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.