Mismatch negativity: a tool for the assessment of stimuli discrimination in cochlear implant subjects

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.

Electrically evoked mismatch negativity responses to loudness and pitch cues in cochlear implant users

Objective measurements could improve cochlear implant (CI) fitting, especially for CI users who have difficulty assessing their hearing impressions. In this study, we investigated the electrically evoked mismatch negativity (eMMN) brain potential as a mainly preattentive response to pitch and loudness changes. In an electrophysiological exploratory study with 21 CI users, pitch and loudness cues were presented in controlled oddball paradigms that directly electrically stimulated the CI via software. Out of them 17 valid data sets were analyzed. A pitch cue was produced by changing the stimulating CI electrodes (pairs of adjacent electrodes). A loudness cue originated from changing the stimulation amplitude on one CI electrode. MMN responses were measured unsing clinical electroencephalography recording according to a standard recording protocol. At the group level, significant eMMN responses were elicited for loudness cues and for pitch cues at basal electrode pairs but not at apical electrode pairs. The effect of deviance direction was not significant and no stimulus artifacts were observed. Recording an electrically evoked MMN in response to loudness changes in CI users is generally feasible, and is, therefore, promising to support CI fitting procedures in the future. Detection of pitch cues would require a greater electrode distance between selected electrodes for standard and deviant stimuli, especially in apical regions. A routine clinical setup can be used to measure eMMN.

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.

Recording EEG in Cochlear Implant Users: Guidelines for Experimental Design and Data Analysis for Optimizing Signal Quality and Minimizing Artifacts

Cochlear implants (CI) are neural prostheses that can restore hearing in individuals with severe to profound hearing loss. Although CIs significantly improve quality of life, clinical outcomes are still highly variable. An important part of this variability is explained by the brain reorganization following cochlear implantation. Therefore, clinicians and researchers are seeking objective measurements to investigate post-implantation brain plasticity. Electroencephalography (EEG) is a promising technique because it is objective, non-invasive, and implant-compatible, but is nonetheless susceptible to massive artifacts generated by the prosthesis's electrical activity. CI artifacts can blur and distort brain responses; thus, it is crucial to develop reliable techniques to remove them from EEG recordings. Despite numerous artifact removal techniques used in previous studies, there is a paucity of documentation and consensus on the optimal EEG procedures to reduce these artifacts. Herein, and through a comprehensive review process, we provide a guideline for designing an EEG-CI experiment minimizing the effect of the artifact. We provide some technical guidance for recording an accurate neural response from CI users and discuss the current challenges in detecting and removing CI-induced artifacts from a recorded signal. The aim of this paper is also to provide recommendations to better appraise and report EEG-CI findings.

Neuromagnetic evaluation of a communication support system for hearing-impaired patients

Hearing-impaired patients often encounter obstacles in communication. Not all of them wear hearing aids, citing issues with usage difficulty and discomfort in wearing. To overcome these difficulties, a new endeavor was started to improve sound intelligibility from the speaker's side. The present study objectively evaluated an intelligible-hearing (IH) loudspeaker by means of magnetoencephalography. Magnetic counterparts of mismatch negativity (MMNm) to pronunciation ('mi' and 'ni') were recorded and compared when they were transmitted from the IH loudspeaker and from a normal-hearing loudspeaker. On using the IH loudspeaker, the peak latency was found to be significantly shortened. In the case of hearing-impaired participants, marked MMNm responses were observed only when the IH loudspeaker was used. These findings suggest that improving sound intelligibility may be a supportive and rehabilitative approach for hearing-impaired patients.

