Cross-modal reorganization in cochlear implant users: Auditory cortex contributes to visual face processing

Event Abstract Back to Event Altered hemispheric asymmetries of auditory evoked potentials after cochlear implantation Pascale Sandmann1*, T. Eichele2, S. Debener3, 4, M. Buechler5, L. Jancke1, N. Dillier5, Kenneth Hugdahl2, 6 and M. Meyer1 1 University of Zurich, Switzerland 2 University of Bergen, Norway 3 MRC Institute of Hearing Research of Southampton, United Kingdom 4 University of Southampton, United Kingdom 5 University Hospital Zurich, Switzerland 6 Haukeland University Hospital, Norway Hearing can be restored in individuals suffering from severe and profound hearing loss using a cochlear implant (CI). A CI bypasses the outer and middle ear and directly stimulates the (residual) fibres of the auditory nerve. To assess auditory cortex functions, late auditory evoked potentials (AEPs) are widely used in clinical context. However, in CI users electrophysiological measures are of limited utility due to the generation of electrical artefacts in the electroencephalogram (EEG). In order to evaluate the functional outcome after cochlear implantation, the present study examined hemispheric asymmetries of AEPs to complex sound processing in CI users. Two dyadic tonal intervals were presented in an active oddball design as well as in a passive listening condition. Using independent component analysis (ICA), CI-related artefacts could be successfully reduced in EEGs of CI users (n=12). BESA dipole source analysis of recovered AEPs allowed for the evaluation of hemispheric differences in the primary auditory cortex. The results are remarkable for two reasons. First, they indicate altered hemispheric asymmetries for complex sound processing in CI users compared to normal-hearing listeners. Second, the results demonstrate that ICA can solve the problem of CI-related artefacts, thereby enabling a detailed investigation of auditory cortex activity in CI users. This is of utmost clinical relevance to make AEP applicable in investigating auditory cortical reorganization after cochlear implantation. Conference: 10th International Conference on Cognitive Neuroscience, Bodrum, Turkey, 1 Sep - 5 Sep, 2008. Presentation Type: Poster Presentation Topic: Cerebral Asymmetry Citation: Sandmann P, Eichele T, Debener S, Buechler M, Jancke L, Dillier N, Hugdahl K and Meyer M (2008). Altered hemispheric asymmetries of auditory evoked potentials after cochlear implantation. Conference Abstract: 10th International Conference on Cognitive Neuroscience. doi: 10.3389/conf.neuro.09.2009.01.149 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Dec 2008; Published Online: 05 Dec 2008. * Correspondence: Pascale Sandmann, University of Zurich, Zurich, Switzerland, p.sandmann@psychologie.uzh.ch Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Pascale Sandmann T. Eichele S. Debener M. Buechler L. Jancke N. Dillier Kenneth Hugdahl M. Meyer Google Pascale Sandmann T. Eichele S. Debener M. Buechler L. Jancke N. Dillier Kenneth Hugdahl M. Meyer Google Scholar Pascale Sandmann T. Eichele S. Debener M. Buechler L. Jancke N. Dillier Kenneth Hugdahl M. Meyer PubMed Pascale Sandmann T. Eichele S. Debener M. Buechler L. Jancke N. Dillier Kenneth Hugdahl M. Meyer Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Some cochlear implant (CI) users report having difficulty accessing indexical information in the speech signal, presumably due to limitations in the transmission of fine spectrotemporal cues. The purpose of this review article was to systematically review and evaluate the existing research on talker processing in CI users. Specifically, we reviewed the performance of CI users in three types of talker- and voice-related tasks. We also examined the different factors (such as participant, hearing, and device characteristics) that might influence performance in these specific tasks. We completed a systematic search of the literature with select key words using citation aggregation software to search Google Scholar. We included primary reports that tested (a) talker discrimination, (b) voice perception, and (c) talker identification. Each report must have had at least one group of participants with CIs. Each included study was also evaluated for quality of evidence. The searches resulted in 1,561 references, which were first screened for inclusion and then evaluated in full. Forty-three studies examining talker discrimination, voice perception, and talker identification were included in the final review. Most studies were focused on postlingually deafened and implanted adult CI users, with fewer studies focused on prelingual implant users. In general, CI users performed above chance in these tasks. When there was a difference between groups, CI users performed less accurately than their normal-hearing (NH) peers. A subset of CI users reached the same level of performance as NH participants exposed to noise-vocoded stimuli. Some studies found that CI users and NH participants relied on different cues for talker perception. Within groups of CI users, there is moderate evidence for a bimodal benefit for talker processing, and there are mixed findings about the effects of hearing experience. The current review highlights the challenges faced by CI users in tracking and recognizing voices and how they adapt to it. Although large variability exists, there is evidence that CI users can process indexical information from speech, though with less accuracy than their NH peers. Recent work has described some of the factors that might ease the challenges of talker processing in CI users. We conclude by suggesting some future avenues of research to optimize real-world speech outcomes.

