Two are better than one: Differences in cortical EEG patterns during auditory and visual verbal working memory processing between Unilateral and Bilateral Cochlear Implanted children

Despite the proven effectiveness of cochlear implant (CI) in the hearing restoration of deaf or hard-of-hearing (DHH) children, to date, extreme variability in verbal working memory (VWM) abilities is observed in both unilateral and bilateral CI user children (CIs). Although clinical experience has long observed deficits in this fundamental executive function in CIs, the cause to date is still unknown. Here, we have set out to investigate differences in brain functioning regarding the impact of monaural and binaural listening in CIs compared with normal hearing (NH) peers during a three-level difficulty n-back task undertaken in two sensory modalities (auditory and visual). The objective of this pioneering study was to identify electroencephalographic (EEG) marker pattern differences in visual and auditory VWM performances in CIs compared to NH peers and possible differences between unilateral cochlear implant (UCI) and bilateral cochlear implant (BCI) users. The main results revealed differences in theta and gamma EEG bands. Compared with hearing controls and BCIs, UCIs showed hypoactivation of theta in the frontal area during the most complex condition of the auditory task and a correlation of the same activation with VWM performance. Hypoactivation in theta was also observed, again for UCIs, in the left hemisphere when compared to BCIs and in the gamma band in UCIs compared to both BCIs and NHs. For the latter two, a correlation was found between left hemispheric gamma oscillation and performance in the audio task. These findings, discussed in the light of recent research, suggest that unilateral CI is deficient in supporting auditory VWM in DHH. At the same time, bilateral CI would allow the DHH child to approach the VWM benchmark for NH children. The present study suggests the possible effectiveness of EEG in supporting, through a targeted approach, the diagnosis and rehabilitation of VWM in DHH children.

Mismatch negativity as a marker of music perception in individual cochlear implant users: A spike density component analysis study

OBJECTIVE

Ninety percent of cochlear implant (CI) users are interested in improving their music perception. However, only few objective behavioral and neurophysiological tests have been developed for tracing the development of music discrimination skills in CI users. In this study, we aimed to obtain an accurate individual mismatch negativity (MMN) marker that could predict behavioral auditory discrimination thresholds.

METHODS

We measured the individual MMN response to four magnitudes of deviations in four different musical features (intensity, pitch, timbre, and rhythm) in a rare sample of experienced CI users and a control sample of normally hearing participants. We applied a recently developed spike density component analysis (SCA), which can suppress confounding alpha waves, and contrasted it with previously proposed methods.

RESULTS

Statistically detected individual MMN predicted attentive sound discrimination ability with high accuracy: for CI users 89.2% (278/312 cases) and for controls 90.5% (384/424 cases). As expected, MMN was detected for fewer CI users when the sound deviants were of smaller magnitude.

CONCLUSIONS

The findings support the use of MMN responses in individual CI users as a diagnostic tool for testing music perception.

SIGNIFICANCE

For CI users, the new SCA method provided more accurate and replicable diagnostic detections than preceding state-of-the-art.

Long-term speech perception and morphosyntactic outcomes in adolescents and young adults implanted in childhood

BACKGROUND

Long-term assessments of children with cochlear implants (CI) are important inputs to help guide families and professionals in therapeutic and counselling processes. Based on these premises, the primary aim of the present study was to assess the long-term speech and language outcomes in a sample of prelingually deaf or hard of hearing (DHH) adolescents and young adults with unilateral or bilateral implantation in childhood. The secondary aim was to investigate the correlations of age at implantation with long-term speech and language outcomes.

MATERIALS AND METHODS

Retrospective observational study on 54 long-term CI users, 33 unilateral and 21 bilateral (mean age at CI surgery 38.1 ± 24.6 months; mean age at last follow-up assessment 19.1 ± 4.3 years of age and mean follow-up time 16 ± 3.7 years). Means and standards were used to describe speech perception (in quiet, in fixed noise and in adaptive noise using It-Matrix) and morphosyntactic comprehension (TROG-2) outcomes. A univariate analysis was used to evaluate outcome differences between unilateral and bilateral patients. Bivariate analysis was performed to investigate the relationships between age at CI, audiological variables, and language outcomes. Finally, multivariate analysis was performed to quantify the relationship between It-Matrix, sentence recognition in quiet and at SNR+10 and TROG-2.

