Design and Evaluation of a Cochlear Implant Strategy Based on a “Phantom” Channel

Abstract

Unbalanced bipolar stimulation, delivered using charge balanced pulses, was used to produce “Phantom stimulation”, stimulation beyond the most apical contact of a cochlear implant’s electrode array. The Phantom channel was allocated audio frequencies below 300Hz in a speech coding strategy, conveying energy some two octaves lower than the clinical strategy and hence delivering the fundamental frequency of speech and of many musical tones. A group of 12 Advanced Bionics cochlear implant recipients took part in a chronic study investigating the fitting of the Phantom strategy and speech and music perception when using Phantom. The evaluation of speech in noise was performed immediately after fitting Phantom for the first time (Session 1) and after one month of take-home experience (Session 2). A repeated measures of analysis of variance (ANOVA) within factors strategy (Clinical, Phantom) and interaction time (Session 1, Session 2) revealed a significant effect for the interaction time and strategy. Phantom obtained a significant improvement in speech intelligibility after one month of use. Furthermore, a trend towards a better performance with Phantom (48%) with respect to F120 (37%) after 1 month of use failed to reach significance after type 1 error correction. Questionnaire results show a preference for Phantom when listening to music, likely driven by an improved balance between high and low frequencies.

Validation of a Cochlear Implant Patient-Specific Model of the Voltage Distribution in a Clinical Setting

“…For example, FEM models are used to analyze simultaneous stimulation sound coding strategies (Kalkman et al, 2014, 2016). These strategies try to shape or focus the electrical field to be more focused and to produce different pitch sensations (Nogueira et al, 2009, 2015a). Patient-specific 3D volume conduction models can be used to optimize the parameters of the focusing and the current steering coefficients (Litvak et al, 2007).…”

“…The fitting levels (loudness perception) depend not only on the current spread in the cochlea but also on the auditory nerve activity. As shown in this manuscript, the voltage predicted by the volume conduction model can be sampled at the auditory nerve positions and coupled to an auditory nerve model (Smit et al, 2008; Nogueira et al, 2015a,b). Such a model could be used to predict the loudness of sound and is a potential tool to speed up and objectivize the fitting procedure.…”

“…New sound coding strategies use multiple electrode stimulation to perform electric field shaping (e.g., Litvak et al, 2007; Landsberger et al, 2012; Nogueira et al, 2015a). However, multiple electrode CI coding strategies require precise knowledge of the voltage distribution and current flow within an electrically stimulated cochlea (Kalkman et al, 2014).…”

Assessment and improvement of sound quality in cochlear implant users

“…The study findings showed that CI users with greater apical stimulation reported sound quality ratings that more closely resembled their NH counterparts, suggesting superior sound quality perception. More recently, a sound processing strategy called partial bipolar stimulation emerged as means to expand low‐frequency range available to CI users 55, 56. Partial bipolar stimulation relies on current steering to create virtual “phantom” channels that extend beyond the physical end of an electrode array.…”

“…A study enrolling 12 post‐lingually deaf CI users compared Phantom stimulation to the standard Advanced Bionics HiRes Fidelity 120 processing strategy. Although there was no significant difference between Phantom and the control processing strategy for most components of the music questionnaire, Phantom CI users reported a statistically significant difference in improved sound balance and preferred listening to music using this strategy 55. In another recent study, Munjal et al51 utilized the CI‐MUSHRA to find that creation of a phantom electrode through partial bipolar stimulation allowed for superior (more normalized) sound quality perception relative to Fidelity 120 processing strategy.…”