Dec 2020 The Hearing Journal
Cochlear implants (CIs) have dramatically improved auditory, speech, and language outcomes for children with bilateral severe-to-profound sensorineural hearing loss (SNHL). However, too many children with CIs continue to display persistent language and literacy deficits despite early implantation and speech/language intervention. Research has shown that children tend to exhibit language delay equivalent to the duration of deafness prior to cochlear implantation. The source of delay can be at least partially attributed to a period of auditory deprivation prior to implantation; however, evidence also shows that the impoverished CI signal is also responsible as it fails to afford normal representation of incoming spectral detail.
CI programming in the clinic typically involves the mapping of incoming sound using a one-size-fits-all approach of current limiting, frequency allocation, channel stimulation rate, and stimulation of all electrodes in the array. For some recipients, it is likely that default programming parameters offer a fair approximation to the patient's individualised anatomy and electrode location and that activation of all electrodes yields optimal outcomes. For other recipients—particularly individuals exhibiting below-average outcomes, electrode dislocation, or extracochlear electrodes—a one-size-fits-all approach cannot afford the restoration of hearing that could be achieved had the recipient's anatomy and intracochlear electrode positioning been considered. Improving the quality of the CI signal can be achieved, at least partly, with clinical CI programming attempting to reduce channel interaction—or spread of electrical excitation patterns—which contributes to poor spectral resolution. Studies have shown improved spectral resolution using current focusing or selective electrode deactivation based on psychophysical measures or CT scans, which inform electrodeposition as well as electrode-to-modiolus distance. CT-based programming adjustments have been referred to as image-guided CI programming (IGCIP).
Our latest iteration of IGCIP uses automated electrode position analysis for CI users based on individualised cochlear anatomy done by comparing pre- and post-implant CT scans. However, if a patient does not have preoperative CT, it is not required for effective IGCIP application. Ultimately our goal is to drive improvements in auditory processing, which we hypothesise will improve “downstream” developmental domains, including speech and language, and subsequently, literacy skills.
Because children are routinely implanted in the first year of life, for the first three to five years following CI activation, we must rely on external factors for CI programming and verification of CI mapping. Such factors include CI “aided” audiometry, auditory skill development gauged via parental questionnaire, and progress on measures of language and speech production. Even if a child is making progress, using an individualised approach to CI programming could lead to better performance at a faster rate, resulting in greater overall outcomes. Indeed, we have documented that both adult and paediatric CI recipients exhibit significant benefit from individualised IGCIP on measures of speech recognition in quiet and noise with average improvement ranging from 10 to 15 percentage points.
The focus of our current NIH-funded clinical trial is to investigate the impact of personalised IGCIP in paediatric CI recipients on various measures of auditory, speech, and language outcomes. This research brings together the expertise of audiologists, speech-language pathologists, an otologist and engineers. This study is implementing a double-blind, waitlist deferred randomised clinical trial (RCT) design to describe how CI-mediated changes in basic auditory resolution drive benefit for speech perception, speech production, language, and literacy. We will be enrolling up to 72 children with CIs who are 6-12 years old. Half of the sample will be randomised to immediate IGCIP intervention following baseline assessment. The other half will be randomised to deferred IGCIP intervention for which they will receive the custom program at the one-year point. All children will be studied for two years, with auditory and speech perception assessments completed semi-annually and speech production, language, and literacy assessments completed annually.