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Reiss LAJ, Goupell MJ. Binaural fusion: Complexities in definition and measurement. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2024; 156:2395-2408. [PMID: 39392352 PMCID: PMC11470809 DOI: 10.1121/10.0030476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2024] [Revised: 09/10/2024] [Accepted: 09/20/2024] [Indexed: 10/12/2024]
Abstract
Despite the growing interest in studying binaural fusion, there is little consensus over its definition or how it is best measured. This review seeks to describe the complexities of binaural fusion, highlight measurement challenges, provide guidelines for rigorous perceptual measurements, and provide a working definition that encompasses this information. First, it is argued that binaural fusion may be multidimensional and might occur in one domain but not others, such as fusion in the spatial but not the spectral domain or vice versa. Second, binaural fusion may occur on a continuous scale rather than on a binary one. Third, binaural fusion responses are highly idiosyncratic, which could be a result of methodology, such as the specific experimental instructions, suggesting a need to explicitly report the instructions given. Fourth, it is possible that direct ("Did you hear one sound or two?") and indirect ("Where did the sound come from?" or "What was the pitch of the sound?") measurements of fusion will produce different results. In conclusion, explicit consideration of these attributes and reporting of methodology are needed for rigorous interpretation and comparison across studies and listener populations.
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Affiliation(s)
- Lina A J Reiss
- Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health and Science University, Portland, Oregon 97239, USA
| | - Matthew J Goupell
- Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland 20742, USA
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Thakkar T, Kan A, Litovsky RY. Lateralization of interaural time differences with mixed rates of stimulation in bilateral cochlear implant listeners. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2023; 153:1912. [PMID: 37002065 PMCID: PMC10036141 DOI: 10.1121/10.0017603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Revised: 02/23/2023] [Accepted: 02/25/2023] [Indexed: 05/18/2023]
Abstract
While listeners with bilateral cochlear implants (BiCIs) are able to access information in both ears, they still struggle to perform well on spatial hearing tasks when compared to normal hearing listeners. This performance gap could be attributed to the high stimulation rates used for speech representation in clinical processors. Prior work has shown that spatial cues, such as interaural time differences (ITDs), are best conveyed at low rates. Further, BiCI listeners are sensitive to ITDs with a mixture of high and low rates. However, it remains unclear whether mixed-rate stimuli are perceived as unitary percepts and spatially mapped to intracranial locations. Here, electrical pulse trains were presented on five, interaurally pitch-matched electrode pairs using research processors, at either uniformly high rates, low rates, or mixed rates. Eight post-lingually deafened adults were tested on perceived intracranial lateralization of ITDs ranging from 50 to 1600 μs. Extent of lateralization depended on the location of low-rate stimulation along the electrode array: greatest in the low- and mixed-rate configurations, and smallest in the high-rate configuration. All but one listener perceived a unitary auditory object. These findings suggest that a mixed-rate processing strategy can result in good lateralization and convey a unitary auditory object with ITDs.
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Affiliation(s)
- Tanvi Thakkar
- Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
| | - Alan Kan
- School of Engineering, Macquarie University, New South Wales 2109, Australia
| | - Ruth Y Litovsky
- Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
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Pieper SH, Hamze N, Brill S, Hochmuth S, Exter M, Polak M, Radeloff A, Buschermöhle M, Dietz M. Considerations for Fitting Cochlear Implants Bimodally and to the Single-Sided Deaf. Trends Hear 2022; 26:23312165221108259. [PMID: 35726211 PMCID: PMC9218456 DOI: 10.1177/23312165221108259] [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: 01/06/2022] [Revised: 04/28/2022] [Accepted: 05/02/2022] [Indexed: 11/16/2022] Open
Abstract
When listening with a cochlear implant through one ear and acoustically through the other, binaural benefits and spatial hearing abilities are generally poorer than in other bilaterally stimulated configurations. With the working hypothesis that binaural neurons require interaurally matched inputs, we review causes for mismatch, their perceptual consequences, and experimental methods for mismatch measurements. The focus is on the three primary interaural dimensions of latency, frequency, and level. Often, the mismatch is not constant, but rather highly stimulus-dependent. We report on mismatch compensation strategies, taking into consideration the specific needs of the respective patient groups. Practical challenges typically faced by audiologists in the proposed fitting procedure are discussed. While improvement in certain areas (e.g., speaker localization) is definitely achievable, a more comprehensive mismatch compensation is a very ambitious endeavor. Even in the hypothetical ideal fitting case, performance is not expected to exceed that of a good bilateral cochlear implant user.
