Cortical reorganization in postlingually deaf cochlear implant users: Intra-modal and cross-modal considerations

Significant influence of prelingual deafness but less impact of elderly age at implantation on long-term psychoacoustic CI programming parameters

OBJECTIVE

This study aimed to elucidate the long-term impact of prelingual deafness and elderly age at cochlear implantation on cochlear implant (CI) programming parameters and CI thresholds METHODS: We retrospectively reviewed patients who underwent cochlear implantation less than 5 years (Prelingual group) and equal and more than 18 years in our institute. The latter group was further divided into Adult and Elderly groups according to whether the patient was younger or older than 65 at implantation. From 152, 69, and 55 patients in the Prelingual, Adult, and Elderly groups, 242, 92, and 58 ears were included. We compared CI thresholds and CI programming parameters, including impedances, T/C levels, and dynamic ranges for 8 years after implantation between the Prelingual, Adult, and Elderly groups.

RESULTS

The Prelingual group showed consistently lower CI thresholds than the Adult and Elderly groups during the postoperative 2-8 years, but no difference was detected between the Elderly and Adult groups, except at the postoperative 4 years. The elderly group's CI thresholds did not deteriorate until postoperative 8 years. The Prelingual group showed consistently larger T/C levels (minimum/maximum current strength from CI), especially C levels, than the other two groups. At the same time, there was no significant difference between the Elderly and Adult groups except for smaller dynamic ranges in the Elderly group until postoperative 2 years. These results in the CI programming parameters might explain the lower CI thresholds in the Prelingual group than in the other groups. Focusing on CI maps 1 and 3 years after implantation, the strength of the T/C levels was similar for all channels in the Prelingual group, but the Adult and Elderly groups showed larger electrical stimuli in channels responsible for the middle frequencies than those for the lower or higher frequencies.

CONCLUSIONS

Our results suggest a significant influence of prelingual deafness but less impact of elderly age at implantation on long-term CI programming parameters and CI thresholds. The larger C levels and lower CI thresholds in the Prelingual group than in the Adult and Elderly groups implied that CI children with prelingual deafness tolerate and prefer larger CI stimuli, which may reflect the CI-dependent development of their auditory system before the critical period. No age-related reduction in hearing thresholds was observed in the Elderly group, probably because the CI compensates for age-related dysfunction of the peripheral auditory system.

Adaptive Strategies of Single-Sided Deaf Cochlear-Implant Users Revealed Through Resting State Activity: an Auditory PET Brain Imaging Study

Brain plasticity refers to the brain's ability to reorganize its structure or function in response to experiences, learning, and environmental influences. This phenomenon is particularly significant in individuals with deafness, as the brain adapts to compensate for the lack of auditory stimulation. The aim of this study is to investigate whether cochlear implantation can restore a normal pattern of brain activation following auditory stimulation in cases of asymmetric hearing loss. We used a PET-scan technique to assess brain activity after cochlear implantation, specifically during an auditory voice/non-voice discrimination task. The results indicated a nearly normal pattern of brain activity during the auditory discrimination task, except for increased activation in areas related to attentional processes compared to controls. Additionally, brain activity at rest showed significant changes in implanted participants, including cross modal visuo-auditory processing. Therefore, cochlear implants can restore the brain's activation pattern through long-term adaptive adjustments in intrinsic brain activity.

Neurocognitive outcomes in young adults with cochlear implants: The role of early language access and crossmodal plasticity

Many children with profound hearing loss have received cochlear implants (CI) to help restore some sense of hearing. There is, however, limited research on long-term neurocognitive outcomes in young adults who have grown up hearing through a CI. This study compared the cognitive outcomes of early-implanted (n = 20) and late-implanted (n = 21) young adult CI users, and typically hearing (TH) controls (n=56), all of whom were enrolled in college. Cognitive fluidity, nonverbal intelligence, and American Sign Language (ASL) comprehension were assessed, revealing no significant differences in cognition and nonverbal intelligence between the early and late-implanted groups. However, there was a difference in ASL comprehension, with the late-implanted group having significantly higher ASL comprehension. Although young adult CI users showed significantly lower scores in a working memory and processing speed task than TH age-matched controls, there were no significant differences in tasks involving executive function shifting, inhibitory control, and episodic memory between young adult CI and young adult TH participants. In an exploratory analysis of a subset of CI participants (n = 17) in whom we were able to examine crossmodal plasticity, we saw greater evidence of crossmodal recruitment from the visual system in late-implanted compared with early-implanted CI young adults. However, cortical visual evoked potential latency biomarkers of crossmodal plasticity were not correlated with cognitive measures or ASL comprehension. The results suggest that in the late-implanted CI users, early access to sign language may have served as a scaffold for appropriate cognitive development, while in the early-implanted group early access to oral language benefited cognitive development. Furthermore, our results suggest that the persistence of crossmodal neuroplasticity into adulthood does not necessarily impact cognitive development. In conclusion, early access to language - spoken or signed - may be important for cognitive development, with no observable effect of crossmodal plasticity on cognitive outcomes.

P1 and N1 Characteristics in Individuals with Normal Hearing and Hearing Loss, and Cochlear Implant Users: A Pilot Study

Background: It has been reported in many previous studies that the lack of auditory input due to hearing loss (HL) can induce changes in the brain. However, most of these studies have focused on individuals with pre-lingual HL and have predominantly compared the characteristics of those with normal hearing (NH) to cochlear implant (CI) users in children. This study examined the visual and auditory evoked potential characteristics in NH listeners, individuals with bilateral HL, and CI users, including those with single-sided deafness. Methods: A total of sixteen participants (seven NH listeners, four individuals with bilateral sensorineural HL, and five CI users) completed speech testing in quiet and noise and evoked potential testing. For speech testing, the Korean version of the Hearing in Noise Test was used to assess individuals' speech understanding ability in quiet and in noise (noise from the front, +90 degrees, and -90 degrees). For evoked potential testing, visual and auditory (1000 Hz, /ba/, and /da/) evoked potentials were measured. Results: The results showed that CI users understood speech better than those with HL in all conditions except for the noise from +90 and -90 degrees. In the CI group, a decrease in P1 amplitudes was noted across all channels after implantation. The NH group exhibited the highest amplitudes, followed by the HL group, with the CI group (post-CI) showing the lowest amplitudes. In terms of auditory evoked potentials, the smallest amplitude was observed in the pre-CI condition regardless of the type of stimulus. Conclusions: To the best of our knowledge, this is the first study that examined visual and auditory evoked potentials based on various hearing profiles. The characteristics of evoked potentials varied across participant groups, and further studies with CI users are necessary, as there are significant challenges in collecting and analyzing evoked potentials due to artifact issues on the CI side.

fNIRS Changes in the Middle Temporal and Occipital Cortices After a Cochlear Implant

OBJECTIVES

The relationship between the middle temporal (MTG) and occipital cortices in post-lingually deaf (PLD) individuals is unclear. This study aimed to investigate changes in the MTG and occipital cortices excitability and their effects on the occipital cortex in individuals with PLD after receiving a cochlear implant (CI).

METHODS

Twenty-six individuals with severe-to-profound binaural sensorineural PLD were assessed clinically. Nine individuals had received a unilateral cochlear implant over 6 months, while 17 had not. Brodmann area 19 (BA19, extra-striate occipital cortex) and MTG (auditory-related area of cortex) were selected as regions of interest. The excitability of the ROI was observed and compared in the surgery and no-surgery groups by functional near-infrared spectroscopy (fNIRS) in the resting state, and correlations between connectivity of the MTG and occipital cortex, and as well as the duration of time that had elapsed following CI surgery, were investigated.

RESULTS

fNIRS revealed enhanced global cortical connectivity in the BA19 and MTG on the operative side (p < 0.05) and the connectivity between BA19 and the MTG also increased (p < 0.05). The connectivity between the MTG and BA19 was positively correlated with the duration of cochlear implantation, as was the case for BA18.

CONCLUSION

There was evidence for remodeling of the cerebral cortex: increased excitability was observed in the MTG and BA19, and their connectivity was enhanced, indicating a synergistic effect. Moreover, the MTG may further stimulate the visual cortex by strengthening their connectivity after CI.

