Acoustic Change Complex: Clinical Implications

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.

Feasibility exploration of cortical auditory evoked potentials evoked by spectro-temporal modulation signals

BACKGROUND

An objective measurement of speech perception would be valuable in hearing-impaired patients who are unable to perform auditory tasks reliably.

OBJECTIVES

To investigate the feasibility of cortical auditory evoked potentials (CAEPs) evoked by different spectro-temporal modulation (STM) signals and provide reference for the further exploration of acoustic change complex (ACC) in hearing-impaired patients.

METHOD

29 normal hearing (NH) adults were recruited and stimulated randomly by STM signals at 6 spectral modulation rates: 0, 1, 2, 4, 8, 16 cycles/octave, at each of 4 temporal modulation rates: 0, 2, 4, 8 Hz, to elicit ACC response.

RESULTS

The change of spectral modulation rates ≤ 16 cycles/octave at 0 Hz temporal modulation rate had different impacts on latency. 0, 1 cycles/octave, and 4, 8 Hz made a difference to the P2-N1 amplitude easily. 8, 16 cycles/octave were more unstable in rejection rate. No significant difference existed in waveform repetition rate among different STM rates. No significant interaction effect existed in spectral and temporal modulation.

CONCLUSIONS

STM as a stimulus signal to induce ACC response had its feasibility. 2 cycles/octave at spectral modulation rate and 2 Hz at temporal modulation rate had better stability and waveform repeatability in NH adults.

Age-related differences in auditory spatial processing revealed by acoustic change complex

Objectives

The auditory spatial processing abilities mature throughout childhood and degenerate in older adults. This study aimed to compare the differences in onset cortical auditory evoked potentials (CAEPs) and location-evoked acoustic change complex (ACC) responses among children, adults, and the elderly and to investigate the impact of aging and development on ACC responses.

Design

One hundred and seventeen people were recruited in the study, including 57 typically-developed children, 30 adults, and 30 elderlies. The onset-CAEP evoked by white noise and ACC by sequential changes in azimuths were recorded. Latencies and amplitudes as a function of azimuths were analyzed using the analysis of variance, Pearson correlation analysis, and multiple linear regression model.

Results

The ACC N1'-P2' amplitudes and latencies in adults, P1'-N1' amplitudes in children, and N1' amplitudes and latencies in the elderly were correlated with angles of shifts. The N1'-P2' and P2' amplitudes decreased in the elderly compared to adults. In Children, the ACC P1'-N1' responses gradually differentiated into the P1'-N1'-P2' complex. Multiple regression analysis showed that N1'-P2' amplitudes (R2 = 0.33) and P2' latencies (R2 = 0.18) were the two most variable predictors in adults, while in the elderly, N1' latencies (R2 = 0.26) explained most variances. Although the amplitudes of onset-CAEP differed at some angles, it could not predict angle changes as effectively as ACC responses.

Conclusion

The location-evoked ACC responses varied among children, adults, and the elderly. The N1'-P2' amplitudes and P2' latencies in adults and N1' latencies in the elderly explained most variances of changes in spatial position. The differentiation of the N1' waveform was observed in children. Further research should be conducted across all age groups, along with behavioral assessments, to confirm the relationship between aging and immaturity in objective ACC responses and poorer subjective spatial performance.

Significance

ACCs evoked by location changes were assessed in adults, children, and the elderly to explore the impact of aging and development on these differences.

Amplitude Modulation Perception and Cortical Evoked Potentials in Children With Listening Difficulties and Their Typically Developing Peers

PURPOSE

Amplitude modulations (AMs) are important for speech intelligibility, and deficits in speech intelligibility are a leading source of impairment in childhood listening difficulties (LiD). The present study aimed to explore the relationships between AM perception and speech-in-noise (SiN) comprehension in children and to determine whether deficits in AM processing contribute to childhood LiD. Evoked responses were used to parse the neural origins of AM processing.

METHOD

Forty-one children with LiD and 44 typically developing children, ages 8-16 years, participated in the study. Behavioral AM depth thresholds were measured at 4 and 40 Hz. SiN tasks included the Listening in Spatialized Noise-Sentences Test (LiSN-S) and a coordinate response measure (CRM)-based task. Evoked responses were obtained during an AM change detection task using alternations between 4 and 40 Hz, including the N1 of the acoustic change complex, auditory steady-state response (ASSR), P300, and a late positive response (late potential [LP]). Maturational effects were explored via age correlations.

