Age-matched Normal-hearing Controls Research Articles

Hebrew Digits in Noise (DIN) Test in Cochlear Implant Users and Normal Hearing Listeners.

This study aimed to compare the Hebrew version of the digits-in-noise (DIN) thresholds among cochlear implant (CI) users and their normal-hearing (NH) counterparts, explore the influence of age on these thresholds, examine the effects of early auditory exposure versus its absence on DIN threshold, and assess the correlation between DIN thresholds and other speech perception tests. A total of 13 children with CI (aged 5.5-11 years), 15 pre-lingual CI users (aged 14-30 years), and 15 post-lingual CI users (aged 22-77 years), and their age-matched NH controls (n = 45) participated in the study. Speech perception tasks, including the DIN test, one-syllable word test, and sentence identification tasks in various auditory conditions, served as the main outcome measures. The results indicated that CI users exhibited higher speech reception thresholds in noise across all age groups compared to NH peers, with no significant difference between pre-lingual and post-lingual CI users. Significant differences were also observed in monosyllabic word and sentence accuracy in both quiet and noise conditions between CI and NH groups. Furthermore, correlations were observed between the DIN and other speech perception tests. The study concludes that CI users require a notably higher signal-to-noise ratio to discern digits in noise, underscoring the DIN test's utility in assessing speech recognition capabilities in CI users while emphasizing the need for a comprehensive test battery to fully gauge their speech perception abilities.

Aberrant auditory metabolite levels and topological properties are associated with cognitive decline in presbycusis patients.

Presbycusis has been reported as related to cognitive decline, but its underlying neurophysiological mechanism is still unclear. This study aimed to investigate the relationship between metabolite levels, cognitive function, and node characteristics in presbycusis based on graph theory methods. Eighty-four elderly individuals with presbycusis and 63 age-matched normal hearing controls underwent magnetic resonance spectroscopy, functional magnetic resonance imaging scans, audiological assessment, and cognitive assessment. Compared with the normal hearing group, presbycusis patients exhibited reduced gamma-aminobutyric acid and glutamate levels in the auditory region, increased nodal characteristics in the temporal lobe and precuneus, as well as decreased nodal characteristics in the superior occipital gyrus and medial orbital. The right gamma-aminobutyric acid levels were negatively correlated with the degree centrality in the right precuneus and the executive function. Degree centrality in the right precuneus exhibited significant correlations with information processing speed and executive function, while degree centrality in the left medial orbital demonstrated a negative association with speech recognition ability. The degree centrality and node efficiency in the superior occipital gyrus exhibited a negative association with hearing loss and speech recognition ability, respectively. These observed changes indicate alterations in metabolite levels and reorganization patterns at the brain network level after auditory deprivation.

Cortical compensation for hearing loss, but not age, in neural tracking of the fundamental frequency of the voice.

Auditory processing is affected by advancing age and hearing loss, but the underlying mechanisms are still unclear. We investigated the effects of age and hearing loss on temporal processing of naturalistic stimuli in the auditory system. We used a recently developed objective measure for neural phase-locking to the fundamental frequency of the voice (f0) which uses continuous natural speech as a stimulus, that is, "f0-tracking." The f0-tracking responses from 54 normal-hearing and 14 hearing-impaired adults of varying ages were analyzed. The responses were evoked by a Flemish story with a male talker and contained contributions from both subcortical and cortical sources. Results indicated that advancing age was related to smaller responses with less cortical response contributions. This is consistent with an age-related decrease in neural phase-locking ability at frequencies in the range of the f0, possibly due to decreased inhibition in the auditory system. Conversely, hearing-impaired subjects displayed larger responses compared with age-matched normal-hearing controls. This was due to additional cortical response contributions in the 38- to 50-ms latency range, which were stronger for participants with more severe hearing loss. This is consistent with hearing-loss-induced cortical reorganization and recruitment of additional neural resources to aid in speech perception.NEW & NOTEWORTHY Previous studies disagree on the effects of age and hearing loss on the neurophysiological processing of the fundamental frequency of the voice (f0), in part due to confounding effects. Using a novel electrophysiological technique, natural speech stimuli, and controlled study design, we quantified and disentangled the effects of age and hearing loss on neural f0 processing. We uncovered evidence for underlying neurophysiological mechanisms, including a cortical compensation mechanism for hearing loss, but not for age.