RESULTS

The participants showed good speech recognition performance in quiet (94% for words and 89% for sentences) whilst their speech-in-noise scores decreased significantly. For the It-Matrix, only 9.2% of the participants showed scores within the normative range. This value was 60% for TROG-2 performance. For both auditory and language skills, group differences for unilateral versus bilateral CI users were not statistically significant (p > 0.05). Bivariate analysis showed that age at CI correlated significantly with overall results at TROG-2 (r = -0.6; p < 0.001) and with It-Matrix (r = 0.5; p < 0.001). TROG-2 was negatively correlated with results for It-Matrix (r = -0.5; p < 0.001). In the multivariate analysis with It-Matrix as a dependent variable, the model explained 63% of the variance, of which 60% was related to sentence recognition and 3% to morphosyntax.

CONCLUSIONS

These data contribute to the definition of average long-term outcomes expected in subjects implanted during childhood whilst increasing our knowledge of the effects of variables such as age at CI and morphosyntactic comprehension on speech perception. Although the majority of this prelingually DHH cohort did not achieve scores within a normative range, remarkably better It-Matrix scores were observed when compared to those from postlingually deafened adult CI users.

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.

Vocal Emotion Identification by Children Using Cochlear Implants, Relations to Voice Quality, and Musical Interests

PURPOSE

Listening tests for emotion identification were conducted with 8-17-year-old children with hearing impairment (HI; N = 25) using cochlear implants, and their 12-year-old peers with normal hearing (N = 18). The study examined the impact of musical interests and acoustics of the stimuli on correct emotion identification.

METHOD

The children completed a questionnaire with their background information and noting musical interests. They then listened to vocal stimuli produced by actors (N = 5) and consisting of nonsense sentences and prolonged vowels ([a:], [i:], and [u:]; N = 32) expressing excitement, anger, contentment, and fear. The children's task was to identify the emotions they heard in the sample by choosing from the provided options. Acoustics of the samples were studied using Praat software, and statistics were examined using SPSS 24 software.

RESULTS

The children with HI identified the emotions with 57% accuracy and the normal hearing children with 75% accuracy. Female listeners were more accurate than male listeners in both groups. Those who were implanted before age of 3 years identified emotions more accurately than others (p < .05). No connection between the child's audiogram and correct identification was observed. Musical interests and voice quality parameters were found to be related to correct identification.

CONCLUSIONS

Implantation age, musical interests, and voice quality tended to have an impact on correct emotion identification. Thus, in developing the cochlear implants, it may be worth paying attention to the acoustic structures of vocal emotional expressions, especially the formant frequency of F3. Supporting the musical interests of children with HI may help their emotional development and improve their social lives.

Consonant and Vowel Identification in Cochlear Implant Users Measured by Nonsense Words: A Systematic Review and Meta-Analysis

PURPOSE

The purpose of this systematic review and meta-analysis was to establish a baseline of the vowel and consonant identification scores in prelingually and postlingually deaf users of multichannel cochlear implants (CIs) tested with consonant-vowel-consonant and vowel-consonant-vowel nonsense syllables.

METHOD

Six electronic databases were searched for peer-reviewed articles reporting consonant and vowel identification scores in CI users measured by nonsense words. Relevant studies were independently assessed and screened by 2 reviewers. Consonant and vowel identification scores were presented in forest plots and compared between studies in a meta-analysis.

RESULTS

Forty-seven articles with 50 studies, including 647 participants, thereof 581 postlingually deaf and 66 prelingually deaf, met the inclusion criteria of this study. The mean performance on vowel identification tasks for the postlingually deaf CI users was 76.8% (N = 5), which was higher than the mean performance for the prelingually deaf CI users (67.7%; N = 1). The mean performance on consonant identification tasks for the postlingually deaf CI users was higher (58.4%; N = 44) than for the prelingually deaf CI users (46.7%; N = 6). The most common consonant confusions were found between those with same manner of articulation (/k/ as /t/, /m/ as /n/, and /p/ as /t/).

