Bilateral versus Unilateral Implants for Deaf Children

The issue

For over three decades, unilateral cochlear implants (CIs) have provided hearing to children with severe-profound hearing loss, although they do not restore normal hearing. With improving technology over time, there have been enormous improvements in speech perception outcomes for children with CIs. However, good speech perception ability does not ensure age-appropriate outcomes in learning and development for all children. Although many children with CIs have been able to develop spoken language and other skills that would not have been possible with conventional hearing aids, others are still delayed in their development of language, speech production, literacy, academic, and social skills. For a significant number of children, these developmental delays have remained or increased through to adulthood.

Until recently, it was considered that a single CI was sufficient for children. However, we were born with two ears for a reason. For a child with hearing in both ears, there are several listening advantages: the brain can focus on the sound source closest to the listener and ‘block out’ the input from the ear closest to the noise, and can also ‘add up’ information from both ears, resulting in the perception of a louder signal. In difficult listening conditions, such as the noisy classrooms or playgrounds that children spend most of their day in, children with a unilateral CI will experience significant difficulties, and the amount and quality of speech they are exposed to will be reduced compared to that for children with normal hearing. Understanding speech in background noise and speakers in group conversations are examples of such difficulties. Being able to locate the sound source in space and focus on that also gives a great advantage to being able to understand what is being said. Without these listening advantages, it is unlikely that children with unilateral CIs will have the ability to learn incidentally through ‘overhearing’, as do children with normal hearing, and this may limit their development. Although it is accepted that bilateral CIs offer additional speech perception and localization benefits to many children with severe-profound hearing loss, whether these benefits lead to significantly better real-life development in language, academic performance, and social development has only very recently been established.

What we know

A few recent studies have investigated outcomes for children with unilateral and bilateral CIs across a wide range of real-life outcomes, and have also looked at what predicts better outcomes for these children. There has also been research into whether, for children who have bilateral CIs, these should be given simultaneously or sequentially. So far, the evidence shows that:

  • On average, children with bilateral CIs develop vocabulary and language faster than do children using unilateral CIs.
  • On average, children with bilateral CIs achieve significantly better academic outcomes (in maths, oral and written language) in elementary school than do children with unilateral CIs.
  • Elementary school-aged children with bilateral CIs experience significantly fewer difficulties with emotional development and peer relationships.
  • Having bilateral CIs earlier significantly improves outcomes across all areas of development.
  • High levels of parental involvement, less screen time, and more time spent by adults reading to children (when young) and time spent by children reading to themselves facilitate significantly better vocabulary, language, academic and social outcomes for children with both unilateral and bilateral CIs.

What we don’t know

  • There is a lack of evidence about what happens once children leave elementary school, and particularly when they are young adults. We don’t know how what the longer term outcomes are for older children with early unilateral and bilateral CIs.
  • Although children with simultaneous bilateral CIs appear to adjust to wearing two devices more easily, and the risk of rejection of one device appears lower, we don’t know whether there is a difference in developmental outcomes for children with simultaneous CIs compared to those with sequential CIs.

Implications

A decision faced by many parents who have children with bilateral severe-profound hearing loss is whether to give their child unilateral or bilateral CIs. Factors such as surgical risk, cost, and ongoing maintenance and expenses come into play in making this decision. Evidence of the significant benefits from bilateral CIs may be helpful in the decision-making process.

Parents are the most important conversation partners and teachers for their children, particularly when they are young. They should be empowered with knowledge about how greatly they can influence their children’s development, and supported to implement parenting practices such as reading to their children that will facilitate the best possible outcomes.

Posted on October 2, 2018 by
Julia Sarant
Department of Audiology & Speech Pathology
The University of Melbourne, Australia

 

Further reading