Search

In cochlear implants, loudness has been shown to grow more slowly with increasing pulse phase duration (PPD) than with pulse amplitude (PA), possibly due to "leaky" charge integration. This leakiness has been recently quantified in terms of "charge integration efficiency," defined as the log difference between the PPD dynamic range and PA dynamic range (both expressed in charge units), relative to a common threshold anchor. Such leakiness may differ across electrodes and/or test ears, and may reflect underlying neural health. In this study, we examined the across-site variation of charge integration in recipients of Cochlear© devices. PPD and PA dynamic ranges were measured relative to two threshold anchors with either a 25- or 50-microsecond PPD. Strength-duration functions, previously shown to relate to survival of spiral ganglion cells and peripheral processes, were compared to charge integration efficiency on selected electrodes. Results showed no significant or systematic relationship between the across-site variation in charge integration efficiency and electrode position or threshold levels. Charge integration efficiency was poorer with the 50-μs threshold anchor, suggesting that greater leakiness was associated with larger PPD dynamic ranges. Poorer and more variable charge integration efficiency across electrodes was associated with longer duration of any hearing loss, consistent with the idea that poor integration is related to neural degeneration. More variable integration efficiency was also associated with poorer speech recognition performance across test ears. The slopes of the strength-duration functions at maximum acceptable loudness were significantly correlated with charge integration efficiency. However, the strength-duration slopes were not predictive of duration of any hearing loss or speech recognition performance in our participants. As such, charge integration efficiency may be a better candidate to measure leakiness in neural populations across the electrode array, as well as the general health of the auditory nerve in human cochlear implant recipients.

Background: Adults with single sided deafness (SSD) have lost binaural function, which limits sound source localization, speech understanding in noise, and quality of life. For SSD patients, restoration of bilateral auditory input is possible only with a cochlear implant (CI). In this study, cortical auditory evoked potentials (CAEPs) and behavioral performance were measured in left-implanted (SSD-CI-L) and right-implanted (SSD-CI-R) patients before and after cochlear implantation. We hypothesized that improvements in behavioral performance would be accompanied by changes in CAEPs after cochlear implantation., Design: Prospective longitudinal study., Setting: Tertiary referral center., Method: Nine right-handed adult SSD CI patients participated in the study. CAEPs were recorded before cochlear implantation and at 6 and 12 months post-implantation. CAEPs were elicited using speech stimuli (/ba/) delivered in sound field at 70 dBA. Global field power (GFP) latency and amplitude were calculated for P1, N1 and P2 peaks at each test session. CAEP were analyzed at frontocentral (Cz) and temporal (P7, P8, T7 and T8) and mastoid electrodes (M1 and M2) contralateral to the CI ear. Behavioral measures (sentence recognition in noise, with and without spatial cues) were collected at the same test sessions as for CAEPs. Speech performance and CAEPs were also measured in a control group of normal-hearing (NH) subjects., Results: While increased N1 amplitude was observed in the scalp potential maps for GFP and Cz for SSD-CI-L patients after implantation, the changes were not statistically significant. Peak CAEP amplitude at electrodes to contralateral to the CI ear increased after cochlear implantation for all SSD-CI patients, but significant increases were observed only for mastoid sites. Peak latencies for some components at temporal and mastoid sites remained significantly longer than for the NH control group, even after cochlear implantation. For SSD-CI-R patients, P2 peak amplitude for baseline GFP and Cz was significantly lower than for the NH control group. A significant improvement for speech understanding in noise was observed at 12 months post-implantation when speech was presented to the CI ear and noise to the non-implanted ear., Conclusion: After cochlear implantation, speech understanding significantly improved when speech and noise were spatially separated. The increased N1 amplitude for SSD-CI-L patients and the increased bilateral activation for all SSD-CI patients may reflect cortical reorganization and restoration of binaural function after one year of experience with the CI. However, because of the limited number of SSD patients, significant changes in cortical activity after cochlear implantation were often difficult to observe., Competing Interests: The authors have declared that no competing interests exist.

Objectives: For prelingually deaf children, cochlear implants (CIs) can restore auditory input to the auditory cortex and the ability to acquire spoken language. Language development is strongly intertwined with voice perception. The aim of this electrophysiological study was to investigate human voice processing using measures of cortical auditory evoked potentials (AEPs) in pediatric CI users., Design: Cortical AEPs were measured in 8 CI children (4 to 12 years old) with good auditory and language performance and 8 normal-hearing (NH) age-matched controls. The auditory stimuli were nonspeech vocal sounds (laughing, sighing, coughing) and environmental sounds (e.g., telephones, alarms, cars, bells, water, wind). Independent component analysis was used to minimize the CI artifact in cortical AEPs., Results: Fronto-temporal positivity to vocal sounds was found in NH children, with a significant effect in the 140 to 240 msec latency range. In CI children, there was a positive response to vocal sounds in the 170 to 250 msec latency range, with a more diffuse and anterior distribution than in the NH children., Conclusions: Cortical responses to vocal sounds were recorded in CI children. The topography and latency of response to voice differed from that of NH children. The results suggest that cortical reorganization for processing vocal sounds may occur in congenitally deaf children fitted with a CI.