Change in Speech Perception and Auditory Evoked Potentials over Time after Unilateral Cochlear Implantation in Postlingually Deaf Adults

Speech perception varies widely across cochlear implant (CI) users and typically improves over time after implantation. There is also some evidence for improved auditory evoked potentials (shorter latencies, larger amplitudes) after implantation but few longitudinal studies have examined the relationship between behavioral and evoked potential measures after implantation in postlingually deaf adults. The relationship between speech perception and auditory evoked potentials was investigated in newly implanted cochlear implant users from the day of implant activation to 9 months postimplantation, on five occasions, in 10 adults age 27 to 57 years who had been bilaterally profoundly deaf for 1 to 30 years prior to receiving a unilateral CI24 cochlear implant. Changes over time in middle latency response (MLR), mismatch negativity, and obligatory cortical auditory evoked potentials and word and sentence speech perception scores were examined. Speech perception improved significantly over the 9-month period. MLRs varied and showed no consistent change over time. Three participants aged in their 50s had absent MLRs. The pattern of change in N1 amplitudes over the five visits varied across participants. P2 area increased significantly for 1,000- and 4,000-Hz tones but not for 250 Hz. The greatest change in P2 area occurred after 6 months of implant experience. Although there was a trend for mismatch negativity peak latency to reduce and width to increase after 3 months of implant experience, there was considerable variability and these changes were not significant. Only 60% of participants had a detectable mismatch initially; this increased to 100% at 9 months. The continued change in P2 area over the period evaluated, with a trend for greater change for right hemisphere recordings, is consistent with the pattern of incremental change in speech perception scores over time. MLR, N1, and mismatch negativity changes were inconsistent and hence P2 may be a more robust measure of auditory plasticity in adult implant recipients. P2 was still improving at 9 months postimplantation. Future studies should explore longitudinal changes over a longer period.

The Basis for Language Acquisition: Congenitally Deaf Infants Discriminate Vowel Length in the First Months after Cochlear Implantation

One main incentive for supplying hearing impaired children with a cochlear implant is the prospect of oral language acquisition. Only scarce knowledge exists, however, of what congenitally deaf children actually perceive when receiving their first auditory input, and specifically what speech-relevant features they are able to extract from the new modality. We therefore presented congenitally deaf infants and young children implanted before the age of 4 years with an oddball paradigm of long and short vowel variants of the syllable /ba/. We measured the EEG in regular intervals to study their discriminative ability starting with the first activation of the implant up to 8 months later. We were thus able to time-track the emerging ability to differentiate one of the most basic linguistic features that bears semantic differentiation and helps in word segmentation, namely, vowel length. Results show that already 2 months after the first auditory input, but not directly after implant activation, these early implanted children differentiate between long and short syllables. Surprisingly, after only 4 months of hearing experience, the ERPs have reached the same properties as those of the normal hearing control group, demonstrating the plasticity of the brain with respect to the new modality. We thus show that a simple but linguistically highly relevant feature such as vowel length reaches age-appropriate electrophysiological levels as fast as 4 months after the first acoustic stimulation, providing an important basis for further language acquisition.

Peripheral and Central Contributions to Cortical Responses in Cochlear Implant Users

OBJECTIVES

The primary goal of this study was to describe relationships between peripheral and central electrophysiologic measures of auditory processing within individual cochlear implant (CI) users. The distinctiveness of neural excitation patterns resulting from the stimulation of different electrodes, referred to as 'spatial selectivity,' was evaluated. The hypothesis was that if central representations of spatial interactions differed across participants semi-independently of peripheral input, then the within-subject relationships between peripheral and central electrophysiologic measures of spatial selectivity would reflect those differences. Cross-subject differences attributable to processing central to the auditory nerve may help explain why peripheral electrophysiologic measures of spatial selectivity have not been found to correlate with speech perception.

DESIGN

Eleven adults participated in this and a companion study. All were peri- or post-lingually deafened with more than 1 year of CI experience. Peripheral spatial selectivity was evaluated at 13 cochlear locations using 13 electrodes as probes to elicit electrically evoked compound action potentials (ECAPs). Masker electrodes were varied across the array for each probe electrode to derive channel-interaction functions. The same 13 electrodes were used to evaluate spatial selectivity represented at a cortical level. Electrode pairs were stimulated sequentially to elicit the auditory change complex (ACC), an obligatory cortical potential suggestive of discrimination. For each participant, the relationship between ECAP channel-interaction functions (quantified as channel-separation indices) and ACC N1-P2 amplitudes was modeled using the saturating exponential function y = a * (1-e). Both a and b coefficients were varied using a least-squares approach to optimize the fits.

