Comparison of Place-versus-Pitch Mismatch between a Perimodiolar and Lateral Wall Cochlear Implant Electrode Array in Patients with Single-Sided Deafness and a Cochlear Implant

Abstract

Background: In electric-acoustic pitch matching experiments in patients with single-sided deafness and a cochlear implant, the observed “mismatch” between perceived pitch and predicted pitch, based on the amended Greenwood frequency map, ranges from –1 to –2 octaves. It is unknown if and how this mismatch differs for perimodiolar versus lateral wall electrode arrays. Objectives: We aimed to investigate if the type of electrode array design is of influence on the electric-acoustic pitch match. Method: Fourteen patients (n = 8 with CI422 + lateral wall electrode array, n = 6 with CI512 + perimodiolar electrode array; Cochlear Ltd.) compared the pitch of acoustic stimuli to the pitch of electric stimuli at two test sessions (average interval 4.3 months). We plotted these “pitch matches” per electrode contact against insertion angle, calculated from high-resolution computed tomography scans. The difference between these pitch matches and two references (the spiral ganglion map and the default frequency allocation by Cochlear Ltd.) was defined as “mismatch.” Results: We found average mismatches of –2.2 octaves for the CI422 group and –1.3 octaves for the CI512 group. For any given electrode contact, the mismatch was smaller for the CI512 electrode array than for the CI422 electrode array. For all electrode contacts together, there was a significant difference between the mismatches of the two groups (p < 0.05). Results remained stable over time, with no significant difference between the two test sessions considering all electrode contacts. Neither group showed a significant correlation between the mismatch and phoneme recognition scores. Conclusion: The pitch mismatch was smaller for the perimodiolar electrode array than for the lateral wall electrode array.

Place Coding in the Human Cochlea

“…A patient with auditory neuropathy spectrum disorder (with present distortion product otoacoustic emissions-DPOAEs) was also tested, revealing an expected shift towards Greenwood 17 and Stakhovskaya et al 6 with reduction in stimulus level to the limits of the equipment. Stimulation at conversational speech levels showed responses similar to high-level stimulation rather than threshold, suggesting that frequency place maps during conversation are more similar to those reported in pitch-matching experiments with cochlear implants 21 than those described by the Greenwood equation (Fig. 3).…”

Three-Dimensional Modeling and Measurement of the Human Cochlear Hook Region: Considerations for Tonotopic Mapping

“…Cochlear size and shape vary significantly across individuals resulting in variable place-pitch maps (1)(2)(3)(4). However, current cochlear implants (CI) are programmed using a generalized pitch-mapping scheme for all patients, resulting in suboptimal hearing outcomes (5)(6)(7)(8)(9). When a generalized pitch-mapping approach is used, each electrode within a CI array will stimulate with a prespecified frequency, independent of a patient's individual tonotopy or postoperative electrode location.…”

“…When individual tonotopy is ignored, specific portions of the auditory nerves can be stimulated with an incorrect frequency, resulting in a perceived pitch mismatch. Current generalized pitch maps have been reported to result in pitch mismatches of over one octave (6). This mismatch inhibits the pitch perception required for complex hearing tasks such as music appreciation and tonal language understanding (7)(8)(9).…”

Characterization of the human helicotrema: Implications for cochlear duct length and frequency mapping

“…CIs currently have limitations due to their insertion depth and the resolution of electrode stimulation, however this hypothetical situation provides evidence that the size of the helicotrema has a measurable effect on the frequency distribution and perception in individuals. Generalized CI pitch-maps have been reported to result in a pitch-mismatch of over one octave [28,29], due to variance in cochlear size and difficulties measuring the BM in the helicotrema and hook region. Accurate modelling of the helicotrema has the potential to reduce a portion of this error.…”