DOI: 10.5061/dryad.jh9w0vtm2
title: Speech, timbre, and pitch perception in cochlear implant users after chronic use with flat panel CT-based frequency reallocations

description: Cochlear implants (CI) utilize default frequency allocation tables (“pitch
 maps”) to distribute the frequency range important for speech perception
 across their electrode array. Default pitch maps do not address the
 significant pitch-place mismatch that is inherent in cochlear
 implantation, nor the variability between subjects or array lengths.
 Recent research has utilized postoperative high-resolution flat-panel
 computed tomography (CT) imaging to measure the precise location of
 electrode contacts within an individual's cochlea, to generate a
 custom pitch map and decrease the pitch-place mismatch. The objective was
 to determine whether chronic use of CT pitch maps would improve CI user
 performance in the areas of speech and music perception, as compared to
 the non-custom default pitch maps provided by the CI
 manufacturer. A cohort of 10 experienced CI users (14 CI ears)
 were recruited to receive CT scans and then use a custom CT pitch map for
 1 month. The efficacy of these maps was measured using a battery of speech
 and music tests. No change was found at the group level; however,
 large inter-subject variability of the benefit of the CT maps was
 correlated to CI electrode array placement. This application of a custom,
 strict CT mapping is not beneficial for all CI users. Results may be
 limited by long acclimation periods to default pitch maps before CT map
 usage.
description: Subjects Study subject demographics,
 describe the 10 MED-EL cochlear implant (CI) participants (14 CI ears).
 Four men and six women participated, with an average age of 64.3 ± 12.2
 years. All participants were adults with at least 6 months of CI listening
 experience, implanted with a MED-EL CI, postlingually deafened, native
 speakers of American English, and used oral/aural communication as their
 primary modality of communication. The mean length of CI use was 3.6 ± 1.8
 years and the mean duration of severe-profound hearing loss before
 implantation was 6.9 ± 9.6 years. The CI users utilized a variety of sound
 processor models and processing strategies. Subjects were excluded if they
 had intracochlear electrodes with open or short circuits, 4 or more
 extracochlear electrodes (≥1/3 of the array), or documented concomitant
 conditions that may affect performance (e.g., cognitive impairment). The
 Institutional Review Board at the University of California, San Francisco
 (UCSF) approved this study and informed consent was obtained from all
 participants. Study Design
 Experienced CI recipients were asked to use a CT experimental
 pitch map, full-time, for one month. Subjects completed a battery of
 speech and music tasks at the beginning and end of month on both their
 clinical (Clin) and experimental (Exp) pitch maps. CI users entered the
 study with chronic exposure (6+ months) to their clinical pitch maps. Our
 primary hypothesis, namely that CT mapping would improve speech and music
 perception, was thus best revealed by comparing performance following
 chronic use of each map, specifically the clinical map at the first test
 session and the experimental CT map at the second test session.
 CT Experimental Map The CT map experimental
 was intended to create a strict tonotopic pitch map while utilizing the
 full 70-8500Hz bandwidth available in the CI software. To this end, the
 characteristic frequency (CF) of each electrode was calculated and, in the
 CI programming software, the center of each channel band was matched to a
 corresponding electrode CF. This approach created a frequency allocation
 table that minimized pitch-place mismatch, such that frequencies of
 incoming sounds were directed to the most anatomically correct location in
 the cochlea. If there were electrodes whose CFs fell too far outside the
 programmable frequency range (&gt;4 semitones from a channel center),
 then they were deactivated. The only fitting aspect that was explicitly
 changed for the CT maps was the frequency allocation table. Other fitting
 parameters, such as upper and lower electrical stimulation levels, for
 example, were held constant between the clinical and experimental
 maps. Test Conditions All study
 participants used their sound processors for the chronic trial period(s)
 and any corresponding speech and music testing. Speech and music stimuli
 were presented at 65 dBA and the non-test ear was masked. All CI users
 were asked if they could hear the test stimuli with the non-test ear while
 the CI on their test ear was turned off; all subjects confirmed being
 unable to hear the test stimuli with the non-test ear.
 During speech and music testing, any additional sound processing
 (i.e., directional microphones, steady-state noise reduction algorithms)
 were deactivated, and the volume and sensitivity settings were fixed to
 100% and 75%, respectively. Upper stimulation levels (MCLs) for bilateral
 users were globally adjusted as needed to ensure a comfortable listening
 level in both ears; any global MCL adjustments needed for testing were
 replicated in both control and experimental fittings.
