Gap detection measured with electrically evoked auditory event-related potentials and speech-perception abilities in children with auditory neuropathy spectrum disorder

The Performance of the Acoustic Change Complex Versus Psychophysical Behavioral Measures: A Systematic Review of Measurements in Adults

OBJECTIVES

The acoustic change complex (ACC) is a cortical auditory evoked potential that shows promise as an objective test of the neural capacity for speech and sound discrimination, particularly for difficult-to-test populations, for example, cognitively impaired adults. There is uncertainty, however, surrounding the performance of the ACC with behavioral measures. The objective of this study was to systematically review the literature, focusing on adult studies, to investigate the relationship between ACC responses and behavioral psychophysical measures.

DESIGN

Original peer-reviewed articles conducting performance comparisons between ACCs and behavioral measures in adults were identified through systematic searches. The review was conducted using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for reporting, and the methodological quality of the included articles was assessed.

RESULTS

A total of 66 studies were retrieved that conducted adult ACC measurements, of which 27 studies included performance comparisons. Meta-analysis revealed a total of 41 significant correlations between ACC responses (amplitudes, latencies, and thresholds) and behavioral measures of speech perception (2 weak, 28 moderate, and 11 strong correlations), and 12 significant moderate/strong correlations were identified with behavioral measures of frequency discrimination.

CONCLUSIONS

This systematic review finds that ACC responses are associated with speech perception and frequency discrimination, in addition to other types of sound discrimination. The choice of evoking stimuli, ACC outcome measure, and behavioral measure used may influence the strength and visibility of potential correlations between the objective (ACC) and behavioral measures. The performance of the ACC technique highlighted in this review suggests that this tool may serve as an alternative measure of auditory discrimination when corresponding behavioral measures prove challenging or unfeasible.

Postoperative Auditory Progress in Cochlear-Implanted Children With Auditory Neuropathy

PURPOSE

This study aims to evaluate the effect of auditory neuropathy spectrum disorder (ANSD) on postoperative auditory perception and listening difficulties in pediatric cochlear implant (CI) recipients.

METHOD

The Children's Auditory Perception Test (CAPT) assesses auditory perception skills, and the Children's Home Inventory of Listening Difficulties (CHILD) Scale evaluates daily listening difficulties. The study involved pediatric CI recipients (n = 40) aged between 5 and 7 years, with and without diagnosis of ANSD. The research ensured homogeneity across various factors, including chronological age, age at diagnosis, age at initial implantation, bilateral simultaneous surgery, etiologies of hearing loss, and family education level.

RESULTS

The findings have demonstrated that children without ANSD exhibited better performance in integrating visual-auditory stimuli and overall listening performance, distant sound source scores, and noisy environment scores (respectively p = .047, p = .001, p = .028, and p = .010). Additionally, children with better speech perception also have a better ability to integrate audiovisual stimuli (p = .005, r = .438).

CONCLUSIONS

There are significant differences in postoperative listening skills and auditory perceptions between children with and without an ANSD who have CIs. Accordingly, children without an ANSD perform better.

A systematic review of acoustic change complex (ACC) measurements and applicability in children for the assessment of the neural capacity for sound and speech discrimination

OBJECTIVE

The acoustic change complex (ACC) is a cortical auditory evoked potential (CAEP) and can be elicited by a change in an otherwise continuous sound. The ACC has been highlighted as a promising tool in the assessment of sound and speech discrimination capacity, and particularly for difficult-to-test populations such as infants with hearing loss, due to the objective nature of ACC measurements. Indeed, there is a pressing need to develop further means to accurately and thoroughly establish the hearing status of children with hearing loss, to help guide hearing interventions in a timely manner. Despite the potential of the ACC method, ACC measurements remain relatively rare in a standard clinical settings. The objective of this study was to perform an up-to-date systematic review on ACC measurements in children, to provide greater clarity and consensus on the possible methodologies, applications, and performance of this technique, and to facilitate its uptake in relevant clinical settings.

DESIGN

Original peer-reviewed articles conducting ACC measurements in children (< 18 years). Data were extracted and summarised for: (1) participant characteristics; (2) ACC methods and auditory stimuli; (3) information related to the performance of the ACC technique; (4) ACC measurement outcomes, advantages, and challenges. The systematic review was conducted using PRISMA guidelines for reporting and the methodological quality of included articles was assessed.

RESULTS

A total of 28 studies were identified (9 infant studies). Review results show that ACC responses can be measured in infants (from < 3 months), and there is evidence of age-dependency, including increased robustness of the ACC response with increasing childhood age. Clinical applications include the measurement of the neural capacity for speech and non-speech sound discrimination in children with hearing loss, auditory neuropathy spectrum disorder (ANSD) and central auditory processing disorder (CAPD). Additionally, ACCs can be recorded in children with hearing aids, auditory brainstem implants, and cochlear implants, and ACC results may guide hearing intervention/rehabilitation strategies. The review identified that the time taken to perform ACC measurements was often lengthy; the development of more efficient ACC test procedures for children would be beneficial. Comparisons between objective ACC measurements and behavioural measures of sound discrimination showed significant correlations for some, but not all, included studies.

CONCLUSIONS

ACC measurements of the neural capacity to discriminate between speech and non-speech sounds are feasible in infants and children, and a wide range of possible clinical applications exist, although more time-efficient procedures would be advantageous for clinical uptake. A consideration of age and maturational effects is recommended, and further research is required to investigate the relationship between objective ACC measures and behavioural measures of sound and speech perception for effective clinical implementation.

Assessing Neural Synchrony in the Cochlear Nerve to Electrical Stimulation in Children With Auditory Neuropathy Spectrum Disorder

OBJECTIVES

This study reported phase locking values (PLVs) that quantified the trial-to-trial phase coherence of electrically evoked compound action potentials in children with auditory neuropathy spectrum disorders (ANSD) and children with Gap Junction Beta 2 (GJB2) mutations, a patient population without noticeable cochlear nerve damage.

DESIGN

PLVs were measured at three electrode locations in 11 children with ANSD and 11 children with GJB2 mutations. Smaller PLVs indicated poorer neural synchrony. A linear mixed-effects model was used to compare PLVs measured at different electrode locations between participant groups.

RESULTS

After controlling for the stimulation level effect, children with ANSD had smaller PLVs than children with GJB2 mutations at all three electrode locations.