RESULTS

Age correlated with 4-Hz AM thresholds, CRM separated talker scores, and N1 amplitude. Age-normed LiSN-S scores obtained without spatial or talker cues correlated with age-corrected 4-Hz AM thresholds and area under the LP curve. CRM separated talker scores correlated with AM thresholds and area under the LP curve. Most behavioral measures of AM perception correlated with the signal-to-noise ratio and phase coherence of the 40-Hz ASSR. AM change response time also correlated with area under the LP curve. Children with LiD exhibited deficits with respect to 4-Hz thresholds, AM change accuracy, and area under the LP curve.

CONCLUSIONS

The observed relationships between AM perception and SiN performance extend the evidence that modulation perception is important for understanding SiN in childhood. In line with this finding, children with LiD demonstrated poorer performance on some measures of AM perception, but their evoked responses implicated a primarily cognitive deficit.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.25009103.

Amplitude modulation perception and cortical evoked potentials in children with listening difficulties and their typically-developing peers

Purpose

Amplitude modulations (AM) are important for speech intelligibility, and deficits in speech intelligibility are a leading source of impairment in childhood listening difficulties (LiD). The present study aimed to explore the relationships between AM perception and speech-in-noise (SiN) comprehension in children and to determine whether deficits in AM processing contribute to childhood LiD. Evoked responses were used to parse the neural origin of AM processing.

Method

Forty-one children with LiD and forty-four typically-developing children, ages 8-16 y.o., participated in the study. Behavioral AM depth thresholds were measured at 4 and 40 Hz. SiN tasks included the LiSN-S and a Coordinate Response Measure (CRM)-based task. Evoked responses were obtained during an AM Change detection task using alternations between 4 and 40 Hz, including the N1 of the acoustic change complex, auditory steady-state response (ASSR), P300, and a late positive response (LP). Maturational effects were explored via age correlations.

Results

Age correlated with 4 Hz AM thresholds, CRM Separated Talker scores, and N1 amplitude. Age-normed LiSN-S scores obtained without spatial or talker cues correlated with age-corrected 4 Hz AM thresholds and area under the LP curve. CRM Separated Talker scores correlated with AM thresholds and area under the LP curve. Most behavioral measures of AM perception correlated with the SNR and phase coherence of the 40 Hz ASSR. AM Change RT also correlated with area under the LP curve. Children with LiD exhibited deficits with respect to 4 Hz thresholds, AM Change accuracy, and area under the LP curve.

Conclusions

The observed relationships between AM perception and SiN performance extend the evidence that modulation perception is important for understanding SiN in childhood. In line with this finding, children with LiD demonstrated poorer performance on some measures of AM perception, but their evoked responses implicated a primarily cognitive deficit.

The Impact of Patient Factors on Objective Cochlear Implant Verification Using Acoustic Cortical Auditory-Evoked Potentials

INTRODUCTION

Hearing loss is a major global public health issue that negatively impacts quality of life, communication, cognition, social participation, and mental health. The cochlear implant (CI) is the most efficacious treatment for severe-to-profound sensorineural hearing loss. However, variability in outcomes remains high among CI users. Our previous research demonstrated that the existing subjective methodology of CI programming does not consistently produce optimal stimulation for speech perception, thereby limiting the potential for CI users to derive the maximum device benefit to achieve their peak potential. We demonstrated the benefit of utilising the objective method of measuring auditory-evoked cortical responses to speech stimuli as a reliable tool to guide and verify CI programming and, in turn, significantly improve speech perception performance. The present study was designed to investigate the impact of patient- and device-specific factors on the application of acoustically-evoked cortical auditory-evoked potential (aCAEP) measures as an objective clinical tool to verify CI mapping in adult CI users with bilateral deafness (BD).

METHODS

aCAEP responses were elicited using binaural peripheral auditory stimulation for four speech tokens (/m/, /g/, /t/, and /s/) and recorded by HEARLab™ software in adult BD CI users. Participants were classified into groups according to subjective or objective CI mapping procedures to elicit present aCAEP responses to all four speech tokens. The impact of patient- and device-specific factors on the presence of aCAEP responses and speech perception was investigated between participant groups.

