (ms) Sharma et al., The Influence of a Sensitive Period on Central Auditory Development in Children with Unilateral and Bilateral cochlear Implants. Hearing Research 2005; 203:134-143.
- 20. Age and Inter Implant Interval Sharma et al., The Influence of a Sensitive Period on Central Auditory Development in Children with Unilateral and Bilateral cochlear Implants. Hearing Research 2005; 203:134-143.
- 21. Is there Expert Consensus? • Most would benefit from binaural CI. • There is a – not yet fully understood- ‘window of opportunity’ in children. • Surgery is low risk, simultaneous procedure is to be considered from 6 months of age. • Insurance companies and governments should fund bilateral CI.
Editor's Notes
- Hearing with two ears is better than with one – this sounds reasonable.
- But what are we talking about? Let us clarify the terms: Bilateral simply means on both sides and bilateral CI means consequently that a CI is placed in the two cochleae of an individual recipient Bimodal means two different modes and bimodal hearing then is when the recipient has a CI on one ear and a hearing aid on the other ear, the non-implanted side. Binaural Hearing is the integration of input along the auditory pathway following sound or stimulation from both ears. It is important to realize that a CI and an optimally fitted HA on the non-implanted ear also provides binaural hearing input to the auditory cortex.
- We know that there are more than 5.500 bilateral Nucleus CI recipients worldwide and 80% of these are children under the age of 18 years. Based on a market share of 65% for the Nucleus device we can assume that there are approx. 8.500 bilateral CI wearers worldwide, which is still below 10% of all people, who have a CI.
- Why is binaural hearing important? Because: the ability to localize sound as well as the ability to detect speech in complex acoustical environments is achieved by the central auditory system’s ability to calculate minute differences in the characteristics of sound arriving at each ear. On the right side sounds arrives earlier and louder, on the left side it arrives later and softer.
- Improved sound localization – with a second CI the precision to localize sound more than doubles! With only one CI the mean angular error is 67 degrees, with bilateral CIs it is only 24%. ___________________________________________________________________________________________________ Verschuur et al. , 2005 N = 20 adults tested following sequential implantation. All subjects had at least 9 months experience with their bilateral CIs; Duration of deafness < 15 years in either ear; minimal benefit from hearing aid in 2 nd implanted ear Horizontal plane localization with 5 stimuli: speech, tones, noise, transients, and reverberant speech; 11 loudspeaker array in a 180-degree horizontal arc Within-subject: unilateral versus bilateral; also with dual-microphones (sound combined to the SPrint processor) CIs = Nucleus 24M or 24K (with either SPEAK or ACE, but same strategy used both ears and loudness balanced) Stimuli presented at 60 dB SPL except pink noise also given at 70 dB SPL to activate AGC. Roving over +/- 5 dB range. Calculation of mean localization error; repeated measures AOV with post-hoc tests. Results: Bilateral performance significantly better than unilateral for all subjects across stimulus types and sound sources.
- Improved speech understanding in noise is one of the most important criteria for a CI recipient. With a second CI it can increase by a factor of 9. Compare only 8% correct scores with one CI closest to noise, 55% with the CI closest to speech and 70% in the bilateral condition. _______________________________________________________________________________________________________________ In spatially separated speech and noise, this graph illustrates the improvement that can be gained from adding a second CI (see “Bilateral” performance bar), compared to the performance in the monaural condition for the CI with the less favourable signal to noise ratio (see “ CI closest to noise” performance bar). Note also the range of performance for the Hochmair-Schulz-Moser recorded sentences in Noise (10dB SNR) in the bilateral condition, in which excellent speech comprehension is demonstrated by some subjects.
- What are the functional benefits of binaural hearing with CI? Feel safer based on better sound localization and being more aware of the sound environment Join in because of better speech understanding in noise and socially more interactive in conversations Relax by listening in an easier way, enjoying more balanced sound and the possibility of “incidental learning” and being confident that the better ear is implanted.
- In addition to the functional benefits there are also objective benefits of binaural hearing with CI The head shadow effect is a physical phenomenon and it means there is a measurable benefit from adding the ear with the more favourable Signal-to-Noise Ratio when listening in spatially separated speech and noise. A mean improvement of 10dB in Critical SNR for 50% speech recognition for Oldenburger Sentences can be achieved as shown in this study with patients 6 months post-operative at the University Clinic in Freiburg. _______________________________________________________________________________________________________________ The Head Shadow Effect is a major contributor to the understanding of speech in noise because it enables the listener to use the ear with the most favourable signal to noise ratio. Laszig et al 2004: demonstrated a significant head shadow benefit resulting in mean -10 to -11.4dB in the SNR required for 50% speech comprehension for the Oldenburger sentences and a mean improvement in the maximum score of up to 55% for the ear closest to the speech signal vs. the ear farthest away for the Hochmair-Schulz-Moser (HSM) sentences.
- When adding the ear with the less favourable Signal-to-Noise Ratio – the Squelch effect - the benefit is an up to 3dB improvement in SNR for speech recognition. __________________________________________________________________________________________________________________________ Binaural squelch enables the brain to take advantage of amplitude and phase differences between the signals arriving at the two ears leading to a 3-6dB advantage in normal hearing subjects (Markides 1977).
- Finally we see a 1 – 2 dB increase in perceived loudness when two ears are listening to speech in quiet or noise presented from the same location. This we call binaural redundancy. _________________________________________________________________________ Binaural redundancy refers to the small advantage arising from listening with two ears even though identical combinations of signal and noise are presented to each ear. The phenomenon has also been referred to as diotic summation or duplication.