 Participants completed the experiment using a tablet computer
 (Microsoft Surface Pro 3) and were given the option of using a touchscreen
 or mouse. The computer ran the speech and music stimuli with the following
 software programs: Windows Media Player (v12, 2009), MATLAB (vR2012b,
 Mathworks, Natick, MA, USA), and LabView (v11.0, National Instruments,
 Austin, TX, USA). Test Metrics
 CNC Words and Phonemes The
 Consonant-Nucleus-Consonant (CNC) Monosyllabic Word Test (Peterson and
 Lehiste, 1962),used to test recognition of open-set monosyllabic words in
 quiet, was sourced from the Minimum Speech Test Battery for Adult CI Users
 (Luxford et al., 2001; MTSB, 2011).  Sentences in
 Noise The Bamford-Kowal-Bamford Speech-in-Noise
 (BKB-SIN) Test (Bench, Kowal and Bamford, 1979; Etymōtic Research, 2005;
 Luxford et al., 2001) employs a modified adaptive approach wherein
 sentences are presented at a fixed level and four-talker babble (Auditec
 of St. Louis, 1971) is presented at increasingly more difficult
 signal-to-noise ratios (SNRs). An SNR-50 score was calculated for each
 sentence list-pair, which represents the level of SNR (in dB) at which the
 subject correctly recognized exactly half of the keywords
 throughout.  Synthetic Vowels The
 Iowa Medial Vowel Test (Tyler et al.,1986) utilizes eight synthetic vowel
 stimuli presented in an ‘‘/h/vowel/d/’’ context (e.g., had, hid, heed,
 etc.). After familiarization with a practice module with the test
 interface and all eight stimuli, the subject then completed a closed-set
 test with five blocks of eight tokens each, where the token stimulus order
 was randomized. The test was administered twice, yielding 80 total
 trials.  Timbre Discrimination
 Musical timbre is conveyed by spectrotemporal features, beyond
 fundamental frequency and amplitude, that give a particular sound its
 characteristic tone color. Timbre perception is typically examined using
 musical instrument identification tasks that generally reveal poor
 performance in cochlear implant (CI) users (Kang et al., 2009; Gfeller et
 al., 2002; Spitzer et al., 2008). Relatively little is known, however,
 regarding timbre discrimination—the ability to differentiate between two
 notes of different timbres—a task which may provide greater insight into
 CI-mediated listening than whether or not instruments can be correctly
 identified. A task developed by the present
 investigators was used to measure timbre discrimination through acoustic
 blends of source instruments (clarinet, flute, French horn, tuba, violin,
 and cello) which were combined in varying amplitude ratios while
 maintaining constant overall volume (Gilbert et al., 2019a). Higher
 performance on the timbre discrimination task indicates better ability to
 distinguish between musical instrument stimuli using timbre-related cues
 only.  Pitch Ranking Our lab
 designed a test paradigm to characterize pitch height (for pure tones)
 across the entire stimulable frequency range of the MED-EL CI (70-8500Hz)
 (Jiam et al., 2019). Better performance on this task is indicated by a
 lower number of errors. During the analysis of this test, we
 dropped/didn’t count the errors/responses that corresponded to areas of
 the frequency range where the Clinical and CT Maps were overlapping.
 Overlapping was defined as the upper ends of the channels and the lower
 ends of the channels were each within 3 ST of each other. 
 Statistical Analysis All statistical
 analyses were completed in JASP software (JASP, Version 0.18.3; Amsterdam,
 Netherlands) using p&lt;0.05 to determine statistical significance.
 The primary comparison of interest was between performance with the
 incoming Clinical Map and following one month of chronic use of the
 Experimental Map. Shapiro-Wilk tests were used to test normal distribution
 of the data. All the performance test results were normally distributed,
 and so paired sample student t-tests assessed whether mean performance on
 the clinical and experimental maps were different. Linear correlations
 between test results and subject- or ear-specific factors (i.e., CI array
 alignment, demographic data, and hearing history) were explored with
 either Pearson’s r (for parametric) or Spearman’s rho (for non-parametric)
 tests. 
description: # Speech, timbre, and pitch perception in cochlear implant users after
 chronic use with flat panel CT-based frequency reallocations
 [https://doi.org/10.5061/dryad.jh9w0vtm2](https://doi.org/10.5061/dryad.jh9w0vtm2) Data is in comma-separated value format. ## Description of the data and file structure The top row is headers. Each subsequent row represents one ear in the study. * ID: Subject ID * Currently_Listens_to_Music_HoursPerWeek: Questionnaire responses by subjects indicating the number of hours per week they spend listening to music. * Formal_Music_Training_NumberOfYears: Questionnaire responses by subjects indicating the number of years of formal musical training they have received in their lifetime. * V1 - indicates data was obtained on Visit 1 * V2 - indicates data was obtained on Visit 2 * Clin - indicates data was obtained with the Clinical Map (control condition) * Exp - indicates data was obtained with the CT-Based Experimental Map (experimental condition) Test metrics: * CNC Words & CNC Phonemes: Percent correct on the CNC test * BKB-SIN: Results of the BKB (Bamford-Kowal-Bench) sentence lists, measured in SNR-50 (dB) * Vowels: Percent correct on the vowel perception test * Timbre G3: Percent correct on the timbre discrimination test * Pitch Ranking: Results of the pitch ranking test, measured in number of errors * Chronic Diff: The difference in scores between the V1_Clin and the V2_Exp columns for each test metric. * Acute Diff: The difference in scores between the V1_Exp and the V2_Clin columns for each test metric. * DOD (yrs): Duration of severe-to-profound deafness before cochlear implantation * Length CI Use (yrs): Duration of cochlear implant use at the time of testing * Coch Duct Length (mm): Length of cochlear duct in millimeters * E1, E2, E3, etc.: Electrode number and the corresponding location in the cochlear duct in millimeters. * E1 (%, mm): The percentage of the cochlear duct covered by the cochlear implant * E1 Err (ST, AbsVal): ERROR by Electrode: The number of semitones (ST) of pitch-place mismatch between the characteristic frequency of the electrode location and the corresponding center frequency of the default frequency allocation table. #### Description of empty cells If a test metric column has an empty cell it means the subject did not complete that test metric. If a column with "E12" in the title has an empty cell it means that the corresponding electrode is extra-cochlear and thus not measurable (specifically for subjects 3L and 5R).