FEATURE

Bilateral Cochlear Implantation for Children: What Do We Know and What Are We Still Learning About?

By Karen A. Gordon, PhD, Reg. CASLPO, CCC-A and Gina Sohn, M.Cl.Sc, AUD (C), Reg. CASLPO

Cochlear implants have made it possible for many children with severe to profound hearing loss to access speech sounds that they would

not be able to detect with very powerful hearing aids. As a result, many children with significant hearing loss have been able to develop

excellent speech and language. Over the past two decades, we have learned much about how cochlear implants work and who might

benefit from receiving one. However, there is still much more that we need to know. One of our current focuses is on the use of bilateral

cochlear implants in children.

What Are the Goals of Bilateral Cochlear Implants?
The aim of bilateral implantation is to take advantage of the fact that we have two ears to hear with. When both ears can hear,
the auditory nerves are able to compare the sounds reaching each of the ears. Of most interest is whether there are any timing
differences or any differences in intensity (or loudness) between the ears. For example, a sound coming from the right
will sound louder in the right ear than the left ear, and/or the right ear will hear the sound slightly sooner than the left ear.
These differences in timing and intensity help us to locate where sounds are coming from and help us to hear better in
noisy environments.

What’s wrong with Using Only One Cochlear Implant?
Unilateral cochlear implants have allowed many children to develop good speech and language skills. This was something
that was only a dream before cochlear implants were available. Yet, despite all the benefits, we must be aware that cochlear
implants do not restore normal hearing. For one thing, the cochlear implant cannot do all the things that the normal cochlea (inner ear)

can do. Also, there may be changes in the auditory system due to the hearing loss that we aren’t aware of. However, the most

obvious limitation is that children using a single cochlear implant hear from one side only.

Hearing from one side (unilateral hearing) is particularly difficult in noise. Of course, noise is everywhere! This means that a

child with unilateral hearing probably has more troubles hearing in the classroom, on the playground, and even at home than

in an audiologist’s sound booth. Unilateral hearing also affects the ability to tell which direction sound is coming from. Because

of this, children who have hearing loss in one ear or who use one cochlear implant need to use other cues (like their vision) to find

the person who is calling them or to figure out where that car horn was coming from. Clearly, this can be a safety issue and children

with unilateral hearing loss as well as children using a single cochlear implant should be encouraged to look around whenever they are

close to roads or traffic.

Do We Know if Bilateral Cochlear Implants Work?
We have provided bilateral cochlear implants to some of the children followed in our program through a research study. We are

assessing how the hearing nerves and brain respond to each implant separately and to both implants together. We are also looking
at whether the children are able to understand speech better with two cochlear implants versus one.

All families and children who would like to participate in our study are made aware that a second cochlear implant means a second
surgery which comes with all the risks of the first one. Many of these risks are understood and include the risks of anesthesia,
potential damage to the facial nerve, and loss of residual hearing. Other risks such as possible damage to the balance (vestibular) organs
are not yet clear. Thus, the decision to undergo bilateral cochlear implantation can be a difficult one particularly when a child appears to
be doing very well with one implant.

To date, over 100 children have received bilateral cochlear implants in our study. Most children were provided with their first
implant at young ages. We have divided the children into three groups according to the duration of unilateral implant use prior to
receiving the second implant: (1) children with more than 2 years of unilateral implant use; (2) children who use their first implant
for 6 to 12 months of unilateral implant use; and (3) children who receive both implants at the same time (simultaneously).

Our initial findings are that, in relatively easy listening environments (e.g., a quiet room), children find it easier to hear speech
with two cochlear implants rather than one. We think that this is because having input from both ears makes sounds louder and
thus easier to hear and understand. When we examine how well children can understand speech in noise, most children show
improvements in their scores when they are wearing both implants as opposed to just one. How much improvement one child
receives from a second device depends on many factors including where the speech and noise are located and when the second
implant was received. To determine what factors are most important, we are studying how the hearing nerves work and change in

children using bilateral cochlear implants.

We have found that most children benefit from auditory verbal therapy for their new implant just as they benefit from therapy for
their first implant. Children often don’t realize that it took time to understand sounds with their first implant and sometimes expect
to be hearing well from their second implant right away. We must be sure to counsel children and families of the challenges they may
face particularly in the beginning stages of bilateral implant use. We have not recommended removing the first implant for an
extended period of time after receiving a second cochlear implant but there are some centres which do encourage this.

We are continuing to explore how the hearing system changes when two cochlear implants are used in the children we are following.
We are measuring any differences between the ears, as well as tracking auditory abilities when both implants are worn. We
are also examining ways which might help the hearing nerves best compare the information provided by both implants.

Conclusions
Cochlear implant technology continues to evolve and we are beginning to learn how the auditory system develops with one or two
cochlear implants. Our research examines whether children receiving two implants can develop binaural hearing to help them hear
more easily. We are finding that there are some advantages for children when listening through both implants compared to one. As
always, our research goals are to provide children with severe-to-profound hearing loss the best opportunities to hear.

For further information please consult
Dr. Blake C. Papsin and Karen A. Gordon’s
“Bilateral Cochlear Implants Should be the Standard for Children with Bilateral Sensorineural Deafness” (Current Opinion in
Otolaryngology & Head and Neck Surgery 2008;16:69–74).

Karen A. Gordon, PhD, Reg. CASLPO, CCC-A,

is an assistant professor, Department of Otolaryngology, University of Toronto and director of research, The Cochlear Implant
Program, The Hospital for Sick Children.

Gina Sohn, M.Cl.Sc, AUD(C), Reg. CASLPO

is an audiologist in the Cochlear Implant Program at the Hospital for Sick Children.