RESULTS

Electrophysiologic measures of spatial selectivity assessed at peripheral (ECAP) and central (ACC) levels varied across participants. The results indicate that differences in ACC amplitudes observed across participants for the same stimulus conditions were not solely the result of differences in peripheral excitation patterns. This finding supports the view that processing at multiple points along the auditory neural pathway from the periphery to the cortex may vary across individuals with different etiologies and auditory experiences.

CONCLUSIONS

The distinctiveness of neural excitation resulting from electrical stimulation varies across CI recipients, and this variability was observed in both peripheral and cortical electrophysiologic measures. The ACC amplitude differences observed across participants were partially independent from differences in peripheral neural spatial selectivity. These findings are clinically relevant because they imply that there may be limits (1) to the predictive ability of peripheral measures and (2) in the extent to which improving the selectivity of electrical stimulation via programming options (e.g., current focusing/steering) will result in more specific central neural excitation patterns or will improve speech perception.

Cochlear implant artifact attenuation in late auditory evoked potentials: a single channel approach

Recent evidence suggests that late auditory evoked potentials (LAEP) provide a useful objective metric of performance in cochlear implant (CI) subjects. However, the CI produces a large electrical artifact that contaminates LAEP recordings and confounds their interpretation. Independent component analysis (ICA) has been used in combination with multi-channel recordings to effectively remove the artifact. The applicability of the ICA approach is limited when only single channel data are needed or available, as is often the case in both clinical and research settings. Here we developed a single-channel, high sample rate (125 kHz), and high bandwidth (0-100 kHz) acquisition system to reduce the CI stimulation artifact. We identified two different artifacts in the recording: 1) a high frequency artifact reflecting the stimulation pulse rate, and 2) a direct current (DC, or pedestal) artifact that showed a non-linear time varying relationship to pulse amplitude. This relationship was well described by a bivariate polynomial. The high frequency artifact was completely attenuated by a 35 Hz low-pass filter for all subjects (n = 22). The DC artifact could be caused by an impedance mismatch. For 27% of subjects tested, no DC artifact was observed when electrode impedances were balanced to within 1 kΩ. For the remaining 73% of subjects, the pulse amplitude was used to estimate and then attenuate the DC artifact. Where measurements of pulse amplitude were not available (as with standard low sample rate systems), the DC artifact could be estimated from the stimulus envelope. The present artifact removal approach allows accurate measurement of LAEPs from CI subjects from single channel recordings, increasing their feasibility and utility as an accessible objective measure of CI function.

Towards a closed-loop cochlear implant system: application of embedded monitoring of peripheral and central neural activity

Although the cochlear implant (CI) is widely considered the most successful neural prosthesis, it is essentially an open-loop system that requires extensive initial fitting and frequent tuning to maintain a high, but not necessarily optimal, level of performance. Two developments in neuroscience and neuroengineering now make it feasible to design a closed-loop CI. One development is the recording and interpretation of evoked potentials (EPs) from the peripheral to the central nervous system. The other is the embedded hardware and software of a modern CI that allows recording of EPs. We review EPs that are pertinent to behavioral functions from simple signal detection and loudness growth to speech discrimination and recognition. We also describe signal processing algorithms used for electric artifact reduction and cancellation, critical to the recording of electric EPs. We then present a conceptual design for a closed-loop CI that utilizes in an innovative way the embedded implant receiver and stimulators to record short latency compound action potentials ( ~1 ms), auditory brainstem responses (1-10 ms) and mid-to-late cortical potentials (20-300 ms). We compare EPs recorded using the CI to EPs obtained using standard scalp electrodes recording techniques. Future applications and capabilities are discussed in terms of the development of a new generation of closed-loop CIs and other neural prostheses.

