Evaluating the Impact of Age, Acoustic Exposure, and Electrical Stimulation on Binaural Sensitivity in Adult Bilateral Cochlear Implant Patients

Abstract

Deafness in both ears is highly disruptive to communication in everyday listening situations. Many individuals with profound deafness receive bilateral cochlear implants (CIs) to gain access to spatial cues used in localization and speech understanding in noise. However, the benefit of bilateral CIs, in particular sensitivity to interaural time and level differences (ITD and ILDs), varies among patients. We measured binaural sensitivity in 46 adult bilateral CI patients to explore the relationship between binaural sensitivity and three classes of patient-related factors: age, acoustic exposure, and electric hearing experience. Results show that ILD sensitivity increased with shorter years of acoustic exposure, younger age at testing, or an interaction between these factors, moderated by the duration of bilateral hearing impairment. ITD sensitivity was impacted by a moderating effect between years of bilateral hearing impairment and CI experience. When age at onset of deafness was treated as two categories (<18 vs. >18 years of age), there was no clear effect for ILD sensitivity, but some differences were observed for ITD sensitivity. Our findings imply that maximal binaural sensitivity is obtained by listeners with a shorter bilateral hearing impairment, a longer duration of CI experience, and potentially a younger age at testing. 198/200.

Sound source localization patterns and bilateral cochlear implants: Age at onset of deafness effects

“…Together these factors capture information relevant to a listener’s early and later auditory deprivation and experience. For additional details, please see [ 4 ]. To determine which factors to include in regression models associated with the different measures of performance, we used the step function in the lmerTest package for mixed-effects models and stats package for fixed-effects models in R. This performs stepwise model comparison to determine the model with the smallest Akaike information criterion (i.e., a measure of predictive power similar to adjusted R 2 in regression), removing factors that provide the least prediction and balancing the number of parameters with the increased model fit.…”

“…There is extensive literature documenting the impact of patient-dependent factors on localization error for listeners with BiCIs. Several factors associated with auditory deprivation and experience with BiCIs are predictive of sensitivity to cues used for localization, outlined by Thakkar and colleagues [ 4 ]. Age at onset of deafness [ 5 – 11 ], the duration of experience with unilateral or bilateral, acoustic or CI stimulation [ 5 , 6 , 8 , 10 , 12 – 14 ], and age at testing [ 15 – 17 ] are predictive of localization performance in children and adults.…”

Reweighting of Binaural Localization Cues in Bilateral Cochlear-Implant Listeners

“…In addition, perceptual factors play a role in the low contribution of ITDs in electric hearing. Even when ITDs are presented under the most favorable conditions (i.e., via the pulse timing and at a single interaurally place-matched electrode pair, directly stimulated via a research interface using the most sensitive pulse rate), CI listeners’ ITD sensitivity is lower and much more variable across listeners compared to that of NH listeners (Laback et al 2007 ; Majdak et al 2006 ; van Hoesel 2007 ; Thakkar et al 2020 ). Several explanations have been proposed for this perceptual deficit in electric hearing (see Laback et al 2015 , for a review).…”

“…For instance, deprivation of binaural experience due to long periods before or between implantation on both ears results in cortical anomalies (Gordon et al 2010 ) as well as degraded neural ITD coding (Chung et al 2019 ; Hancock et al 2010 ). Accordingly, Thakkar et al ( 2020 ) reported that ITD sensitivity is related to the duration of bilateral hearing impairment and to CI experience. Another factor may be a mismatch between stimulation rate and membrane and synaptic parameters of binaural cells, which may explain the decline in sensitivity with increasing rate (Chung et al 2015 ).…”

Central Auditory Plasticity from Molecules to Behavior

“…Improving binaural hearing has become highly relevant in clinical settings due to the appreciation of deaf patients’ needs to communicate and function in realistic, complex auditory environments. The study by Thakkar and colleagues [ 6 ] aimed to unrevealed how age-related, acoustic, and electric experience impact binaural sensitivity in adults with bilateral cochlear implants. Individuals with unilateral cochlear implant have difficulty with pitch perception, and adding a hearing aid in the non-implanted ear is potentially beneficial.…”