CONCLUSIONS

The mean performance on consonant identification tasks for the prelingually and postlingually deaf CI users was found. There were no statistically significant differences between the scores for prelingually and postlingually deaf CI users. The consonants that were incorrectly identified were typically confused with other consonants with the same acoustic properties, namely, voicing, duration, nasality, and silent gaps. A univariate metaregression model, although not statistically significant, indicated that duration of implant use in postlingually deaf adults predict a substantial portion of their consonant identification ability. As there is no ceiling effect, a nonsense syllable identification test may be a useful addition to the standard test battery in audiology clinics when assessing the speech perception of CI users.

Impact of cognition and noise reduction on speech perception in adults with unilateral cochlear implants

OBJECTIVES

The purpose of this study was to investigate the impact of cognition and noise reduction (NR) technology in cochlear implants (CIs) on speech perception and listening effort.

METHODS

Thirteen adults fitted with unilateral CIs (Nucleus^® 6, CP900) participated in this study. Participants performed: (I) cognitive tests of working memory and processing speed, (II) speech perception in noise tests, and (III) an auditory-visual dual-task paradigm to quantify listening effort, as a part of the three-phase experimental study. Both the participant and the tester, performing the outcome measures, were blinded to the NR settings (ON/OFF) of the CI for phases II and III.

RESULTS

Speech intelligibility significantly improved with the NR activated, but was independent of individual differences in cognitive abilities. Listening effort did not significantly change with NR setting; however, there was a trend for participants with good working memory to have better speech perception scores with NR activated during the effortful listening task (dual-task paradigm).

CONCLUSION

Future studies are warranted to explore the interaction between cognition and CI NR algorithms during an effortful listening task.

Cognitive Compensation of Speech Perception With Hearing Impairment, Cochlear Implants, and Aging

External degradations in incoming speech reduce understanding, and hearing impairment further compounds the problem. While cognitive mechanisms alleviate some of the difficulties, their effectiveness may change with age. In our research, reviewed here, we investigated cognitive compensation with hearing impairment, cochlear implants, and aging, via (a) phonemic restoration as a measure of top-down filling of missing speech, (b) listening effort and response times as a measure of increased cognitive processing, and (c) visual world paradigm and eye gazing as a measure of the use of context and its time course. Our results indicate that between speech degradations and their cognitive compensation, there is a fine balance that seems to vary greatly across individuals. Hearing impairment or inadequate hearing device settings may limit compensation benefits. Cochlear implants seem to allow the effective use of sentential context, but likely at the cost of delayed processing. Linguistic and lexical knowledge, which play an important role in compensation, may be successfully employed in advanced age, as some compensatory mechanisms seem to be preserved. These findings indicate that cognitive compensation in hearing impairment can be highly complicated—not always absent, but also not easily predicted by speech intelligibility tests only.

Trials of a Contralateral Hearing Aid After Long-Term Unilateral Cochlear Implant Use in Early-Onset Deafness

PURPOSE

The purpose of this study was to evaluate the practicability of binaural hearing by adding a contralateral hearing aid (HA) after long-term cochlear implant (CI) use in prelingually deaf adults.

METHOD

Five individuals with 1 CI volunteered for a 3-week bimodal (CI + HA) trial. HA gain was set low until sound was tolerable, then increased as listeners acclimated. Participants logged their daily listening experiences and were closely monitored by the audiologist. Measures included pre- and posttrial consonant-nucleus-consonant (CNC) word and phoneme scores and self-reports of satisfaction and listening ability in difficult situations.

RESULTS

Acoustic stimulation was initially unpleasant, but approached comfort at target gain within the 3-week period. Benefit was demonstrated in continued voluntary HA use and higher bimodal phoneme scores compared to CI alone (8%-31% increases) for 4 of the participants.

CONCLUSIONS

When a second CI is not a consideration, a contralateral HA should be pursued as the standard of care for prelingually deaf adults despite substantial auditory deprivation in the previously unaided ear, unpleasant sensations at initial HA fit, or lack of dramatic objective test gains. Frequent audiologist contact, repeated HA adjustments, and client journals are valuable in promoting favorable outcomes with bimodal hearing (adaptation, acceptance, and benefit) for this population.