LEVEL OF EVIDENCE

3 Laryngoscope, 2024.

Speech Quality Perception in Unilateral Cochlear Implant Users With Single-Sided Deafness

OBJECTIVE

Cochlear implant (CI) users frequently complain about speech quality perception (SQP). In patients undergoing cochlear implantation for single-sided deafness, there is concern that poor SQP from the implanted ear will negatively impact binaural (CI + normal hearing [NH]) SQP. In this study, we investigate if binaural SQP is measurably different than unimplanted NH alone.

STUDY DESIGN

Cross-sectional study.

SETTING

Tertiary care center.

METHODS

Fifteen unilateral CI users with NH in the contralateral ear completed the validated Columbia Speech Quality Instrument. This instrument consists of 9 audio clips rated across 14 specific speech qualities using a 10-point visual analog scale. SQP was assessed in 3 conditions: CI only, NH only, and CI + NH.

RESULTS

Median speech quality scores were worse in the CI only condition compared to the NH only (50.0 vs 72.6, P = .0003) and binaural (50.0 vs 71.0, P = .007) conditions. Median speech quality scores were not significantly different between the NH only and binaural conditions (72.6 vs 71, P = .8). Compared to NH, CI speech quality sounded less clear, less natural, and more mechanical.

CONCLUSION

Compared to NH, SQP is poorer with a CI alone. However, in contrast to expectation, there is no significant difference between NH and binaural SQP. This suggests poorer CI speech perception does not negatively impact binaural SQP in patients undergoing cochlear implantation for single-sided deafness.

Cortical volumetric changes after cochlear implantation in postlingually deaf adults: correlation with speech perception abilities

This study aims to analyse the volumetric changes in brain MRI after cochlear implantation (CI), focusing on the speech perception in postlingually deaf adults. We conducted a prospective cohort study with 16 patients who had bilateral hearing loss and received unilateral CI. Based on the surgical side, patients were categorized into left and right CI groups. Volumetric T1-weighted brain MRI were obtained before and one year after the surgery. To overcome the artifact caused by the internal device in post-CI scan, image reconstruction method was newly devised and applied using the contralateral hemisphere of the pre-CI MRI data, to run FreeSurfer. We conducted within-subject template estimation for unbiased longitudinal image analysis, based on the linear mixed effect models. When analyzing the contralateral cerebral hemisphere before and after CI, a substantial increase in superior frontal gyrus and superior temporal gyrus (STG) volumes was observed in the left CI group. A positive correlation was observed in the STG and post-CI word recognition score in both groups. As far as we know, this is the first study attempting longitudinal brain volumetry based on post-CI MRI scans. We demonstrate that better auditory performance after CI is associated with structural restoration in central auditory structures.

Cross-modal plasticity in children with cochlear implant: converging evidence from EEG and functional near-infrared spectroscopy

Over the first years of life, the brain undergoes substantial organization in response to environmental stimulation. In a silent world, it may promote vision by (i) recruiting resources from the auditory cortex and (ii) making the visual cortex more efficient. It is unclear when such changes occur and how adaptive they are, questions that children with cochlear implants can help address. Here, we examined 7-18 years old children: 50 had cochlear implants, with delayed or age-appropriate language abilities, and 25 had typical hearing and language. High-density electroencephalography and functional near-infrared spectroscopy were used to evaluate cortical responses to a low-level visual task. Evidence for a 'weaker visual cortex response' and 'less synchronized or less inhibitory activity of auditory association areas' in the implanted children with language delays suggests that cross-modal reorganization can be maladaptive and does not necessarily strengthen the dominant visual sense.

Motor Processing in Children With Cochlear Implants as Assessed by Functional Near-Infrared Spectroscopy

Auditory-motor and visual-motor networks are often coupled in daily activities, such as when listening to music and dancing; but these networks are known to be highly malleable as a function of sensory input. Thus, congenital deafness may modify neural activities within the connections between the motor, auditory, and visual cortices. Here, we investigated whether the cortical responses of children with cochlear implants (CI) to a simple and repetitive motor task would differ from that of children with typical hearing (TH) and we sought to understand whether this response related to their language development. Participants were 75 school-aged children, including 50 with CI (with varying language abilities) and 25 controls with TH. We used functional near-infrared spectroscopy (fNIRS) to record cortical responses over the whole brain, as children squeezed the back triggers of a joystick that vibrated or not with the squeeze. Motor cortex activity was reflected by an increase in oxygenated hemoglobin concentration (HbO) and a decrease in deoxygenated hemoglobin concentration (HbR) in all children, irrespective of their hearing status. Unexpectedly, the visual cortex (supposedly an irrelevant region) was deactivated in this task, particularly for children with CI who had good language skills when compared to those with CI who had language delays. Presence or absence of vibrotactile feedback made no difference in cortical activation. These findings support the potential of fNIRS to examine cognitive functions related to language in children with CI.

Features of the speech processing network in post- and prelingually deaf cochlear implant users

The onset of hearing loss can lead to altered brain structure and functions. However, hearing restoration may also result in distinct cortical reorganization. A differential pattern of functional remodeling was observed between post- and prelingual cochlear implant users, but it remains unclear how these speech processing networks are reorganized after cochlear implantation. To explore the impact of language acquisition and hearing restoration on speech perception in cochlear implant users, we conducted assessments of brain activation, functional connectivity, and graph theory-based analysis using functional near-infrared spectroscopy. We examined the effects of speech-in-noise stimuli on three groups: postlingual cochlear implant users (n = 12), prelingual cochlear implant users (n = 10), and age-matched individuals with hearing controls (HC) (n = 22). The activation of auditory-related areas in cochlear implant users showed a lower response compared with the HC group. Wernicke's area and Broca's area demonstrated differences network attributes in speech processing networks in post- and prelingual cochlear implant users. In addition, cochlear implant users maintain a high efficiency of the speech processing network to process speech information. Taken together, our results characterize the speech processing networks, in varying noise environments, in post- and prelingual cochlear implant users and provide new insights for theories of how implantation modes impact remodeling of the speech processing functional networks.

Improved speech intelligibility in the presence of congruent vibrotactile speech input

Vibrotactile stimulation is believed to enhance auditory speech perception, offering potential benefits for cochlear implant (CI) users who may utilize compensatory sensory strategies. Our study advances previous research by directly comparing tactile speech intelligibility enhancements in normal-hearing (NH) and CI participants, using the same paradigm. Moreover, we assessed tactile enhancement considering stimulus non-specific, excitatory effects through an incongruent audio-tactile control condition that did not contain any speech-relevant information. In addition to this incongruent audio-tactile condition, we presented sentences in an auditory only and a congruent audio-tactile condition, with the congruent tactile stimulus providing low-frequency envelope information via a vibrating probe on the index fingertip. The study involved 23 NH listeners and 14 CI users. In both groups, significant tactile enhancements were observed for congruent tactile stimuli (5.3% for NH and 5.4% for CI participants), but not for incongruent tactile stimulation. These findings replicate previously observed tactile enhancement effects. Juxtaposing our study with previous research, the informational content of the tactile stimulus emerges as a modulator of intelligibility: Generally, congruent stimuli enhanced, non-matching tactile stimuli reduced, and neutral stimuli did not change test outcomes. We conclude that the temporal cues provided by congruent vibrotactile stimuli may aid in parsing continuous speech signals into syllables and words, consequently leading to the observed improvements in intelligibility.

Audiovisual integration in children with cochlear implants revealed through EEG and fNIRS

Sensory deprivation can offset the balance of audio versus visual information in multimodal processing. Such a phenomenon could persist for children born deaf, even after they receive cochlear implants (CIs), and could potentially explain why one modality is given priority over the other. Here, we recorded cortical responses to a single speaker uttering two syllables, presented in audio-only (A), visual-only (V), and audio-visual (AV) modes. Electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) were successively recorded in seventy-five school-aged children. Twenty-five were children with normal hearing (NH) and fifty wore CIs, among whom 26 had relatively high language abilities (HL) comparable to those of NH children, while 24 others had low language abilities (LL). In EEG data, visual-evoked potentials were captured in occipital regions, in response to V and AV stimuli, and they were accentuated in the HL group compared to the LL group (the NH group being intermediate). Close to the vertex, auditory-evoked potentials were captured in response to A and AV stimuli and reflected a differential treatment of the two syllables but only in the NH group. None of the EEG metrics revealed any interaction between group and modality. In fNIRS data, each modality induced a corresponding activity in visual or auditory regions, but no group difference was observed in A, V, or AV stimulation. The present study did not reveal any sign of abnormal AV integration in children with CI. An efficient multimodal integrative network (at least for rudimentary speech materials) is clearly not a sufficient condition to exhibit good language and literacy.