Cochlear implantation (CI) can benefit patients with single-sided deafness (SSD) in terms of sound localization, speech understanding in noise, tinnitus severity, and quality of life (QoL). In previous studies, CI outcomes have been largely reported for SSD patients with normal "unrestricted" hearing in the contralateral ear. However, SSD patients may often have some degree of hearing loss in the contralateral ear ("restricted" acoustic hearing). In this study, we report results from a French clinical trial for CI in in SSD patients (NCT02204618). Localization, speech reception thresholds (SRTs) in noise, tinnitus severity, and QoL were evaluated in 18 SSD patients 1 year after CI. Data were analyzed for 2 subject groups according to the pure-tone average thresholds in the non-implanted ear: unrestricted acoustic hearing (UNRES; ≤25 dB HL; n = 10) and restricted acoustic hearing (RES; > 25 dB HL; n = 8). Across all subjects, localization was significantly better with the CI on than off (p = 0.005); there was no significant difference between subject groups (p = 0.301). When speech and noise were co-located (S0N0), there was no significant difference in SRTs with the CI on or off (p = 0.480); SRTs were significantly better for the UNRES than for the RES group (p = 0.005). When speech and noise were spatially separated (SCINNH), SRTs were significantly better with the CI on than off (p < 0.001). While SRTs were better for the UNRES than for the RES group (p = 0.024), the CI benefit was more than 50% greater for the RES group due to the restoration of high-frequency speech cues. Questionnaire data showed that tinnitus severity was significantly reduced (p = 0.045) and QoL was significantly improved after one year of experience with the CI (p < 0.001). Age at testing was significantly correlated with SRTs for the S0N0 condition; duration of deafness was correlated with SRTs for the SCINNH condition. There were relatively few correlations between behavioral and subjective measures, suggesting that both were valuable when assessing CI benefits for SSD patients. The present data suggest that indications for CI should be expanded to include unilaterally deaf patients who have normal hearing or mild-to-moderate hearing loss in the non-implanted ear., (© 2018 S. Karger AG, Basel.)

In cochlear implants (CIs), different talkers often produce different levels of speech understanding because of the spectrally distorted speech patterns provided by the implant device. A spectral normalization approach was used to transform the spectral characteristics of one talker to those of another talker. In Experiment 1, speech recognition with two talkers was measured in CI users, with and without spectral normalization. Results showed that the spectral normalization algorithm had small but significant effect on performance. In Experiment 2, the effects of spectral normalization were measured in CI users and normal-hearing (NH) subjects; a pitch-stretching technique was used to simulate six talkers with different fundamental frequencies and vocal tract configurations. NH baseline performance was nearly perfect with these pitch-shift transformations. For CI subjects, while there was considerable intersubject variability in performance with the different pitch-shift transformations, spectral normalization significantly improved the intelligibility of these simulated talkers. The results from Experiments 1 and 2 demonstrate that spectral normalization toward more-intelligible talkers significantly improved CI users' speech understanding with less-intelligible talkers. The results suggest that spectral normalization using optimal reference patterns for individual CI patients may compensate for some of the acoustic variability across talkers.

Cochlear implants provide a limited number of electrodes, each of which represents a channel of spectral information. Studies have shown that implant recipients are not receiving all of the information from the channels presented to their implant. The present paper provides a quantitative framework for evaluating how many spectral channels of information are necessary for speech recognition. Speech and melody recognition data from previous studies with cochlear implant simulations are compared as a function of the number of spectral channels of information. A quantitative model is applied to the results. Speech recognition performance increases as the number of spectral channels increases. A sigmoid function best describes this increase when plotted as a function of the log number of channels. As speech materials become more difficult, the function shifts to the right, indicating that more spectral channels of information are required. A model proposed by Plomp provides a single index to relate the difficulty of the task to the number of spectral channels needed for moderate recognition performance. In conclusion, simple sentence recognition in quiet can be achieved with only 3-4 channels of spectral information, while more complex materials can require 30 or more channels for an equivalent level of performance. The proposed model provides a single index that not only quantifies the number of functional channels in a cochlear implant, but also predicts the level of performance for different listening tasks.

This study evaluated the effects of time compression and expansion on sentence recognition by normal-hearing (NH) listeners and cochlear-implant (CI) recipients of the Nucleus-22 device. Sentence recognition was measured in five CI users using custom 4-channel continuous interleaved sampler (CIS) processors and five NH listeners using either 4-channel or 32-channel noise-band processors. For NH listeners, recognition was largely unaffected by time expansion, regardless of spectral resolution. However, recognition of time-compressed speech varied significantly with spectral resolution. When fine spectral resolution (32 channels) was available, speech recognition was unaffected even when the duration of sentences was shortened to 40% of their original length (equivalent to a mean duration of 40 ms/phoneme). However, a mean duration of 60 ms/phoneme was required to achieve the same level of recognition when only coarse spectral resolution (4 channels) was available. Recognition patterns were highly variable across CI listeners. The best CI listener performed as well as NH subjects listening to corresponding spectral conditions; however, three out of five CI listeners performed significantly poorer in recognizing time-compressed speech. Further investigation revealed that these three poorer-performing CI users also had more difficulty with simple temporal gap-detection tasks. The results indicate that limited spectral resolution reduces the ability to recognize time-compressed speech. Some CI listeners have more difficulty with time-compressed speech, as produced by rapid speakers, because of reduced spectral resolution and deficits in auditory temporal processing.

