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Schleich P, Wirtz C, Schatzer R, Nopp P. Similar performance in sound localisation with unsynchronised and synchronised automatic gain controls in bilateral cochlear implant recipients. Int J Audiol 2025; 64:411-417. [PMID: 39075948 DOI: 10.1080/14992027.2024.2383700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 07/16/2024] [Accepted: 07/17/2024] [Indexed: 07/31/2024]
Abstract
OBJECTIVE One proposed method to improve sound localisation for bilateral cochlear implant (BiCI) users is to synchronise the automatic gain control (AGC) of both audio processors. In this study we tested whether AGC synchronisation in a dual-loop front-end processing scheme with a 3:1 compression ratio improves sound localisation acuity. DESIGN Source identification in the frontal hemifield was tested in in an anechoic chamber as a function of (roving) presentation level. Three different methods of AGC synchronisation were compared to the standard unsynchronised approach. Both root mean square error (RMSE) and signed bias were calculated to evaluate sound localisation in the horizontal plane. STUDY SAMPLE Six BiCI users. RESULTS None of the three AGC synchronisation methods yielded significant improvements in either localisation error or bias, neither across presentation levels nor for individual presentation levels. For synchronised AGC, the pooled mean (standard deviation) localisation error of the three synchronisation methods was 24.7 (5.8) degrees RMSE, for unsynchronised AGC it was 27.4 (7.5) degrees. The localisation bias was 5.1 (5.5) degrees for synchronised AGC and 5.0 (3.8) for unsynchronised. CONCLUSIONS These findings do not support the hypothesis that the tested AGC synchronisation configurations improves localisation acuity in bilateral users of MED-EL cochlear implants.
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Affiliation(s)
| | | | | | - Peter Nopp
- MED-EL Medical Electronics, Innsbruck, Austria
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2
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Tan X, Liu N, Yu C, Han T, Zhang Z, Ahmed-Kristensen S. A preliminary study to identify critical factors for evaluating the effect of car-lock sounds on drivers. ERGONOMICS 2025; 68:496-512. [PMID: 39023126 DOI: 10.1080/00140139.2024.2379953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2024] [Accepted: 07/08/2024] [Indexed: 07/20/2024]
Abstract
Car-lock sounds are designed to inform the lock status of vehicles. However, drivers often experience a lack of confidence regarding whether the car is locked, and car thefts persistently occur, frequently attributed to unlocked doors. Without identification of critical factors for evaluating effects of car-lock sounds on drivers, a strategy to car-lock sound design with increased locking efficiency remains implicit. This study proposes a method to identify critical factors influencing drivers' perceived certainty of car-lock status and behaviours during car-locking. An experiment was conducted to simulate the locking process and verbal protocol analysis was employed to comprehend participants' cognitive processes and behaviours. The results show that mechanical sound yielded high certainty and few hesitations, while tonal and crisp sound elicited low certainty and frequent hesitations. Seven critical factors on participants' behaviours and cognitive processes were identified, which provides a data-driven approach for future research in car-lock sounds evaluation and design.
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Affiliation(s)
- Xinyang Tan
- School of Design, Shanghai Jiao Tong University, Shanghai, China
| | - Naixin Liu
- School of Design, Shanghai Jiao Tong University, Shanghai, China
| | - Cong Yu
- School of Design, Shanghai Jiao Tong University, Shanghai, China
| | - Ting Han
- School of Design, Shanghai Jiao Tong University, Shanghai, China
| | - Zhan Zhang
- School of Design, Shanghai Jiao Tong University, Shanghai, China
| | - Saeema Ahmed-Kristensen
- Dept. Innovation, Technology, Entrepreneurship, University of Exeter Business School, Faculty of Environment, Science, Economy, University of Exeter, UK
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3
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Carlyon RP, Deeks JM, Delgutte B, Chung Y, Vollmer M, Ohl FW, Kral A, Tillein J, Litovsky RY, Schnupp J, Rosskothen-Kuhl N, Goldsworthy RL. Limitations on Temporal Processing by Cochlear Implant Users: A Compilation of Viewpoints. Trends Hear 2025; 29:23312165251317006. [PMID: 40095543 PMCID: PMC12076235 DOI: 10.1177/23312165251317006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2024] [Revised: 12/19/2024] [Accepted: 01/03/2025] [Indexed: 03/19/2025] Open
Abstract
Cochlear implant (CI) users are usually poor at using timing information to detect changes in either pitch or sound location. This deficit occurs even for listeners with good speech perception and even when the speech processor is bypassed to present simple, idealized stimuli to one or more electrodes. The present article presents seven expert opinion pieces on the likely neural bases for these limitations, the extent to which they are modifiable by sensory experience and training, and the most promising ways to overcome them in future. The article combines insights from physiology and psychophysics in cochlear-implanted humans and animals, highlights areas of agreement and controversy, and proposes new experiments that could resolve areas of disagreement.
