Relationships Between Electrically Evoked Potentials and Loudness Growth in Bilateral Cochlear Implant Users

Kirby, Benjamin; Brown, Carolyn J.; Abbas, Paul J.; Etler, Christine P.; O'Brien, Sara

doi:10.1097/aud.0b013e318239adb8

Cited by 17 publications

(12 citation statements)

References 35 publications

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“…In line with our results for 40-Hz ASSR amplitudes, they found that current levels that evoke the same EABR wave V amplitude were judged as balanced across the ears by 69% of children, and that lateralization occurred toward the side with the larger amplitude response. However, Kirby, Brown, Abbas, Etler, and O’Brien (2012) did not find evidence of equal loudness percepts at equal amplitudes for the two ears in bilateral CI users, for EABRs and electrically evoked compound action potentials, as the differences in perceived loudness across ears for stimuli matched for response amplitudes were 13% to 50%. Loudness growth for each ear was measured by using a loudness scale from 1 to 100.…”

Section: Discussionmentioning

confidence: 74%

Objective Binaural Loudness Balancing Based on 40-Hz Auditory Steady-State Responses. Part II: Asymmetric and Bimodal Hearing

et al. 2018

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In Part I, we investigated 40-Hz auditory steady-state response (ASSR) amplitudes for the use of objective loudness balancing across the ears for normal-hearing participants and found median across-ear ratios in ASSR amplitudes close to 1. In this part, we further investigated whether the ASSR can be used to estimate binaural loudness balance for listeners with asymmetric hearing, for whom binaural loudness balancing is of particular interest. We tested participants with asymmetric hearing and participants with bimodal hearing, who hear with electrical stimulation through a cochlear implant (CI) in one ear and with acoustical stimulation in the other ear. Behavioral loudness balancing was performed at different percentages of the dynamic range. Acoustical carrier frequencies were 500, 1000, or 2000 Hz, and CI channels were stimulated in apical or middle regions in the cochlea. For both groups, the ASSR amplitudes at balanced loudness levels were similar for the two ears, with median ratios between left and right ear stimulation close to 1. However, individual variability was observed. For participants with asymmetric hearing loss, the difference between the behavioral balanced levels and the ASSR-predicted balanced levels was smaller than 10 dB in 50% and 56% of cases, for 500 Hz and 2000 Hz, respectively. For bimodal listeners, these percentages were 89% and 60%. Apical CI channels yielded significantly better results (median difference near 0 dB) than middle CI channels, which had a median difference of −7.25 dB.

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Section: Discussionmentioning

confidence: 74%

Objective Binaural Loudness Balancing Based on 40-Hz Auditory Steady-State Responses. Part II: Asymmetric and Bimodal Hearing

et al. 2018

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“…First, such a procedure is likely to be too time-consuming for clinical use, at least with currently available procedures. Second, it would ideally need to occur at multiple stimulus levels, as the growth of loudness may differ between ears (Kirby et al, 2012), which means that an appropriate ‘localization map’ could vary with input signal level. Finally, the proposed procedure for a localization map may not facilitate fusing input from each ear into a single auditory image, as it cannot account for differences in electrode insertion depth, or neural survival.…”

Section: Discussionmentioning

confidence: 99%

Bilateral Loudness Balancing and Distorted Spatial Perception in Recipients of Bilateral Cochlear Implants

