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Leclère T, Johannesen PT, Wijetillake A, Segovia-Martínez M, Lopez-Poveda EA. A computational modelling framework for assessing information transmission with cochlear implants. Hear Res 2023; 432:108744. [PMID: 37004271 DOI: 10.1016/j.heares.2023.108744] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 03/05/2023] [Accepted: 03/24/2023] [Indexed: 03/28/2023]
Abstract
Computational models are useful tools to investigate scientific questions that would be complicated to address using an experimental approach. In the context of cochlear-implants (CIs), being able to simulate the neural activity evoked by these devices could help in understanding their limitations to provide natural hearing. Here, we present a computational modelling framework to quantify the transmission of information from sound to spikes in the auditory nerve of a CI user. The framework includes a model to simulate the electrical current waveform sensed by each auditory nerve fiber (electrode-neuron interface), followed by a model to simulate the timing at which a nerve fiber spikes in response to a current waveform (auditory nerve fiber model). Information theory is then applied to determine the amount of information transmitted from a suitable reference signal (e.g., the acoustic stimulus) to a simulated population of auditory nerve fibers. As a use case example, the framework is applied to simulate published data on modulation detection by CI users obtained using direct stimulation via a single electrode. Current spread as well as the number of fibers were varied independently to illustrate the framework capabilities. Simulations reasonably matched experimental data and suggested that the encoded modulation information is proportional to the total neural response. They also suggested that amplitude modulation is well encoded in the auditory nerve for modulation rates up to 1000 Hz and that the variability in modulation sensitivity across CI users is partly because different CI users use different references for detecting modulation.
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Affiliation(s)
- Thibaud Leclère
- Instituto de Neurociencias de Castilla y León, Universidad de Salamanca, Salamanca 37007, Spain; Instituto de Investigación Biomédica de Salamanca, Universidad de Salamanca, Salamanca 37007, Spain
| | - Peter T Johannesen
- Instituto de Neurociencias de Castilla y León, Universidad de Salamanca, Salamanca 37007, Spain; Instituto de Investigación Biomédica de Salamanca, Universidad de Salamanca, Salamanca 37007, Spain
| | | | | | - Enrique A Lopez-Poveda
- Instituto de Neurociencias de Castilla y León, Universidad de Salamanca, Salamanca 37007, Spain; Instituto de Investigación Biomédica de Salamanca, Universidad de Salamanca, Salamanca 37007, Spain; Departamento de Cirugía, Facultad de Medicina, Universidad de Salamanca, Salamanca 37007, Spain.
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Zhou N, Shi X, Dixit O, Firszt JB, Holden TA. Relationship between electrode position and temporal modulation sensitivity in cochlear implant users: Are close electrodes always better? Heliyon 2023; 9:e12467. [PMID: 36852047 PMCID: PMC9958279 DOI: 10.1016/j.heliyon.2022.e12467] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2022] [Revised: 10/21/2022] [Accepted: 12/11/2022] [Indexed: 12/24/2022] Open
Abstract
Temporal modulation sensitivity has been studied extensively for cochlear implant (CI) users due to its strong correlation to speech recognition outcomes. Previous studies reported that temporal modulation detection thresholds (MDTs) vary across the tonotopic axis and attributed this variation to patchy neural survival. However, correlates of neural health identified in animal models depend on electrode position in humans. Nonetheless, the relationship between MDT and electrode location has not been explored. We tested 13 ears for the effect of distance on modulation sensitivity, specifically targeting the question of whether electrodes closer to the modiolus are universally beneficial. Participants in this study were postlingually deafened and users of Cochlear Nucleus CIs. The distance of each electrode from the medial wall (MW) of the cochlea and mid-modiolar axis (MMA) was measured from scans obtained using computerized tomography (CT) imaging. The distance measures were correlated with slopes of spatial tuning curves measured on selected electrodes to investigate if electrode position accounts, at least in part, for the width of neural excitation. In accordance with previous findings, electrode position explained 24% of the variance in slopes of the spatial tuning curves. All functioning electrodes were also measured for MDTs. Five ears showed a positive correlation between MDTs and at least one distance measure across the array; 6 ears showed negative correlations and the remaining two ears showed no relationship. The ears showing positive MDT-distance correlations, thus benefiting from electrodes being close to the neural elements, were those who performed better on the two speech recognition measures, i.e., speech reception thresholds (SRTs) and recognition of the AzBio sentences. These results could suggest that ears able to take advantage of the proximal placement of electrodes are likely to have better speech recognition outcomes. Previous histological studies of humans demonstrated that speech recognition is correlated with spiral ganglion cell counts. Alternatively, ears with good speech recognition outcomes may have good overall neural health, which is a precondition for close electrodes to produce spatially confined neural excitation patterns that facilitate modulation sensitivity. These findings suggest that the methods to reduce channel interaction, e.g., perimodiolar electrode array or current focusing, may only be beneficial for a subgroup of CI users. Additionally, it suggests that estimating neural survival preoperatively is important for choosing the most appropriate electrode array type (perimodiolar vs. lateral wall) for optimal implant function.