When Hearing Does Not Mean Understanding: On the Neural Processing of Syntactically Complex Sentences by Listeners With Hearing Loss.

Purpose Adults with mild-to-moderate age-related hearing loss typically exhibit issues with speech understanding, but their processing of syntactically complex sentences is not well understood. We test the hypothesis that listeners with hearing loss' difficulties with comprehension and processing of syntactically complex sentences are due to the processing of degraded input interfering with the successful processing of complex sentences. Method We performed a neuroimaging study with a sentence comprehension task, varying sentence complexity (through subject-object order and verb-arguments order) and cognitive demands (presence or absence of a secondary task) within subjects. Groups of older subjects with hearing loss (n = 20) and age-matched normal-hearing controls (n = 20) were tested. Results The comprehension data show effects of syntactic complexity and hearing ability, with normal-hearing controls outperforming listeners with hearing loss, seemingly more so on syntactically complex sentences. The secondary task did not influence off-line comprehension. The imaging data show effects of group, sentence complexity, and task, with listeners with hearing loss showing decreased activation in typical speech processing areas, such as the inferior frontal gyrus and superior temporal gyrus. No interactions between group, sentence complexity, and task were found in the neuroimaging data. Conclusions The results suggest that listeners with hearing loss process speech differently from their normal-hearing peers, possibly due to the increased demands of processing degraded auditory input. Increased cognitive demands by means of a secondary visual shape processing task influence neural sentence processing, but no evidence was found that it does so in a different way for listeners with hearing loss and normal-hearing listeners.

Poor early cortical differentiation of speech predicts perceptual difficulties of severely hearing-impaired listeners in multi-talker environments

Hearing impairment disrupts processes of selective attention that help listeners attend to one sound source over competing sounds in the environment. Hearing prostheses (hearing aids and cochlear implants, CIs), do not fully remedy these issues. In normal hearing, mechanisms of selective attention arise through the facilitation and suppression of neural activity that represents sound sources. However, it is unclear how hearing impairment affects these neural processes, which is key to understanding why listening difficulty remains. Here, severely-impaired listeners treated with a CI, and age-matched normal-hearing controls, attended to one of two identical but spatially separated talkers while multichannel EEG was recorded. Whereas neural representations of attended and ignored speech were differentiated at early (~ 150 ms) cortical processing stages in controls, differentiation of talker representations only occurred later (~250 ms) in CI users. CI users, but not controls, also showed evidence for spatial suppression of the ignored talker through lateralized alpha (7–14 Hz) oscillations. However, CI users’ perceptual performance was only predicted by early-stage talker differentiation. We conclude that multi-talker listening difficulty remains for impaired listeners due to deficits in early-stage separation of cortical speech representations, despite neural evidence that they use spatial information to guide selective attention.

Effects of Sensorineural Hearing Loss on Cortical Synchronization to Competing Speech during Selective Attention.

When selectively attending to a speech stream in multi-talker scenarios, low-frequency cortical activity is known to synchronize selectively to fluctuations in the attended speech signal. Older listeners with age-related sensorineural hearing loss (presbycusis) often struggle to understand speech in such situations, even when wearing a hearing aid. Yet, it is unclear whether a peripheral hearing loss degrades the attentional modulation of cortical speech tracking. Here, we used psychoacoustics and electroencephalography (EEG) in male and female human listeners to examine potential effects of hearing loss on EEG correlates of speech envelope synchronization in cortex. Behaviorally, older hearing-impaired (HI) listeners showed degraded speech-in-noise recognition and reduced temporal acuity compared with age-matched normal-hearing (NH) controls. During EEG recordings, we used a selective attention task with two spatially separated simultaneous speech streams where NH and HI listeners both showed high speech recognition performance. Low-frequency (<10 Hz) envelope-entrained EEG responses were enhanced in the HI listeners, both for the attended speech, but also for tone sequences modulated at slow rates (4 Hz) during passive listening. Compared with the attended speech, responses to the ignored stream were found to be reduced in both HI and NH listeners, allowing for the attended target to be classified from single-trial EEG data with similar high accuracy in the two groups. However, despite robust attention-modulated speech entrainment, the HI listeners rated the competing speech task to be more difficult. These results suggest that speech-in-noise problems experienced by older HI listeners are not necessarily associated with degraded attentional selection.SIGNIFICANCE STATEMENT People with age-related sensorineural hearing loss often struggle to follow speech in the presence of competing talkers. It is currently unclear whether hearing impairment may impair the ability to use selective attention to suppress distracting speech in situations when the distractor is well segregated from the target. Here, we report amplified envelope-entrained cortical EEG responses to attended speech and to simple tones modulated at speech rates (4 Hz) in listeners with age-related hearing loss. Critically, despite increased self-reported listening difficulties, cortical synchronization to speech mixtures was robustly modulated by selective attention in listeners with hearing loss. This allowed the attended talker to be classified from single-trial EEG responses with high accuracy in both older hearing-impaired listeners and age-matched normal-hearing controls.