CONCLUSIONS

Cochlear-implanted children with ANSD show poorer peripheral neural synchrony than children with GJB2 mutations.

Devising a framework of optogenetic coding in the auditory pathway: Insights from auditory midbrain recordings

Cochlear implants (CIs) restore activity in the deafened auditory system via electrical stimulation of the auditory nerve. As the spread of electric current in biological tissues is rather broad, the spectral information provided by electrical CIs is limited. Optogenetic stimulation of the auditory nerve has been suggested for artificial sound coding with improved spectral selectivity, as light can be conveniently confined in space. Yet, the foundations for optogenetic sound coding strategies remain to be established. Here, we parametrized stimulus-response-relationships of the auditory pathway in gerbils for optogenetic stimulation. Upon activation of the auditory pathway by waveguide-based optogenetic stimulation of the spiral ganglion, we recorded neuronal activity of the auditory midbrain, in which neural representations of spectral, temporal, and intensity information can be found. Screening a wide range of optical stimuli and taking the properties of optical CI emitters into account, we aimed to optimize stimulus paradigms for potent and energy-efficient activation of the auditory pathway. We report that efficient optogenetic coding builds on neural integration of millisecond stimuli built from microsecond light pulses, which optimally accommodate power-efficient laser diode operation. Moreover, we performed an activity-level-dependent comparison of optogenetic and acoustic stimulation in order to estimate the dynamic range and the maximal stimulation intensity amenable to single channel optogenetic sound encoding, and indicate that it complies well with speech comprehension in a typical conversation (65 dB). Our results provide a first framework for the development of coding strategies for future optogenetic hearing restoration.

Effect of speech-stimulus degradation on phoneme-related potential

Auditory evoked potential (AEP) has been used to evaluate the degree of hearing and speech cognition. Because AEP generates a very small voltage relative to ambient noise, a repetitive presentation of a stimulus, such as a tone, word, or short sentence, should be employed to generate ensemble averages over trials. However, the stimulation of repetitive short words and sentences may present an unnatural situation to a subject. Phoneme-related potentials (PRPs), which are evoked-responses to typical phonemic stimuli, can be extracted from electroencephalography (EEG) data in response to a continuous storybook. In this study, we investigated the effects of spectrally degraded speech stimuli on PRPs. The EEG data in response to the spectrally degraded and natural storybooks were recorded from normal listeners, and the PRP components for 10 vowels and 12 consonants were extracted. The PRP responses to a vocoded (spectrally-degraded) storybook showed a statistically significant lower peak amplitude and were prolonged compared with those of a natural storybook. The findings in this study suggest that PRPs can be considered a potential tool to evaluate hearing and speech cognition as other AEPs. Moreover, PRPs can provide the details of phonological processing and phonemic awareness to understand poor speech intelligibility. Further investigation with the hearing impaired is required prior to clinical application.

Systematic Literature Review and Early Benefit of Cochlear Implantation in Two Pediatric Auditory Neuropathy Cases

Approximately 1 in 10 children with hearing loss is affected by auditory neuropathy spectrum disorder (ANSD). People who have ANSD usually have great difficulty understanding speech or communicating. However, it is possible for these patients to have audiograms that may indicate profound hearing loss up to normal hearing. This disorder is prognosed with positive, intact or present otoacoustic emissions (OAE) and/or cochlear microphonics (CM) as well as abnormal or absent auditory brainstem responses (ABR). Treatment methods include conventional hearing aids as well as cochlear implants. Cochlear implants (CI) usually promise better speech understanding for ANSD patients. We performed a systematic literature review aiming to show what improvements can effectively be achieved with cochlear implants in children with ANSD and compare this with our experience with two cases of ANSD implanted at our clinic. The retrospective review of two young CI patients diagnosed with ANSD during infancy demonstrated improvements over time in speech development communicated by their parents.

Within- and across-frequency temporal processing and speech perception in cochlear implant users

OBJECTIVE

Cochlear implant (CI) recipient's speech perception performance is highly variable and is influenced by temporal processing abilities. Temporal processing is commonly assessed using a behavioral task that requires the participant to detect a silent gap with the pre- and post-gap stimuli of the same frequency (within-frequency gap detection) or of different frequencies (across-frequency gap detection). The purpose of the study was to evaluate behavioral and electrophysiological measures of within- and across-frequency temporal processing and their correlations with speech perception performance in CI users.

DESIGN

Participants included 11 post-lingually deafened adult CI users (n = 15 ears; Mean Age = 50.2 yrs) and 11 age- and gender-matched normal hearing (NH) individuals (n = 15 ears; Mean Age = 49.0 yrs). Speech perception was assessed with Consonant-Nucleus-Consonant Word Recognition (CNC), Arizona Biomedical Sentence Recognition (AzBio), and Bamford-Kowal-Bench Speech-in-Noise Test (BKB-SIN) tests. Within- and across-frequency behavioral gap detection thresholds (referred to as the GDTwithin and GDTacross) were measured using an adaptive, two-alternative, forced-choice procedure. Cortical auditory evoked potentials (CAEPs) were elicited using within- and across-frequency gap stimuli under four gap duration conditions (no gap, GDT, sub-threshold GDT, and supra-threshold GDT). Correlations among speech perception, GDTs, and CAEPs were examined.

RESULTS

CI users had poorer speech perception scores compared to NH listeners (p < 0.05), but the GDTs were not different between groups (p > 0.05). Compared to NH peers, CI users showed increased N1 latency in the CAEPs evoked by the across-frequency gap stimuli (p < 0.05). No group difference was observed for the CAEPs evoked by the within-frequency gap (p > 0.05). Three CI ears showing the longest GDTwithin also showed the poorest performance in speech in noise. The within-frequency CAEP increased in amplitude with the increase of gap duration; while the across-frequency CAEP displayed a similar amplitude for all gap durations. There was a significant correlation between speech scores and within-frequency CAEP measures for the supra-threshold GDT condition, with CI users with poorer speech performance having a smaller N1-P2 amplitude and longer N1 latency. No correlations were found among GDTacross, speech perception, and across-frequency CAEP measures.

CONCLUSIONS

Within- and across-frequency gap detection may involve different neural mechanisms. The within-frequency gap detection task can help identify CI users with poor speech performance for rehabilitation. The within-frequency CAEP is a better predictor for speech perception performance than the across-frequency CAEP.