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Affiliation(s)
- Robert P. Carlyon
- Cambridge Hearing Group, MRC Cognition & Brain Sciences Unit, University of Cambridge, Cambridge, UK
| | - John M. Deeks
- Cambridge Hearing Group, MRC Cognition & Brain Sciences Unit, University of Cambridge, Cambridge, UK
| | - Bertrand Delgutte
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, USA
| | - Yoojin Chung
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, USA
| | - Maike Vollmer
- Department of Experimental Audiology, University Clinic of Otolaryngology, Head and Neck Surgery, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Frank W. Ohl
- Leibniz Institute for Neurobiology (LIN), Magdeburg, Germany
| | - Andrej Kral
- Institute of Audio-Neuro-Technology & Department of Experimental Otology, Clinics of Otolaryngology, Head and Neck Surgery, Hannover Medical School, Hannover, Germany
| | - Jochen Tillein
- Clinics of Otolaryngology, Head and Neck Surgery, J.W.Goethe University, Frankfurt, Germany
- MedEl Company, Hannover, Germany
| | - Ruth Y. Litovsky
- Waisman Center, University of Wisconsin-Madison, Madison, WI, USA
| | - Jan Schnupp
- Gerald Choa Neuroscience Institute and Department of Otolaryngology, Chinese University of Hong Kong, Hong Kong (NB Hong Kong is a Special Administrative Region) of China
| | - Nicole Rosskothen-Kuhl
- Neurobiological Research Laboratory, Section for Experimental and Clinical Otology, Department of Oto-Rhino-Laryngology, Medical Center, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- Bernstein Center Freiburg & Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Raymond L. Goldsworthy
- Auditory Research Center, Caruso Department of Otolaryngology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
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4
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Lindenbeck MJ, Majdak P, Srinivasan S, Laback B. Pitch discrimination in electric hearing with inconsistent and consistent amplitude-modulation and inter-pulse rate cues. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2023; 153:3268. [PMID: 37307025 PMCID: PMC10264086 DOI: 10.1121/10.0019452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 04/28/2023] [Accepted: 05/01/2023] [Indexed: 06/13/2023]
Abstract
Users of cochlear implants (CIs) struggle in situations that require selective hearing to focus on a target source while ignoring other sources. One major reason for that is the limited access to timing cues such as temporal pitch or interaural time differences (ITDs). Various approaches to improve timing-cue sensitivity while maintaining speech understanding have been proposed, among them inserting extra pulses with short inter-pulse intervals (SIPIs) into amplitude-modulated (AM) high-rate pulse trains. Indeed, SIPI rates matching the naturally occurring AM rates improve pitch discrimination. For ITD, however, low SIPI rates are required, potentially mismatching the naturally occurring AM rates and thus creating unknown pitch effects. In this study, we investigated the perceptual contribution of AM and SIPI rate to pitch discrimination in five CI listeners and with two AM depths (0.1 and 0.5). Our results show that the SIPI-rate cue generally dominated the percept for both consistent and inconsistent cues. When tested with inconsistent cues, also the AM rate contributed, however, at the large AM depth only. These findings have implications when aiming at jointly improving temporal-pitch and ITD sensitivity in a future mixed-rate stimulation approach.