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Affiliation(s)
- Ning Zhou
- Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC, 27834, USA
| | - Xuyang Shi
- Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC, 27834, USA
| | - Omkar Dixit
- Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC, 27834, USA
| | - Jill B Firszt
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, Missouri, 63110, USA
| | - Timothy A Holden
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, Missouri, 63110, USA
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Neural Modulation Transmission Is a Marker for Speech Perception in Noise in Cochlear Implant Users. Ear Hear 2021; 41:591-602. [PMID: 31567565 DOI: 10.1097/aud.0000000000000783] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES Cochlear implants (CIs) restore functional hearing in persons with a severe hearing impairment. Despite being one of the most successful bionic prosthesis, performance with CI (in particular speech understanding in noise) varies considerably across its users. The ability of the auditory pathway to encode temporal envelope modulations (TEMs) and the effect of degenerative processes associated with hearing loss on TEM encoding is assumed to be one of the reasons underlying the large intersubject differences in CI performance. The objective of the present study was to investigate how TEM encoding of the stimulated neural ensembles of human CI recipients is related to speech perception in noise (SPIN). DESIGN We used electroencephalography as a noninvasive electrophysiological measure to assess TEM encoding in the auditory pathway of CI users by means of the 40-Hz electrically evoked auditory steady state response (EASSR). Nine CI users with a wide range of SPIN outcome were included in the present study. TEM encoding was assessed for each stimulation electrode of each subject and new metrics; the CI neural modulation transmission difference (CIMTD) and the CI neural modulation transmission index (CIMTI) were developed to quantify the amount of variability in TEM encoding across the stimulated neural ensembles of the CI electrode array. RESULTS EASSR patterns varied across the CI electrode array and subjects. We found a strong correlation (r = 0.89, p = 0.001) between the SPIN outcomes and the variability in EASSR amplitudes across the array as assessed with CIMTD/CIMTI. CONCLUSIONS The results of the present study show that the 40-Hz EASSR can be used to objectively assess the neural encoding of TEMs in human CI recipients. Overall reduced or largely variable TEM encoding of the neural ensembles across the electrode array, as quantified with the CIMTD/CIMTI, is highly correlated with speech perception in noise outcome with a CI.