RESULTS

Participants were categorised based on the presence or absence of the P1-N1-P2 aCAEP response to speech tokens. Out of the total cohort of adult CI users (n = 132), 63 participants demonstrated present responses pre-optimisation, 37 participants exhibited present responses post-optimisation, and the remaining 32 participants either showed an absent response for at least one speech token post-optimisation or did not accept the optimised CI map adjustments. Overall, no significant correlation was shown between patient and device-specific factors and the presence of aCAEP responses or speech perception scores.

CONCLUSION

This study reinforces that aCAEP measures offer an objective, non-invasive approach to verify CI mapping, irrespective of patient or device factors. These findings further our understanding of the importance of personalised CI rehabilitation through CI mapping to minimise the degree of speech perception variation post-CI and allow all CI users to achieve maximum device benefit.

Acoustic change complex for assessing speech discrimination in normal-hearing and hearing-impaired infants

OBJECTIVE

This study examined (1) the utility of a clinical system to record acoustic change complex (ACC, an event-related potential recorded by electroencephalography) for assessing speech discrimination in infants, and (2) the relationship between ACC and functional performance in real life.

METHODS

Participants included 115 infants (43 normal-hearing, 72 hearing-impaired), aged 3-12 months. ACCs were recorded using [szs], [uiu], and a spectral rippled noise high-pass filtered at 2 kHz as stimuli. Assessments were conducted at age 3-6 months and at 7-12 months. Functional performance was evaluated using a parent-report questionnaire, and correlations with ACC were examined.

RESULTS

The rates of onset and ACC responses of normal-hearing infants were not significantly different from those of aided infants with mild or moderate hearing loss but were significantly higher than those with severe loss. On average, response rates measured at 3-6 months were not significantly different from those at 7-12 months. Higher rates of ACC responses were significantly associated with better functional performance.

CONCLUSIONS

ACCs demonstrated auditory capacity for discrimination in infants by 3-6 months. This capacity was positively related to real-life functional performance.

SIGNIFICANCE

ACCs can be used to evaluate the effectiveness of amplification and monitor development in aided hearing-impaired infants.

Functional Hearing Difficulties in Veterans: Retrospective Chart Review of Auditory Processing Assessments in the VA Health Care System

PURPOSE

Approximately 23 million Americans might have functional hearing difficulties (FHDs) that are not well explained by their audiometric thresholds. Clinical management of patients with FHDs is the subject of considerable debate, with few evidence-based guidelines to direct patient care. A better understanding of the characteristics of patients who seek help for FHDs, as well as current audiological management practices, is needed to direct research efforts to the areas greatest opportunity for advancement of clinical care.

METHOD

A retrospective chart review was conducted examining the medical records of a random sample of 100 Veterans who underwent auditory processing assessments across the VA Health Care System between 2008 and 2020.

RESULTS

Patients were young to middle-age, often with previous traumatic brain injury or blast exposure. Mental health, sleep, and pain disorders were common. No consistent relationships emerged between specific patient factors and domains of auditory processing deficits. Low-gain hearing aids were provided to 35 patients, 69% of whom continued wearing their hearing aids for at least 2 years.

CONCLUSION

Future research should address the potential overlap in symptoms and treatment for comorbid health conditions and FHDs, as well as the conditions underlying successful hearing aid use in this patient population.

The Acoustic Change Complex Compared to Hearing Performance in Unilaterally and Bilaterally Deaf Cochlear Implant Users

OBJECTIVES

Clinical measures evaluating hearing performance in cochlear implant (CI) users depend on attention and linguistic skills, which limits the evaluation of auditory perception in some patients. The acoustic change complex (ACC), a cortical auditory evoked potential to a sound change, might yield useful objective measures to assess hearing performance and could provide insight in cortical auditory processing. The aim of this study is to examine the ACC in response to frequency changes as an objective measure for hearing performance in CI users.

DESIGN

Thirteen bilaterally deaf and six single-sided deaf subjects were included, all having used a unilateral CI for at least 1 year. Speech perception was tested with a consonant-vowel-consonant test (+10 dB signal-to-noise ratio) and a digits-in-noise test. Frequency discrimination thresholds were measured at two reference frequencies, using a 3-interval, 2-alternative forced-choice, adaptive staircase procedure. The two reference frequencies were selected using each participant's frequency allocation table and were centered in the frequency band of an electrode that included 500 or 2000 Hz, corresponding to the apical electrode or the middle electrode, respectively. The ACC was evoked with pure tones of the same two reference frequencies with varying frequency increases: within the frequency band of the middle or the apical electrode (+0.25 electrode step), and steps to the center frequency of the first (+1), second (+2), and third (+3) adjacent electrodes.