Does experience with hearing aid amplification influence electrophysiological measures of speech comprehension?

OBJECTIVE

To explore if experience with hearing aid (HA) amplification affects speech-evoked cortical potentials reflecting comprehension abilities.

DESIGN

N400 and late positive complex (LPC) responses as well as behavioural response times to congruent and incongruent digit triplets were measured. The digits were presented against stationary speech-shaped noise 10 dB above individually measured speech recognition thresholds. Stimulus presentation was either acoustic (digits 1-3) or first visual (digits 1-2) and then acoustic (digit 3).

STUDY SAMPLE

Three groups of older participants (N = 3 × 15) with (1) pure-tone average hearing thresholds <25 dB HL from 500-4000 Hz, (2) mild-to-moderate sensorineural hearing loss (SNHL) but no prior HA experience, and (3) mild-to-moderate SNHL and >2 years of HA experience. Groups 2-3 were fitted with test devices in accordance with clinical gain targets.

RESULTS

No group differences were found in the electrophysiological data. N400 amplitudes were larger and LPC latencies shorter with acoustic presentation. For group 1, behavioural response times were shorter with visual-then-acoustic presentation.

CONCLUSION

When speech audibility is ensured, comprehension-related electrophysiological responses appear intact in individuals with mild-to-moderate SNHL, regardless of prior experience with amplified sound. Further research into the effects of audibility versus acclimatisation-related neurophysiological changes is warranted.

Music in noise recognition: An EEG study of listening effort in cochlear implant users and normal hearing controls

Despite the plethora of studies investigating listening effort and the amount of research concerning music perception by cochlear implant (CI) users, the investigation of the influence of background noise on music processing has never been performed. Given the typical speech in noise recognition task for the listening effort assessment, the aim of the present study was to investigate the listening effort during an emotional categorization task on musical pieces with different levels of background noise. The listening effort was investigated, in addition to participants' ratings and performances, using EEG features known to be involved in such phenomenon, that is alpha activity in parietal areas and in the left inferior frontal gyrus (IFG), that includes the Broca's area. Results showed that CI users performed worse than normal hearing (NH) controls in the recognition of the emotional content of the stimuli. Furthermore, when considering the alpha activity corresponding to the listening to signal to noise ratio (SNR) 5 and SNR10 conditions subtracted of the activity while listening to the Quiet condition-ideally removing the emotional content of the music and isolating the difficulty level due to the SNRs- CI users reported higher levels of activity in the parietal alpha and in the homologous of the left IFG in the right hemisphere (F8 EEG channel), in comparison to NH. Finally, a novel suggestion of a particular sensitivity of F8 for SNR-related listening effort in music was provided.

Cross-modal functional connectivity supports speech understanding in cochlear implant users

Sensory deprivation can lead to cross-modal cortical changes, whereby sensory brain regions deprived of input may be recruited to perform atypical function. Enhanced cross-modal responses to visual stimuli observed in auditory cortex of postlingually deaf cochlear implant (CI) users are hypothesized to reflect increased activation of cortical language regions, but it is unclear if this cross-modal activity is "adaptive" or "mal-adaptive" for speech understanding. To determine if increased activation of language regions is correlated with better speech understanding in CI users, we assessed task-related activation and functional connectivity of auditory and visual cortices to auditory and visual speech and non-speech stimuli in CI users (n = 14) and normal-hearing listeners (n = 17) and used functional near-infrared spectroscopy to measure hemodynamic responses. We used visually presented speech and non-speech to investigate neural processes related to linguistic content and observed that CI users show beneficial cross-modal effects. Specifically, an increase in connectivity between the left auditory and visual cortices-presumed primary sites of cortical language processing-was positively correlated with CI users' abilities to understand speech in background noise. Cross-modal activity in auditory cortex of postlingually deaf CI users may reflect adaptive activity of a distributed, multimodal speech network, recruited to enhance speech understanding.

Plasticity After Hearing Rehabilitation in the Aging Brain

Age-related hearing loss, presbycusis, is an unavoidable sensory degradation, often associated with the progressive decline of cognitive and social functions, and dementia. It is generally considered a natural consequence of the inner-ear deterioration. However, presbycusis arguably conflates a wide array of peripheral and central impairments. Although hearing rehabilitation maintains the integrity and activity of auditory networks and can prevent or revert maladaptive plasticity, the extent of such neural plastic changes in the aging brain is poorly appreciated. By reanalyzing a large-scale dataset of more than 2200 cochlear implant users (CI) and assessing the improvement in speech perception from 6 to 24 months of use, we show that, although rehabilitation improves speech understanding on average, age at implantation only minimally affects speech scores at 6 months but has a pejorative effect at 24 months post implantation. Furthermore, older subjects (>67 years old) were significantly more likely to degrade their performances after 2 years of CI use than the younger patients for each year increase in age. Secondary analysis reveals three possible plasticity trajectories after auditory rehabilitation to account for these disparities: Awakening, reversal of deafness-specific changes; Counteracting, stabilization of additional cognitive impairments; or Decline, independent pejorative processes that hearing rehabilitation cannot prevent. The role of complementary behavioral interventions needs to be considered to potentiate the (re)activation of auditory brain networks.

Is there a change in P300 evoked potential after 6 months in cochlear implant users?

OBJECTIVE

There are few studies on long-latency auditory evoked potential (P300) in people with hearing loss who use a cochlear implant. Central auditory system evaluation with behavioral and electrophysiological tests is believed to help understand the neuroplasticity mechanisms involved in auditory functioning after cochlear implant surgery. This study investigated the electrophysiological processing of cortical level acoustic signals in a group of 21 adult individuals with postlingual bilateral severe-to-profound hearing loss who were submitted to cochlear implant surgery.

METHODS

Data were collected in three phases: pre-cochlear implant surgery, at cochlear implant activation, and 6 months after surgery. P300 measures were also registered during all phases. Tone-burst and speech stimuli were used to elicit P300 and were presented in free field.

RESULTS

Mean P3 component latency with tone-burst and speech stimuli were 352.9 and 321.9 ms in the pre-cochlear implant phase, 364.9 and 368.7 ms in the activation phase, 336.2 and 343.6 ms 6 months after the surgery. The P3 component mean latency values using tone-burst at activation were significantly different from those 6 months after cochlear implant. They were also significantly different using speech, between pre-cochlear implant and activation phases. Lower P3 component latency occurred 6 months after cochlear implant activation with tone-burst and pre-cochlear implant with speech stimulus. There was a weak correlation between mean P3 component latency with speech stimulus and time of hearing loss. There was no difference in amplitude between phases or in the comparison with the other variables.

CONCLUSION

There were changes in P3 component latency during the period assessed, for both speech and pure-tone stimuli, with increased latency in the activation phase and similar lower results in the two other phases, Pre-CI and 6 months after CI use. Mean amplitude measures did not vary in the three phases.

Evidence of visual crossmodal reorganization positively relates to speech outcomes in cochlear implant users

Deaf individuals who use a cochlear implant (CI) have remarkably different outcomes for auditory speech communication ability. One factor assumed to affect CI outcomes is visual crossmodal plasticity in auditory cortex, where deprived auditory regions begin to support non-auditory functions such as vision. Previous research has viewed crossmodal plasticity as harmful for speech outcomes for CI users if it interferes with sound processing, while others have demonstrated that plasticity related to visual language may be beneficial for speech recovery. To clarify, we used electroencephalography (EEG) to measure brain responses to a partial face speaking a silent single-syllable word (visual language) in 15 CI users and 13 age-matched typical-hearing controls. We used source analysis on EEG activity to measure crossmodal visual responses in auditory cortex and then compared them to CI users' speech-in-noise listening ability. CI users' brain response to the onset of the video stimulus (face) was larger than controls in left auditory cortex, consistent with crossmodal activation after deafness. CI users also produced a mixture of alpha (8-12 Hz) synchronization and desynchronization in auditory cortex while watching lip movement while controls instead showed desynchronization. CI users with higher speech scores had stronger crossmodal responses in auditory cortex to the onset of the video, but those with lower speech scores had increases in alpha power during lip movement in auditory areas. Therefore, evidence of crossmodal reorganization in CI users does not necessarily predict poor speech outcomes, and differences in crossmodal activation during lip reading may instead relate to strategies or differences that CI users use in audiovisual speech communication.