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Quass GL, Kurt S, Hildebrandt KJ, Kral A. Electrical stimulation of the midbrain excites the auditory cortex asymmetrically. Brain Stimul 2018; 11:1161-1174. [PMID: 29853311 DOI: 10.1016/j.brs.2018.05.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2018] [Revised: 05/09/2018] [Accepted: 05/10/2018] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND Auditory midbrain implant users cannot achieve open speech perception and have limited frequency resolution. It remains unclear whether the spread of excitation contributes to this issue and how much it can be compensated by current-focusing, which is an effective approach in cochlear implants. OBJECTIVE The present study examined the spread of excitation in the cortex elicited by electric midbrain stimulation. We further tested whether current-focusing via bipolar and tripolar stimulation is effective with electric midbrain stimulation and whether these modes hold any advantage over monopolar stimulation also in conditions when the stimulation electrodes are in direct contact with the target tissue. METHODS Using penetrating multielectrode arrays, we recorded cortical population responses to single pulse electric midbrain stimulation in 10 ketamine/xylazine anesthetized mice. We compared monopolar, bipolar, and tripolar stimulation configurations with regard to the spread of excitation and the characteristic frequency difference between the stimulation/recording electrodes. RESULTS The cortical responses were distributed asymmetrically around the characteristic frequency of the stimulated midbrain region with a strong activation in regions tuned up to one octave higher. We found no significant differences between monopolar, bipolar, and tripolar stimulation in threshold, evoked firing rate, or dynamic range. CONCLUSION The cortical responses to electric midbrain stimulation are biased towards higher tonotopic frequencies. Current-focusing is not effective in direct contact electrical stimulation. Electrode maps should account for the asymmetrical spread of excitation when fitting auditory midbrain implants by shifting the frequency-bands downward and stimulating as dorsally as possible.
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Affiliation(s)
- Gunnar Lennart Quass
- Institute of AudioNeuroTechnology (VIANNA), Dept. of Experimental Otology, ENT Clinics, Hannover Medical School, 30625 Hannover, Germany; Cluster of Excellence "Hearing4all", Germany.
| | - Simone Kurt
- Institute of AudioNeuroTechnology (VIANNA), Dept. of Experimental Otology, ENT Clinics, Hannover Medical School, 30625 Hannover, Germany; Cluster of Excellence "Hearing4all", Germany
| | - K Jannis Hildebrandt
- Cluster of Excellence "Hearing4all", Germany; Research Center Neurosensory Science, University of Oldenburg, 26111 Oldenburg, Germany
| | - Andrej Kral
- Institute of AudioNeuroTechnology (VIANNA), Dept. of Experimental Otology, ENT Clinics, Hannover Medical School, 30625 Hannover, Germany; Cluster of Excellence "Hearing4all", Germany
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Alarautalahti V, Hiltunen M, Onnela N, Nymark S, Kellomäki M, Hyttinen J. Polypyrrole-coated electrodes show thickness-dependent stability in different conditions during 42-day follow-up in vitro. J Biomed Mater Res B Appl Biomater 2017; 106:2202-2213. [PMID: 29058808 DOI: 10.1002/jbm.b.34024] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Revised: 09/01/2017] [Accepted: 10/02/2017] [Indexed: 01/09/2023]
Abstract
Electroconductive polypyrrole/dodecylbenzenesulphonate (PPy/DBS) has been proposed as novel electrode coating for biomedical applications. However, as yet, little is known about its long-term stability in moist conditions. This study compares the stability of PPy/DBS-coated platinum electrodes that are either dry-stored, incubated, or both incubated and electrically stimulated. The electrical and material properties of three different coating thicknesses were monitored for 42 days. Initially, the PPy/DBS-coating decreased the low frequency impedance of the platinum electrodes by 52% to 79%. The dry-stored electrodes remained stable during the follow-up, whereas the properties of all the incubated electrodes were altered in three stages with thickness-dependent duration: stabilization, stable, and degradation. The coated electrodes would be applicable for short-term, low-frequency in vitro measurements of up to 14 days without electrical stimulation, and up to 7 days with stimulation. The coating thickness is bound to other coating properties, and should therefore be selected according to the specific target application. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2202-2213, 2018.