RESULTS

Reproducible ACCs were recorded in 17 out of 19 subjects. Most successful recordings were obtained with the largest frequency change (+3 electrode step). Larger frequency changes resulted in shorter N1 latencies and larger N1-P2 amplitudes. In both unilaterally and bilaterally deaf subjects, the N1 latency and N1-P2 amplitude of the CI ears correlated to speech perception as well as frequency discrimination, that is, short latencies and large amplitudes were indicative of better speech perception and better frequency discrimination. No significant differences in ACC latencies or amplitudes were found between the CI ears of the unilaterally and bilaterally deaf subjects, but the CI ears of the unilaterally deaf subjects showed substantially longer latencies and smaller amplitudes than their contralateral normal-hearing ears.

CONCLUSIONS

The ACC latency and amplitude evoked by tone frequency changes correlate well to frequency discrimination and speech perception capabilities of CI users. For patients unable to reliably perform behavioral tasks, the ACC could be of added value in assessing hearing performance.

Intracorporeal Cortical Telemetry as a Step to Automatic Closed-Loop EEG-Based CI Fitting: A Proof of Concept

Electrically evoked auditory potentials have been used to predict auditory thresholds in patients with a cochlear implant (CI). However, with exception of electrically evoked compound action potentials (eCAP), conventional extracorporeal EEG recording devices are still needed. Until now, built-in (intracorporeal) back-telemetry options are limited to eCAPs. Intracorporeal recording of auditory responses beyond the cochlea is still lacking. This study describes the feasibility of obtaining longer latency cortical responses by concatenating interleaved short recording time windows used for eCAP recordings. Extracochlear reference electrodes were dedicated to record cortical responses, while intracochlear electrodes were used for stimulation, enabling intracorporeal telemetry (i.e., without an EEG device) to assess higher cortical processing in CI recipients. Simultaneous extra- and intra-corporeal recordings showed that it is feasible to obtain intracorporeal slow vertex potentials with a CI similar to those obtained by conventional extracorporeal EEG recordings. Our data demonstrate a proof of concept of closed-loop intracorporeal auditory cortical response telemetry (ICT) with a cochlear implant device. This research breaks new ground for next generation CI devices to assess higher cortical neural processing based on acute or continuous EEG telemetry to enable individualized automatic and/or adaptive CI fitting with only a CI.

Cortical Auditory Evoked Potentials in Cognitive Impairment and Their Relevance to Hearing Loss: A Systematic Review Highlighting the Evidence Gap

Background: Alzheimer’s disease (AD) is the most prevalent cause of dementia which affects a growing number of people worldwide. Early identification of people at risk to develop AD should be prioritized. Hearing loss is considered an independent potentially modifiable risk factor for accelerated cognitive decline and dementia in older adults. The main outcome of interest of this review is the alteration of Cortical Auditory Evoked Potential (CAEP) morphology in an AD or mild cognitive impairment (MCI) population with and without hearing loss.

Methods: Two investigators independently and systematically searched publications regarding auditory processing on a cortical level in people with cognitive impairment (MCI or AD) with and without hearing loss. Only articles which mentioned at least one auditory elicited event-related potential (ERP) component and that were written in English or Dutch were included. Animal studies were excluded. No restrictions were imposed regarding publication date. The reference list of potential sources were screened for additional articles.

Results: This systematic review found no eligible articles that met all inclusion criteria. Therefore, no results were included, resulting in an empty systematic review.

Conclusion: In general, dysfunction – being either from cognitive or auditory origin – reduces CAEP amplitudes and prolongs latencies. Therefore, CAEPs may be a prognostic indicator in the early stages of cognitive decline. However, it remains unclear which CAEP component alteration is due to cognitive impairment, and which is due to hearing loss (or even both). In addition, vestibular dysfunction – associated with hearing loss, cognitive impairment and AD – may also alter CAEP responses. Further CAEP studies are warranted, integrating cognitive, hearing, and vestibular evaluations.