Relationship Between the Ability to Detect Frequency Changes or Temporal Gaps and Speech Perception Performance in Post-lingual Cochlear Implant Users

Previous studies, using modulation stimuli, on the relative effects of frequency resolution and time resolution on CI users’ speech perception failed to reach a consistent conclusion. In this study, frequency change detection and temporal gap detection were used to investigate the frequency resolution and time resolution of CI users, respectively. Psychophysical and neurophysiological methods were used to simultaneously investigate the effects of frequency and time resolution on speech perception in post-lingual cochlear implant (CI) users. We investigated the effects of psychophysical results [frequency change detection threshold (FCDT), gap detection threshold (GDT)], and acoustic change complex (ACC) responses (evoked threshold, latency, or amplitude of ACC induced by frequency change or temporal gap) on speech perception [recognition rate of monosyllabic words, disyllabic words, sentences in quiet, and sentence recognition threshold (SRT) in noise]. Thirty-one adult post-lingual CI users of Mandarin Chinese were enrolled in the study. The stimuli used to induce ACCs to frequency changes were 800-ms pure tones (fundamental frequency was 1,000 Hz); the frequency change occurred at the midpoint of the tones, with six percentages of frequency changes (0, 2, 5, 10, 20, and 50%). Temporal silences with different durations (0, 5, 10, 20, 50, and 100 ms) were inserted in the middle of the 800-ms white noise to induce ACCs evoked by temporal gaps. The FCDT and GDT were obtained by two 2-alternative forced-choice procedures. The results showed no significant correlation between the CI hearing threshold and speech perception in the study participants. In the multiple regression analysis of the influence of simultaneous psychophysical measures and ACC responses on speech perception, GDT significantly predicted every speech perception index, and the ACC amplitude evoked by the temporal gap significantly predicted the recognition of disyllabic words in quiet and SRT in noise. We conclude that when the ability to detect frequency changes and the temporal gap is considered simultaneously, the ability to detect frequency changes may have no significant effect on speech perception, but the ability to detect temporal gaps could significantly predict speech perception.

Reliability of Serological Prestin Levels in Humans and its Relation to Otoacoustic Emissions, a Functional Measure of Outer Hair Cells

OBJECTIVES

Serological biomarkers, common to many areas of medicine, have the potential to inform on the health of the human body and to give early warning of risk of compromised function or illness before symptoms are experienced. Serological measurement of prestin, a motor protein uniquely produced and expressed in outer hair cells, has recently been identified as a potential biomarker to inform on the health of the cochlea. Before any test can be introduced into the clinical toolkit, the reproducibility of the measurement when repeated in the same subject must be considered. The primary objective of this study is to outline the test-retest reliability estimates and normative ranges for serological prestin in healthy young adults with normal hearing. In addition, we examine the relation between serum prestin levels and otoacoustic emissions (OAEs) to compare this OHC-specific protein to the most common measure of OHC function currently used in hearing assessments.

DESIGN

We measured prestin levels serologically from circulating blood in 34 young adults (18 to 24 years old) with clinically normal pure-tone audiometric averages at five different timepoints up to six months apart (average intervals between measurements ranged from <1 week to 7 weeks apart). To guide future studies of clinical populations, we present the standard error of the measurement, reference normative values, and multiple measures of reliability. Additionally, we measured transient evoked OAEs at the same five timepoints and used correlation coefficients to examine the relation between OAEs and prestin levels (pg/mL).

RESULTS

Serum prestin levels demonstrated good to excellent reliability between and across the five different time points, with correlation coefficients and intraclass correlations >0.8. Across sessions, the average serum prestin level was 250.20 pg/mL, with a standard error of measurement of 7.28 pg/mL. Moreover, positive correlations (generally weak to moderate) were found between prestin levels and OAE magnitudes and signal-to-noise ratios.

CONCLUSIONS

Findings characterize serum prestin in healthy young adults with normal hearing and provide initial normative data that may be critical to interpreting results from individuals with sensorineural hearing loss. Our results demonstrate reliability of serum prestin levels in a sample of normal-hearing young adults across five test sessions up to 6 months apart, paving the way for testing larger samples to more accurately estimate test-retest standards for clinical protocols, including those involving serial monitoring. The positive correlations between serum prestin and OAE levels, although weak to moderate, reinforce that the source of serum prestin is likely the outer hair cells in the inner ear, but also that serum prestin and OAEs each may also index aspects of biologic function not common to the other.

Electrophysiological assessment of temporal envelope processing in cochlear implant users

Cochlear-implant (CI) users rely on temporal envelope modulations (TEMs) to understand speech, and clinical outcomes depend on the accuracy with which these TEMs are encoded by the electrically-stimulated neural ensembles. Non-invasive EEG measures of this encoding could help clinicians identify and disable electrodes that evoke poor neural responses so as to improve CI outcomes. However, recording EEG during CI stimulation reveals huge stimulation artifacts that are up to orders of magnitude larger than the neural response. Here we used a custom-built EEG system having an exceptionally high sample rate to accurately measure the artefact, which we then removed using linear interpolation so as to reveal the neural response during continuous electrical stimulation. In ten adult CI users, we measured the 40-Hz electrically evoked auditory steady-state response (eASSR) and electrically evoked auditory change complex (eACC) to amplitude-modulated 900-pulses-per-second pulse trains, stimulated in monopolar mode (i.e. the clinical default), and at different modulation depths. We successfully measured artifact-free 40-Hz eASSRs and eACCs. Moreover, we found that the 40-Hz eASSR, in contrast to the eACC, showed substantial responses even at shallow modulation depths. We argue that the 40-Hz eASSR is a clinically feasible objective measure to assess TEM encoding in CI users.

Music and psychoacoustic perception abilities in cochlear implant users with auditory neuropathy spectrum disorder

OBJECTIVE

Auditory neuropathy spectrum disorder (ANSD) is a condition wherein the pre-neural or cochlear outer hair cell activity is intact, but the neural activity in the auditory nerve is disrupted. Cochlear implant (CI) can be beneficial for subjects with ANSD; however, little is known about the music perception and psychoacoustic abilities of CI users with ANSD. Music perception in CI users is a multidimensional and complex ability requiring the contribution of both auditory and nonauditory abilities. Even though auditory abilities lay the foundation, the contribution of patient-related variables such as ANSD may affect the music perception. This study aimed to evaluate the psychoacoustic and music perception abilities of CI recipients with ANSD.