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Affiliation(s)
- Martin J Lindenbeck
- Acoustics Research Institute, Austrian Academy of Sciences, Wohllebengasse 12-14, A-1040 Vienna, Austria
| | - Piotr Majdak
- Acoustics Research Institute, Austrian Academy of Sciences, Wohllebengasse 12-14, A-1040 Vienna, Austria
| | - Sridhar Srinivasan
- Acoustics Research Institute, Austrian Academy of Sciences, Wohllebengasse 12-14, A-1040 Vienna, Austria
| | - Bernhard Laback
- Acoustics Research Institute, Austrian Academy of Sciences, Wohllebengasse 12-14, A-1040 Vienna, Austria
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5
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Dennison SR, Thakkar T, Kan A, Litovsky RY. Lateralization of binaural envelope cues measured with a mobile cochlear-implant research processora). THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2023; 153:3543-3558. [PMID: 37390320 PMCID: PMC10314808 DOI: 10.1121/10.0019879] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Revised: 06/09/2023] [Accepted: 06/09/2023] [Indexed: 07/02/2023]
Abstract
Bilateral cochlear implant (BICI) listeners do not have full access to the binaural cues that normal hearing (NH) listeners use for spatial hearing tasks such as localization. When using their unsynchronized everyday processors, BICI listeners demonstrate sensitivity to interaural level differences (ILDs) in the envelopes of sounds, but interaural time differences (ITDs) are less reliably available. It is unclear how BICI listeners use combinations of ILDs and envelope ITDs, and how much each cue contributes to perceived sound location. The CCi-MOBILE is a bilaterally synchronized research processor with the untested potential to provide spatial cues to BICI listeners. In the present study, the CCi-MOBILE was used to measure the ability of BICI listeners to perceive lateralized sound sources when single pairs of electrodes were presented amplitude-modulated stimuli with combinations of ILDs and envelope ITDs. Young NH listeners were also tested using amplitude-modulated high-frequency tones. A cue weighting analysis with six BICI and ten NH listeners revealed that ILDs contributed more than envelope ITDs to lateralization for both groups. Moreover, envelope ITDs contributed to lateralization for NH listeners but had negligible contribution for BICI listeners. These results suggest that the CCi-MOBILE is suitable for binaural testing and developing bilateral processing strategies.
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Affiliation(s)
| | - Tanvi Thakkar
- University of Wisconsin-La Crosse, La Crosse, Wisconsin 54601, USA
| | - Alan Kan
- Macquarie University, Macquarie Park, New South Wales, Australia
| | - Ruth Y Litovsky
- University of Wisconsin-Madison, Madison, Wisconsin 53711, USA
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6
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Buck AN, Buchholz S, Schnupp JW, Rosskothen-Kuhl N. Interaural time difference sensitivity under binaural cochlear implant stimulation persists at high pulse rates up to 900 pps. Sci Rep 2023; 13:3785. [PMID: 36882473 PMCID: PMC9992369 DOI: 10.1038/s41598-023-30569-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 02/27/2023] [Indexed: 03/09/2023] Open
Abstract
Spatial hearing remains one of the major challenges for bilateral cochlear implant (biCI) users, and early deaf patients in particular are often completely insensitive to interaural time differences (ITDs) delivered through biCIs. One popular hypothesis is that this may be due to a lack of early binaural experience. However, we have recently shown that neonatally deafened rats fitted with biCIs in adulthood quickly learn to discriminate ITDs as well as their normal hearing litter mates, and perform an order of magnitude better than human biCI users. Our unique behaving biCI rat model allows us to investigate other possible limiting factors of prosthetic binaural hearing, such as the effect of stimulus pulse rate and envelope shape. Previous work has indicated that ITD sensitivity may decline substantially at the high pulse rates often used in clinical practice. We therefore measured behavioral ITD thresholds in neonatally deafened, adult implanted biCI rats to pulse trains of 50, 300, 900 and 1800 pulses per second (pps), with either rectangular or Hanning window envelopes. Our rats exhibited very high sensitivity to ITDs at pulse rates up to 900 pps for both envelope shapes, similar to those in common clinical use. However, ITD sensitivity declined to near zero at 1800 pps, for both Hanning and rectangular windowed pulse trains. Current clinical cochlear implant (CI) processors are often set to pulse rates ≥ 900 pps, but ITD sensitivity in human CI listeners has been reported to decline sharply above ~ 300 pps. Our results suggest that the relatively poor ITD sensitivity seen at > 300 pps in human CI users may not reflect the hard upper limit of biCI ITD performance in the mammalian auditory pathway. Perhaps with training or better CI strategies good binaural hearing may be achievable at pulse rates high enough to allow good sampling of speech envelopes while delivering usable ITDs.
