Event-related neuronal responses to acoustic novelty in single-sided deaf cochlear implant users: Initial findings

A cortical biomarker of audibility and processing efficacy in children with single-sided deafness using a cochlear implant

The goals of the current study were to evaluate audibility and cortical speech processing, and to provide insight into binaural processing in children with single-sided deafness (CHwSSD) using a cochlear implant (CI). The P1 potential to acoustically-presented speech stimuli (/m/, /g/, /t/) was recorded during monaural [Normal hearing (NH), CI], and bilateral (BIL, NH + CI) listening conditions within a clinical setting in 22 CHwSSD (mean age at CI/testing 4.7, 5.7 years). Robust P1 potentials were elicited in all children in the NH and BIL conditions. In the CI condition: (1) P1 prevalence was reduced yet was elicited in all but one child to at least one stimulus; (2) P1 latency was prolonged and amplitude was reduced, consequently leading to absence of binaural processing manifestations; (3) Correlation between P1 latency and age at CI/testing was weak and not significant; (4) P1 prevalence for /m/ was reduced and associated with CI manufacturer and duration of CI use. Results indicate that recording CAEPs to speech stimuli in clinical settings is feasible and valuable for the management of CHwSSD. While CAEPs provided evidence for effective audibility, a substantial mismatch in timing and synchrony of early-stage cortical processing between the CI and NH ear remains a barrier for the development of binaural interaction components.

Exploring neurocognitive factors and brain activation in adult cochlear implant recipients associated with speech perception outcomes-A scoping review

Background

Cochlear implants (CIs) are considered an effective treatment for severe-to-profound sensorineural hearing loss. However, speech perception outcomes are highly variable among adult CI recipients. Top-down neurocognitive factors have been hypothesized to contribute to this variation that is currently only partly explained by biological and audiological factors. Studies investigating this, use varying methods and observe varying outcomes, and their relevance has yet to be evaluated in a review. Gathering and structuring this evidence in this scoping review provides a clear overview of where this research line currently stands, with the aim of guiding future research.

Objective

To understand to which extent different neurocognitive factors influence speech perception in adult CI users with a postlingual onset of hearing loss, by systematically reviewing the literature.

Methods

A systematic scoping review was performed according to the PRISMA guidelines. Studies investigating the influence of one or more neurocognitive factors on speech perception post-implantation were included. Word and sentence perception in quiet and noise were included as speech perception outcome metrics and six key neurocognitive domains, as defined by the DSM-5, were covered during the literature search (Protocol in open science registries: 10.17605/OSF.IO/Z3G7W of searches in June 2020, April 2022).

Results

From 5,668 retrieved articles, 54 articles were included and grouped into three categories using different measures to relate to speech perception outcomes: (1) Nineteen studies investigating brain activation, (2) Thirty-one investigating performance on cognitive tests, and (3) Eighteen investigating linguistic skills.

Conclusion

The use of cognitive functions, recruiting the frontal cortex, the use of visual cues, recruiting the occipital cortex, and the temporal cortex still available for language processing, are beneficial for adult CI users. Cognitive assessments indicate that performance on non-verbal intelligence tasks positively correlated with speech perception outcomes. Performance on auditory or visual working memory, learning, memory and vocabulary tasks were unrelated to speech perception outcomes and performance on the Stroop task not to word perception in quiet. However, there are still many uncertainties regarding the explanation of inconsistent results between papers and more comprehensive studies are needed e.g., including different assessment times, or combining neuroimaging and behavioral measures.

Systematic review registration

https://doi.org/10.17605/OSF.IO/Z3G7W.

A direct comparison of voice pitch processing in acoustic and electric hearing

In single-sided deafness patients fitted with a cochlear implant (CI) in the affected ear and preserved normal hearing in the other ear, acoustic and electric hearing can be directly compared without the need for an external control group. Although poor pitch perception is a crucial limitation when listening through CIs, it remains unclear how exactly the cortical processing of pitch information differs between acoustic and electric hearing. Hence, we separately presented both ears of 20 of these patients with vowel sequences in which the pitch contours were either repetitive or variable, while simultaneously recording functional near-infrared spectroscopy (fNIRS) and EEG data. Overall, the results showed smaller and delayed auditory cortex activity in electric hearing, particularly for the P2 event-related potential component, which appears to reflect the processing of voice pitch information. Both the fNIRS data and EEG source reconstructions furthermore showed that vowel sequences with variable pitch contours evoked additional activity in posterior right auditory cortex in electric but not acoustic hearing. This surprising discrepancy demonstrates, firstly, that the acoustic detail transmitted by CIs is sufficient to distinguish between speech sounds that only vary regarding their pitch information. Secondly, the absence of a condition difference when stimulating the normal-hearing ears suggests a saturation of cortical activity levels following unilateral deafness. Taken together, these results provide strong evidence in favour of using CIs in this patient group.

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.