STUDY DESIGN

Twelve CI users with ANSD and twelve age- and gendermatched CI users with sensorineural hearing loss (SNHL) were evaluated. Music perception abilities were measured using the Turkish version of the Clinical Assessment of Music Perception (T-CAMP) test. Psychoacoustic abilities were measured using the spectral ripple discrimination (SRD) and temporal modulation transfer function (TMTF) tests. In addition, the age of diagnosis and implantation was recorded.

RESULTS

Pitch direction discrimination (PDD), timbre recognition, SRD, and TMTF performance of CI users with ANSD were concordant with those reported in previous studies, and differences between ANSD and SNHL groups were not statistically significant. However, the ANSD group performed poorly compared with SNHL group in melody recognition subtest of T-CAMP, and the difference was statistically significant.

CONCLUSION

CI can prove beneficial for patients with ANSD with respect to their music and psychoacoustic abilities, similar to patients with SNHL, except for melody recognition. Recognition of melodies requires both auditory and non-auditory abilities, and ANSD may have an extensive but subtle effect in the life of CI users.

Evidence of Vowel Discrimination Provided by the Acoustic Change Complex

OBJECTIVES

The objectives of this study were to measure the effects of level and vowel contrast on the latencies and amplitudes of acoustic change complex (ACC) in the mature auditory system. This was done to establish how the ACC in healthy young adults is affected by these stimulus parameters that could then be used to inform translation of the ACC into a clinical measure for the pediatric population. Another aim was to demonstrate that a normalized amplitude metric, calculated by dividing the ACC amplitude in the vowel contrast condition by the ACC amplitude obtained in a control condition (no vowel change) would demonstrate good sensitivity with respect to perceptual measures of vowel-contrast detection. The premises underlying this research were that: (1) ACC latencies and amplitudes would vary with level, in keeping with principles of an increase in neural synchrony and activity that takes place as a function of increasing stimulus level; (2) ACC latencies and amplitudes would vary with vowel contrast, because cortical auditory evoked potentials are known to be sensitive to the spectro-temporal characteristics of speech.

DESIGN

Nineteen adults, 14 of them female, with a mean age of 24.2 years (range 20 to 38 years) participated in this study. All had normal-hearing thresholds. Cortical auditory evoked potentials were obtained from all participants in response to synthesized vowel tokens (/a/, /i/, /o/, /u/), presented in a quasi-steady state fashion at a rate of 2/sec in an oddball stimulus paradigm, with a 25% probability of the deviant stimulus. The ACC was obtained in response to the deviant stimulus. All combinations of vowel tokens were tested at 2 stimulus levels: 40 and 70 dBA. In addition, listeners were tested for their ability to detect the vowel contrasts using behavioral methods.

RESULTS

ACC amplitude varied systematically with level, and test condition (control versus contrast) and vowel token, but ACC latency did not. ACC amplitudes were significantly larger when tested at 70 dBA compared with 40 dBA and for contrast trials compared with control trials at both levels. Amplitude ratios (normalized amplitudes) were largest for contrast pairs in which /a/ was the standard token. The amplitude ratio metric at the individual level demonstrated up to 97% sensitivity with respect to perceptual measures of discrimination.

CONCLUSIONS

The present study establishes the effects of stimulus level and vowel type on the latency and amplitude of the ACC in the young adult auditory system and supports the amplitude ratio as a sensitive metric for cortical acoustic salience of vowel spectral features. Next steps are to evaluate these methods in infants and children with hearing loss with the long-term goal of its translation into a clinical method for estimating speech feature discrimination.

The Electrically Evoked Auditory Change Complex Evoked by Temporal Gaps Using Cochlear Implants or Auditory Brainstem Implants in Children With Cochlear Nerve Deficiency

OBJECTIVES

This study aimed to (1) establish the feasibility of measuring the electrically evoked auditory change complex (eACC) in response to temporal gaps in children with cochlear nerve deficiency (CND) who are using cochlear implants (CIs) and/or auditory brainstem implants (ABIs); and (2) explore the association between neural encoding of, and perceptual sensitivity to, temporal gaps in these patients.

DESIGN

Study participants included 5 children (S1 to S5) ranging in age from 3.8 to 8.2 years (mean: 6.3 years) at the time of testing. All subjects were unilaterally implanted with a Nucleus 24M ABI due to CND. For each subject, two or more stimulating electrodes of the ABI were tested. S2, S3, and S5 previously received a CI in the contralateral ear. For these 3 subjects, at least two stimulating electrodes of their CIs were also tested. For electrophysiological measures, the stimulus was an 800-msec biphasic pulse train delivered to individual electrodes at the maximum comfortable level (C level). The electrically evoked responses, including the onset response and the eACC, were measured for two stimulation conditions. In the standard condition, the 800-msec pulse train was delivered uninterrupted to individual stimulating electrodes. In the gapped condition, a temporal gap was inserted into the pulse train after 400 msec of stimulation. Gap durations tested in this study ranged from 2 up to 128 msec. The shortest gap that could reliably evoke the eACC was defined as the objective gap detection threshold (GDT). For behavioral GDT measures, the stimulus was a 500-msec biphasic pulse train presented at the C level. The behavioral GDT was measured for individual stimulating electrodes using a one-interval, two-alternative forced-choice procedure.

RESULTS

The eACCs to temporal gaps were recorded successfully in all subjects for at least one stimulating electrode using either the ABI or the CI. Objective GDTs showed intersubject variations, as well as variations across stimulating electrodes of the ABI or the CI within each subject. Behavioral GDTs were measured for one ABI electrode in S2 and for multiple ABI and CI electrodes in S5. All other subjects could not complete the task. S5 showed smaller behavioral GDTs for CI electrodes than those measured for ABI electrodes. One CI and two ABI electrodes in S5 showed comparable objective and behavioral GDTs. In contrast, one CI and two ABI electrodes in S5 and one ABI electrode in S2 showed measurable behavioral GDTs but no identifiable eACCs.