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Affiliation(s)
- Sabrina H. Pieper
- Department of Medical Physics and Acoustic, University of Oldenburg, Oldenburg, Germany
- Cluster of Excellence Hearing4all, University of Oldenburg, Oldenburg, Germany
| | - Noura Hamze
- MED-EL Medical Electronics GmbH, Innsbruck, Austria
| | - Stefan Brill
- MED-EL Medical Electronics Germany GmbH, Starnberg, Germany
| | - Sabine Hochmuth
- Division of Otorhinolaryngology, University of Oldenburg, Oldenburg, Germany
| | - Mats Exter
- Cluster of Excellence Hearing4all, University of Oldenburg, Oldenburg, Germany
- Hörzentrum Oldenburg gGmbH, Oldenburg, Germany
| | - Marek Polak
- MED-EL Medical Electronics GmbH, Innsbruck, Austria
| | - Andreas Radeloff
- Cluster of Excellence Hearing4all, University of Oldenburg, Oldenburg, Germany
- Division of Otorhinolaryngology, University of Oldenburg, Oldenburg, Germany
- Research Center Neurosensory Science, University of Oldenburg, Oldenburg, Germany
| | | | - Mathias Dietz
- Department of Medical Physics and Acoustic, University of Oldenburg, Oldenburg, Germany
- Cluster of Excellence Hearing4all, University of Oldenburg, Oldenburg, Germany
- Research Center Neurosensory Science, University of Oldenburg, Oldenburg, Germany
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Bernstein JGW, Jensen KK, Stakhovskaya OA, Noble JH, Hoa M, Kim HJ, Shih R, Kolberg E, Cleary M, Goupell MJ. Interaural Place-of-Stimulation Mismatch Estimates Using CT Scans and Binaural Perception, But Not Pitch, Are Consistent in Cochlear-Implant Users. J Neurosci 2021; 41:10161-10178. [PMID: 34725189 PMCID: PMC8660045 DOI: 10.1523/jneurosci.0359-21.2021] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Revised: 08/23/2021] [Accepted: 10/01/2021] [Indexed: 11/21/2022] Open
Abstract
Bilateral cochlear implants (BI-CIs) or a CI for single-sided deafness (SSD-CI; one normally functioning acoustic ear) can partially restore spatial-hearing abilities, including sound localization and speech understanding in noise. For these populations, however, interaural place-of-stimulation mismatch can occur and thus diminish binaural sensitivity that relies on interaurally frequency-matched neurons. This study examined whether plasticity-reorganization of central neural pathways over time-can compensate for peripheral interaural place mismatch. We hypothesized differential plasticity across two systems: none for binaural processing but adaptation for pitch perception toward frequencies delivered by the specific electrodes. Interaural place mismatch was evaluated in 19 BI-CI and 23 SSD-CI human subjects (both sexes) using binaural processing (interaural-time-difference discrimination with simultaneous bilateral stimulation), pitch perception (pitch ranking for single electrodes or acoustic tones with sequential bilateral stimulation), and physical electrode-location estimates from computed-tomography (CT) scans. On average, CT scans revealed relatively little BI-CI interaural place mismatch (26° insertion-angle mismatch) but a relatively large SSD-CI mismatch, particularly at low frequencies (166° for an electrode tuned to 300 Hz, decreasing to 14° at 7000 Hz). For BI-CI subjects, the three metrics were in agreement because there was little mismatch. For SSD-CI subjects, binaural and CT measurements were in agreement, suggesting little binaural-system plasticity induced by mismatch. The pitch measurements disagreed with binaural and CT measurements, suggesting place-pitch plasticity or a procedural bias. These results suggest that reducing interaural place mismatch and potentially improving binaural processing by reprogramming the CI frequency allocation would be better done using CT-scan than pitch information.SIGNIFICANCE STATEMENT Electrode-array placement for cochlear implants (bionic prostheses that partially restore hearing) does not explicitly align neural representations of frequency information. The resulting interaural place-of-stimulation mismatch can diminish spatial-hearing abilities. In this study, adults with two cochlear implants showed reasonable interaural alignment, whereas those with one cochlear implant but normal hearing in the other ear often showed mismatch. In cases of mismatch, binaural sensitivity was best when the same cochlear locations were stimulated in both ears, suggesting that binaural brainstem pathways do not experience plasticity to compensate for mismatch. In contrast, interaurally pitch-matched electrodes deviated from cochlear-location estimates and did not optimize binaural sensitivity. Clinical correction of interaural place mismatch using binaural or computed-tomography (but not pitch) information may improve spatial-hearing benefits.
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Affiliation(s)
- Joshua G W Bernstein
- National Military Audiology and Speech Pathology Center, Walter Reed National Military Medical Center, Bethesda, Maryland 20889
| | - Kenneth K Jensen
- National Military Audiology and Speech Pathology Center, Walter Reed National Military Medical Center, Bethesda, Maryland 20889
| | - Olga A Stakhovskaya
- Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland 20742
| | - Jack H Noble
- Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37232
| | - Michael Hoa
- Department of Otolaryngology Head and Neck Surgery, Georgetown University Medical Center, Washington, DC 20057
| | - H Jeffery Kim
- Department of Otolaryngology Head and Neck Surgery, Georgetown University Medical Center, Washington, DC 20057
| | - Robert Shih
- Department of Radiology, Walter Reed National Military Medical Center, Bethesda, Maryland 20889
| | - Elizabeth Kolberg
- Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland 20742
| | - Miranda Cleary
- Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland 20742
| | - Matthew J Goupell
- Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland 20742
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