Gamma-Band Modulation in Parietal Area as the Electroencephalographic Signature for Performance in Auditory-Verbal Working Memory: An Exploratory Pilot Study in Hearing and Unilateral Cochlear Implant Children

This pilot study investigates the neurophysiological patterns of visual and auditory verbal working memory (VWM) in unilateral cochlear implant users (UCIs). We compared the task-related electroencephalogram (EEG) power spectral density of 7- to 13-year-old UCIs (n = 7) with a hearing control group (HC, n = 10) during the execution of a three-level n-back task with auditory and visual verbal (letters) stimuli. Performances improved as memory load decreased regardless of sensory modality (SM) and group factors. Theta EEG activation over the frontal area was proportionally influenced by task level; the left hemisphere (LH) showed greater activation in the gamma band, suggesting lateralization of VWM function regardless of SM. However, HCs showed stronger activation patterns in the LH than UCIs regardless of SM and in the parietal area (PA) during the most challenging audio condition. Linear regressions for gamma activation in the PA suggest the presence of a pattern-supporting auditory VWM only in HCs. Our findings seem to recognize gamma activation in the PA as the signature of effective auditory VWM. These results, although preliminary, highlight this EEG pattern as a possible cause of the variability found in VWM outcomes in deaf children, opening up new possibilities for interdisciplinary research and rehabilitation intervention.

Side-of-Implantation Effect on Functional Asymmetry in the Auditory Cortex of Single-Sided Deaf Cochlear-Implant Users

Cochlear implants (CIs) allow to restore the hearing function in profoundly deaf individuals. Due to the degradation of the stimulus by CI signal processing, implanted individuals with single-sided deafness (SSD) have the specific challenge that the input highly differs between their ears. The present study compared normal-hearing (NH) listeners (N = 10) and left- and right-ear implanted SSD CI users (N = 10 left, N = 9 right), to evaluate cortical speech processing between CI- and NH-ears and to explore for side-of-implantation effects. The participants performed a two-deviant oddball task, separately with the left and the right ear. Auditory event-related potentials (ERPs) in response to syllables were compared between proficient and non-proficient CI users, as well as between CI and NH ears. The effect of the side of implantation was analysed on the sensor and the source level. CI proficiency could be distinguished based on the ERP amplitudes of the N1 and the P3b. Moreover, syllable processing via the CI ear, when compared to the NH ear, resulted in attenuated and delayed ERPs. In addition, the left-ear implanted SSD CI users revealed an enhanced functional asymmetry in the auditory cortex than right-ear implanted SSD CI users, regardless of whether the syllables were perceived via the CI or the NH ear. Our findings reveal that speech-discrimination proficiency in SSD CI users can be assessed by N1 and P3b ERPs. The results contribute to a better understanding of the rehabilitation success in SSD CI users by showing that cortical speech processing in SSD CI users is affected by CI-related stimulus degradation and experience-related functional changes in the auditory cortex.

Neural Activity During Audiovisual Speech Processing: Protocol For a Functional Neuroimaging Study

BACKGROUND

Functional near-infrared spectroscopy (fNIRS) studies have demonstrated associations between hearing outcomes after cochlear implantation and plastic brain changes. However, inconsistent results make it difficult to draw conclusions. A major problem is that many variables need to be controlled. To gain further understanding, a careful preparation and planning of such a functional neuroimaging task is key.

OBJECTIVE

Using fNIRS, our main objective is to develop a well-controlled audiovisual speech comprehension task to study brain activation in individuals with normal hearing and hearing impairment (including cochlear implant users). The task should be deductible from clinically established tests, induce maximal cortical activation, use optimal coverage of relevant brain regions, and be reproducible by other research groups.

METHODS

The protocol will consist of a 5-minute resting state and 2 stimulation periods that are 12 minutes each. During the stimulation periods, 13-second video recordings of the clinically established Oldenburg Sentence Test (OLSA) will be presented. Stimuli will be presented in 4 different modalities: (1) speech in quiet, (2) speech in noise, (3) visual only (ie, lipreading), and (4) audiovisual speech. Each stimulus type will be repeated 10 times in a counterbalanced block design. Interactive question windows will monitor speech comprehension during the task. After the measurement, we will perform a 3D scan to digitize optode positions and verify the covered anatomical locations.

RESULTS

This paper reports the study protocol. Enrollment for the study started in August 2021. We expect to publish our first results by the end of 2022.

CONCLUSIONS

The proposed audiovisual speech comprehension task will help elucidate neural correlates to speech understanding. The comprehensive study will have the potential to provide additional information beyond the conventional clinical standards about the underlying plastic brain changes of a hearing-impaired person. It will facilitate more precise indication criteria for cochlear implantation and better planning of rehabilitation.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/38407.

The timecourse of multisensory speech processing in unilaterally stimulated cochlear implant users revealed by ERPs

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Both normal-hearing (NH) and cochlear implant (CI) users show a clear benefit in multisensory speech processing.

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Group differences in ERP topographies and cortical source activation suggest distinct audiovisual speech processing in CI users when compared to NH listeners.

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Electrical neuroimaging, including topographic and ERP source analysis, provides a suitable tool to study the timecourse of multisensory speech processing in CI users.

A cochlear implant (CI) is an auditory prosthesis which can partially restore the auditory function in patients with severe to profound hearing loss. However, this bionic device provides only limited auditory information, and CI patients may compensate for this limitation by means of a stronger interaction between the auditory and visual system. To better understand the electrophysiological correlates of audiovisual speech perception, the present study used electroencephalography (EEG) and a redundant target paradigm. Postlingually deafened CI users and normal-hearing (NH) listeners were compared in auditory, visual and audiovisual speech conditions. The behavioural results revealed multisensory integration for both groups, as indicated by shortened response times for the audiovisual as compared to the two unisensory conditions. The analysis of the N1 and P2 event-related potentials (ERPs), including topographic and source analyses, confirmed a multisensory effect for both groups and showed a cortical auditory response which was modulated by the simultaneous processing of the visual stimulus. Nevertheless, the CI users in particular revealed a distinct pattern of N1 topography, pointing to a strong visual impact on auditory speech processing. Apart from these condition effects, the results revealed ERP differences between CI users and NH listeners, not only in N1/P2 ERP topographies, but also in the cortical source configuration. When compared to the NH listeners, the CI users showed an additional activation in the visual cortex at N1 latency, which was positively correlated with CI experience, and a delayed auditory-cortex activation with a reversed, rightward functional lateralisation. In sum, our behavioural and ERP findings demonstrate a clear audiovisual benefit for both groups, and a CI-specific alteration in cortical activation at N1 latency when auditory and visual input is combined. These cortical alterations may reflect a compensatory strategy to overcome the limited CI input, which allows the CI users to improve the lip-reading skills and to approximate the behavioural performance of NH listeners in audiovisual speech conditions. Our results are clinically relevant, as they highlight the importance of assessing the CI outcome not only in auditory-only, but also in audiovisual speech conditions.

Distinct multisensory perceptual processes guide enhanced auditory recognition memory in older cochlear implant users

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Congruent audio-visual encoding enhances later auditory processing in the elderly.

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CI users benefit from additional congruent visual information, similar to controls.

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CI users show distinct neurophysiological processes, compared to controls.

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CI users show an earlier modulation of event-related topographies, compared to controls.