CONCLUSIONS

The eACCs to temporal gaps were recorded in children with CND using either ABIs or CIs. Both objective and behavioral GDTs showed inter- and intrasubject variations. Consistency between results of eACC recordings and psychophysical measures of GDT was observed for some but not all ABI or CI electrodes in these subjects.

Cortical Auditory Evoked Potentials in Children with Auditory Neuropathy/Dys-Synchrony

Auditory neuropathy/spectrum disorder (ANSD), also referred to as auditory neuropathy/dys-synchrony (AN/AD) is a recently described form of hearing impairment. Many studies have shown that changing the pattern of afferent input to the cortex significantly affects cortical organization and there is little studies about cortical neuromaturation and plasticity in children with ANSD. Study of P1 component of cortical auditory evoked potentials (CAEPs) in children with ANSD. This survey was descriptive cross-sectional. During that 97 hearing impairment children were under hearing screening tests. Of these, 14 selected subjects (ear = 28) diagnosed with ANSD (an average age of 8.5 years) and evaluated by P1 component of CAEPs. Based on latency results of p1 wave, the ears of the subjects fell into two seperate groups: Control (normal: n = 10) and case {total: n = 18 (delayed: n = 12) + (absent: n = 6)}. The averages of mean latency of P1 components of the case group in the right and the left ears compared to the control group had significant differences (p < 0.05). Abnormal latency of p1 component in ANSD children shows the possibility of different scales of disturbances in cortical auditory maturation and grow.

Clinically recorded cortical auditory evoked potentials from paediatric cochlear implant users fitted with electrically elicited stapedius reflex thresholds

OBJECTIVES

This study aimed to objectively evaluate access to soft sounds (55 dB SPL) in paediatric CI users, all wearing MED-EL (Innsbruck, Austria) devices who were fitted with the objective electrically elicited stapedius reflex threshold (eSRT) fitting method, to track their cortical auditory evoked potential (CAEP) presence and latency, and to compare their CAEPs to those of normal-hearing peers.

METHODS

Forty-five unilaterally implanted, pre-lingually deafened MED-EL CI users, aged 12-48 months, underwent CAEP testing in the clinic at regular monthly intervals post switch-on. CAEPs were recorded in response to short speech tokens /m/, /g/ and /t/ presented in the free field at 55 dB SPL. Twenty children with normal hearing (NH), similarly aged, underwent CAEP testing once.

RESULTS

The proportion of present CAEPs increased and CAEP P1 latencies reduced significantly with post-implantation duration. CAEPs were scored based on their presence and age-appropriate P1 latency. These CAEP scores increased significantly with post-implantation duration. CAEP scores were significantly worse for the /m/ speech token compared to the other two tokens. Compared to the NH group, CAEP scores were significantly smaller for all post-implantation test intervals.

CONCLUSIONS

This study provides clinicians with a first step towards typical ranges of CAEP presence, latency, and derived CAEP score over the first months of MED-EL CI use. CAEPs within these typical ranges could validate intervention whereas less than optimum CAEPs could prompt clinicians to seek solutions in a timely manner. CAEPs could clinically validate whether a CI provides adequate access to soft sounds. This approach could form an alternative to behavioural soft sound access verification.

Objective Test of Cochlear Dead Region: Electrophysiologic Approach using Acoustic Change Complex

The goal of this study was to develop an objective and neurophysiologic method of identifying the presence of cochlear dead region (CDR) by combining acoustic change complex (ACC) responses with threshold-equalizing noise (TEN) test. The goal of the first study was to confirm whether ACC could be evoked with TEN stimuli and to also optimize the test conditions. The goal of the second study was to determine whether the TEN-ACC test is capable of detecting CDR(s). The ACC responses were successfully recorded from all study participants. Both behaviorally and electrophysiologically obtained masked thresholds (TEN threshold and TEN-ACC threshold) were similar and below 10 and 12 dB SNR in NH listeners, respectively. HI listeners were divided into HI (non-CDR) and CDR groups based on the behavioral TEN test. For the non-CDR group, TEN-ACC thresholds were below 12 dB which were similar to NH listeners. However, for the CDR group, TEN-ACC thresholds were significantly higher (≥12 dB SNR) than those in the NH and HI groups, indicating that CDR(s) can be objectively detected using the ACC. Results of this study demonstrate that it is possible to detect the presence of CDR using an electrophysiologic method.

Electrically Evoked Auditory Event-Related Responses in Patients with Auditory Brainstem Implants: Morphological Characteristics, Test-Retest Reliability, Effects of Stimulation Level, and Association with Auditory Detection

OBJECTIVE

This study aimed to (1) characterize morphological characteristics of the electrically evoked cortical auditory event-related potentials (eERPs) and explore the potential association between onset eERP morphology and auditory versus nonauditory stimulation; (2) assess test-retest reliability of onset eERPs; (3) investigate effects of stimulation level on onset eERPs; and (4) explore the feasibility of using the onset eERP to estimate the lowest stimulation level that can be detected for individual stimulating electrodes in patients with auditory brainstem implants (ABIs).

DESIGN

Study participants included 5 children (S1 to S5) and 2 adults (S6 to S7) with unilateral Cochlear Nucleus 24M ABIs. Pediatric ABI recipients ranged in age from 2.6 to 10.2 years (mean: 5.2 years) at the time of testing. S6 and S7 were 21.2 and 24.6 years of age at the time of testing, respectively. S6 and S7 were diagnosed with neurofibromatosis II (NF2) and implanted with an ABI after a surgical removal of the tumors. All pediatric subjects received ABIs after being diagnosed with cochlear nerve deficiency. The lowest stimulation level that could be detected (behavioral T level) and the estimated maximum comfortable level (C level) was measured for individual electrodes using clinical procedures. For electrophysiological measures, the stimulus was a 100-msec biphasic pulse train that was delivered to individual electrodes in a monopolar-coupled stimulation mode at stimulation levels ranging from subthreshold to C levels. Electrophysiological recordings of the onset eERP were obtained in all subjects. For studies evaluating the test-retest reliability of the onset eERP, responses were measured using the same set of parameters in two test sessions. The time interval between test sessions ranged from 2 to 6 months. The lowest stimulation level that could evoke the onset eERP was defined as the objective T level.