The mismatch negativity (MMN)--a unique window to disturbed central auditory processing in ageing and different clinical conditions

In this article, we review clinical research using the mismatch negativity (MMN), a change-detection response of the brain elicited even in the absence of attention or behavioural task. In these studies, the MMN was usually elicited by employing occasional frequency, duration or speech-sound changes in repetitive background stimulation while the patient was reading or watching videos. It was found that in a large number of different neuropsychiatric, neurological and neurodevelopmental disorders, as well as in normal ageing, the MMN amplitude was attenuated and peak latency prolonged. Besides indexing decreased discrimination accuracy, these effects may also reflect, depending on the specific stimulus paradigm used, decreased sensory-memory duration, abnormal perception or attention control or, most importantly, cognitive decline. In fact, MMN deficiency appears to index cognitive decline irrespective of the specific symptomatologies and aetiologies of the different disorders involved.

Effects of mental workload on long-latency auditory-evoked-potential, salivary cortisol, and immunoglobulin A

This paper researches on the effects of mental workload on long-latency auditory-evoked-potential (AEP), salivary cortisol, and immunoglobulin A (IgA). 20 Healthy subjects (11 males and 9 females) participated in the experiment voluntarily. The mental task consisted of two parts: arithmetic task and reading comprehension task. The Latencies of N1, P2, N2, P3, and mismatch negativity (MMN) all increased significantly after the mental tasks were adopted at all of the three recording sites: Cz, Fz, and Pz (p<0.05). In this experiment, changes of salivary cortisol and s-IgA levels due to mental tasks were not significant. With the introduction of mental tasks, more processing resources are allocated to the primary task (mental task), and decreased processing resources available for the secondary task (auditory task), which is reflected on the increases in the latencies of probe-evoked AEP components.

Mismatch negativity and adaptation measures of the late auditory evoked potential in cochlear implant users

A better understanding of the neural correlates of large variability in cochlear implant (CI) patients' speech performance may allow us to find solutions to further improve CI benefits. The present study examined the mismatch negativity (MMN) and the adaptation of the late auditory evoked potential (LAEP) in 10 CI users. The speech syllable /da/ and 1-kHz tone burst were used to examine the LAEP adaptation. The amount of LAEP adaptation was calculated according to the averaged N1-P2 amplitude for the LAEPs evoked by the last 3 stimuli and the amplitude evoked by the first stimulus. For the MMN recordings, the standard stimulus (1-kHz tone) and the deviant stimulus (2-kHz tone) were presented in an oddball condition. Additionally, the deviants alone were presented in a control condition. The MMN was derived by subtracting the response to the deviants in the control condition from the oddball condition. Results showed that good CI performers displayed a more prominent LAEP adaptation than moderate-to-poor performers. Speech performance was significantly correlated to the amount of LAEP adaptation for the 1-kHz tone bursts. Good performers displayed large MMNs and moderate-to-poor performers had small or absent MMNs. The abnormal electrophysiological findings in moderate-to-poor performers suggest that long-term deafness may cause damage not only at the auditory cortical level, but also at the cognitive level.

Phonetic processing in children with cochlear implants: an auditory event-related potentials study

OBJECTIVES

To investigate the effect of increasing acoustic-phonetic difficulty in children with cochlear implants (CI) by means of auditory event-related potentials (AERPs).

DESIGN

AERPs were recorded from a group of ten 9- to 14-year-old prelingually deafened children who exhibited open-set speech recognition, using the Nucleus 22 CI for at least 5 years. AERPs were recorded in sound field while children were performing oddball discrimination tasks with increasing acoustic-phonetic demand. The tasks consisted pairs of naturally produced stimuli that differed by one phonetic feature: vowel place (/ki/ versus/ku/), vowel height (/ki/ versus /ke/), voicing (/ka/ versus /ga/), and place of articulation (/ka/ versus /ta/). Using a repeated measure design, the effect of increasing acoustic-phonetic difficulty on P3 latency, amplitude, and scalp distribution as well as on the simultaneously obtained behavioral measures, performance accuracy, and reaction time was evaluated.