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ObjectivesMany studies have suggested that cochlear implant (CI) users vary in terms of speech recognition in noise. Studies in this field attribute this variety partly to subcortical auditory processing. Studying speech-Auditory Brainstem Response (speech-ABR) provides good information about speech processing; thus, this work was designed to compare speech-ABR components between two groups of CI users with good and poor speech recognition in noise scores. Materials & MethodsThe present study was conducted on two groups of CI users aged 8-10 years old. The first group (CI-good) consisted of 15 children with prelingual CI who had good speech recognition in noise performance. The second group (CI-poor) was matched with the first group, but they had poor speech recognition in noise performance. The speech-ABR test in a sound-field presentation was performed for all the participants. Results The speech-ABR response showed more delay in C, D, E, F, O latencies in CI-poor than CI-good users (P <0.05), meanwhile no significant difference was observed in initial wave (V(t= -0.293, p= 0.771 and A (t= -1.051, p= 0.307). Analysis in spectral-domain showed a weaker representation of fundamental frequency as well as the first formant and high-frequency component of speech stimuli in the CI users with poor auditory performance.ConclusionsResults revealed that CI users who showed poor auditory performance in noise performance had deficits in encoding the periodic portion of speech signals at the brainstem level. Also, this study could be as physiological evidence for poorer pitch processing in CI users with poor speech recognition in noise performance.

Aging may limit speech understanding outcomes in cochlear-implant (CI) users.Here, we examined age-related declines in auditory temporal processing as apotential mechanism that underlies speech understanding deficits associated withaging in CI users. Auditory temporal processing was assessed with acategorization task for the words dish and ditch (i.e., identify each token asthe word dish or ditch) on a continuum ofspeech tokens with varying silence duration (0 to 60 ms) prior to the finalfricative. In Experiments 1 and 2, younger CI (YCI), middle-aged CI (MCI), andolder CI (OCI) users participated in the categorization task across a range ofpresentation levels (25 to 85 dB). Relative to YCI, OCI required longer silencedurations to identify ditch and exhibited reduced ability to distinguish thewords dish and ditch (shallower slopes in the categorization function).Critically, we observed age-related performance differences only at higherpresentation levels. This contrasted with findings from normal-hearing listenersin Experiment 3 that demonstrated age-related performance differencesindependent of presentation level. In summary, aging in CI users appears todegrade the ability to utilize brief temporal cues in word identification,particularly at high levels. Age-specific CI programming may potentially improveclinical outcomes for speech understanding performance by older CIlisteners.

Auditory cortical activity to different voice onset times in cochlear implant users

On the relationship between auditory cognition and speech intelligibility in cochlear implant users: An ERP study

An intact auditory system is essential for the development and maintenance of voice quality and speech prosody. On the contrary hearing loss affects the adjustments and appropriate use of organs involved in speech and voice production. Spectro-acoustic voice parameters have been evaluated in Cochlear Implant (CI) users, and the authors of previous systematic reviews on the topic concluded that fundamental frequency (F0) seemed preliminarily the most reliable parameter to evaluate voice alterations in adult CI users. The main aim of this systematic review and meta-analysis was to clarify the vocal parameters and prosodic alterations of speech in pediatric CI users. The protocol of the systematic review was registered on the PROSPERO database, International prospective register of systematic reviews. We conducted a search of the English literature published in the period between January 1, 2005 and April 1, 2022 on the Pubmed and Scopus databases. A meta-analysis was conducted to compare the values of voice acoustic parameters in CI users and non-hearing-impaired controls. The analysis was conducted using the standardized mean difference as the outcome measure. A random-effects model was fitted to the data. A total of 1334 articles were initially evaluated using title and abstract screening. After applying inclusion/exclusion criteria, 20 articles were considered suitable for this review. The age of the cases ranged between 25 and 132 months at examination. The most studied parameters were F0, Jitter, Shimmer and Harmonics-to-Noise Ratio (HNR); other parameters were seldom reported. A total of 11 studies were included in the meta-analysis of F0, with the majority of estimates being positive (75%); the estimated average standardized mean difference based on the random-effects model was 0.3033 (95% CI: 0.0605 to 0.5462; P = 0.0144). For Jitter (0.2229; 95% CI: -0.1862 to 0.7986; P = 0.2229) and shimmer (0.2540; 95% CI: -0.1404 to 0.6485; P = 0.2068) there was a trend toward positive values without reaching statistical significance. This meta-analysis confirmed that higher F0 values have been observed in the pediatric population of CI users compared to age-matched normal hearing volunteers, whereas the parameters of voice noise were not significantly different between cases and controls. Prosodic aspects of language need further investigations. In longitudinal contexts, prolonged auditory experience with CI has brought voice parameters closer to the norm. Following the available evidence, we stress the utility of inclusion of vocal acoustic analysis in the clinical evaluation and follow-up of CI patients to optimize the rehabilitation process of pediatric patients with hearing loss.