Dichotic Listening Can Improve Perceived Clarity of Music in Cochlear Implant Users

Musical enjoyment for cochlear implant (CI) recipients is often reported to be unsatisfactory. Our goal was to determine whether the musical experience of postlingually deafened adult CI recipients could be enriched by presenting the bass and treble clef parts of short polyphonic piano pieces separately to each ear (dichotic). Dichotic presentation should artificially enhance the lateralization cues of each part and help the listeners to better segregate them and thus provide greater clarity. We also hypothesized that perception of the intended emotion of the pieces and their overall enjoyment would be enhanced in the dichotic mode compared with the monophonic (both parts in the same ear) and the diotic mode (both parts in both ears). Twenty-eight piano pieces specifically composed to induce sad or happy emotions were selected. The tempo of the pieces, which ranged from lento to presto covaried with the intended emotion (from sad to happy). Thirty participants (11 normal-hearing listeners, 11 bimodal CI and hearing-aid users, and 8 bilaterally implanted CI users) participated in this study. Participants were asked to rate the perceived clarity, the intended emotion, and their preference of each piece in different listening modes. Results indicated that dichotic presentation produced small significant improvements in subjective ratings based on perceived clarity. We also found that preference and clarity ratings were significantly higher for pieces with fast tempi compared with slow tempi. However, no significant differences between diotic and dichotic presentation were found for the participants’ preference ratings, or their judgments of intended emotion.

Deaf children's non-verbal working memory is impacted by their language experience

Several recent studies have suggested that deaf children perform more poorly on working memory tasks compared to hearing children, but these studies have not been able to determine whether this poorer performance arises directly from deafness itself or from deaf children's reduced language exposure. The issue remains unresolved because findings come mostly from (1) tasks that are verbal as opposed to non-verbal, and (2) involve deaf children who use spoken communication and therefore may have experienced impoverished input and delayed language acquisition. This is in contrast to deaf children who have been exposed to a sign language since birth from Deaf parents (and who therefore have native language-learning opportunities within a normal developmental timeframe for language acquisition). A more direct, and therefore stronger, test of the hypothesis that the type and quality of language exposure impact working memory is to use measures of non-verbal working memory (NVWM) and to compare hearing children with two groups of deaf signing children: those who have had native exposure to a sign language, and those who have experienced delayed acquisition and reduced quality of language input compared to their native-signing peers. In this study we investigated the relationship between NVWM and language in three groups aged 6-11 years: hearing children (n = 28), deaf children who were native users of British Sign Language (BSL; n = 8), and deaf children who used BSL but who were not native signers (n = 19). We administered a battery of non-verbal reasoning, NVWM, and language tasks. We examined whether the groups differed on NVWM scores, and whether scores on language tasks predicted scores on NVWM tasks. For the two executive-loaded NVWM tasks included in our battery, the non-native signers performed less accurately than the native signer and hearing groups (who did not differ from one another). Multiple regression analysis revealed that scores on the vocabulary measure predicted scores on those two executive-loaded NVWM tasks (with age and non-verbal reasoning partialled out). Our results suggest that whatever the language modality-spoken or signed-rich language experience from birth, and the good language skills that result from this early age of acquisition, play a critical role in the development of NVWM and in performance on NVWM tasks.

Critical periods in speech perception: new directions

A continuing debate in language acquisition research is whether there are critical periods (CPs) in development during which the system is most responsive to environmental input. Recent advances in neurobiology provide a mechanistic explanation of CPs, with the balance between excitatory and inhibitory processes establishing the onset and molecular brakes establishing the offset of windows of plasticity. In this article, we review the literature on human speech perception development within the context of this CP model, highlighting research that reveals the interplay of maturational and experiential influences at key junctures in development and presenting paradigmatic examples testing CP models in human subjects. We conclude with a discussion of how a mechanistic understanding of CP processes changes the nature of the debate: The question no longer is, "Are there CPs?" but rather what processes open them, keep them open, close them, and allow them to be reopened.