- There is Evidence that hearing with two ears is better than with only one as you will find in this publication by John Murphy and Gerard O’Donoghue.
- As mentioned at the beginning there is also the bimodal option, which means a CI and a contra-lateral HA. The greatest benefit of this solution was improved speech understanding in quiet and in noise for adult recipients who scored at least 20% correct on bisyllabic word lists pre-operatively with their HA.
- In children the degree of benefit is related to the amount of residual hearing, optimal HA fitting and the experience with bimodal hearing. Taking these factors into consideration binaural gains are seen to be superior to the monaural condition and optimize academic and social functioning for the child.
- What are the criteria for making the decision to move from bimodal to bilateral CI stimulation, i.e. implant the other ear for adults? Two thirds of polled clinical experts suggest to consider a second implant if the subject scores 45% or less on open set word tests in the contra-lateral aided only condition. Experts also suggest to consider a second implant if the subject scores 55% or less on open set word tests in best aided bimodal listening condition. __________________________________________________________________________________________________________________________ 18 clinicians responded from 17 CI centres representing experience in approximately 2000 bilateral CI candidates globally. Majority of the polled clinical responders had more experience with bilateral children (and this is reflected in their response).
- In children an optimally fitted HA in the non-implanted ear will enable some maturation of the auditory pathways. This will occur, however, only to the degree related to the amount of residual hearing. The good news is, that the effectiveness of a HA for this purpose can be monitored with Compound Action Potential. In case the P1 latency fails to show a time course of development, CI is the only way to achieve central binaural development. ____________________________________________________________________________________________________________________________ P1 latencies of the CAEP are thought to reflect synaptic propagation through the thalamo-cortical portions of the central auditory pathways, and hence an index of maturation in these areas. CAEP testing in the aided condition yields an indication of the development of binaural mechanisms
- Many parents will ask whether simultaneous cochlear implantation is preferable to sequential and how long is the time window to achieve better outcomes after a second implant. Studies demonstrate indeed, that there is a critical time period for binaural auditory development and this is in favour of early simultaneous implantation. Bauer, Sharma et al say: “Our data suggest a high degree of plasticity of the central auditory pathways seen only after early implantation of bilateral implants” And Gordon et al state “Clear differences in auditory brainstem responses were seen in sequentially implanted children, even when the delay of the second implant was less than one year”.
- Many parents will also ask whether it is not a good idea to save the second ear for future CI technologies. B. Robert Peters et al published the following statement in 2006: “ Given that binaural hearing depends on bilateral input during a critical development period, if the second ear does not receive auditory input during the critical period of cortical development, later technology, no matter how advanced, will only provide input to a cortex incapable of receiving it”. This is what I call a very powerful argument to fight for providing the opportunity of bilateral CI to all suitable paediatric candidates. ______________________________________________________________________________ Implication: If no effective connection within the cortical layers and to the higher order auditory and language cortex, even hair cell regeneration will be of limited benefit after the critical sensitive period has elapsed, regardless of whether the user is a successful unilateral user or not.
- Everybody agrees that the earlier a child receives the CI the higher the probability to achieve excellent outcomes. The same is true for children with bilateral implantation. Older children also benefit, but less as compared to younger children. In children under the age of 8 years the gap in speech perception for the first and the second ear is closed within the first 6 – 12 months. In children between the age of 8 and 13 years the gap closure was generally not seen and the gap persists even after 2 to 3 years (except in isolated cases). ____________________________________________________________ Children who receive their first CI prior to age 3.5 years have normal P1 latencies within 6 months of implant use that approach the range for normal hearing peers. If 7 years of age or older, they never achieve normal P1 latencies, correlating with the observed poorer speech and language outcomes.
- Sharma shows the difference in the following slides. Here a child who received the first CI at the age of 1.07 years and the second at the age of 2.06. The P1 latency falls within the normal range already one month after the first fitting of the second implant. _____________________________________________________________ Illustrates the effect of both early sequential CI implantation, noting that the PI latency of the Cortical Auditory Evoked Response (CAEP) for this subject falls within the normal range within 3 months of the initial activation of the CI for the first side implant, and the P1 latency for the second implanted side falls within the normal range of P1 latencies after only 1 month following activation of the second device. This recipient received both cochlear implants by age 2.06 years.
- Here we have a child who received the first implant at the age of 2.08 years and the second at the age of 10.10 years. The P1 latency does not fall within the normal range after a period of 9 months. This is very strong evidence that the time window between the two implants should be kept as short as possible.
- Not surprisingly there is an Expert Consensus and it was achieved during the conference in Marseille in June last year. The key statements are: Most would benefit from binaural CI. There is a – not yet fully understood - window of opportunity in children. Surgery carries a low risk and simultaneous procedure is to be considered from 6 months of age. Insurance companies and governments should fund bilateral CI. _____________________________________________________________________ Burdo, Gantz, Luntz, Manrique, Morera, Mueller, Robier The large majority of CI candidates or unilateral CI users could enjoy the benefit of binaural listening. As long as the better ear can not make efficient use of a hearing aid, bilateral CI is the only way to achieve binaural hearing. Maximum benefit in children will be achieved if binaural listening is enabled within a critical development period; i.e. as early in life as possible. The length of that critical period and impact of which is not yet fully understood. Preferably, suitable children should be provided with bilateral CI in one surgery, before the age of one. However, until today, most users received their second CI some time after the first, reporting excellent results. The risk associated with bilateral CI is very low and very acceptable above the age of 6 months. The scientific and clinical experience supports bilateral CI for appropriately selected candidates. Health insurances and governmental agencies should reimburse the procedure.
- Slide 22 Child with two implants Thank you for your attention!