RESULTS

AERPs elicited in the range of 350 msec poststimulus onset were contaminated by the CI stimulus artifact, thus enabling reliable identification of the P3 component only. Increasing acoustic-phonetic difficulty was manifested in all measures in a hierarchical manner: P3 latency and reaction time increased, whereas P3 amplitude and performance accuracy decreased. The correlations, however, between behavioral and electrophysiological measures were not significant. Further support for P3 sensitivity to increasing acoustic-phonetic demand was its absence in four of the 10 children, but only in the most difficult place of articulation task. P3 amplitude was maximal at the midline parietal cite, with equal amplitudes over the right and left scalp regardless of side of implant.

CONCLUSIONS

The results underscore the significant value of the P3 potential as a sensitive neural index of speech-sound processing in children with CI. The similar hierarchy of acoustic-phonetic demand manifested in both behavioral and electrophysiological measures suggests that speech perception performance relates to neurophysiologic responses at cortical levels of the auditory system. Thus, recording the P3 potential to distinct phonetic contrasts may be useful for studying accessibility and neural encoding at the cortical level in CI recipients.

The mismatch negativity (MMN) in basic research of central auditory processing: a review

In the present article, the basic research using the mismatch negativity (MMN) and analogous results obtained by using the magnetoencephalography (MEG) and other brain-imaging technologies is reviewed. This response is elicited by any discriminable change in auditory stimulation but recent studies extended the notion of the MMN even to higher-order cognitive processes such as those involving grammar and semantic meaning. Moreover, MMN data also show the presence of automatic intelligent processes such as stimulus anticipation at the level of auditory cortex. In addition, the MMN enables one to establish the brain processes underlying the initiation of attention switch to, conscious perception of, sound change in an unattended stimulus stream.

Effects of auditory pathway anatomy and deafness characteristics? Part 2: On electrically evoked late auditory responses

The purpose of this study was to distinguish the effects of different parameters on latencies of wave N1, wave P2, and inter-peak interval N1-P2 of electrical late auditory responses (ELARs). ELARs were recorded from four intra-cochlear electrodes in fourteen adult HiRes90K cochlear implant users who had at least three months of experience. The relationship between latencies and stimulation sites in the cochlea was characterized to assess the influence of the auditory pathway anatomy on ELARs, i.e., whether the speed of neural propagation varies according to the place that is activated in the cochlea. Audiograms before implantation, duration of deafness, and psychophysics at first fitting were used to describe the influence of deafness characteristics on latencies. The stimulation sites were found to have no effect on ELAR latency and, while there was no influence of psychophysics on latency, a strong relationship was shown with duration of deafness and the pre-implantation audiogram. Thus, ELAR latency was longer for poorer audiograms and longer durations of deafness and this relationship appeared to be independent of stimulation parameters such as stimulation site. Comparison between these findings and those from the equivalent study on EABR waves IIIe and Ve latency [Guiraud, J., Gallego, S., Arnold, L., Boyle, P., Truy, E., Collet, L., 2007. Effects of auditory pathway anatomy and deafness characteristics? (1): On electrically evoked auditory brainstem responses. Hear. Res. 223 (1-2), 48-60] shows that, while ELAR and EABR latencies are related with parameters that reflect the integrity of the auditory pathway, ELAR latency is less dependent on stimulation parameters than EABR latency.

Electrophysiological and speech perception measures of auditory processing in experienced adult cochlear implant users

OBJECTIVE

This study determined the relationship between auditory evoked potential measures and speech perception in experienced adult cochlear implant (CI) users and compared the CI evoked potential results to those of a group of age- and sex-matched control subjects.

