Hearing with Hearing with two ears two ears is better than with one

Dr. Dr. hc. Monika Lehnhardt

May 2008

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.

How many bilateral Nucleus cochlear implant recipients are there

currently worldwide?

More than 5’500

As of March 2008

of whom approximately 80% of whom approximately 80% are under the age of 18.

Sound arrives earlier and louder

Sound arrives later and softerSound arrives later and softer

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.

Why is Binaural Hearing important?

With a second CI, With a second CI, precision to localise sound precision to localise sound more than doubles!more than doubles!

Mean angularerror:

Unilateral CI: 67°

Unilateral CI: 67°

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

Improved sound localisation

Bilat

eral

CI:

24°

Bilat

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CI:

24°

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Speech +45 Noise -45

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CI closest to speech

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Improved speech understanding in noise

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.

With a second CI, speech understanding in noise can increase by a factor of 9

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

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.

Mean improvement of 10dB in Critical SNR for 50% speech recognition for Oldenburger sentences

Speech Noise

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.

*

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

Noise

Up to 3 dB improvement in SNR for speech recognition

*

Cochlear White paper B. Robert Peters et al., Rationale for Bilateral Cochlear Implantation in Children and Adults. 2006

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

Speechand Noise

Speecand Noise

1 – 2 dB increase in perceived loudness

Cochlear White Paper. B. Robert Peters et al., Rationale for Bilateral Cochlear Implantation in Children and Adults. 2006

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

Are two ears better than one?

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.

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

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)

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

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.

1. B. Robert Peters et al., Rationale for Bilateral Cochlear Implantation in Children and Adults. 2006

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)

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

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.

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.

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)

Age and Inter Implant IntervalP

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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.

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.

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.