MicroRNAs in sudden hearing loss.

To compare the circulating microRNA (miRNA) expression profiles between sudden sensory neural hearing loss (SSNHL) patients and age-matched normal hearing controls. Prospective cohort multi-center study. Patients presenting within 28 days of onset of SSNHL were prospectively recruited along with contemporaneous age-matched controls. Pooled sera of four patient (n = 09, mean age = 53.0 years; 07, 55.0; 10, 52.9; 10, 51.6) and two control (09, 51.2 and 03, 50.0) groups were assessed using a TaqMan Low Density Array. The patients' sera were also divided into two pools, untreated (04, 57.7) and treated (32, 52.6) for additional analysis. miRNA expression level was derived from cycle threshold (Ct) values normalized to a global mean. Inter-group mean Ct differences with fold changes ≥2.0 and ≤0.5 at P < .05 were considered significant. Bioinformatic databases were used to identify putative target mRNAs or validated genes and their functional annotations. Thirty-six SSNHL patients (mean age 53.0 ± standard deviation (SD) 15.2 years) and 12 controls (50.9 ± 11.9) were studied. Eight miRNAs hsa-miR-590-5p/ -186-5p/ -195-5p/ -140-3p/ -128-3p/ -132-3p/ -375-3p, and -30a-3p were identified as significantly differentially expressed in SSNHL patients. Most of these miRNAs were abundantly identified in the nervous system and the putative target messenger RNAs (mRNAs) were enriched in signaling pathways such as phosphatidyl inositol 3 kinase/protein Kinase B (PI3K/Akt), Ras and mitogen-activated protein kinase (MAPK). These findings suggest the possible cellular signaling pathways that underlie the disruption of auditory signal transmission in SSNHL. 2 Laryngoscope, 130:E416-E422, 2020.

Gray Matter Atrophy Is Associated With Cognitive Impairment in Patients With Presbycusis: A Comprehensive Morphometric Study.

Presbycusis (PC) is characterized by bilateral sensorineural hearing loss at high frequencies and speech-perception difficulties in noisy environments and has a strikingly detrimental impact on cognitive function. As the neural consequences of PC may involve the whole brain, we hypothesized that patients with PC would show structural alterations not only in the auditory cortex but also in the cortexes involved in cognitive function. The purpose of this study was to use surface-based morphometry (SBM) analysis to elucidate whole-brain structural differences between patients with PC and age-matched normal hearing controls. Three-dimensional T1-weighted MR images of 26 patients with mild PC and 26 age-, sex- and education-matched healthy controls (HCs) were acquired. All participants underwent a battery of neuropsychological tests. Our results revealed gray matter atrophy in several auditory cortical areas, nodes of the default mode network (DMN), including the bilateral precuneus and inferior parietal lobule, the right posterior cingulate cortex (PCC), and the right insula of patients with PC compared to that in the HCs. Our findings also revealed that hearing loss was associated with reduced gray matter volume in the right primary auditory cortex of patients with PC. Moreover, structural alterations in the nodes of the DMN were associated with cognitive impairments in PC patients. Additionally, this study provides evidence that a thicker right insula is associated with better speech perception in patients with PC. Based on these findings, we argue that the onset of PC seems to trigger its own cascade of conditions, including a need for increased cognitive resources during speech comprehension, which might lead to auditory and cognition-related cortical reorganization.