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Affiliation(s)
- V Alarautalahti
- Computational Biophysics and Imaging Group, BioMediTech Institute and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, Tampere, Finland
| | - M Hiltunen
- Biomaterials and Tissue Engineering Group, BioMediTech Institute and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, Tampere, Finland
| | - N Onnela
- Computational Biophysics and Imaging Group, BioMediTech Institute and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, Tampere, Finland
| | - S Nymark
- Biophysics of the Eye Research Group, BioMediTech Institute and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, Tampere, Finland
| | - M Kellomäki
- Biomaterials and Tissue Engineering Group, BioMediTech Institute and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, Tampere, Finland
| | - J Hyttinen
- Computational Biophysics and Imaging Group, BioMediTech Institute and Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, Tampere, Finland
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George SS, Shivdasani MN, Fallon JB. Effect of current focusing on the sensitivity of inferior colliculus neurons to amplitude-modulated stimulation. J Neurophysiol 2016; 116:1104-16. [PMID: 27306672 DOI: 10.1152/jn.00126.2016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Accepted: 06/15/2016] [Indexed: 11/22/2022] Open
Abstract
In multichannel cochlear implants (CIs), current is delivered to specific electrodes along the cochlea in the form of amplitude-modulated pulse trains, to convey temporal and spectral cues. Our previous studies have shown that focused multipolar (FMP) and tripolar (TP) stimulation produce more restricted neural activation and reduced channel interactions in the inferior colliculus (IC) compared with traditional monopolar (MP) stimulation, suggesting that focusing of stimulation could produce better transmission of spectral information. The present study explored the capability of IC neurons to detect modulated CI stimulation with FMP and TP stimulation compared with MP stimulation. The study examined multiunit responses of IC neurons in acutely deafened guinea pigs by systematically varying the stimulation configuration, modulation depth, and stimulation level. Stimuli were sinusoidal amplitude-modulated pulse trains (carrier rate of 120 pulses/s). Modulation sensitivity was quantified by measuring modulation detection thresholds (MDTs), defined as the lowest modulation depth required to differentiate the response of a modulated stimulus from an unmodulated one. Whereas MP stimulation showed significantly lower MDTs than FMP and TP stimulation (P values <0.05) at stimulation ≤2 dB above threshold, all stimulation configurations were found to have similar modulation sensitivities at 4 dB above threshold. There was no difference found in modulation sensitivity between FMP and TP stimulation. The present study demonstrates that current focusing techniques such as FMP and TP can adequately convey amplitude modulation and are comparable to MP stimulation, especially at higher stimulation levels, although there may be some trade-off between spectral and temporal fidelity with current focusing stimulation.
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Affiliation(s)
- Shefin S George
- The Bionics Institute, East Melbourne, Australia; and Department of Medical Bionics, University of Melbourne, Melbourne, Australia
| | - Mohit N Shivdasani
- The Bionics Institute, East Melbourne, Australia; and Department of Medical Bionics, University of Melbourne, Melbourne, Australia
| | - James B Fallon
- The Bionics Institute, East Melbourne, Australia; and Department of Medical Bionics, University of Melbourne, Melbourne, Australia
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Fielden CA, Kluk K, Boyle PJ, McKay CM. The perception of complex pitch in cochlear implants: A comparison of monopolar and tripolar stimulation. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2015; 138:2524-36. [PMID: 26520335 DOI: 10.1121/1.4931910] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Cochlear implant listeners typically perform poorly in tasks of complex pitch perception (e.g., musical pitch and voice pitch). One explanation is that wide current spread during implant activation creates channel interactions that may interfere with perception of temporal fundamental frequency information contained in the amplitude modulations within channels. Current focusing using a tripolar mode of stimulation has been proposed as a way of reducing channel interactions, minimising spread of excitation and potentially improving place and temporal pitch cues. The present study evaluated the effect of mode in a group of cochlear implant listeners on a pitch ranking task using male and female singing voices separated by either a half or a quarter octave. Results were variable across participants, but on average, pitch ranking was at chance level when the pitches were a quarter octave apart and improved when the difference was a half octave. No advantage was observed for tripolar over monopolar mode at either pitch interval, suggesting that previously published psychophysical advantages for focused modes may not translate into improvements in complex pitch ranking. Evaluation of the spectral centroid of the stimulation pattern, plus a lack of significant difference between male and female voices, suggested that participants may have had difficulty in accessing temporal pitch cues in either mode.