2015

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OBJECTIVE Determine if bilateral loudness balancing during mapping of bilateral cochlear implants (CIs) facilitates fused, punctate, and centered auditory images that facilitate lateralization with stimulation on single-electrode pairs. DESIGN Adopting procedures similar to those that are practiced clinically, we used direct stimulation to obtain most-comfortable levels (C levels) in recipients of bilateral Cis. Three pairs of electrodes, located in the base, middle, and apex of the electrode array, were tested. These electrode pairs were loudness-balanced by playing right-left electrode pairs sequentially. In experiment 1, we measured the location, number, and compactness of auditory images in 11 participants in a subjective fusion experiment. In experiment 2, we measured the location and number of the auditory images while imposing a range of interaural level differences (ILDs) in 13 participants in a lateralization experiment. Six of these participants repeated the mapping process and lateralization experiment over three separate days to determine the variability in the procedure. RESULTS In approximately 80% of instances, bilateral loudness balancing was achieved from relatively small adjustments to the C levels (≤3 clinical current units, CU). More important, however, was the observation that in four of eleven participants, simultaneous bilateral stimulation regularly elicited percepts that were not fused into a single auditory object. Across all participants, approximately 23% of percepts were not perceived as fused; this contrasts with the 1-2% incidence of diplacusis observed with normal-hearing individuals. In addition to the unfused images, the perceived location was often offset from the physical ILD. On the whole, only 45% of percepts presented with an ILD of 0 CU were perceived as fused and heard in the center of the head. Taken together, these results suggest that distortions to the spatial map remain common in bilateral CI recipients even after careful bilateral loudness balancing. CONCLUSION The primary conclusion from these experiments is that, even after bilateral loudness balancing, bilateral CI recipients still regularly perceive stimuli that are either unfused, offset from the assumed zero ILD, or both. Thus, while current clinical mapping procedures for bilateral CIs are sufficient to enable many of the benefits of bilateral hearing, they may not elicit percepts that are thought to be optimal for sound-source location. As a result, in the absence of new developments in signal processing for CIs, new mapping procedures may need to be developed for bilateral CI recipients to maximize the benefits of bilateral hearing.

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“…However, it is reasonable to assume that more specific psychoacoustical perceptions, like enhanced loudness growth or pitch perception [ 11 , 12 , 22 ] are directly linked to the activation of the residual auditory neurons by the electrical stimulation delivered by the electrode array. Indeed Cohen [ 12 ] and Kirby et al [ 23 ] clearly showed that loudness growth function was proportional to e-CAP growth function, meaning that a stimulation with an increased current level causes an enhanced activation of auditory neurons, either directly by a recruitment of more neurons in the same region of the spiral ganglion, or indirectly by the spread of excitation of the electrical stimulation. However, e-CAP amplitude does not directly predict loudness, since it depends on additional factors discussed hereafter.…”

Section: Discussionmentioning

confidence: 99%

Modeling of Auditory Neuron Response Thresholds with Cochlear Implants

Venail

Mura

Akkari

et al. 2015

BioMed Research International

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The quality of the prosthetic-neural interface is a critical point for cochlear implant efficiency. It depends not only on technical and anatomical factors such as electrode position into the cochlea (depth and scalar placement), electrode impedance, and distance between the electrode and the stimulated auditory neurons, but also on the number of functional auditory neurons. The efficiency of electrical stimulation can be assessed by the measurement of e-CAP in cochlear implant users. In the present study, we modeled the activation of auditory neurons in cochlear implant recipients (nucleus device). The electrical response, measured using auto-NRT (neural responses telemetry) algorithm, has been analyzed using multivariate regression with cubic splines in order to take into account the variations of insertion depth of electrodes amongst subjects as well as the other technical and anatomical factors listed above. NRT thresholds depend on the electrode squared impedance (β = −0.11 ± 0.02, P < 0.01), the scalar placement of the electrodes (β = −8.50 ± 1.97, P < 0.01), and the depth of insertion calculated as the characteristic frequency of auditory neurons (CNF). Distribution of NRT residues according to CNF could provide a proxy of auditory neurons functioning in implanted cochleas.

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Relationships Between Electrically Evoked Potentials and Loudness Growth in Bilateral Cochlear Implant Users

Cited by 17 publications

References 35 publications

Objective Binaural Loudness Balancing Based on 40-Hz Auditory Steady-State Responses. Part II: Asymmetric and Bimodal Hearing

Objective Binaural Loudness Balancing Based on 40-Hz Auditory Steady-State Responses. Part II: Asymmetric and Bimodal Hearing

Bilateral Loudness Balancing and Distorted Spatial Perception in Recipients of Bilateral Cochlear Implants

Modeling of Auditory Neuron Response Thresholds with Cochlear Implants

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