Auditory brainstem implants (ABI) use the same processing strategy as was developed for cochlear implants (CI). However, the cochlear nucleus (CN), the stimulation site of ABIs, is anatomically and physiologically more complex than the auditory nerve and consists of neurons with differing roles in auditory processing. The aim of this study was to evaluate the hypotheses that ABI users are less able than CI users to access speech spectro-temporal information delivered by the existing strategies and that the sites stimulated by different locations of CI and ABI electrode arrays differ in encoding of temporal patterns in the stimulation. Six CI users and four ABI users of Nucleus implants with ACE processing strategy participated in this study. Closed-set perception of aCa syllables (16 consonants) and bVd words (11 vowels) was evaluated via experimental processing strategies that activated one, two, or four of the electrodes of the array in a CIS manner as well as subjects' clinical strategies. Three single-channel strategies presented the overall temporal envelope variations of the signal on a single-implant electrode located at the high-, medium-, and low-frequency regions of the array. Implantees' ability to discriminate within electrode temporal patterns of stimulation for phoneme perception and their ability to make use of spectral information presented by increased number of active electrodes were assessed in the single- and multiple-channel strategies, respectively. Overall percentages and information transmission of phonetic features were obtained for each experimental program. Phoneme perception performance of three ABI users was within the range of CI users in most of the experimental strategies and improved as the number of active electrodes increased. One ABI user performed close to chance with all the single and multiple electrode strategies. There was no significant difference between apical, basal, and middle CI electrodes in transmitting speech temporal information, except a trend that the voicing feature was the least transmitted by the basal electrode. A similar electrode-location pattern could be observed in most ABI subjects. Although the number of tested ABI subjects was small, their wide range of phoneme perception performance was consistent with previous reports of overall speech perception in ABI patients. The better-performing ABI user participants had access to speech temporal and spectral information that was comparable to that of average CI user. The poor-performing ABI user did not have access to within-channel speech temporal information and did not benefit from an increased number of spectral channels. The within-subject variability between different ABI electrodes was less than the variability across users in transmission of speech temporal information. The difference in the performance of ABI users could be related to the location of their electrode array on the CN, anatomy, and physiology of their CN or the damage to their auditory brainstem due to tumor or surgery.

Musical and vocal emotion perception for cochlear implants users

Objective To investigate electrically evoked auditory cortical responses (eACR) elicited from the stimulation of intracochlear electrodes based on individually fitted stimulation parameters in cochlear implant (CI) users. Design An eACR setup based on individual fitting parameters is proposed. A 50-ms alternating biphasic pulse train was used to stimulate apical, medial, and basal electrodes and to evoke auditory cortical potentials (N1-P2 complex). Study sample The eACR setup proposed was validated with 14 adult CI users. Results Individual and grand-average eACR waveforms were obtained. The eACR amplitudes were lower in the basal than in the apical and medial regions. Earlier N1 latencies were found in CI users with lower maximum comfortable loudness levels and shorter phase duration in response to apical stimulation, while medial and basal stimulation resulted in earlier N1 latencies and larger N1-P2 amplitudes in users with longer CI experience. Conclusions eACR could be elicited by direct intracochlear stimulation using individual fitting parameters with a success rate of 71%. The highest cortical peak-to-peak amplitudes were obtained in response to apical stimulation. Unlike the P2, the N1 component appeared to be a consistent cortical potential to determine eACR and gain knowledge of the auditory processing beyond the cochlea in CI users. Highlights eACR can be elicited through direct stimulation of intracochlear electrodes. Stimulation of apical and medial regions yielded the highest N1-P2 amplitudes. CI users with lower maximum comfortable loudness levels had shorter N1 latencies during apical stimulation. The present dataset of mainly well-performing CI users suggests better cortical processing, that is, higher amplitudes and shorter latencies of N1. The N1 potential appears a more consistent and reliable potential than the P2 to determine eACR responses in CI users.