The Acoustic Change Complex in Response to Frequency Changes and Its Correlation to Cochlear Implant Speech Outcomes

One of the biggest challenges that face cochlear implant (CI) users is the highly variable hearing outcomes of implantation across patients. Since speech perception requires the detection of various dynamic changes in acoustic features (e.g., frequency, intensity, timing) in speech sounds, it is critical to examine the ability to detect the within-stimulus acoustic changes in CI users. The primary objective of this study was to examine the auditory event-related potential (ERP) evoked by the within-stimulus frequency changes (F-changes), one type of the acoustic change complex (ACC), in adult CI users, and its correlation to speech outcomes. Twenty-one adult CI users (29 individual CI ears) were tested with psychoacoustic frequency change detection tasks, speech tests including the Consonant-Nucleus-Consonant (CNC) word recognition, Arizona Biomedical Sentence Recognition in quiet and noise (AzBio-Q and AzBio-N), and the Digit-in-Noise (DIN) tests, and electroencephalographic (EEG) recordings. The stimuli for the psychoacoustic tests and EEG recordings were pure tones at three different base frequencies (0.25, 1, and 4 kHz) that contained a F-change at the midpoint of the tone. Results showed that the frequency change detection threshold (FCDT), ACC N1' latency, and P2' latency did not differ across frequencies (p > 0.05). ACC N1'-P2 amplitude was significantly larger for 0.25 kHz than for other base frequencies (p < 0.05). The mean N1' latency across three base frequencies was negatively correlated with CNC word recognition (r = -0.40, p < 0.05) and CNC phoneme (r = -0.40, p < 0.05), and positively correlated with mean FCDT (r = 0.46, p < 0.05). The P2' latency was positively correlated with DIN (r = 0.47, p < 0.05) and mean FCDT (r = 0.47, p < 0.05). There was no statistically significant correlation between N1'-P2' amplitude and speech outcomes (all ps > 0.05). Results of this study indicated that variability in CI speech outcomes assessed with the CNC, AzBio-Q, and DIN tests can be partially explained (approximately 16-21%) by the variability of cortical sensory encoding of F-changes reflected by the ACC.

Relationship between objective measures of hearing discrimination elicited by non-linguistic stimuli and speech perception in adults

Some people using hearing aids have difficulty discriminating between sounds even though the sounds are audible. As such, cochlear implants may provide greater benefits for speech perception. One method to identify people with auditory discrimination deficits is to measure discrimination thresholds using spectral ripple noise (SRN). Previous studies have shown that behavioral discrimination of SRN was associated with speech perception, and behavioral discrimination was also related to cortical responses to acoustic change or ACCs. We hypothesized that cortical ACCs could be directly related to speech perception. In this study, we investigated the relationship between subjective speech perception and objective ACC responses measured using SRNs. We tested 13 normal-hearing and 10 hearing-impaired adults using hearing aids. Our results showed that behavioral SRN discrimination was correlated with speech perception in quiet and in noise. Furthermore, cortical ACC responses to phase changes in the SRN were significantly correlated with speech perception. Audibility was a major predictor of discrimination and speech perception, but direct measures of auditory discrimination could contribute information about a listener’s sensitivity to acoustic cues that underpin speech perception. The findings lend support for potential application of measuring ACC responses to SRNs for identifying people who may benefit from cochlear implants.

Extracting human cortical responses to sound onsets and acoustic feature changes in real music, and their relation to event rate

Evoked cortical responses (ERs) have mainly been studied in controlled experiments using simplified stimuli. Though, an outstanding question is how the human cortex responds to the complex stimuli encountered in realistic situations. Few electroencephalography (EEG) studies have used Music Information Retrieval (MIR) tools to extract cortical P1/N1/P2 to acoustical changes in real music. However, less than ten events per music piece could be detected leading to ERs due to limitations in automatic detection of sound onsets. Also, the factors influencing a successful extraction of the ERs have not been identified. Finally, previous studies did not localize the sources of the cortical generators. This study is based on an EEG/MEG dataset from 48 healthy normal hearing participants listening to three real music pieces. Acoustic features were computed from the audio signal of the music with the MIR Toolbox. To overcome limits in automatic methods, sound onsets were also manually detected. The chance of obtaining detectable ERs based on ten randomly picked onset points was less than 1:10,000. For the first time, we show that naturalistic P1/N1/P2 ERs can be reliably measured across 100 manually identified sound onsets, substantially improving the signal-to-noise level compared to <10 trials. More ERs were measurable in musical sections with slow event rates (0.2 Hz-2.5 Hz) than with fast event rates (>2.5 Hz). Furthermore, during monophonic sections of the music only P1/P2 were measurable, and during polyphonic sections only N1. Finally, MEG source analysis revealed that naturalistic P2 is located in core areas of the auditory cortex.