In naturalistic situations, sounds are often perceived in conjunction with matching visual impressions. For example, we see and hear the neighbor’s dog barking in the garden. Still, there is a good chance that we recognize the neighbor’s dog even when we only hear it barking, but do not see it behind the fence. Previous studies with normal-hearing (NH) listeners have shown that the audio-visual presentation of a perceptual object (like an animal) increases the probability to recognize this object later on, even if the repeated presentation of this object occurs in a purely auditory condition. In patients with a cochlear implant (CI), however, the electrical hearing of sounds is impoverished, and the ability to recognize perceptual objects in auditory conditions is significantly limited. It is currently not well understood whether CI users – as NH listeners – show a multisensory facilitation for auditory recognition. The present study used event-related potentials (ERPs) and a continuous recognition paradigm with auditory and audio-visual stimuli to test the prediction that CI users show a benefit from audio-visual perception. Indeed, the congruent audio-visual context resulted in an improved recognition ability of objects in an auditory-only condition, both in the NH listeners and the CI users. The ERPs revealed a group-specific pattern of voltage topographies and correlations between these ERP maps and the auditory recognition ability, indicating a different processing of congruent audio-visual stimuli in CI users when compared to NH listeners. Taken together, our results point to distinct cortical processing of naturalistic audio-visual objects in CI users and NH listeners, which however allows both groups to improve the recognition ability of these objects in a purely auditory context. Our findings are of relevance for future clinical research since audio-visual perception might also improve the auditory rehabilitation after cochlear implantation.

Treatment of Age-Related Hearing Loss Alters Audiovisual Integration and Resting-State Functional Connectivity: A Randomized Controlled Pilot Trial

Untreated age-related hearing loss increases audiovisual integration and impacts resting state functional brain connectivity. Further, there is a relation between crossmodal plasticity and audiovisual integration strength in cochlear implant patients. However, it is currently unclear whether amplification of the auditory input by hearing aids influences audiovisual integration and resting state functional brain connectivity. We conducted a randomized controlled pilot study to investigate how the McGurk illusion, a common measure for audiovisual integration, and resting state functional brain connectivity of the auditory cortex are altered by six-month hearing aid use. Thirty-two older participants with slight-to-moderate, symmetric, age-related hearing loss were allocated to a treatment or waiting control group and measured one week before and six months after hearing aid fitting with functional magnetic resonance imaging. Our results showed a statistical trend for an increased McGurk illusion after six months of hearing aid use. We further demonstrated that an increase in McGurk susceptibility is related to a decreased hearing aid benefit for auditory speech intelligibility in noise. No significant interaction between group and time point was obtained in the whole-brain resting state analysis. However, a region of interest (ROI)-to-ROI analysis indicated that hearing aid use of six months was associated with a decrease in resting state functional connectivity between the auditory cortex and the fusiform gyrus and that this decrease was related to an increase of perceived McGurk illusions. Our study, therefore, suggests that even short-term hearing aid use alters audiovisual integration and functional brain connectivity between auditory and visual cortices.

Electrically evoked auditory brainstem responses to electrical stimulation at round window membrane in congenitally deaf children at different ages

OBJECTIVES

To investigate the usefulness of measuring the electrically evoked auditory brainstem responses (eABRs) to electrical stimulation at the round window niche (RWN) and round window membrane (RWM) and the effect of deafness duration on functions of the auditory pathway to the level of the brainstem.

METHODS

According to the age at cochlear implantation (CI), 99 children with profound sensorineural hearing loss were divided into four groups: ≤12 months (group A), 13-36 months (group B), 37-60 months (group C) and >60 months (group D). The eABRs were evoked by electrical stimulation at RWN and RWM during the operation of CI.

RESULTS

The higher eABR extraction rate and lower threshold for RWM stimulation was found than those for RWN stimulation. The eⅢ latencies and eⅢ-eⅤ latency intervals for RWM stimulation were similar among four groups. However, children with earlier CI (group A) showed a significantly shorter eⅤ latency than others.

CONCLUSION

The eABR evoked by the electrical stimulation at RWM is more stable and sensitive compared with that at RWN for evaluating functions of the auditory conduction pathway. Development in the upper brainstem pathway may be more vulnerable to long-term deafness as revealed by the eⅤ latency.

Neural correlates of visual stimulus encoding and verbal working memory differ between cochlear implant users and normal-hearing controls

A common concern for individuals with severe‐to‐profound hearing loss fitted with cochlear implants (CIs) is difficulty following conversations in noisy environments. Recent work has suggested that these difficulties are related to individual differences in brain function, including verbal working memory and the degree of cross‐modal reorganization of auditory areas for visual processing. However, the neural basis for these relationships is not fully understood. Here, we investigated neural correlates of visual verbal working memory and sensory plasticity in 14 CI users and age‐matched normal‐hearing (NH) controls. While we recorded the high‐density electroencephalogram (EEG), participants completed a modified Sternberg visual working memory task where sets of letters and numbers were presented visually and then recalled at a later time. Results suggested that CI users had comparable behavioural working memory performance compared with NH. However, CI users had more pronounced neural activity during visual stimulus encoding, including stronger visual‐evoked activity in auditory and visual cortices, larger modulations of neural oscillations and increased frontotemporal connectivity. In contrast, during memory retention of the characters, CI users had descriptively weaker neural oscillations and significantly lower frontotemporal connectivity. We interpret the differences in neural correlates of visual stimulus processing in CI users through the lens of cross‐modal and intramodal plasticity.

Free-Field Cortical Steady-State Evoked Potentials in Cochlear Implant Users

Auditory steady-state evoked potentials (SS-EPs) are phase-locked neural responses to periodic stimuli, believed to reflect specific neural generators. As an objective measure, steady-state responses have been used in different clinical settings, including measuring hearing thresholds of normal and hearing-impaired subjects. Recent studies are in favor of recording these responses as a part of the cochlear implant (CI) device-fitting procedure. Considering these potential benefits, the goals of the present study were to assess the feasibility of recording free-field SS-EPs in CI users and to compare their characteristics between CI users and controls. By taking advantage of a recently developed dual-frequency tagging method, we attempted to record subcortical and cortical SS-EPs from adult CI users and controls and measured reliable subcortical and cortical SS-EPs in the control group. Independent component analysis (ICA) was used to remove CI stimulation artifacts, yet subcortical responses of several CIs were heavily contaminated by these artifacts. Consequently, only cortical SS-EPs were compared between groups, which were found to be larger in the controls. The lower cortical SS-EPs' amplitude in CI users might indicate a reduction in neural synchrony evoked by the modulation rate of the auditory input across different neural assemblies in the auditory pathway. The brain topographies of cortical auditory SS-EPs, the time course of cortical responses, and the reconstructed cortical maps were highly similar between groups, confirming their neural origin and possibility to obtain such responses also in CI recipients. As for subcortical SS-EPs, our results highlight a need for sophisticated denoising algorithms to pinpoint and remove artifactual components from the biological response.

Oscillatory signatures of Repetition Suppression and Novelty Detection reveal altered induced visual responses in early deafness

The ability to differentiate between repeated and novel events represents a fundamental property of the visual system. Neural responses are typically reduced upon stimulus repetition, a phenomenon called Repetition Suppression (RS). On the contrary, following a novel visual stimulus, the neural response is generally enhanced, a phenomenon referred to as Novelty Detection (ND). Here, we aimed to investigate the impact of early deafness on the oscillatory signatures of RS and ND brain responses. To this aim, electrophysiological data were acquired in early deaf and hearing control individuals during processing of repeated and novel visual events unattended by participants. By studying evoked and induced oscillatory brain activities, as well as inter-trial phase coherence, we linked response modulations to feedback and/or feedforward processes. Results revealed selective experience-dependent changes on both RS and ND mechanisms. Compared to hearing controls, early deaf individuals displayed: (i) greater attenuation of the response following stimulus repetition, selectively in the induced theta-band (4-7 Hz); (ii) reduced desynchronization following the onset of novel visual stimuli, in the induced alpha and beta bands (8-12 and 13-25 Hz); (iii) comparable modulation of evoked responses and inter-trial phase coherence. The selectivity of the effects in the induced responses parallels findings observed in the auditory cortex of deaf animal models following intracochlear electric stimulation. The present results support the idea that early deafness alters induced oscillatory activity and the functional tuning of basic visual processing.