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Affiliation(s)
- Alexa N Buck
- Department of Neuroscience, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China.,City University of Hong Kong Shenzhen Research Institute, Shenzhen, China.,Plasticity of Central Auditory Circuits, Institut de l'Audition, Institut Pasteur, Paris, France
| | - Sarah Buchholz
- Neurobiological Research Laboratory, Section of Clinical and Experimental Otology, Department of Oto-Rhino-Laryngology, Faculty of Medicine, Medical Center-University of Freiburg, University of Freiburg, Killianst. 5, 79106, Freiburg im Breisgau, Germany
| | - Jan W Schnupp
- Department of Neuroscience, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China.,City University of Hong Kong Shenzhen Research Institute, Shenzhen, China
| | - Nicole Rosskothen-Kuhl
- Department of Neuroscience, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China. .,Neurobiological Research Laboratory, Section of Clinical and Experimental Otology, Department of Oto-Rhino-Laryngology, Faculty of Medicine, Medical Center-University of Freiburg, University of Freiburg, Killianst. 5, 79106, Freiburg im Breisgau, Germany. .,Bernstein Center Freiburg and Faculty of Biology, University of Freiburg, Freiburg, Germany.
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7
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Reweighting of Binaural Localization Cues in Bilateral Cochlear-Implant Listeners. J Assoc Res Otolaryngol 2021; 23:119-136. [PMID: 34812980 PMCID: PMC8782964 DOI: 10.1007/s10162-021-00821-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Accepted: 10/13/2021] [Indexed: 11/24/2022] Open
Abstract
Normal-hearing (NH) listeners rely on two binaural cues, the interaural time (ITD) and level difference (ILD), for azimuthal sound localization. Cochlear-implant (CI) listeners, however, rely almost entirely on ILDs. One reason is that present-day clinical CI stimulation strategies do not convey salient ITD cues. But even when presenting ITDs under optimal conditions using a research interface, ITD sensitivity is lower in CI compared to NH listeners. Since it has recently been shown that NH listeners change their ITD/ILD weighting when only one of the cues is consistent with visual information, such reweighting might add to CI listeners’ low perceptual contribution of ITDs, given their daily exposure to reliable ILDs but unreliable ITDs. Six bilateral CI listeners completed a multi-day lateralization training visually reinforcing ITDs, flanked by a pre- and post-measurement of ITD/ILD weights without visual reinforcement. Using direct electric stimulation, we presented 100- and 300-pps pulse trains at a single interaurally place-matched electrode pair, conveying ITDs and ILDs in various spatially consistent and inconsistent combinations. The listeners’ task was to lateralize the stimuli in a virtual environment. Additionally, ITD and ILD thresholds were measured before and after training. For 100-pps stimuli, the lateralization training increased the contribution of ITDs slightly, but significantly. Thresholds were neither affected by the training nor correlated with weights. For 300-pps stimuli, ITD weights were lower and ITD thresholds larger, but there was no effect of training. On average across test sessions, adding azimuth-dependent ITDs to stimuli containing ILDs increased the extent of lateralization for both 100- and 300-pps stimuli. The results suggest that low-rate ITD cues, robustly encoded with future CI systems, may be better exploitable for sound localization after increasing their perceptual weight via training.
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8
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Auditory Brainstem Models: Adapting Cochlear Nuclei Improve Spatial Encoding by the Medial Superior Olive in Reverberation. J Assoc Res Otolaryngol 2021; 22:289-318. [PMID: 33861395 DOI: 10.1007/s10162-021-00797-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Accepted: 03/22/2021] [Indexed: 10/21/2022] Open
Abstract
Listeners typically perceive a sound as originating from the direction of its source, even as direct sound is followed milliseconds later by reflected sound from multiple different directions. Early-arriving sound is emphasised in the ascending auditory pathway, including the medial superior olive (MSO) where binaural neurons encode the interaural-time-difference (ITD) cue for spatial location. Perceptually, weighting of ITD conveyed during rising sound energy is stronger at 600 Hz than at 200 Hz, consistent with the minimum stimulus rate for binaural adaptation, and with the longer reverberation times at 600 Hz, compared with 200 Hz, in many natural outdoor environments. Here, we computationally explore the combined efficacy of adaptation prior to the binaural encoding of ITD cues, and excitatory binaural coincidence detection within MSO neurons, in emphasising ITDs conveyed in early-arriving sound. With excitatory inputs from adapting, nonlinear model spherical bushy cells (SBCs) of the bilateral cochlear nuclei, a nonlinear model MSO neuron with low-threshold potassium channels reproduces the rate-dependent emphasis of rising vs. peak sound energy in ITD encoding; adaptation is equally effective in the model MSO. Maintaining adaptation in model SBCs, and adjusting membrane speed in model MSO neurons, 'left' and 'right' populations of computationally efficient, linear model SBCs and MSO neurons reproduce this stronger weighting of ITD conveyed during rising sound energy at 600 Hz compared to 200 Hz. This hemispheric population model demonstrates a link between strong weighting of spatial information during rising sound energy, and correct unambiguous lateralisation of a speech source in reverberation.