Towards cognitive control of hearing instruments using EEG measures of selective attention

Single-trial EEG measures of selective auditory attention have recently suggested the perspective of decoding who a listener is focusing on in multi-talker scenarios. Here, we report results from work within the COCOHA (Cognitive Control of a Hearing Aid) project investigating the possibility of integrating EEG into neuro-steered hearing instruments. Our EEG decoding strategy relies on measuring cortical activity entrained to envelope fluctuations in the attended speech signal. Currently, a major challenge has been to obtain robust EEG measures of selective attention in older hearing-impaired (HI) listeners. We report our recent COCOHA attempts to decode selective attention from the EEG of hearing-impaired (HI) listeners. Aided HI listeners and age-matched normal-hearing controls were presented with competing talkers at 0 dB target-to-masker ratio and instructed to attend to one talker. We show that single-trial decoding accuracies similar to those reported for younger listeners can be obtained with both groups of older listeners (70–100% correct single-trial classification). Importantly, we did not find differences in decoding accuracies between the NH and the aided HI listeners. Although numerous other challenges involved in integrating EEG signals in hearing instruments are evident, our results suggest that single-trial attention decoding is possible with hearing impaired listeners.

Increased cross-modal functional connectivity in cochlear implant users

Previous studies have reported increased cross-modal auditory and visual cortical activation in cochlear implant (CI) users, suggesting cross-modal reorganization of both visual and auditory cortices in CI users as a consequence of sensory deprivation and restoration. How these processes affect the functional connectivity of the auditory and visual system in CI users is however unknown. We here investigated task-induced intra-modal functional connectivity between hemispheres for both visual and auditory cortices and cross-modal functional connectivity between visual and auditory cortices using functional near infrared spectroscopy in post-lingually deaf CI users and age-matched normal hearing controls. Compared to controls, CI users exhibited decreased intra-modal functional connectivity between hemispheres and increased cross-modal functional connectivity between visual and left auditory cortices for both visual and auditory stimulus processing. Importantly, the difference between cross-modal functional connectivity for visual and for auditory stimuli correlated with speech recognition outcome in CI users. Higher cross-modal connectivity for auditory than for visual stimuli was associated with better speech recognition abilities, pointing to a new pattern of functional reorganization that is related to successful hearing restoration with a CI.

The Acoustics of Word-Initial Fricatives and Their Effect on Word-Level Intelligibility in Children With Bilateral Cochlear Implants.

Previous research has found that relative to their peers with normal hearing (NH), children with cochlear implants (CIs) produce the sibilant fricatives /s/ and /∫/ less accurately and with less subphonemic acoustic contrast. The present study sought to further investigate these differences across groups in two ways. First, subphonemic acoustic properties were investigated in terms of dynamic acoustic features that indexed more than just the contrast between /s/ and /∫/. Second, the authors investigated whether such differences in subphonemic acoustic contrast between sibilant fricatives affected the intelligibility of sibilant-initial single word productions by children with CIs and their peers with NH. In experiment 1, productions of /s/ and /∫/ in word-initial prevocalic contexts were elicited from 22 children with bilateral CIs (aged 4 to 7 years) who had at least 2 years of CI experience and from 22 chronological age-matched peers with NH. Acoustic features were measured from 17 points across the fricatives: peak frequency was measured to index the place of articulation contrast; spectral variance and amplitude drop were measured to index the degree of sibilance. These acoustic trajectories were fitted with growth-curve models to analyze time-varying spectral change. In experiment 2, phonemically accurate word productions that were elicited in experiment 1 were embedded within four-talker babble and played to 80 adult listeners with NH. Listeners were asked to repeat the words, and their accuracy rate was used as a measure of the intelligibility of the word productions. Regression analyses were run to test which acoustic properties measured in experiment 1 predicted the intelligibility scores from experiment 2. The peak frequency trajectories indicated that the children with CIs produced less acoustic contrast between /s/ and /∫/. Group differences were observed in terms of the dynamic aspects (i.e., the trajectory shapes) of the acoustic properties. In the productions by children with CIs, the peak frequency and the amplitude drop trajectories were shallower, and the spectral variance trajectories were more asymmetric, exhibiting greater increases in variance (i.e., reduced sibilance) near the fricative-vowel boundary. The listeners' responses to the word productions indicated that when produced by children with CIs, /∫/-initial words were significantly more intelligible than /s/-initial words. However, when produced by children with NH, /s/-initial words and /∫/-initial words were equally intelligible. Intelligibility was partially predicted from the acoustic properties (Cox & Snell pseudo-R > 0.190), and the significant predictors were predominantly dynamic, rather than static, ones. Productions from children with CIs differed from those produced by age-matched NH controls in terms of their subphonemic acoustic properties. The intelligibility of sibilant-initial single-word productions by children with CIs is sensitive to the place of articulation of the initial consonant (/∫/-initial words were more intelligible than /s/-initial words), but productions by children with NH were equally intelligible across both places of articulation. Therefore, children with CIs still exhibit differential production abilities for sibilant fricatives at an age when their NH peers do not.