How Do We Allocate Our Resources When Listening and Memorizing Speech in Noise? A Pupillometry Study

OBJECTIVES

Actively following a conversation can be demanding and limited cognitive resources must be allocated to the processing of speech, retaining and encoding the perceived content, and preparing an answer. The aim of the present study was to disentangle the allocation of effort into the effort required for listening (listening effort) and the effort required for retention (memory effort) by means of pupil dilation.

DESIGN

Twenty-five normal-hearing German speaking participants underwent a sentence final word identification and recall test, while pupillometry was conducted. The participants' task was to listen to a sentence in four-talker babble background noise and to repeat the final word afterward. At the end of a list of sentences, they were asked to recall as many of the final words as possible. Pupil dilation was recorded during different list lengths (three sentences versus six sentences) and varying memory load (recall versus no recall). Additionally, the effect of a noise reduction algorithm on performance, listening effort, and memory effort was evaluated.

RESULTS

We analyzed pupil dilation both before each sentence (sentence baseline) as well as the dilation in response to each sentence relative to the sentence baseline (sentence dilation). The pupillometry data indicated a steeper increase of sentence baseline under recall compared to no recall, suggesting higher memory effort due to memory processing. This increase in sentence baseline was most prominent toward the end of the longer lists, that is, during the second half of six sentences. Without a recall task, sentence baseline declined over the course of the list. Noise reduction appeared to have a significant influence on effort allocation for listening, which was reflected in generally decreased sentence dilation.

CONCLUSION

Our results showed that recording pupil dilation in a speech identification and recall task provides valuable insights beyond behavioral performance. It is a suitable tool to disentangle the allocation of effort to listening versus memorizing speech.

An event-related brain potential study of auditory attention in cochlear implant users

OBJECTIVE

Cochlear implants (CIs) provide access to the auditory world for deaf individuals. We investigated whether CIs enforce attentional alterations of auditory cortical processing in post-lingually deafened CI users compared to normal-hearing (NH) controls.

METHODS

Event-related potentials (ERPs) were recorded in 40 post-lingually deafened CI users and in a group of 40 NH controls using an auditory three-stimulus oddball task, which included frequent standard tones (Standards) and infrequent deviant tones (Targets), as well as infrequently occurring unique sounds (Novels). Participants were exposed twice to the three-stimulus oddball task, once under the instruction to ignore the stimuli (ignore condition), and once under the instruction to respond to infrequently occurring deviant tones (attend condition).

RESULTS

The allocation of attention to auditory oddball stimuli exerted stronger effects on N1 amplitudes at posterior electrodes in response to Standards and to Targets in CI users than in NH controls. Other ERP amplitudes showed similar attentional modulations in both groups (P2 in response to Standards, N2 in response to Targets and Novels, P3 in response to Targets). We also observed a statistical trend for an attenuated attentional modulation of Novelty P3 amplitudes in CI users compared to NH controls.

CONCLUSIONS

ERP correlates of enhanced CI-mediated auditory attention are confined to the latency range of the auditory N1, suggesting that enhanced attentional modulation during auditory stimulus discrimination occurs primarily in associative auditory cortices of CI users.

SIGNIFICANCE

The present ERP data support the hypothesis of attentional alterations of auditory cortical processing in CI users. These findings may be of clinical relevance for the CI rehabilitation.

Dopaminergic modulation of novelty repetition in Parkinson's disease: A study of P3 event-related brain potentials

OBJECTIVE

Parkinson's Disease (PD) is a neurodegenerative disease caused by the loss of dopaminergic neurons. Cognitive impairments have been reported using the event-related potential (ERP) technique. Patients show reduced novelty P3 (nP3) amplitudes in oddball experiments, a response to infrequent, surprising stimuli, linked to the orienting response of the brain. The nP3 is thought to depend on dopaminergic neuronal pathways though the effect of dopaminergic medication in PD has not yet been investigated.

METHODS

Twenty-two patients with PD were examined "on" and "off" their regular dopaminergic medication in a novelty 3-stimulus-oddball task. Thirty-four healthy controls were also examined over two sessions, but received no medication. P3 amplitudes were compared throughout experimental conditions.

RESULTS

All participants showed sizeable novelty difference ERP effects, i.e. n_dP3 amplitudes, during both testing sessions. An interaction of diagnosis, medication and testing order was also found, indicating that dopaminergic medication modulated n_dP3 in patients with PD across the two testing sessions: We observed enhanced n_dP3 amplitudes from PD patients who were off medication on the second testing session.

CONCLUSION

Patients with PD 'off' medication showed ERP evidence for repetition-related enhancement of novelty responses. Dopamine depletion in neuronal pathways that are affected by mid-stage PD possibly accounts for this modulation of novelty processing.

SIGNIFICANCE

The data in this study potentially suggest that repetition effects on novelty processing in patients with PD are enhanced by dopaminergic depletion.