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9
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Rosskothen-Kuhl N, Buck AN, Li K, Schnupp JW. Microsecond interaural time difference discrimination restored by cochlear implants after neonatal deafness. eLife 2021; 10:59300. [PMID: 33427644 PMCID: PMC7815311 DOI: 10.7554/elife.59300] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 01/07/2021] [Indexed: 01/03/2023] Open
Abstract
Spatial hearing in cochlear implant (CI) patients remains a major challenge, with many early deaf users reported to have no measurable sensitivity to interaural time differences (ITDs). Deprivation of binaural experience during an early critical period is often hypothesized to be the cause of this shortcoming. However, we show that neonatally deafened (ND) rats provided with precisely synchronized CI stimulation in adulthood can be trained to lateralize ITDs with essentially normal behavioral thresholds near 50 μs. Furthermore, comparable ND rats show high physiological sensitivity to ITDs immediately after binaural implantation in adulthood. Our result that ND-CI rats achieved very good behavioral ITD thresholds, while prelingually deaf human CI patients often fail to develop a useful sensitivity to ITD raises urgent questions concerning the possibility that shortcomings in technology or treatment, rather than missing input during early development, may be behind the usually poor binaural outcomes for current CI patients.
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Affiliation(s)
- Nicole Rosskothen-Kuhl
- Department of Biomedical Sciences, City University of Hong Kong, Hong Kong, China.,Neurobiological Research Laboratory, Section for Clinical and Experimental Otology, University Medical Center Freiburg, Freiburg, Germany
| | - Alexa N Buck
- Department of Biomedical Sciences, City University of Hong Kong, Hong Kong, China
| | - Kongyan Li
- Department of Biomedical Sciences, City University of Hong Kong, Hong Kong, China
| | - Jan Wh Schnupp
- Department of Biomedical Sciences, City University of Hong Kong, Hong Kong, China.,CityU Shenzhen Research Institute, Shenzhen, China
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10
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Improving Interaural Time Difference Sensitivity Using Short Inter-pulse Intervals with Amplitude-Modulated Pulse Trains in Bilateral Cochlear Implants. J Assoc Res Otolaryngol 2020; 21:105-120. [PMID: 32040655 DOI: 10.1007/s10162-020-00743-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Accepted: 01/22/2020] [Indexed: 10/25/2022] Open
Abstract
Interaural time differences (ITDs) at low frequencies are important for sound localization and spatial speech unmasking. These ITD cues are not encoded in commonly used envelope-based stimulation strategies for cochlear implants (CIs) using high pulse rates. However, ITD sensitivity can be improved by adding extra pulses with short inter-pulse intervals (SIPIs) in unmodulated high-rate trains. Here, we investigated whether this improvement also applies to amplitude-modulated (AM) high-rate pulse trains. To this end, we systematically varied the temporal position of SIPI pulses within the envelope cycle (SIPI phase), the fundamental frequency (F0) of AM (125 Hz and 250 Hz), and AM depth (from 0.1 to 0.9). Stimuli were presented at an interaurally place-matched electrode pair at a reference pulse rate of 1000 pulses/s. Participants performed an ITD-based left/right discrimination task. SIPI insertion resulted in improved ITD sensitivity throughout the range of modulation depths and for both male and female F0s. The improvements were largest for insertion at and around the envelope peak. These results are promising for conveying salient ITD cues at high pulse rates commonly used to encode speech information.