What Can We Learn about Auditory Processing from Adult Hearing Questionnaires?

Questionnaires addressing auditory disability may identify and quantify specific symptoms in adult patients with listening difficulties. (1) To assess validity of the Speech, Spatial, and Qualities of Hearing Scale (SSQ), the (Modified) Amsterdam Inventory for Auditory Disability (mAIAD), and the Hyperacusis Questionnaire (HYP) in adult patients experiencing listening difficulties in the presence of a normal audiogram. (2) To examine which individual questionnaire items give the worse scores in clinical participants with an auditory processing disorder (APD). A prospective correlational analysis study. Clinical participants (N = 58) referred for assessment because of listening difficulties in the presence of normal audiometric thresholds to audiology/ear, nose, and throat or audiovestibular medicine clinics. Normal control participants (N = 30). The mAIAD, HYP, and the SSQ were administered to a clinical population of nonneurological adults who were referred for auditory processing (AP) assessment because of hearing complaints, in the presence of normal audiogram and cochlear function, and to a sample of age-matched normal-hearing controls, before the AP testing. Clinical participants with abnormal results in at least one ear and in at least two tests of AP (and at least one of these tests to be nonspeech) were classified as clinical APD (N = 39), and the remaining (16 of whom had a single test abnormality) as clinical non-APD (N = 19). The SSQ correlated strongly with the mAIAD and the HYP, and correlation was similar within the clinical group and the normal controls. All questionnaire total scores and subscores (except sound distinction of mAIAD) were significantly worse in the clinical APD versus the normal group, while questionnaire total scores and most subscores indicated greater listening difficulties for the clinical non-APD versus the normal subgroups. Overall, the clinical non-APD group tended to give better scores than the APD in all questionnaires administered. Correlation was strong for the worse-ear gaps-in-noise threshold with the SSQ, mAIAD, and HYP; strong to moderate for the speech in babble and left-ear dichotic digit test scores (at p < 0.01); and weak to moderate for the remaining AP tests except the frequency pattern test that did not correlate. The worse-scored items in all three questionnaires concerned speech-in-noise questions. This is similar to worse-scored items by hearing-impaired participants as reported in the literature. Worse-scored items of the clinical group also included quality aspects of listening questions from the SSQ, which most likely pertain to cognitive aspects of listening, such as ability to ignore other sounds and listening effort. Hearing questionnaires may help assess symptoms of adults with APD. The listening difficulties and needs of adults with APD to some extent overlap with those of hearing-impaired listeners, but there are significant differences. The correlation of the gaps-in-noise and duration pattern (but not frequency pattern) tests with the questionnaire scores indicates that temporal processing deficits may play an important role in clinical presentation.

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

There is converging evidence that the auditory cortex takes over visual functions during a period of auditory deprivation. A residual pattern of cross-modal take-over may prevent the auditory cortex to adapt to restored sensory input as delivered by a cochlear implant (CI) and limit speech intelligibility with a CI. The aim of the present study was to investigate whether visual face processing in CI users activates auditory cortex and whether this has adaptive or maladaptive consequences. High-density electroencephalogram data were recorded from CI users (n=21) and age-matched normal hearing controls (n=21) performing a face versus house discrimination task. Lip reading and face recognition abilities were measured as well as speech intelligibility. Evaluation of event-related potential (ERP) topographies revealed significant group differences over occipito-temporal scalp regions. Distributed source analysis identified significantly higher activation in the right auditory cortex for CI users compared to NH controls, confirming visual take-over. Lip reading skills were significantly enhanced in the CI group and appeared to be particularly better after a longer duration of deafness, while face recognition was not significantly different between groups. However, auditory cortex activation in CI users was positively related to face recognition abilities. Our results confirm a cross-modal reorganization for ecologically valid visual stimuli in CI users. Furthermore, they suggest that residual takeover, which can persist even after adaptation to a CI is not necessarily maladaptive.