Activities of the Right Temporo-Parieto-Occipital Junction Reflect Spatial Hearing Ability in Cochlear Implant Users

Spatial hearing is critical for us not only to orient ourselves in space, but also to follow a conversation with multiple speakers involved in a complex sound environment. The hearing ability of people who suffered from severe sensorineural hearing loss can be restored by cochlear implants (CIs), however, with a large outcome variability. Yet, the causes of the CI performance variability remain incompletely understood. Despite the CI-based restoration of the peripheral auditory input, central auditory processing might still not function fully. Here we developed a multi-modal repetition suppression (MMRS) paradigm that is capable of capturing stimulus property-specific processing, in order to identify the neural correlates of spatial hearing and potential central neural indexes useful for the rehabilitation of sound localization in CI users. To this end, 17 normal hearing and 13 CI participants underwent the MMRS task while their brain activity was recorded with a 256-channel electroencephalography (EEG). The participants were required to discriminate between the probe sound location coming from a horizontal array of loudspeakers. The EEG MMRS response following the probe sound was elicited at various brain regions and at different stages of processing. Interestingly, the more similar this differential MMRS response in the right temporo-parieto-occipital (TPO) junction in CI users was to the normal hearing group, the better was the spatial hearing performance in individual CI users. Based on this finding, we suggest that the differential MMRS response at the right TPO junction could serve as a central neural index for intact or impaired sound localization abilities.

The Listening Network and Cochlear Implant Benefits in Hearing-Impaired Adults

Older adults with mild or no hearing loss make more errors and expend more effort listening to speech. Cochlear implants (CI) restore hearing to deaf patients but with limited fidelity. We hypothesized that patient-reported hearing and health-related quality of life in CI patients may similarly vary according to age. Speech Spatial Qualities (SSQ) of hearing scale and Health Utilities Index Mark III (HUI) questionnaires were administered to 543 unilaterally implanted adults across Europe, South Africa, and South America. Data were acquired before surgery and at 1, 2, and 3 years post-surgery. Data were analyzed using linear mixed models with visit, age group (18–34, 35–44, 45–54, 55–64, and 65+), and side of implant as main factors and adjusted for other covariates. Tinnitus and dizziness prevalence did not vary with age, but older groups had more preoperative hearing. Preoperatively and postoperatively, SSQ scores were significantly higher (Δ0.75–0.82) for those aged <45 compared with those 55+. However, gains in SSQ scores were equivalent across age groups, although postoperative SSQ scores were higher in right-ear implanted subjects. All age groups benefited equally in terms of HUI gain (0.18), with no decrease in scores with age. Overall, younger adults appeared to cope better with a degraded hearing before and after CI, leading to better subjective hearing performance.

Neural Mechanisms of Hearing Recovery for Cochlear-Implanted Patients: An Electroencephalogram Follow-Up Study

Background

Patients with severe profound hearing loss could benefit from cochlear implantation (CI). However, the neural mechanism of such benefit is still unclear. Therefore, we analyzed the electroencephalogram (EEG) and behavioral indicators of auditory function remodeling in patients with CI. Both indicators were sampled at multiple time points after implantation (1, 90, and 180 days).

Methods

First, the speech perception ability was evaluated with the recording of a list of Chinese words and sentences in 15 healthy controls (HC group) and 10 patients with CI (CI group). EEG data were collected using an oddball paradigm. Then, the characteristics of event-related potentials (ERPs) and mismatch negative (MMN) were compared between the CI group and the HC group. In addition, we analyzed the phase lag indices (PLI) in the CI group and the HC group and calculated the difference in functional connectivity between the two groups at different stages after implantation.

Results

The behavioral indicator, speech recognition ability, in CI patients improved as the implantation time increased. The MMN analysis showed that CI patients could recognize the difference between standard and deviation stimuli just like the HCs 90 days after cochlear implantation. Comparing the latencies of N1/P2/MMN between the CI group and the HC group, we found that the latency of N1/P2 in CI patients was longer, while the latency of MMN in CI users was shorter. In addition, PLI-based whole-brain functional connectivity (PLI-FC) showed that the difference between the CI group and the HC group mainly exists in electrode pairs between the bilateral auditory area and the frontal area. Furthermore, all those differences gradually decreased with the increase in implantation time.

Conclusion

The N1 amplitude, N1/P2/MMN latency, and PLI-FC in the alpha band may reflect the process of auditory function remodeling and could be an objective index for the assessment of speech perception ability and the effect of cochlear implantation.

Cortical reorganization following auditory deprivation predicts cochlear implant performance in postlingually deaf adults

Long‐term hearing loss in postlingually deaf (PD) adults may lead to brain structural changes that affect the outcomes of cochlear implantation. We studied 94 PD patients who underwent cochlear implantation and 37 patients who were MRI‐scanned within 2 weeks after the onset of sudden hearing loss and expected with minimal brain structural changes in relation to deafness. Compared with those with sudden hearing loss, we found lower gray matter (GM) probabilities in bilateral thalami, superior, middle, inferior temporal cortices as well as the central cortical regions corresponding to the movement and sensation of the lips, tongue, and larynx in the PD group. Among these brain areas, the GM in the middle temporal cortex showed negative correlation with disease duration, whereas the other areas displayed positive correlations. Left superior, middle temporal cortical, and bilateral thalamic GMs were the most accurate predictors of post‐cochlear implantation word recognition scores (mean absolute error [MAE] = 10.1, r = .82), which was superior to clinical variables used (MAE: 12.1, p < .05). Using the combined brain morphological and clinical features, we achieved the best prediction of the outcome (MAE: 8.51, r = .90). Our findings suggest that the cross‐modal plasticity allowing the superior temporal cortex and thalamus to process other modal sensory inputs reverses the initially lower volume when deafness becomes persistent. The middle temporal cortex processing higher‐level language comprehension shows persistent negative correlations with disease duration, suggesting this area's association with degraded speech comprehensions due to long‐term deafness. Morphological features combined with clinical variables might play a key role in predicting outcomes of cochlear implantation.

Evaluating hearing performance with cochlear implants within the same patient using daily randomization and imaging-based fitting - The ELEPHANT study

Background

Prospective research in the field of cochlear implants is hampered by methodological issues and small sample sizes. The ELEPHANT study presents an alternative clinical trial design with a daily randomized approach evaluating individualized tonotopical fitting of a cochlear implant (CI).

Methods

A single-blinded, daily-randomized clinical trial will be implemented to evaluate a new imaging-based CI mapping strategy. A minimum of 20 participants will be included from the start of the rehabilitation process with a 1-year follow-up period. Based on a post-operative cone beam CT scan (CBCT), mapping of electrical input will be aligned to natural place-pitch arrangement in the individual cochlea. The CI’s frequency allocation table will be adjusted to match the electrical stimulation of frequencies as closely as possible to corresponding acoustic locations in the cochlea. A randomization scheme will be implemented whereby the participant, blinded to the intervention allocation, crosses over between the experimental and standard fitting program on a daily basis, and thus effectively acts as his own control, followed by a period of free choice between both maps to incorporate patient preference. With this new approach the occurrence of a first-order carryover effect and a limited sample size is addressed.

Discussion

The experimental fitting strategy is thought to give rise to a steeper learning curve, result in better performance in challenging listening situations, improve sound quality, better complement residual acoustic hearing in the contralateral ear and be preferred by recipients of a CI. Concurrently, the suitability of the novel trial design will be considered in investigating these hypotheses.

Trial registration

ClinicalTrials.gov: NCT03892941. Registered 27 March 2019.

Synchronisation of Neural Oscillations and Cross-modal Influences

At any given moment, we receive multiple signals from our different senses. Prior research has shown that signals in one sensory modality can influence neural activity and behavioural performance associated with another sensory modality. Recent human and nonhuman primate studies suggest that such cross-modal influences in sensory cortices are mediated by the synchronisation of ongoing neural oscillations. In this review, we consider two mechanisms proposed to facilitate cross-modal influences on sensory processing, namely cross-modal phase resetting and neural entrainment. We consider how top-down processes may further influence cross-modal processing in a flexible manner, and we highlight fruitful directions for further research.

Altered Gray Matter Volume and White Matter Integrity in Sensorineural Hearing Loss Patients: A VBM and TBSS Study

OBJECTIVE

The purpose of the present study was to detect structural changes in the brains of patients with sensorineural hearing loss (SNHL) by combining voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS).