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Affiliation(s)
- Claire A Fielden
- School of Psychological Sciences, University of Manchester, Ellen Wilkinson Building, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Karolina Kluk
- School of Psychological Sciences, University of Manchester, Ellen Wilkinson Building, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Patrick J Boyle
- Advanced Bionics UK Ltd., 2 Breaks House, Mill Court, Great Shelford, Cambridge, CB22 5LD, United Kingdom
| | - Colette M McKay
- School of Psychological Sciences, University of Manchester, Ellen Wilkinson Building, Oxford Road, Manchester M13 9PL, United Kingdom
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Amplitude Modulation Detection and Speech Recognition in Late-Implanted Prelingually and Postlingually Deafened Cochlear Implant Users. Ear Hear 2015; 36:557-66. [DOI: 10.1097/aud.0000000000000162] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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9
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Assessing temporal modulation sensitivity using electrically evoked auditory steady state responses. Hear Res 2015; 324:37-45. [DOI: 10.1016/j.heares.2015.02.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Revised: 02/19/2015] [Accepted: 02/21/2015] [Indexed: 11/24/2022]
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Pfingst BE, Zhou N, Colesa DJ, Watts MM, Strahl SB, Garadat SN, Schvartz-Leyzac KC, Budenz CL, Raphael Y, Zwolan TA. Importance of cochlear health for implant function. Hear Res 2015; 322:77-88. [PMID: 25261772 PMCID: PMC4377117 DOI: 10.1016/j.heares.2014.09.009] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Revised: 08/14/2014] [Accepted: 09/16/2014] [Indexed: 01/17/2023]
Abstract
Amazing progress has been made in providing useful hearing to hearing-impaired individuals using cochlear implants, but challenges remain. One such challenge is understanding the effects of partial degeneration of the auditory nerve, the target of cochlear implant stimulation. Here we review studies from our human and animal laboratories aimed at characterizing the health of the implanted cochlea and the auditory nerve. We use the data on cochlear and neural health to guide rehabilitation strategies. The data also motivate the development of tissue-engineering procedures to preserve or build a healthy cochlea and improve performance obtained by cochlear implant recipients or eventually replace the need for a cochlear implant. This article is part of a Special Issue entitled .
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Affiliation(s)
- Bryan E Pfingst
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI, USA.
| | - Ning Zhou
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI, USA; East Carolina University, Greenville, NC, USA
| | - Deborah J Colesa
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI, USA
| | - Melissa M Watts
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI, USA
| | | | - Soha N Garadat
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI, USA; The University of Jordan, Amman, Jordan
| | | | - Cameron L Budenz
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI, USA
| | - Yehoash Raphael
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI, USA
| | - Teresa A Zwolan
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI, USA
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Comparison of signal and gap-detection thresholds for focused and broad cochlear implant electrode configurations. J Assoc Res Otolaryngol 2015; 16:273-84. [PMID: 25644786 PMCID: PMC4368655 DOI: 10.1007/s10162-015-0507-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 12/23/2014] [Indexed: 01/04/2023] Open
Abstract
Cochlear implant (CI) users usually exhibit marked across-electrode differences in detection thresholds with "focused" modes of stimulation, such as partial-tripolar (pTP) mode. This may reflect differences either in local neural survival or in the distance of the electrodes from the modiolus. To shed light on these two explanations, we compared stimulus-detection thresholds and gap-detection thresholds (GDTs) at comfortably loud levels for at least four electrodes in each of ten Advanced Bionics CI users, using 1031-pps pulse trains. The electrodes selected for each user had a wide range of stimulus-detection thresholds in pTP mode. We also measured across-electrode variations in both stimulus-detection and gap-detection tasks in monopolar (MP) mode. Both stimulus-detection and gap-detection thresholds correlated across modes. However, there was no significant correlation between stimulus-detection and gap-detection thresholds in either mode. Hence, gap-detection thresholds likely tap a source of across-electrode variation additional to, or different from, that revealed by stimulus-detection thresholds. Stimulus-detection thresholds were significantly lower for apical than for basal electrodes in both modes; this was only true for gap detection in pTP mode. Finally, although the across-electrode standard deviation in stimulus-detection thresholds was greater in pTP than in MP mode, the reliability of these differences--assessed by dividing the across-electrode standard deviation by the standard deviation across adaptive runs for each electrode--was similar for the two modes; this metric was also similar across modes for gap detection. Hence across-electrode differences can be revealed using clinically available MP stimulation, with a reliability comparable to that observed with focused stimulation.