Structural alterations of brain grey and white matter in early deaf adults

Functional and structural brain alterations in the absence of the auditory input have been described, but the observed structural brain changes in the deaf are not uniform. Some of the previous researchers focused only on the auditory areas, while others investigated the whole brain or other selected regions of interest. Majority of studies revealed decreased white matter (WM) volume or altered WM microstructure and preserved grey matter (GM) structure of the auditory areas in the deaf. However, preserved WM and increased or decreased GM volume of the auditory areas in the deaf have also been reported. Several structural alterations in the deaf were found also outside the auditory areas, but these regions differ between the studies. The observed differences between the studies could be due to the use of different single-analysis techniques, or the diverse population sample and its size, or possibly due to the usage of hearing aids by some participating deaf subjects. To overcome the aforementioned limitations four different image-processing techniques were used to investigate changes in the brain morphology of prelingually deaf adults who have never used hearing aids. GM and WM volume of the Heschl's gyrus (HG) were measured using manual volumetry, while whole brain GM volume, thickness and surface area were assessed by voxel-based morphometry (VBM) and surface-based analysis. The microstructural properties of the WM were evaluated by diffusion tensor imaging (DTI). The data were compared between 14 congenitally deaf adults and 14 sex- and age-matched normal hearing controls. Manual volumetry revealed preserved GM volume of the bilateral HG and significantly decreased WM volume of the left HG in the deaf. VBM showed increased cerebellar GM volume in the deaf, while no statistically significant differences were observed in the GM thickness or surface area between the groups. The results of the DTI analysis showed WM microstructural alterations between the groups in the bilateral auditory areas, including the superior temporal gyrus, the HG, the planum temporale and the planum polare, which were more extensive in the right hemisphere. Fractional anisotropy (FA) was significantly reduced in the right and axial diffusivity (AD) in the left auditory areas in the deaf. FA and AD were significantly reduced also in several other brain areas outside the auditory cortex in the deaf.The use of four different methods used in our study, although showing changes that are not directly related, provides additional information and supports the conclusion that in prelingually deaf subjects structural alterations are present both in the auditory areas and elsewhere. Our results support the findings of those studies showing that early deafness results in decreased WM volume and microstructural WM alterations in the auditory areas. As we observed WM microstructural alteration also in several other areas and increased GM volume in the cerebellum in the deaf, we can conclude that early deafness results in widespread structural brain changes. These probably reflect atrophy or degradation as well as compensatory cross-modal reorganisation in the absence of the auditory input and the use of the sign language.

Compensatory changes in cortical resource allocation in adults with hearing loss

Hearing loss has been linked to many types of cognitive decline in adults, including an association between hearing loss severity and dementia. However, it remains unclear whether cortical re-organization associated with hearing loss occurs in early stages of hearing decline and in early stages of auditory processing. In this study, we examined compensatory plasticity in adults with mild-moderate hearing loss using obligatory, passively-elicited, cortical auditory evoked potentials (CAEP). High-density EEG elicited by speech stimuli was recorded in adults with hearing loss and age-matched normal hearing controls. Latency, amplitude and source localization of the P1, N1, P2 components of the CAEP were analyzed. Adults with mild-moderate hearing loss showed increases in latency and amplitude of the P2 CAEP relative to control subjects. Current density reconstructions revealed decreased activation in temporal cortex and increased activation in frontal cortical areas for hearing-impaired listeners relative to normal hearing listeners. Participants' behavioral performance on a clinical test of speech perception in noise was significantly correlated with the increases in P2 latency. Our results indicate that changes in cortical resource allocation are apparent in early stages of adult hearing loss, and that these passively-elicited cortical changes are related to behavioral speech perception outcome.