METHODS

Thirty-five patients with SNHL (mean age: 39.72 ± 1.81 yr) and 23 age-matched control subjects (mean age: 39.83 ± 1.96 yr) were assessed using three-dimensional, T1-weighted imaging, and diffusion tensor imaging. TBSS and VBM analyses were performed to evaluate grey matter (GM) volume changes and white matter (WM) alternations, as measured by mean diffusivity (MD), fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD).

RESULTS

VBM showed decreased GM volume in patients with SNHL in the fusiform gyrus of the right temporal lobe and right middle occipital gyrus. TBSS revealed WM integrity changes, including decreased FA and RD and increased RD in several WM regions. However, MD showed no significant difference between patients with SNHL and age-matched controls.

CONCLUSION

Patients with SNHL showed smaller GM volume and WM integrity changes in several regions.

Multidimensional Timbre Spaces of Cochlear Implant Vocoded and Non-vocoded Synthetic Female Singing Voices

Many post-lingually deafened cochlear implant (CI) users report that they no longer enjoy listening to music, which could possibly contribute to a perceived reduction in quality of life. One aspect of music perception, vocal timbre perception, may be difficult for CI users because they may not be able to use the same timbral cues available to normal hearing listeners. Vocal tract resonance frequencies have been shown to provide perceptual cues to voice categories such as baritone, tenor, mezzo-soprano, and soprano, while changes in glottal source spectral slope are believed to be related to perception of vocal quality dimensions such as fluty vs. brassy. As a first step toward understanding vocal timbre perception in CI users, we employed an 8-channel noise-band vocoder to test how vocoding can alter the timbral perception of female synthetic sung vowels across pitches. Non-vocoded and vocoded stimuli were synthesized with vibrato using 3 excitation source spectral slopes and 3 vocal tract transfer functions (mezzo-soprano, intermediate, soprano) at the pitches C4, B4, and F5. Six multi-dimensional scaling experiments were conducted: C4 not vocoded, C4 vocoded, B4 not vocoded, B4 vocoded, F5 not vocoded, and F5 vocoded. At the pitch C4, for both non-vocoded and vocoded conditions, dimension 1 grouped stimuli according to voice category and was most strongly predicted by spectral centroid from 0 to 2 kHz. While dimension 2 grouped stimuli according to excitation source spectral slope, it was organized slightly differently and predicted by different acoustic parameters in the non-vocoded and vocoded conditions. For pitches B4 and F5 spectral centroid from 0 to 2 kHz most strongly predicted dimension 1. However, while dimension 1 separated all 3 voice categories in the vocoded condition, dimension 1 only separated the soprano stimuli from the intermediate and mezzo-soprano stimuli in the non-vocoded condition. While it is unclear how these results predict timbre perception in CI listeners, in general, these results suggest that perhaps some aspects of vocal timbre may remain.

Changes in Speech-Related Brain Activity During Adaptation to Electro-Acoustic Hearing

Objectives: Hearing improves significantly with bimodal provision, i.e., a cochlear implant (CI) at one ear and a hearing aid (HA) at the other, but performance shows a high degree of variability resulting in substantial uncertainty about the performance that can be expected by the individual CI user. The objective of this study was to explore how auditory event-related potentials (AERPs) of bimodal listeners in response to spoken words approximate the electrophysiological response of normal hearing (NH) listeners. Study Design: Explorative prospective analysis during the first 6 months of bimodal listening using a within-subject repeated measures design. Setting: Academic tertiary care center. Participants: Twenty-seven adult participants with bilateral sensorineural hearing loss who received a HiRes 90K CI and continued use of a HA at the non-implanted ear. Age-matched NH listeners served as controls. Intervention: Cochlear implantation. Main Outcome Measures: Obligatory auditory evoked potentials N1 and P2, and the event-related N2 potential in response to monosyllabic words and their reversed sound traces before, as well as 3 and 6 months post-implantation. The task required word/non-word classification. Stimuli were presented within speech-modulated noise. Loudness of word/non-word signals was adjusted individually to achieve the same intelligibility across groups and assessments. Results: Intelligibility improved significantly with bimodal hearing, and the N1-P2 response approximated the morphology seen in NH with enhanced and earlier responses to the words compared to their reversals. For bimodal listeners, a prominent negative deflection was present between 370 and 570 ms post stimulus onset (N2), irrespective of stimulus type. This was absent for NH controls; hence, this response did not approximate the NH response during the study interval. N2 source localization evidenced extended activation of general cognitive areas in frontal and prefrontal brain areas in the CI group. Conclusions: Prolonged and spatially extended processing in bimodal CI users suggests employment of additional auditory-cognitive mechanisms during speech processing. This does not reduce within 6 months of bimodal experience and may be a correlate of the enhanced listening effort described by CI listeners.

Research Insights on Neural Effects of Auditory Deprivation and Restoration in Unilateral Hearing Loss: A Systematic Review

Neuroplasticity following bilateral deafness and auditory restoration has been repeatedly investigated. In clinical practice, however, a significant number of patients present a severe-to-profound unilateral hearing loss (UHL). To date, less is known about the neuroplasticity following monaural hearing deprivation and auditory input restoration. This article provides an overview of the current research insights on the impact of UHL on the brain and the effect of auditory input restoration with a cochlear implant (CI). An exhaustive systematic review of the literature was performed selecting 38 studies that apply different neural analyses techniques. The main results show that the hearing ear becomes functionally dominant after monaural deprivation, reshaping the lateralization of the neural network for auditory processing, a process that can be considered to influence auditory restoration. Furthermore, animal models predict that the onset time of UHL impacts auditory restoration. Hence, the results seem to advocate for early restoration of UHL, although further research is required to disambiguate the effects of duration and onset of UHL on auditory restoration and on structural neuroplasticity following UHL deprivation and restoration. Ongoing developments on CI devices compatible with Magnetic Resonance Imaging (MRI) examinations will provide a unique opportunity to investigate structural and functional neuroplasticity following CI restoration more directly.

Acoustic Change Responses to Amplitude Modulation in Cochlear Implant Users: Relationships to Speech Perception

Objectives

The ability to understand speech is highly variable in people with cochlear implants (CIs) and to date, there are no objective measures that identify the root of this discrepancy. However, behavioral measures of temporal processing such as the temporal modulation transfer function (TMTF) has previously found to be related to vowel and consonant identification in CI users. The acoustic change complex (ACC) is a cortical auditory-evoked potential response that can be elicited by a “change” in an ongoing stimulus. In this study, the ACC elicited by amplitude modulation (AM) change was related to measures of speech perception as well as the amplitude detection threshold in CI users.

Methods

Ten CI users (mean age: 50 years old) participated in this study. All subjects participated in behavioral tests that included both speech and amplitude modulation detection to obtain a TMTF. CI users were categorized as “good” (n = 6) or “poor” (n = 4) based on their speech-in noise score (<50%). 64-channel electroencephalographic recordings were conducted while CI users passively listened to AM change sounds that were presented in a free field setting. The AM change stimulus was white noise with four different AM rates (4, 40, 100, and 300 Hz).

Results

Behavioral results show that AM detection thresholds in CI users were higher compared to the normal-hearing (NH) group for all AM rates. The electrophysiological data suggest that N1 responses were significantly decreased in amplitude and their latencies were increased in CI users compared to NH controls. In addition, the N1 latencies for the poor CI performers were delayed compared to the good CI performers. The N1 latency for 40 Hz AM was correlated with various speech perception measures.

Conclusion

Our data suggest that the ACC to AM change provides an objective index of speech perception abilities that can be used to explain some of the variation in speech perception observed among CI users.

The use of the MUSS and the SIR scale in late-implanted prelingually deafened adolescents and adults as a subjective evaluation

Background: The SIR scale has been widely used to measure speech improvement in late-implanted prelingually deafened adolescents and adults. However the ceiling effect of the SIR scale may lead to the loss of some information.Aim/objectives: To evaluate the oral ability of late-implanted prelingually deafened adolescents and adults using the MUSS and SIR scale and to analyse the relationship between the SIR score and the MUSS score.Material and methods: Ninety-four prelingually deafened adolescents and adults who had received cochlear implants were investigated. The MUSS and SIR scale were used to evaluate oral ability.Results: The relationship between the duration of implant use and the MUSS score was significantly different. No significant differences were found among the groups for age at implantation, gender and side of cochlear implantation. The total score on the MUSS was positively correlated with the SIR score.Conclusions and significance: The MUSS and the SIR scale could be used to evaluate the oral ability of late implanted patients. The SIR scale could be used to perform a rapid assessment and the MUSS could help provide more information. The combination of the two scales could be used to evaluate vocal ability more accurately and effectively.