RESULTS

Onset eERPs were recorded in all subjects tested in this study. Inter- and intrasubject variations in morphological characteristics of onset eERPs were observed. Onset eERPs with complex waveforms were recorded for electrodes that evoked nonauditory sensations, based on feedback from subjects, as well as for electrodes without any indications of nonauditory stimulations. Onset eERPs in patients with ABIs demonstrated good test-retest reliability. Increasing stimulation levels resulted in increased eERP amplitudes but showed inconsistent effects on response latencies in patients with ABIs. Objective and behavioral T levels were correlated.

CONCLUSIONS

eERPs could be recorded in both non-NF2 and NF2 patients with ABIs. eERPs in both ABI patient groups show inter- and intrasubject variations in morphological characteristics. However, onset eERPs measured within the same subject in this study tended to be stable across study sessions. The onset eERP can potentially be used to estimate behavioral T levels in patients with ABIs. Further studies with more adult ABI recipients are warranted to investigate whether the onset eERP can be used to identify electrodes with nonauditory stimulations.

Temporal Response Properties of the Auditory Nerve in Implanted Children with Auditory Neuropathy Spectrum Disorder and Implanted Children with Sensorineural Hearing Loss

OBJECTIVE

This study aimed to (1) characterize temporal response properties of the auditory nerve in implanted children with auditory neuropathy spectrum disorder (ANSD), and (2) compare results recorded in implanted children with ANSD with those measured in implanted children with sensorineural hearing loss (SNHL).

DESIGN

Participants included 28 children with ANSD and 29 children with SNHL. All subjects used cochlear nucleus devices in their test ears. Both ears were tested in 6 children with ANSD and 3 children with SNHL. For all other subjects, only one ear was tested. The electrically evoked compound action potential (ECAP) was measured in response to each of the 33 pulses in a pulse train (excluding the second pulse) for one apical, one middle-array, and one basal electrode. The pulse train was presented in a monopolar-coupled stimulation mode at 4 pulse rates: 500, 900, 1800, and 2400 pulses per second. Response metrics included the averaged amplitude, latencies of response components and response width, the alternating depth and the amount of neural adaptation. These dependent variables were quantified based on the last six ECAPs or the six ECAPs occurring within a time window centered around 11 to 12 msec. A generalized linear mixed model was used to compare these dependent variables between the 2 subject groups. The slope of the linear fit of the normalized ECAP amplitudes (re. amplitude of the first ECAP response) over the duration of the pulse train was used to quantify the amount of ECAP increment over time for a subgroup of 9 subjects.

RESULTS

Pulse train-evoked ECAPs were measured in all but 8 subjects (5 with ANSD and 3 with SNHL). ECAPs measured in children with ANSD had smaller amplitude, longer averaged P2 latency and greater response width than children with SNHL. However, differences in these two groups were only observed for some electrodes. No differences in averaged N1 latency or in the alternating depth were observed between children with ANSD and children with SNHL. Neural adaptation measured in these 2 subject groups was comparable for relatively short durations of stimulation (i.e., 11 to 12 msec). Children with ANSD showed greater neural adaptation than children with SNHL for a longer duration of stimulation. Amplitudes of ECAP responses rapidly declined within the first few milliseconds of stimulation, followed by a gradual decline up to 64 msec after stimulus onset in the majority of subjects. This decline exhibited an alternating pattern at some pulse rates. Further increases in pulse rate diminished this alternating pattern. In contrast, ECAPs recorded from at least one stimulating electrode in six ears with ANSD and three ears with SNHL showed a clear increase in amplitude over the time course of stimulation. The slope of linear regression functions measured in these subjects was significantly greater than zero.

CONCLUSIONS

Some but not all aspects of temporal response properties of the auditory nerve measured in this study differ between implanted children with ANSD and implanted children with SNHL. These differences are observed for some but not all electrodes. A new neural response pattern is identified. Further studies investigating its underlying mechanism and clinical relevance are warranted.

Longitudinal Changes in Electrically Evoked Auditory Event-Related Potentials in Children With Auditory Brainstem Implants: Preliminary Results Recorded Over 3 Years

OBJECTIVES

This preliminary study aimed (1) to assess longitudinal changes in electrically evoked auditory event-related potentials (eERPs) in children with auditory brainstem implants (ABIs) and (2) to explore whether these changes could be accounted for by maturation in the central auditory system of these patients.

DESIGN

Study participants included 5 children (S1 to S5) with an ABI in the affected ear. The stimulus was a train of electrical pulses delivered to individual ABI electrodes via a research interface. For each subject, the eERP was repeatedly measured in multiple test sessions scheduled over up to 41 months after initial device activation. Longitudinal changes in eERPs recorded for each ABI electrode were evaluated using intraclass correlation tests for each subject.

RESULTS

eERPs recorded in S1 showed notable morphological changes for five ABI electrodes over 41 months. In parallel, signs or symptoms of nonauditory stimulation elicited by these electrodes were observed or reported at 41 months. eERPs could not be observed in S2 after 9 months of ABI use but were recorded at 12 months after initial stimulation. Repeatable eERPs were recorded in S3 in the first 9 months. However, these responses were either absent or showed remarkable morphological changes at 30 months. Longitudinal changes in eERP waveform morphology recorded in S4 and S5 were also observed.

CONCLUSIONS

eERP responses in children with ABIs could change over a long period of time. Maturation of the central auditory system could not fully account for these observed changes. Children with ABIs need to be closely monitored for potential changes in auditory perception and unfavorable nonauditory sensations. Neuroimaging correlates are needed to better understand the emergence of nonauditory stimulation over time in these children.

Acoustically evoked auditory change complex in children with auditory neuropathy spectrum disorder: a potential objective tool for identifying cochlear implant candidates

OBJECTIVES

The overall aim of the study was to evaluate the feasibility of using electrophysiological measures of the auditory change complex (ACC) to identify candidates for cochlear implantation in children with auditory neuropathy spectrum disorder (ANSD). To achieve this overall aim, this study (1) assessed the feasibility of measuring the ACC evoked by temporal gaps in a group of children with ANSD across a wide age range and (2) investigated the association between gap detection thresholds (GDTs) measured by the ACC recordings and open-set speech-perception performance in these subjects.