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11
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Lindenbeck MJ, Laback B, Majdak P, Srinivasan S. Temporal-pitch sensitivity in electric hearing with amplitude modulation and inserted pulses with short inter-pulse intervals. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2020; 147:777. [PMID: 32113255 PMCID: PMC7002171 DOI: 10.1121/10.0000610] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Revised: 12/26/2019] [Accepted: 01/02/2020] [Indexed: 06/10/2023]
Abstract
Listeners with cochlear implants (CIs) typically show poor sensitivity to the temporal-envelope pitch of high-rate pulse trains. Sensitivity to interaural time differences improves when adding pulses with short inter-pulse intervals (SIPIs) to high-rate pulse trains. In the current study, monaural temporal-pitch sensitivity with SIPI pulses was investigated for six CI listeners. Amplitude-modulated single-electrode stimuli, representing the coding of the fundamental frequency (F0) in the envelope of a high-rate carrier, were used. Two SIPI-insertion approaches, five modulation depths, two typical speech-F0s, and two carrier rates were tested. SIPI pulses were inserted either in every amplitude-modulation period (full-rate SIPI) to support the F0 cue or in every other amplitude-modulation period (half-rate SIPI) to circumvent a potential rate limitation at higher F0s. The results demonstrate that full-rate SIPI pulses improve temporal-pitch sensitivity across F0s and particularly at low modulation depths where envelope-pitch cues are weak. The half-rate SIPI pulses did not circumvent the limitation and further increased variability across listeners. Further, no effect of the carrier rate was found. Thus, the SIPI approach appears to be a promising approach to enhance CI listeners' access to temporal-envelope pitch cues at pulse rates used clinically.
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Affiliation(s)
- Martin J Lindenbeck
- Acoustics Research Institute, Austrian Academy of Sciences, Wohllebengasse 12-14, 1040 Vienna, Austria
| | - Bernhard Laback
- Acoustics Research Institute, Austrian Academy of Sciences, Wohllebengasse 12-14, 1040 Vienna, Austria
| | - Piotr Majdak
- Acoustics Research Institute, Austrian Academy of Sciences, Wohllebengasse 12-14, 1040 Vienna, Austria
| | - Sridhar Srinivasan
- Acoustics Research Institute, Austrian Academy of Sciences, Wohllebengasse 12-14, 1040 Vienna, Austria
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12
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Improved Neural Coding of ITD with Bilateral Cochlear Implants by Introducing Short Inter-pulse Intervals. J Assoc Res Otolaryngol 2018; 19:681-702. [PMID: 30191423 DOI: 10.1007/s10162-018-00693-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Accepted: 07/17/2018] [Indexed: 10/28/2022] Open
Abstract
Bilateral cochlear implant (CI) users have poor perceptual sensitivity to interaural time differences (ITDs), which limits their ability to localize sounds and understand speech in noisy environments. This is especially true for high-rate (> 300 pps) periodic pulse trains, which are used as carriers in CI processors. Here, we investigate a novel stimulation strategy in which extra pulses are added to high-rate periodic pulse trains to introduce short inter-pulse intervals (SIPIs). We hypothesized that SIPIs can improve neural ITD sensitivity similarly to the effect observed by randomly jittering IPIs (Hancock et al., J. Neurophysiol. 108:714-28, 2012). To test this hypothesis, we measured ITD sensitivity of single units in the inferior colliculus (IC) of unanesthetized rabbits with bilateral CIs. Introducing SIPIs into high-rate pulse trains significantly increased firing rates for ~ 60 % of IC neurons, and the extra spikes tended to be synchronized to the SIPIs. The additional firings produced by SIPIs uncovered latent ITD sensitivity that was comparable to that observed with low-rate pulse trains. In some neurons, high spontaneous firing rates masked the ITD sensitivity introduced by SIPIs. ITD sensitivity in these neurons could be revealed by emphasizing stimulus-synchronized spikes with a coincidence detection analysis. Overall, these results with SIPIs are consistent with the effects observed previously with jittered pulse trains, with the added benefit of retaining control over the timing and number of SIPIs. A novel CI processing strategy could incorporate SIPIs by inserting them at selected times to high-rate pulse train carriers. Such a strategy could potentially improve ITD perception without degrading speech intelligibility and thereby improve outcomes for bilateral CI users.
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