To assess the impact of rehabilitation systems (CROS: Contralateral Routing of Signal; BAHA: Bone-Anchored Hearing Aid; CI: cochlear implant) on cortical auditory evoked potentials (CAEP) and auditory performance in unilateral hearing loss. Twenty-one adults with unilateral hearing loss, using CROS (n = 6), BAHA (n = 6) or CI (n = 9), were included. Seven normal-hearing subjects served as controls. CAEPs were recorded for a (/ba/) speech stimulus; for patients, tests were conducted with and without their auditory rehabilitation. Amplitude and latency of the various CAEP components of the global field power (GFP) were measured, and scalp potential fields were mapped. Behavioral assessment used sentence recognition in noise, with and without spatial cues. Only CI induced N1 peak amplitude change (P < 0.05). CI and CROS increased polarity inversion amplitude in the contralateral ear, and frontocentral negativity on the scalp potential map. CI improved understanding when speech was presented to the implanted ear and noise to the healthy ear, and vice-versa. Cochlear implantation had the greatest impact on CAEP morphology and auditory performance. A longitudinal study could analyze progression of cortical reorganization. [ABSTRACT FROM AUTHOR]

Objectives: Cochlear implantation (CI) outcomes have been largely reported for single-sided deafness (SSD) patients with normal contralateral hearing (SYM group). However, SSD patients may have some degree of contralateral hearing loss (ASYM group). We report results from a French clinical trial for cochlear implantation in SSD patients. Material and methods: Localization, speech understanding in noise, tinnitus severity, and quality of life (QoL) were evaluated in 18 SSD patients, 1 year after CI. Data were also analyzed for two subject groups according to the pure-tone average threshold (PTA) in the non-implanted ear: SYM group (≤ 25 dB HL; n=10), ASYM group (> 25 dB HL; n=8). Results: Localization was significantly better with the CI on (p<0.05); there was no significant difference between groups (p>0.05). For the ASYM group, 500-Hz thresholds were significantly correlated with localization performance with the CI on. When speech and noise were co-located, there was no significant difference in speech reception thresholds (SRTs) with the CI on or off (p>0.05); SRTs were significantly better for the SYM than for the ASYM group (p<0.05). PTA thresholds were significantly correlated with SRTs with the CI on or off (p<0.05). When speech and noise were spatially separated, SRTs were significantly better with the CI on than off (p<0.05); while SRTs were significantly better for the SYM than for the ASYM group, the benefit of the CI was more than 50% greater for the ASYM group and there was no significant effect of PTA (p>0.05). PTA thresholds were significantly correlated with SRTs with the CI off only (p<0.05). Tinnitus severity was significantly reduced (p<0.05) and QoL was significantly improved (p<0.05). Conclusion: The results suggest that SSD patients with symmetric or asymmetric hearing in the non-implanted ear can benefit from CI and that indications for CI should be broadened to include these patients. [ABSTRACT FROM AUTHOR]

Objectives: Evaluate safety and efficacy of cochlear implantation for single-sided deafness (SSD) patients. Methods: Data are reported for 10 patients who completed the FDA-approved study. Audiological thresholds, localization, speech perception in quiet and in noise, tinnitus severity, dizziness severity, and quality of life (QoL) were measured before implantation and during the six-month period after activation of the cochlear implant (CI). All patients were implanted with the Med-El Flex 28 device. Results: Data reported is six months post-activation of the CI, relative to baseline. Mean pure-tone average thresholds with the CI-only improved from 91.9 to 38.4 dB HL. Mean word and sentence recognition in quiet with the CI-only improved by 51.1 and 84.4 percentage points, respectively. Mean error in localization was reduced by 11.5 degrees. Mean speech reception thresholds in noise (measured with speech presented in front) improved by 0.8 dB when noise was presented to the CI ear, by 2.8 dB when noise was presented in front, and by 2.6 dB when noise was presented to the normal-hearing ear. Mean tinnitus severity according to a visual analog scale was reduced by 1.9 points (scale: 0-10). The mean Tinnitus Functional Index score was reduced by 22.9 points (scale: 0-100). The mean Dizziness Handicap Inventory score was reduced by 4.6 points (scale: 0-100). For the Glasgow Hearing Aid Benefit Profile, mean difficulty was reduced by 0.9 points with the CI on (scale: 0-5); patients generally found the CI to be helpful. For the Speech, Spatial, and Quality of hearing questionnaire (scale: 0-10), mean scores improved by 2.3, 3.0, and 1.0 points for the Speech, Spatial, and Quality categories, respectively. These data suggest that cochlear implantation can improve SSD patients' sound awareness, sound source localization, speech understanding in quiet and in noise, and QoL, while reducing tinnitus and dizziness severity. [ABSTRACT FROM AUTHOR]