Cortical potentials evoked by tone frequency changes compared to frequency discrimination and speech perception: Thresholds in normal-hearing and hearing-impaired subjects

Frequency discrimination ability varies within the normal hearing population, partially explained by factors such as musical training and age, and it deteriorates with hearing loss. Frequency discrimination, while essential for several auditory tasks, is not routinely measured in clinical setting. This study investigates cortical auditory evoked potentials in response to frequency changes, known as acoustic change complexes (ACCs), and explores their value as a clinically applicable objective measurement of frequency discrimination. In 12 normal-hearing and 13 age-matched hearing-impaired subjects, ACC thresholds were recorded at 4 base frequencies (0.5, 1, 2, 4 kHz) and compared to psychophysically assessed frequency discrimination thresholds. ACC thresholds had a moderate to strong correlation to psychophysical frequency discrimination thresholds. In addition, ACC thresholds increased with hearing loss and higher ACC thresholds were associated with poorer speech perception in noise. The ACC threshold in response to a frequency change therefore holds promise as an objective clinical measurement in hearing impairment, indicative of frequency discrimination ability and related to speech perception. However, recordings as conducted in the current study are relatively time consuming. The current clinical application would be most relevant in cases where behavioral testing is unreliable.

Coding of consonant-vowel transition in children with central auditory processing disorder: an electrophysiological study

INTRODUCTION

Acoustic change complex (ACC) is an important tool to investigate the encoding of the acoustic property of speech signals in various populations. However, there is a limited number of research papers that have explored the usefulness of ACC as a tool to study the neural encoding of consonant-vowel (CV) transition in children with central auditory processing disorder (CAPD). Thus, the present study aims to investigate the utility of ACC as an objective tool to study the neural representation of consonant-vowel (CV) transition in children with CAPD.

METHODS

Twenty children diagnosed having CAPD and 20 normal counterparts in the age range of 8-14 years were the participants. The ACC was acquired using naturally produced CV syllable /sa/ with a duration of 380 ms.

RESULTS

Latency of N1' and P2' was found to be prolonged in children with CAPD compared to normal counterparts, whereas the amplitude of N1' and P2' did not show any significant difference. Scalp topography showed significantly different activation patterns for children with and without CAPD.

CONCLUSION

Prolonged latencies of ACC indicated poor encoding of CV transition in children with CAPD. The difference in scalp topography might be because of the involvement of additional brain areas for the neural discrimination task in children with CAPD.

Effects of speech transmission quality on sensory processing indicated by the cortical auditory evoked potential

OBJECTIVE

Degradations of transmitted speech have been shown to affect perceptual and cognitive processing in human listeners, as indicated by the P3 component of the event-related brain potential (ERP). However, research suggests that previously observed P3 modulations might actually be traced back to earlier neural modulations in the time range of the P1-N1-P2 complex of the cortical auditory evoked potential (CAEP). This study investigates whether auditory sensory processing, as reflected by the P1-N1-P2 complex, is already systematically altered by speech quality degradations.

APPROACH

Electrophysiological data from two studies were analyzed to examine effects of speech transmission quality (high-quality, noisy, bandpass-filtered) for spoken words on amplitude and latency parameters of individual P1, N1 and P2 components.

MAIN RESULTS

In the resultant ERP waveforms, an initial P1-N1-P2 manifested at stimulus onset, while a second N1-P2 occurred within the ongoing stimulus. Bandpass-filtered versus high-quality word stimuli evoked a faster and larger initial N1 as well as a reduced initial P2, hence exhibiting effects as early as the sensory stage of auditory information processing.

SIGNIFICANCE

The results corroborate the existence of systematic quality-related modulations in the initial N1-P2, which may potentially have carried over into P3 modulations demonstrated by previous studies. In future psychophysiological speech quality assessments, rigorous control procedures are needed to ensure the validity of P3-based indication of speech transmission quality. An alternative CAEP-based assessment approach is discussed, which promises to be more efficient and less constrained than the established approach based on P3.

