Relationship Between Electrocochleography, Angular Insertion Depth, and Cochlear Implant Speech Perception Outcomes

Abstract

Objectives: Electrocochleography (ECochG), obtained before the insertion of a cochlear implant (CI) array, provides a measure of residual cochlear function that accounts for a substantial portion of variability in postoperative speech perception outcomes in adults. It is postulated that subsequent surgical factors represent independent sources of variance in outcomes. Prior work has demonstrated a positive correlation between angular insertion depth (AID) of straight arrays and speech perception under the CI-alone condition, with an inverse relationship observed for precurved arrays. The purpose of the present study was to determine the combined effects of ECochG, AID, and array design on speech perception outcomes. Design: Participants were 50 postlingually deafened adult CI recipients who received one of three straight arrays (MED-EL Flex24, MED-EL Flex28, and MED-EL Standard) and two precurved arrays (Cochlear Contour Advance and Advanced Bionics HiFocus Mid-Scala). Residual cochlear function was determined by the intraoperative ECochG total response (TR) measured before array insertion, which is the sum of magnitudes of spectral components in response to tones of different stimulus frequencies across the speech spectrum. The AID was then determined with postoperative imaging. Multiple linear regression was used to predict consonant-nucleus-consonant (CNC) word recognition in the CI-alone condition at 6 months postactivation based on AID, TR, and array design. Results: Forty-one participants received a straight array and nine received a precurved array. The AID of the most apical electrode contact ranged from 341° to 696°. The TR measured by ECochG accounted for 43% of variance in speech perception outcomes (p < 0.001). A regression model predicting CNC word scores with the TR tended to underestimate the performance for precurved arrays and deeply inserted straight arrays, and to overestimate the performance for straight arrays with shallower insertions. When combined in a multivariate linear regression, the TR, AID, and array design accounted for 72% of variability in speech perception outcomes (p < 0.001). Conclusions: A model of speech perception outcomes that incorporates TR, AID, and array design represents an improvement over a model based on TR alone. The success of this model shows that peripheral factors including cochlear health and electrode placement may play a predominant role in speech perception with CIs.

Insertion Depth and Cochlear Implant Speech Recognition Outcomes: A Comparative Study of 28- and 31.5-mm Lateral Wall Arrays

“…Importantly, recent work has established that there are likely differential effects dependent on array design (i.e., lateral wall vs precurved) (10,11). When restricting this analysis to lateral wall arrays, studies have shown a positive correlation between AID and speech recognition (6)(7)(8)(9)(10)15,18). This is generally understood to be related to beneficial effects of a closer alignment between the electric speech information and tonotopic organization of the cochlea (18)(19)(20)(21)(22)(23)(24), in addition to distributing speech information across greater channel spacing -theoretically allowing for excitation of discrete neuronal populations (e.g., reduced channel interaction) (18).…”

“…Previous studies investigating the influence of electrode array insertion depth on speech recognition are conflicting, with some demonstrating a decrement in performance with deeper insertions (1,4,13), and others showing a benefit (6)(7)(8)(9)15,17,18). Importantly, recent work has established that there are likely differential effects dependent on array design (i.e., lateral wall vs precurved) (10,11). When restricting this analysis to lateral wall arrays, studies have shown a positive correlation between AID and speech recognition (6)(7)(8)(9)(10)15,18).…”

Promontory Electrocochleography Recordings to Predict Speech-Perception Performance in Cochlear Implant Recipients

“…There were no surgical factors accounted for within this study. Previous studies have shown that greater insertion depths (13) and scala tympani insertions (3,11,28–32) are correlated with superior speech-perception performance. The location of the electrode within the cochlea likely matters, and investigations are underway examining these factors to build a multivariate model using promontory ECochG-TR to predict CI performance.…”

Longitudinal Electrocochleography as an Objective Measure of Serial Behavioral Audiometry in Electro-Acoustic Stimulation Patients

“…Our present study provides a new application of post-operative ECoG in monitoring residual hearing and understanding the pathophysiology of delayed hearing loss. In a future study, we will explore further applications of post-operative ECoG, including the relationship between post-operative ECoG and speech perception, as most data in the literature focuses interoperative ECoG at time of surgery and correlating that with outcome measures (Fontenot et al, 2019, Canfarotta et al, 2021; Walia et al, 2022). In addition, while our measures were conducted using in-house custom-built equipment, cochlear implant companies are also designing and implementing hardware and software adaptations so that their own systems can be used for ECoG recordings.…”

“…CM and ANN thresholds correlate strongly with behavioral audiometric thresholds (Abbas et al, 2017; Koka et al, 2017), which can aid with programming the hearing aid portion of the EAS sound processor (Agrawal et al, 2021). Intraoperative measures of ECoG are used to guide cochlear implantation to minimize cochlear trauma (Bester et al, 2022; Lenarz et al, 2022) and have been shown to correlate with post-operative speech understanding (Fontenot et al, 2019; Canfarotta et al, 2021; Walia et al, 2022). One important aspect of ECoG that hasn’t been sufficiently validated is the long-term stability of these measures.…”