Association Between Flat-Panel Computed Tomographic Imaging-Guided Place-Pitch Mapping and Speech and Pitch Perception in Cochlear Implant Users

Abstract

Importance: Cochlear implant users generally display poor pitch perception. Flat-panel computed tomography (FPCT) has recently emerged as a modality capable of localizing individual electrode contacts within the cochlea in vivo. Significant place-pitch mismatch between the clinical implant processing settings given to patients and the theoretical maps based on FPCT imaging has previously been noted.

Objective: To assess whether place-pitch mismatch is associated with poor cochlear implant-mediated pitch perception through evaluation of an individualized, image-guided approach toward cochlear implant programming on speech and music perception among cochlear implant users.

Design, setting, and participants: A prospective cohort study of 17 cochlear implant users with MED-EL electrode arrays was performed at a tertiary referral center. The study was conducted from June 2016 to July 2017.

Interventions: Theoretical place-pitch maps using FPCT secondary reconstructions and 3-dimensional curved planar re-formation software were developed. The clinical map settings (eg, strategy, rate, volume, frequency band range) were modified to keep factors constant between the 2 maps and minimize confounding. The acclimation period to the maps was 30 minutes.

Main outcomes and measures: Participants performed speech perception tasks (eg, consonant-nucleus-consonant, Bamford-Kowal-Bench Speech-in-Noise, vowel identification) and a pitch-scaling task while using the image-guided place-pitch map (intervention) and the modified clinical map (control). Performance scores between the 2 interventions were measured.

Results: Of the 17 participants, 10 (58.8%) were women; mean (SD) was 59 (11.3) years. A significant median increase in pitch scaling accuracy was noted when using the experimental map compared with the control map (4 more correct answers; 95% CI, 0-8). Specifically, the number of pitch-scaling reversals for notes spaced at 1.65 semitones or greater decreased when an image-based approach to cochlear implant programming was used vs the modified clinical map (4 mistakes; 95% CI, 0.5-7). Although there was no observable median improvement in speech perception during use of an image-based map, the acute changes in frequency allocation and electrode channel deactivations used with the image-guided maps did not worsen consonant-nucleus-consonant (-1% correct phonemes, 95% CI, -2.5% to 6%) and Bamford-Kowal-Bench Speech-in-Noise (0.5-dB difference; 95% CI, -0.75 to 2.25 dB) median performance results relative to the clinical maps used by the patients.

Conclusions and relevance: An image-based approach toward ochlear implant mapping may improve pitch perception outcomes by reducing place-pitch mismatch. Studies using a longer acclimation period with chronic stimulation over months may help assess the full range of the benefits associated with personalized image-guided cochlear implant mapping.

Conflict of interest statement

Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Limb serves as a member of the medical advisory board and receives research funding and support from Advanced Bionics Corporation, is a consultant and has served as scientific chair of the Music Advisory Board for Med-El Corporation, and is a chief medical officer for Oticon Medical, Spiral Therapeutics, and Frequency Therapeutics. No other disclosures were reported.

Figures

Figure 1.. Assessment of Cochlear Implants In Vivo Using High-Resolution Secondary Reconstructions of Flat-Panel Computed Tomographic Imaging

A, Six right-sided cochlear implants are depicted. B, Six left-sided cochlear implants are depicted. The following measures were used in this study: voxel size, 0.02 mm; 512 × 512 section matrix; Hounsfield units kernel types; sharp image characteristics; 0.5-mm distance; and 0.1-mm image thickness.

Figure 2.. User Interface for the Pitch-Scaling Task

A, Participants were presented with sets of 6 or 11 acoustic tokens of random order spanning a defined frequency spectrum on a logarithmic scale. B, Participants were instructed to rank these acoustic tokens from lowest to highest pitch on a 100-point scale, where 0 was defined as the lowest pitch and 100 was defined as the highest pitch in the set. The play all button allows the participant to play the acoustic tokens in the order that they ranked the tones. If the listener could not distinguish between any of the tones, they were instructed to select the all stimuli are the same button.

Figure 3.. Speech Perception Performances While Using the Modified Clinical Map vs the Image-Based Experimental Map

There was no significant difference between the consonant-nucleus-consonant test (150 phonemes per list) (A) and Bamford-Kowal-Bench Speech-in-Noise test (B) (−1.0% correct phonemes; 95% CI, −2.5% to 6.0%). On average, cochlear implant users did better on the Iowa vowel recognition test (80 trials) (C) when using their modified clinical maps compared with their image-based experimental maps (12% increase in correct vowel recognition; 95% CI, 1%-17%). FPCT indicates flat-panel computed tomography. Error bars indicate 95% CIs. aStatistical significance with P < .05.

Figure 4.. Mean Performance Data for the Pitch-Scaling Task Using the Modified Clinical Map vs the Image-Based Experimental Map

A, Number of mistakes in the pitch-scaling task using the modified clinical map vs the image-based experimental map. The left column compares the total number of mistakes made during the pitch-scaling task between the control and experimental groups. These mistakes were broken down into subcategories: minor pitch reversals, major pitch reversals, and inability to discriminate between 2 pitches. There was a significant median difference of 4 more correct answers (95% CI, 0-8) in the pitch-scaling task with the experimental map compared with the control map. A Wilcoxon signed rank test determined that there was a significant increase in the number of major pitch reversals made with use of the control map compared with the experimental map (difference of 4 in number of mistakes; 95% CI, 0.5-7 mistakes). B, The association between the pitch-place map and frequency range and the number of pitch-scaling mistakes. Low-frequency range was defined as 70 to 300 Hz; midfrequency range, 301 to 2000 Hz; and high-frequency range, 2001 to 8500 Hz. A significant difference was noted in the total number of low-frequency (mean [SD] 5.100 [1.046]; 95% CI, 2.258-7.942) and high-frequency (mean [SD] 3.167 [0.804]; 95% CI, 0.981-5.352) range mistakes made in the pitch-scaling task between the control and the experimental maps. Error bars indicate 95% CIs. FPCT indicates flat-panel computed tomography.

Figure 5.. Place-Pitch Mismatch Among 17 Cochlear Implant Users

Each gray dot depicts 1 of 12 electrode channels along the scala tympani. The black numbers along the medial edge of the cochlea report the mean theoretical center frequencies (hertz), using the modified Greenwood function, and flat-panel computed tomographic imaging. Along the lateral aspect of the bony canal is the degree (hertz) to which the clinical map center frequency overshot (blue) or undershot (red) the image-guided map theoretical frequency. Within parenthesis is the aggregated percentage distance from the base of the organ of Corti for that particular electrode channel.