DESIGN

Nineteen children with bilateral ANSD ranging in age between 1.9 and 14.9 years (mean: 7.8 years) participated in this study. Electrophysiological recordings of the auditory event-related potential (ERP), including the onset ERP response and the ACC, were completed in all subjects and open-set speech perception was evaluated for a subgroup of 16 subjects. For the ERP recordings, the stimulus was a Gaussian noise presented through ER-3A insert earphones to the test ear. Two stimulation conditions were used. In the "control condition," the stimulus was an 800-msec Gaussian noise. In the "gapped condition," the stimuli were two noise segments, each being 400 msec in duration, separated by one of five gaps (i.e., 5, 10, 20, 50, or 100 msec). The interstimulation interval was 1200 msec. The aided open-set speech perception ability was assessed using the Phonetically Balanced Kindergarten (PBK) word lists presented at 60 dB SPL using recorded testing material in a sound booth. For speech perception tests, subjects wore their hearing aids at the settings recommended by their clinical audiologists. For a subgroup of five subjects, psychophysical GDTs for the Gaussian noise were also assessed using a three-interval, three-alternative forced-choice procedure.

RESULTS

Responses evoked by the onset of the Gaussian noise (i.e., onset responses) were recorded in all stimulation conditions from all subjects tested in this study. The presence/absence, peak latency and amplitude, and response width of the onset response did not correlate with aided PBK word scores. The objective GDTs measured with the ACC recordings from 17 subjects ranged from 10 to 100 msec. The ACC was not recorded from two subjects for any gap durations tested in this study. There was a robust negative correlation between objective GDTs and aided PBK word scores. In general, subjects with prolonged objective GDTs showed low-aided PBK word scores. GDTs measured using electrophysiological recordings of the ACC correlated well with those measured using psychophysical procedures in four of five subjects who were evaluated using both procedures.

CONCLUSIONS

The clinical application of the onset response in predicting open-set speech-perception ability is relatively limited in children with ANSD. The ACC recordings can be used to objectively evaluate temporal resolution abilities in children with ANSD having no severe comorbidities, and who are older than 1.9 years. The ACC can potentially be used as an objective tool to identify poor performers among children with ANSD using properly fit amplification, and who are thus, cochlear implant candidates.

Acoustic Change Complex: Clinical Implications

The acoustic change complex (ACC) is a cortical auditory evoked potential elicited in response to a change in an ongoing sound. The characteristics and potential clinical implications of the ACC are reviewed in this article. The P1-N1-P2 recorded from the auditory cortex following presentation of an acoustic stimulus is believed to reflect the neural encoding of a sound signal, but this provides no information regarding sound discrimination. However, the neural processing underlying behavioral discrimination capacity can be measured by modifying the traditional methodology for recording the P1-N1-P2. When obtained in response to an acoustic change within an ongoing sound, the resulting waveform is referred to as the ACC. When elicited, the ACC indicates that the brain has detected changes within a sound and the patient has the neural capacity to discriminate the sounds. In fact, results of several studies have shown that the ACC amplitude increases with increasing magnitude of acoustic changes in intensity, spectrum, and gap duration. In addition, the ACC can be reliably recorded with good test-retest reliability not only from listeners with normal hearing but also from individuals with hearing loss, hearing aids, and cochlear implants. The ACC can be obtained even in the absence of attention, and requires relatively few stimulus presentations to record a response with a good signal-to-noise ratio. Most importantly, the ACC shows reasonable agreement with behavioral measures. Therefore, these findings suggest that the ACC might represent a promising tool for the objective clinical evaluation of auditory discrimination and/or speech perception capacity.

Pathophysiological mechanisms and functional hearing consequences of auditory neuropathy

The effects of inner ear abnormality on audibility have been explored since the early 20th century when sound detection measures were first used to define and quantify 'hearing loss'. The development in the 1970s of objective measures of cochlear hair cell function (cochlear microphonics, otoacoustic emissions, summating potentials) and auditory nerve/brainstem activity (auditory brainstem responses) have made it possible to distinguish both synaptic and auditory nerve disorders from sensory receptor loss. This distinction is critically important when considering aetiology and management. In this review we address the clinical and pathophysiological features of auditory neuropathy that distinguish site(s) of dysfunction. We describe the diagnostic criteria for: (i) presynaptic disorders affecting inner hair cells and ribbon synapses; (ii) postsynaptic disorders affecting unmyelinated auditory nerve dendrites; (iii) postsynaptic disorders affecting auditory ganglion cells and their myelinated axons and dendrites; and (iv) central neural pathway disorders affecting the auditory brainstem. We review data and principles to identify treatment options for affected patients and explore their benefits as a function of site of lesion.

Relationships Among Peripheral and Central Electrophysiological Measures of Spatial and Spectral Selectivity and Speech Perception in Cochlear Implant Users

OBJECTIVES

The ability to perceive speech is related to the listener's ability to differentiate among frequencies (i.e., spectral resolution). Cochlear implant (CI) users exhibit variable speech-perception and spectral-resolution abilities, which can be attributed in part to the extent of electrode interactions at the periphery (i.e., spatial selectivity). However, electrophysiological measures of peripheral spatial selectivity have not been found to correlate with speech perception. The purpose of this study was to evaluate auditory processing at the periphery and cortex using both simple and spectrally complex stimuli to better understand the stages of neural processing underlying speech perception. The hypotheses were that (1) by more completely characterizing peripheral excitation patterns than in previous studies, significant correlations with measures of spectral selectivity and speech perception would be observed, (2) adding information about processing at a level central to the auditory nerve would account for additional variability in speech perception, and (3) responses elicited with spectrally complex stimuli would be more strongly correlated with speech perception than responses elicited with spectrally simple stimuli.

DESIGN

Eleven adult CI users participated. Three experimental processor programs (MAPs) were created to vary the likelihood of electrode interactions within each participant. For each MAP, a subset of 7 of 22 intracochlear electrodes was activated: adjacent (MAP 1), every other (MAP 2), or every third (MAP 3). Peripheral spatial selectivity was assessed using the electrically evoked compound action potential (ECAP) to obtain channel-interaction functions for all activated electrodes (13 functions total). Central processing was assessed by eliciting the auditory change complex with both spatial (electrode pairs) and spectral (rippled noise) stimulus changes. Speech-perception measures included vowel discrimination and the Bamford-Kowal-Bench Speech-in-Noise test. Spatial and spectral selectivity and speech perception were expected to be poorest with MAP 1 (closest electrode spacing) and best with MAP 3 (widest electrode spacing). Relationships among the electrophysiological and speech-perception measures were evaluated using mixed-model and simple linear regression analyses.

