Lateralization of Interimplant Timing and Level Differences in Children Who Use Bilateral Cochlear Implants

Abstract

Cochlear implants provide hearing to people who are deaf, by electrically stimulating the auditory nerve. Children with a single cochlear implant suffer deficiencies inherent to unilateral hearing, including inability to locate sounds. A second cochlear implant may improve sound localization, which normally requires interpretation of differences in sound intensity and time of arrival between two ears. Currently, it is unknown whether these cues are available to children who were provided with a second cochlear implant after a period of using one implant alone. We asked whether such children could interpret inter-implant level and timing cues. Results indicated that children using two cochlear implants detected level cues but had difficulty interpreting timing cues. Further, children rarely reported that sounds were perceived to come from the middle. Children receiving bilateral cochlear implants sequentially do not process bilateral auditory cues normally but can use inter-implant level cues to make judgments about where sound is coming from.ii

Congenital and Prolonged Adult-Onset Deafness Cause Distinct Degradations in Neural ITD Coding with Bilateral Cochlear Implants

“…This finding is consistent with psychophysical data indicating that prelingually deaf bilateral CI users who were implanted as adults are unable to lateralize sounds based on ITD, even though most are able to utilize ILDs (Litovsky et al 2010). Even when they are bilaterally implanted at a relatively young age (G 5 years) and use their implants daily, most prelingually deaf subjects still do not acquire ITD sensitivity (Salloum et al 2010). Possibly, these subjects might develop ITD sensitivity if they were implanted even earlier and simultaneously on both sides.…”

“…Bilateral CI users who were implanted as adults can lateralize electric pulse trains based on ITD if they lost hearing in late childhood or later, but not if they lost hearing earlier in life (Litovsky et al 2010). Most congenitally deaf children who use their implants daily do not learn to lateralize based on ITD, even though they do lateralize based on ILD (Salloum et al 2010). Animal models of bilateral CI show parallel deficits in ITD coding by inferior colliculus (IC) and auditory cortex neurons (Tillein et al 2009;Hancock et al 2010).…”

Binaural Interactions Develop in the Auditory Brainstem of Children Who Are Deaf: Effects of Place and Level of Bilateral Electrical Stimulation

“…We asked whether these cues were processed in the brainstem of children who use bilateral CIs. Behavioral results and unilaterally evoked eV amplitudes from this protocol have been previously reported (Salloum et al, 2010).…”

“…Conversion of microamperes to CUs differs slightly between different device generations which would make it difficult to compare data across devices and children. Therefore, for the purposes of data analysis, CUs were first converted into microamperes (A) and then into decibels (dB) as defined by the following formula: dB ϭ 20 log (A/B), where A is the delivered current (A) and B is 100 A. Unilaterally evoked eV amplitude data from electrode 18 at 5 different intensity levels from 19 of the 49 children have been previously reported (Salloum et al, 2010).…”

“…Interaural timing cues are particularly helpful for detecting speech in noise and attending to one sound source among many (Hawley et al, 2004;Akeroyd, 2006;Schnupp and Carr, 2009) but might be disrupted by two independently functioning CIs which are unable to convey fine timing information in speech. This leaves CI users with abnormal perception of binaural timing cues (van Hoesel, 2007;Litovsky et al, 2010;Salloum et al, 2010) and a reliance on interaural level cues for binaural processing. We asked whether these sound cues can be detected by the immature deaf auditory pathways in pediatric CI users.…”