The Cross-Modal Effects of Sensory Deprivation on Spatial and Temporal Processes in Vision and Audition: A Systematic Review on Behavioral and Neuroimaging Research since 2000

One of the most significant effects of neural plasticity manifests in the case of sensory deprivation when cortical areas that were originally specialized for the functions of the deprived sense take over the processing of another modality. Vision and audition represent two important senses needed to navigate through space and time. Therefore, the current systematic review discusses the cross-modal behavioral and neural consequences of deafness and blindness by focusing on spatial and temporal processing abilities, respectively. In addition, movement processing is evaluated as compiling both spatial and temporal information. We examine whether the sense that is not primarily affected changes in its own properties or in the properties of the deprived modality (i.e., temporal processing as the main specialization of audition and spatial processing as the main specialization of vision). References to the metamodal organization, supramodal functioning, and the revised neural recycling theory are made to address global brain organization and plasticity principles. Generally, according to the reviewed studies, behavioral performance is enhanced in those aspects for which both the deprived and the overtaking senses provide adequate processing resources. Furthermore, the behavioral enhancements observed in the overtaking sense (i.e., vision in the case of deafness and audition in the case of blindness) are clearly limited by the processing resources of the overtaking modality. Thus, the brain regions that were previously recruited during the behavioral performance of the deprived sense now support a similar behavioral performance for the overtaking sense. This finding suggests a more input-unspecific and processing principle-based organization of the brain. Finally, we highlight the importance of controlling for and stating factors that might impact neural plasticity and the need for further research into visual temporal processing in deaf subjects.

Audio-visual integration in cochlear implant listeners and the effect of age difference

This study aimed to investigate differences in audio-visual (AV) integration between cochlear implant (CI) listeners and normal-hearing (NH) adults. A secondary aim was to investigate the effect of age differences by examining AV integration in groups of older and younger NH adults. Seventeen CI listeners, 13 similarly aged NH adults, and 16 younger NH adults were recruited. Two speech identification experiments were conducted to evaluate AV integration of speech cues. In the first experiment, reaction times in audio-alone (A-alone), visual-alone (V-alone), and AV conditions were measured during a speeded task in which participants were asked to identify a target sound /aSa/ among 11 alternatives. A race model was applied to evaluate AV integration. In the second experiment, identification accuracies were measured using a closed set of consonants and an open set of consonant-nucleus-consonant words. The authors quantified AV integration using a combination of a probability model and a cue integration model (which model participants' AV accuracy by assuming no or optimal integration, respectively). The results found that experienced CI listeners showed no better AV integration than their similarly aged NH adults. Further, there was no significant difference in AV integration between the younger and older NH adults.

Alterations of structural and functional connectivity in profound sensorineural hearing loss infants within an early sensitive period: A combined DTI and fMRI study

Due to heightened level of neuroplasticity, there is a sensitive period (2-4 years after birth) that exists for optimal central auditory development. Using diffusion tensor imaging combined with resting-state functional connectivity (rsFC) analysis, this study directly investigates the structural connectivity alterations of the whole brain white matter (WM) and the functional reorganization of the auditory network in infants with sensorineural hearing loss (SNHL) during the early sensitive period. 46 bilateral profound SNHL infants prior to cochlear implantation (mean age, 17.59 months) and 33 healthy controls (mean age, 18.55 months) were included in the analysis. Compared with controls, SNHL infants showed widespread WM alterations, including bilateral superior longitudinal fasciculus, inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, right corticospinal tract, posterior thalamic radiation and left uncinate fasciculus. Moreover, SNHL infants demonstrated increased rsFC between left/right primary auditory cortex seeds and right insula and superior temporal gyrus. In conclusion, this study suggests that SNHL in the early sensitive period is associated with diffuse WM alterations that mainly affect the auditory and language pathways. Furthermore, increased rsFC in areas mainly associated with auditory and language networks may potentially reflect reorganization and compensatory activation in response to auditory deprivation during the early sensitive period.

Cortical Speech Processing in Postlingually Deaf Adult Cochlear Implant Users, as Revealed by Functional Near-Infrared Spectroscopy

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.

Brain Plasticity Can Predict the Cochlear Implant Outcome in Adult-Onset Deafness

Sensory plasticity, which is associated with deafness, has not been as thoroughly investigated in the adult brain as it has in the developing brain. In this study, we examined the brain reorganization induced by auditory deprivation in people with adult-onset deafness and its clinical relevance by measuring glucose metabolism before cochlear implant (CI) surgery. F-18 fluorodeoxyglucose positron emission tomography (¹⁸F-FDG-PET) scans were performed in 37 postlingually deafened patients during the preoperative workup period, and in 39 normal-hearing (NH) controls. Behavioral CI outcomes were measured at 1 year after implantation using a phoneme identification test with auditory cueing only. In the deaf individuals, areas involved in the auditory pathway such as the inferior colliculus and bilateral superior temporal gyri were hypometabolic compared to the NH controls. The hypometabolism observed in the deaf auditory cortices gradually returned to levels similar to the controls as the duration of deafness increased. However, contrary to our previous findings in congenitally deaf children, this metabolic recovery failed to have a significant prognostic value for the recovery of the speech perception ability in adult CI patients. In a broad occipital area centered on the primary visual cortices, glucose metabolism was higher in the deaf patients than the controls, suggesting that the area had become visually hyperactive for sensory compensation immediately after the onset of deafness. In addition, a negative correlation between the metabolic activity and behavioral speech perception outcomes was observed in the visual association areas. In the medial frontal cortices, cortical metabolism in most patients decreased, but patients who had preserved metabolic activities showed better speech performance. These results suggest that the auditory cortex in people with adult-onset deafness is relatively resistant to cross-modal plasticity, and instead, individual traits in late-stage visual processing and cognitive control seem to be more reliable prognostic markers for adult-onset deafness.

Cochlear Implantation in Postlingually Deaf Adults is Time-sensitive Towards Positive Outcome: Prediction using Advanced Machine Learning Techniques

Given our aging society and the prevalence of age-related hearing loss that often develops during adulthood, hearing loss is a common public health issue affecting almost all older adults. Moderate-to-moderately severe hearing loss can usually be corrected with hearing aids; however, severe-to-profound hearing loss often requires a cochlear implant (CI). However, post-operative CI results vary, and the performance of the previous prediction models is limited, indicating that a new approach is needed. For postlingually deaf adults (n de120) who received CI with full insertion, we predicted CI outcomes using a Random-Forest Regression (RFR) model and investigated the effect of preoperative factors on CI outcomes. Postoperative word recognition scores (WRS) served as the dependent variable to predict. Predictors included duration of deafness (DoD), age at CI operation (ageCI), duration of hearing-aid use (DoHA), preoperative hearing threshold and sentence recognition score. Prediction accuracy was evaluated using mean absolute error (MAE) and Pearson's correlation coefficient r between the true WRS and predicted WRS. The fitting using a linear model resulted in prediction of WRS with r = 0.7 and MAE = 15.6 ± 9. RFR outperformed the linear model (r = 0.96, MAE = 6.1 ± 4.7, p < 0.00001). Cross-hospital data validation showed reliable performance using RFR (r = 0.91, MAE = 9.6 ± 5.2). The contribution of DoD to prediction was the highest (MAE increase when omitted: 14.8), followed by ageCI (8.9) and DoHA (7.5). After CI, patients with DoD < 10 years presented better WRSs and smaller variations (p < 0.01) than those with longer DoD. Better WRS was also explained by younger age at CI and longer-term DoHA. Machine learning demonstrated a robust prediction performance for CI outcomes in postlingually deaf adults across different institutes, providing a reference value for counseling patients considering CI. Health care providers should be aware that the patients with severe-to-profound hearing loss who cannot have benefit from hearing aids need to proceed with CI as soon as possible and should continue using hearing aids until after CI operation.