RESULTS

All electrophysiological measures were significantly correlated with each other and with speech scores for the mixed-model analysis, which takes into account multiple measures per person (i.e., experimental MAPs). The ECAP measures were the best predictor. In the simple linear regression analysis on MAP 3 data, only the cortical measures were significantly correlated with speech scores; spectral auditory change complex amplitude was the strongest predictor.

CONCLUSIONS

The results suggest that both peripheral and central electrophysiological measures of spatial and spectral selectivity provide valuable information about speech perception. Clinically, it is often desirable to optimize performance for individual CI users. These results suggest that ECAP measures may be most useful for within-subject applications when multiple measures are performed to make decisions about processor options. They also suggest that if the goal is to compare performance across individuals based on a single measure, then processing central to the auditory nerve (specifically, cortical measures of discriminability) should be considered.

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.

Cortical development and neuroplasticity in Auditory Neuropathy Spectrum Disorder

Cortical development is dependent to a large extent on stimulus-driven input. Auditory Neuropathy Spectrum Disorder (ANSD) is a recently described form of hearing impairment where neural dys-synchrony is the predominant characteristic. Children with ANSD provide a unique platform to examine the effects of asynchronous and degraded afferent stimulation on cortical auditory neuroplasticity and behavioral processing of sound. In this review, we describe patterns of auditory cortical maturation in children with ANSD. The disruption of cortical maturation that leads to these various patterns includes high levels of intra-individual cortical variability and deficits in cortical phase synchronization of oscillatory neural responses. These neurodevelopmental changes, which are constrained by sensitive periods for central auditory maturation, are correlated with behavioral outcomes for children with ANSD. Overall, we hypothesize that patterns of cortical development in children with ANSD appear to be markers of the severity of the underlying neural dys-synchrony, providing prognostic indicators of success of clinical intervention with amplification and/or electrical stimulation. This article is part of a Special Issue entitled <Auditory Synaptology>.

Acoustic change responses to amplitude modulation: a method to quantify cortical temporal processing and hemispheric asymmetry

Objective: Sound modulation is a critical temporal cue for the perception of speech and environmental sounds. To examine auditory cortical responses to sound modulation, we developed an acoustic change stimulus involving amplitude modulation (AM) of ongoing noise. The AM transitions in this stimulus evoked an acoustic change complex (ACC) that was examined parametrically in terms of rate and depth of modulation and hemispheric symmetry.

Methods: Auditory cortical potentials were recorded from 64 scalp electrodes during passive listening in two conditions: (1) ACC from white noise to 4, 40, 300 Hz AM, with varying AM depths of 100, 50, 25% lasting 1 s and (2) 1 s AM noise bursts at the same modulation rate. Behavioral measures included AM detection from an attend ACC condition and AM depth thresholds (i.e., a temporal modulation transfer function, TMTF).

Results: The N1 response of the ACC was large to 4 and 40 Hz and small to the 300 Hz AM. In contrast, the opposite pattern was observed with bursts of AM showing larger responses with increases in AM rate. Brain source modeling showed significant hemispheric asymmetry such that 4 and 40 Hz ACC responses were dominated by right and left hemispheres respectively.

Conclusion: N1 responses to the ACC resembled a low pass filter shape similar to a behavioral TMTF. In the ACC paradigm, the only stimulus parameter that changes is AM and therefore the N1 response provides an index for this AM change. In contrast, an AM burst stimulus contains both AM and level changes and is likely dominated by the rise time of the stimulus. The hemispheric differences are consistent with the asymmetric sampling in time hypothesis suggesting that the different hemispheres preferentially sample acoustic time across different time windows.

Significance: The ACC provides a novel approach to studying temporal processing at the level of cortex and provides further evidence of hemispheric specialization for fast and slow stimuli.

Objective measures of electrode discrimination with electrically evoked auditory change complex and speech-perception abilities in children with auditory neuropathy spectrum disorder

OBJECTIVES

This study aimed to (1) determine the sensitivity of the electrically evoked auditory change complex (eACC) to changes in stimulating electrode position; and (2) investigate the association between results of eACC measures and behavioral electrode discrimination and their association with speech-perception performance in pediatric cochlear implant (CI) users who have auditory neuropathy spectrum disorder (ANSD).

DESIGN

Fifteen children with ANSD ranging in age between 5.4 and 18.6 years participated in this study. All subjects used Cochlear Nucleus devices. For each subject, open-set speech-perception ability was assessed using the Phonetically Balanced Kindergarten word lists presented at 60 dB SPL, using monitored live voice in a sound booth. Behavioral and objective measures of electrode discrimination were assessed in a nonclinical test environment. The stimuli used to elicit these measures were 800 msec biphasic pulse trains delivered by a direct interface to the CI. Data were collected from two basic stimulation conditions. In the standard condition, the entire pulse train was delivered to a mid-array electrode (electrode 11 or 12) at the maximum comfortable level (C level). In the change condition, the stimulus was split into two 400 msec pulse train segments presented sequentially on two different electrodes. The stimulation level of the second 400 msec pulse train was loudness balanced to the C level of the mid-array electrode used in the standard condition. The separation between the pair of stimulating electrodes was systematically varied. For behavioral electrode-discrimination measures, each subject was required to determine whether he or she heard one or two sounds for stimuli presented in different stimulation conditions. For the eACC measures, two replicates of 100 artifact-free sweeps were recorded for each stimulation condition.

RESULTS

The eACC in response to changes in stimulating electrode position was recorded from all subjects with ANSD using direct electrical stimulation. Electrode-discrimination thresholds determined with the eACC and behavioral measures were consistent. Children with ANSD using CIs who showed poorer speech performance also required larger separations between the stimulating electrode pair to reliably elicit the eACC than subjects with better speech-perception performance. There was a robust correlation between electrode-discrimination capacities and speech-perception performances in subjects tested in this study. The effect of electrode separation on eACC amplitudes was not monotonic.

CONCLUSIONS

These results demonstrate the feasibility of using eACC to evaluate electrode-discrimination capacities in children with ANSD. These results suggest that the eACC elicited by changes in stimulating electrode position holds great promise as an objective tool for evaluating spectral-pattern detection in such subjects, which may be predictive of their potential speech-perception performance.