METHODS

CI subjects all used the Nucleus CI-22 implant. Middle latency response (MLR), obligatory cortical potentials (CAEP), mismatch negativity (MMN) and P3a auditory evoked potentials were recorded. Speech perception was evaluated using word and sentence tests.

RESULTS

Duration of deafness correlated with speech scores with poor scores reflecting greater years of deafness. Na amplitude correlated negatively with duration of deafness, with small amplitudes reflecting greater duration of deafness. Overall, N1 amplitude was smaller in CI than control subjects. Earlier P2 latencies were associated with shorter durations of deafness and higher speech scores. In general, MMN was absent or degraded in CI subjects with poor speech scores.

CONCLUSIONS

Auditory evoked potentials are related to speech perception ability and provide objective evidence of central auditory processing differences across experienced CI users.

SIGNIFICANCE

Since auditory evoked potentials relate to CI performance, they may be a useful tool for objectively evaluating the efficacy of speech processing strategies and/or auditory training approaches in both adults and children with cochlear implants.

Relationship between auditory perception skills and mismatch negativity recorded in free field in cochlear-implant users

This study investigated the ability of cochlear-implanted patients to discriminate tone bursts in free field using the electrophysiological recordings of mismatch negativity (MMN). Seven cochlear-implanted patients (CIP) and eight control subjects (CS) were tested. Event-related potentials were recorded from either 32 or 64 electrodes in response to binaural stimuli using a passive oddball paradigm. Two stimulus-contrast conditions were used to produce MMN: The standard-tone frequency was fixed at 1 kHz, and the deviant-tone frequency was set at 2 or 1.5 kHz. The results show that response waveforms (N1/P2) are similar in latency and amplitude for CS and CIP, suggesting that pure-tone detection is performed over the same time window in both groups. These waveforms are also similar in left- and right-implanted patients, suggesting that electric stimulation of the auditory nerve activates both hemispheres in profound, bilateral hearing loss. Pure-tone audiograms and word-discrimination scores were also measured in each subject in an anechoic room and their relations with MMN data were examined. Correlations were found between the latency of MMN for a 1.5 kHz deviant and the thresholds obtained for pure-tone detection and word discrimination. MMN appears as a possible complementary clinical tool to objectively assess auditory sensitivity in cochlear-implanted populations. However, further improvements are still necessary before it can be used as a standard clinical examination.

Event-Related Potentials in Pediatric Cochlear Implant Patients

OBJECTIVE

The main objective of this study was to assess the correlation of auditory event related potential (ERP) measures with behavioral assessment data to identify if ERPs including mismatch negativity (MMN) can be used to categorize cochlear implant patients into good and poor performers.

DESIGN

We investigated auditory event-related potentials to standard and deviant speech stimuli presented in a pseudorandom sequence in 35 cochlear implant patients between the ages of 7 and 17 yr. We compared the occurrence, latencies, and amplitudes of P1, N2, and MMN with overall behavioral outcome in these children. Behavioral measures included category of auditory performance scores and speech intelligibility rating scores.

RESULTS

Auditory ERPs in response to standard stimuli were identifiable in 30 of 35 patients, demonstrating a major positive component (P1) followed by a negativity (N2) with absence of N1 in all patients. The P1 component in prelingually deaf patients showed a statistically significant reduction in its latency with increasing duration of implant use. MMN was recorded in 80-85% of star performers but in only 15-20% of poor performers. Patients with higher SIR scores demonstrated statistically significant longer duration of MMN compared with those with a lower SIR score.

CONCLUSIONS

These results indicate that MMN can be used to assess the functional status of the auditory cortex in terms of auditory memory and discrimination in young children with cochlear implants and may provide an objective mechanism for differentiating good from poor performers.

Music perception in cochlear implant users: an event-related potential study

OBJECTIVE

Compare the processing of music-syntactic irregularities and physical oddballs between cochlear implant (CI) users and matched controls.