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Fielden CA, Kluk K, McKay CM. Interpulse interval discrimination within and across channels: comparison of monopolar and tripolar mode of stimulation. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2014; 135:2913-2922. [PMID: 24815271 DOI: 10.1121/1.4869687] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Perception of temporal patterns is crucial to speech understanding and music perception in normal hearing, and is fundamental in the design and implementation of processing strategies for cochlear implants. Two experiments described here investigated the effect of stimulation mode (monopolar versus tripolar) on interpulse interval discrimination using single-electrode stimulation (experiment 1) and dual-electrode stimulation (experiment 2). Experiment 1 required participants to discriminate stimuli containing different interpulse intervals and experiment 2 required listeners to discriminate between two dual-electrode stimuli that had the same temporal pattern on each electrode, but differed in inter-electrode timing. The hypotheses were that (i) stimulation mode would affect the ability to distinguish interpulse interval patterns on a single electrode and (ii) the electrode separation range in which subjects were sensitive to inter-electrode timing would be more restricted in tripolar than in monopolar stimulation. Results in nine cochlear implant users showed that mode did not have a significant mean effect on either the ability to discriminate interpulse intervals in single-electrode stimulation or the range of electrode separation in dual-electrode stimulation in which participants were sensitive to inter-electrode timing. In conclusion, tripolar stimulation did not show any advantage in delivering temporal information within or across channels in this group.
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Affiliation(s)
- Claire A Fielden
- School of Psychological Sciences, Ellen Wilkinson Building, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Karolina Kluk
- School of Psychological Sciences, Ellen Wilkinson Building, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Colette M McKay
- School of Psychological Sciences, Ellen Wilkinson Building, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
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13
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Pfingst BE, Bowling SA, Colesa DJ, Garadat SN, Raphael Y, Shibata SB, Strahl SB, Su GL, Zhou N. Cochlear infrastructure for electrical hearing. Hear Res 2011; 281:65-73. [PMID: 21605648 PMCID: PMC3208788 DOI: 10.1016/j.heares.2011.05.002] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2011] [Revised: 04/29/2011] [Accepted: 05/01/2011] [Indexed: 11/30/2022]
Abstract
Although the cochlear implant is already the world's most successful neural prosthesis, opportunities for further improvement abound. Promising areas of current research include work on improving the biological infrastructure in the implanted cochlea to optimize reception of cochlear implant stimulation and on designing the pattern of electrical stimulation to take maximal advantage of conditions in the implanted cochlea. In this review we summarize what is currently known about conditions in the cochlea of deaf, implanted humans and then review recent work from our animal laboratory investigating the effects of preserving or reinnervating tissues on psychophysical and electrophysiological measures of implant function. Additionally we review work from our human laboratory on optimizing the pattern of electrical stimulation to better utilize strengths in the cochlear infrastructure. Histological studies of human temporal bones from implant users and from people who would have been candidates for implants show a range of pathologic conditions including spiral ganglion cell counts ranging from approximately 2% to 92% of normal and partial hair cell survival in some cases. To duplicate these conditions in a guinea pig model, we use a variety of deafening and implantation procedures as well as post-deafening therapies designed to protect neurons and/or regenerate neurites. Across populations of human patients, relationships between nerve survival and functional measures such as speech have been difficult to demonstrate, possibly due to the numerous subject variables that can affect implant function and the elapsed time between functional measures and postmortem histology. However, psychophysical studies across stimulation sites within individual human subjects suggest that biological conditions near the implanted electrodes contribute significantly to implant function, and this is supported by studies in animal models comparing histological findings to psychophysical and electrophysiological data. Results of these studies support the efforts to improve the biological infrastructure in the implanted ear and guide strategies which optimize stimulation patterns to match patient-specific conditions in the cochlea.
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Affiliation(s)
- Bryan E Pfingst
- Department of Otolaryngology, Kresge Hearing Research Institute, University of Michigan, 1150 West Medical Center Drive, Ann Arbor, MI 48109-5616, USA.
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