Electrophysiological responses to emotional prosody perception in cochlear implant users

The present electroencephalographic (EEG) study investigated the ability of cochlear implant (CI) users to recognize emotional prosody. Two CI speech-processing strategies were compared: the ACE (Advance Combination Encoder) and the newly developed MP3000. Semantically neutral sentences spoken in three different emotional prosodies (neutral, angry, happy) were presented to 20 post-lingually deafened CI users and age-matched normal-hearing controls. Event related potentials (ERPs) were recorded to study the N100 and the P200 responses. In addition, event-related spectral power modulations were calculated to study the brain activity corresponding to the recognition of prosody in earlier (0–400) as well as later (600–1200) part of the stimuli where the prosodic features differed maximally. CI users with MP3000 strategy showed a higher proportion of correctly recognized prosodic information compared to the ACE strategy users. Our ERP results demonstrated that emotional prosody elicited significant N100 and P200 peaks. Furthermore, the P200 amplitude in response to happy prosodic information was significantly more positive for the MP3000 strategy compared to the ACE strategy. On spectral power analysis, two typical gamma activities were observed in the MP3000 users only: (1) an early gamma activity in the 100–250 ms time window reflecting bottom–up attention regulation; and (2) a late gamma activity between 900 and 1100 ms post-stimulus onset, probably reflecting top–down cognitive control. Our study suggests that the MP3000 strategy is better than ACE in regard to happy prosody perception. Furthermore, we show that EEG is a useful tool that, in combination with behavioral analysis, can reveal differences between two CI processing strategies for coding of prosody-specific features of language.

Cochlear implant use following neonatal deafness influences the cochleotopic organization of the primary auditory cortex in cats.

Electrical stimulation of spiral ganglion neurons in a deafened cochlea, via a cochlear implant, provides a means of investigating the effects of the removal and subsequent restoration of afferent input on the functional organization of the primary auditory cortex (AI). We neonatally deafened 17 cats before the onset of hearing, thereby abolishing virtually all afferent input from the auditory periphery. In seven animals the auditory pathway was chronically reactivated with environmentally derived electrical stimuli presented via a multichannel intracochlear electrode array implanted at 8 weeks of age. Electrical stimulation was provided by a clinical cochlear implant that was used continuously for periods of up to 7 months. In 10 long-term deafened cats and three age-matched normal-hearing controls, an intracochlear electrode array was implanted immediately prior to cortical recording. We recorded from a total of 812 single unit and multiunit clusters in AI of all cats as adults using a combination of single tungsten and multichannel silicon electrode arrays. The absence of afferent activity in the long-term deafened animals had little effect on the basic response properties of AI neurons but resulted in complete loss of the normal cochleotopic organization of AI. This effect was almost completely reversed by chronic reactivation of the auditory pathway via the cochlear implant. We hypothesize that maintenance or reestablishment of a cochleotopically organized AI by activation of a restricted sector of the cochlea, as demonstrated in the present study, contributes to the remarkable clinical performance observed among human patients implanted at a young age.

Minimum Audible Angle, Just Noticeable Interaural Differences and Speech Intelligibility with Bilateral Cochlear Implants Using Clinical Speech Processors

Sound localization and speech intelligibility were assessed in 5 patients implanted bilaterally with Medel C40+ or Medel C40 cochlear implant (CI) systems. The minimum audible angle (MAA) around the head in the horizontal plane was assessed in patients with bilateral CI using white noise bursts of 1000 ms duration presented from a loudspeaker mounted on a rotating boom and compared with the MAA of age-matched normal hearing controls. Spatial discrimination was found to be good in front and in the back of the head with near-normal MAA values (patients: 3–8°, controls: 1–4°). In contrast, poor performance on the sides was found (patients: 30 to over 45°, controls 7–10°). Bilateral CI significantly improved spatial discrimination in front for all patients, when compared with the use of either CI alone. Just noticeable differences (JNDs) in interaural intensity and time were assessed using white noise bursts (1000 ms duration; 50 ms linear ramp). In addition, interaural time JNDs were assessed using click trains (800 ms duration, 40 µs clicks, 50 Hz) and noise bursts in which either only the envelope or only the fine structure was shifted in time. In comparison with normal hearing controls, patients with bilateral CI showed near-normal interaural intensity JNDs but substantially poorer interaural time JNDs depending on the type of stimulus. In contrast to envelope onset/offset cues, interaural fine structure time differences were not perceived by the patients using CI systems employing the continuous interleaved sampling strategy without synchronization between their pulse stimulation times. Speech intelligibility in quiet and CCITT noise from the side (±90°) was assessed using the German HSM sentence test and was significantly better when using bilateral CI in comparison with either unilateral CI, mainly due to a head shadow effect. These favorable results are in agreement with the patients’ subjective experiences assessed with a questionnaire and support the use of bilateral CI.