METHODS

Musical chord sequences were presented, some of which contained functionally irregular chords, or a chord with an instrumental timbre that deviated from the standard timbre.

RESULTS

In both controls and CI users, functionally irregular chords elicited early (around 200 ms) and late (around 500 ms) negative electric brain responses (early right anterior negativity,ERAN and N5). Amplitudes of effects depended on the degree of music-syntactic irregularity in both groups; effects elicited in CI users were distinctly smaller than in controls. Physically deviant chords elicited a timbre-mismatch negativity (MMN) and a P3 in both groups, again with smaller amplitudes in CI users.

CONCLUSIONS

ERAN and N5 (as well as timbre-MMN and P3), can be elicited in CI users. Although amplitudes of effects were considerably smaller in the CI group, the presence of MMN and ERAN indicates that neural mechanisms of both physical and music-syntactic irregularity-detection were active in this group.

[Registering event-related auditory potentials (P300) in patients with cochlear implants]

Event-related auditory evoked potentials can contribute to the evaluation of discrimination abilities of cochlear implant users. Auditory P300 potentials to a frequency contrast were obtained in six post-lingually deaf adults using a cochlear implant and in a control group of normal hearing subjects. The aim of this study was to investigate how these potentials were determined by the stimulation pattern of the cochlear implant. To visualise these stimulation patterns colour-coded plots (stimulograms) were calculated based on the stimulus and the fitting file of the individual subject as inputs. These stimulograms were used to evaluate the influence of various stimulation parameters on the stimulation contrast used in an oddball paradigm. The influence of discrimination difficulty on the P300 response is demonstrated.

Auditory late cortical response and speech recognition in Digisonic cochlear implant users

OBJECTIVE

The purpose of the study was to test for differences in late electrically evoked auditory potentials between subjects exhibiting "good" versus "poor" speech recognition performances with their cochlear implants.

METHODS

Late auditory evoked responses were measured in 30 subjects equipped with the Digisonic (MXM, Antibes, France) cochlear implant, 15 of whom had "good" speech recognition scores (i.e., more than 89% correct phoneme identification without lip reading). The 15 other subjects had poorer speech recognition scores (i.e., less than 85%).

RESULTS

Differences in N1P2 amplitude, as well as P1, N1, and P2 latencies, and N1-P1 and N1-P2 latency intervals were tested. Wave P2 latency was found to be significantly different between the two groups (P =.016), being shorter in "good" than in "poor" performers. The strength of the statistical relationship between electrophysiological and speech recognition variables (r2 = 17%) was substantially smaller than that observed using electrically evoked auditory brainstem response (EABR) for the same implanted device (r2 = 49% for the EABR wave III-V latency interval).

CONCLUSIONS

Some characteristics of late electrically evoked auditory potentials differ significantly among cochlear implant users depending on their speech recognition performance. However, the relationship between electrophysiological and speech recognition variables is more pronounced when early (brainstem) rather than late (cortical) evoked responses are considered.

Evaluation of cochlear implant benefit with auditory cortical evoked potentials

Endogenous P300 and exogenous slow vertex potentials were obtained with tone and speech stimuli in a group of five children using a cochlear implant (CI) with poor speech recognition (group A) and compared with those from another group of five children using a CI with good speech recognition (group B). The responses were also compared to those of children with normal hearing (n= 14) and a group of adult CI users (n=9). N1 and P2 latencies of CI group A and group B were prolonged compared to those of normally-hearing children. In group A, P300 was present when contrasts with tone stimuli were used. When speech stimuli were used, P300 potentials were absent or delayed. P300 potentials obtained in group B were no different from those obtained in normally-hearing children. It is suggested that the poor results evoked with speech stimuli in contrast to those evoked with pure-tone stimuli in group A are due to the immaturity of (sub) cortical generators associated with acoustical and phonetic processing. In contrast to the children in group B, all children in group A suffered from congenital deafness.