Cochlear implantation constitutes a successful therapy of inner ear deafness, with the majority of patients showing good outcomes. There is, however, still some unexplained variability in outcomes with a number of cochlear-implant (CI) users, showing major limitations in speech comprehension. The current study used a multimodal diagnostic approach combining single-photon emission computed tomography (SPECT) and electroencephalography (EEG) to examine the mechanisms underlying speech processing in postlingually deafened CI users (N = 21). In one session, the participants performed a speech discrimination task, during which a 96-channel EEG was recorded and the perfusions marker 99mTc-HMPAO was injected intravenously. The SPECT scan was acquired 1.5 h after injection to measure the cortical activity during the speech task. The second session included a SPECT scan after injection without stimulation at rest. Analysis of EEG and SPECT data showed N400 and P600 event-related potentials (ERPs) particularly evoked by semantic violations in the sentences, and enhanced perfusion in a temporo-frontal network during task compared to rest, involving the auditory cortex bilaterally and Broca’s area. Moreover, higher performance in testing for word recognition and verbal intelligence strongly correlated to the activation in this network during the speech task. However, comparing CI users with lower and higher speech intelligibility [median split with cutoff + 7.6 dB signal-to-noise ratio (SNR) in the Göttinger sentence test] revealed for CI users with higher performance additional activations of parietal and occipital regions and for those with lower performance stronger activation of superior frontal areas. Furthermore, SPECT activity was tightly coupled with EEG and cognitive abilities, as indicated by correlations between (1) cortical activation and the amplitudes in EEG, N400 (temporal and occipital areas)/P600 (parietal and occipital areas) and (2) between cortical activation in left-sided temporal and bilateral occipital/parietal areas and working memory capacity. These results suggest the recruitment of a temporo-frontal network in CI users during speech processing and a close connection between ERP effects and cortical activation in CI users. The observed differences in speech-evoked cortical activation patterns for CI users with higher and lower speech intelligibility suggest distinct processing strategies during speech rehabilitation with CI.

An experiment was conducted to investigate the feasibility of using functional near-infrared spectroscopy (fNIRS) to image cortical activity in the language areas of cochlear implant (CI) users and to explore the association between the activity and their speech understanding ability. Using fNIRS, 15 experienced CI users and 14 normal-hearing participants were imaged while presented with either visual speech or auditory speech. Brain activation was measured from the prefrontal, temporal, and parietal lobe in both hemispheres, including the language-associated regions. In response to visual speech, the activation levels of CI users in an a priori region of interest (ROI)—the left superior temporal gyrus or sulcus—were negatively correlated with auditory speech understanding. This result suggests that increased cross-modal activity in the auditory cortex is predictive of poor auditory speech understanding. In another two ROIs, in which CI users showed significantly different mean activation levels in response to auditory speech compared with normal-hearing listeners, activation levels were significantly negatively correlated with CI users’ auditory speech understanding. These ROIs were located in the right anterior temporal lobe (including a portion of prefrontal lobe) and the left middle superior temporal lobe. In conclusion, fNIRS successfully revealed activation patterns in CI users associated with their auditory speech understanding.

Cochlear implants (CI) afford listeners with limited spectral resolution, thereby constraining semantic processing. Prior research has predominantly used isolated words or sentences without context, a method that lacks ecological validity and may place greater demands on working memory (WM) due to the absence of contextual linguistic information. This study examined the semantic processing of experienced CI users (N = 21) and age-matched normal-hearing controls (NH, N = 21) using an audiobook. We measured neuroelectric brain activity while participants listened to a story in which we inserted an incongruent word every 45 s, herein, the E45 condition. WM and behavioral semantic judgment were quantified with a listening span test. Temporal response functions, linear models that characterize how continuous stimulus features are temporally mapped onto neural responses, were used to quantify speech neural tracking of audio features (envelope, word onset, word surprisal) during ongoing speech. Results showed reliable neural tracking of acoustic features and word surprisal. Compared to the Control condition, E45 elicited larger TRF-N400 responses in both groups. Although TRF-N400 amplitudes were comparable between CI and NH listeners, CI users exhibited delayed responses. In NH listeners, larger N400 effects were associated with greater semantic judgment accuracy, linking neural responses to behavioral performance. These results show the validity of an ecologically valid paradigm that does not require an explicit behavioral response to quantify semantic processing in CI users.

ABSTRACTNormal auditory feedback contributes to moment-to-moment control of speech production. Effects of auditory feedback’s absence on hearing-impaired individuals are widely documented, but auditory perturbation has not been investigated. Our objective was to evaluate the effect of delayed auditory feedback (DAF) and frequency altered feedback (FAF) on speech production among prelingual cochlear implant (CI) users and normal hearing (NH) individuals, to evaluate CI users’ reliance on auditory feedback. Twenty young adults (10 CI, 10 NH), without developmental and cognitive impairments, participated in the study. Under variable auditory feedback conditions, speech production (spontaneous or reading aloud) was measured using speech rate, percentage of interruptions, fundamental frequency (F0), and relative intensity. Results showed that (1) both DAF and FAF caused slower speech rates and more interruptions while reading aloud, with DAF having larger effect; (2) altered feedback produced no differences between groups, except an increase in F0 for CI users during DAF; and (3) CI users’ ability to understand speech via phone and without lip-reading was positively correlated with performance under DAF. These findings suggest that auditory perturbation similarly affects speech production among prelingual CI users and NH individuals, indicating CI users depend on auditory feedback to the same degree as normal hearing individuals.