The Effect of Side of Implantation on the Cortical Processing of Frequency Changes in Adult Cochlear Implant Users

Cochlear implants (CI) are widely used in children and adults to restore hearing function. However, CI outcomes are vary widely. The affected factors have not been well understood. It is well known that the right and left hemispheres play different roles in auditory perception in adult normal hearing listeners. It is unknown how the implantation side may affect the outcomes of CIs. In this study, the effect of the implantation side on how the brain processes frequency changes within a sound was examined in 12 right-handed adult CI users. The outcomes of CIs were assessed with behaviorally measured frequency change detection threshold (FCDT), which has been reported to significantly affect CI speech performance. The brain activation and regions were also examined using acoustic change complex (ACC, a type of cortical potential evoked by acoustic changes within a stimulus), on which the waveform analysis and the standardized low-resolution brain electromagnetic tomography (sLORETA) were performed. CI users showed activation in the temporal lobe and non-temporal areas, such as the frontal lobe. Right-ear CIs could more efficiently activate the contralateral hemisphere compared to left-ear CIs. For right-ear CIs, the increased activation in the contralateral temporal lobe together with the decreased activation in the contralateral frontal lobe was correlated with good performance of frequency change detection (lower FCDTs). Such a trend was not found in left-ear CIs. These results suggest that the implantation side may significantly affect neuroplasticity patterns in adults.

A Preliminary Study of the Effects of Attentive Music Listening on Cochlear Implant Users' Speech Perception, Quality of Life, and Behavioral and Objective Measures of Frequency Change Detection

Introduction

Most cochlear implant (CI) users have difficulty in listening tasks that rely strongly on perception of frequency changes (e.g., speech perception in noise, musical melody perception, etc.). Some previous studies using behavioral or subjective assessments have shown that short-term music training can benefit CI users’ perception of music and speech. Electroencephalographic (EEG) recordings may reveal the neural basis for music training benefits in CI users.

Objective

To examine the effects of short-term music training on CI hearing outcomes using a comprehensive test battery of subjective evaluation, behavioral tests, and EEG measures.

Design

Twelve adult CI users were recruited for a home-based music training program that focused on attentive listening to music genres and materials that have an emphasis on melody. The participants used a music streaming program (i.e., Pandora) downloaded onto personal electronic devices for training. The participants attentively listened to music through a direct audio cable or through Bluetooth streaming. The training schedule was 40 min/session/day, 5 days/week, for either 4 or 8 weeks. The pre-training and post-training tests included: hearing thresholds, Speech, Spatial and Qualities of Hearing Scale (SSQ12) questionnaire, psychoacoustic tests of frequency change detection threshold (FCDT), speech recognition tests (CNC words, AzBio sentences, and QuickSIN), and EEG responses to tones that contained different magnitudes of frequency changes.

Results

All participants except one finished the 4- or 8-week training, resulting in a dropout rate of 8.33%. Eleven participants performed all tests except for two who did not participate in EEG tests. Results showed a significant improvement in the FCDTs as well as performance on CNC and QuickSIN after training (p < 0.05), but no significant improvement in SSQ scores (p > 0.05). Results of the EEG tests showed larger post-training cortical auditory evoked potentials (CAEPs) in seven of the nine participants, suggesting a better cortical processing of both stimulus onset and within-stimulus frequency changes.

Conclusion

These preliminary data suggest that extensive, focused music listening can improve frequency perception and speech perception in CI users. Further studies that include a larger sample size and control groups are warranted to determine the efficacy of short-term music training in 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.

Cortical Auditory Evoked Potentials in Response to Frequency Changes with Varied Magnitude, Rate, and Direction

Recent literature on cortical auditory evoked potentials has focused on correlations with hearing performance with the aim to develop an objective clinical tool. However, cortical responses depend on the type of stimulus and choice of stimulus parameters. This study investigates cortical auditory evoked potentials to sound changes, so-called acoustic change complexes (ACC), and the effects of varying three stimulus parameters. In twelve normal-hearing subjects, ACC waveforms were evoked by presenting frequency changes with varying magnitude, rate, and direction. The N1 amplitude and latency were strongly affected by magnitude, which is known from the literature. Importantly, both of these N1 variables were also significantly affected by both rate and direction of the frequency change. Larger and earlier N1 peaks were evoked by increasing the magnitude and rate of the frequency change and with downward rather than upward direction of the frequency change. The P2 amplitude increased with magnitude and depended, to a lesser extent, on rate of the frequency change while direction had no effect on this peak. The N1–P2 interval was not affected by any of the stimulus parameters. In conclusion, the ACC is most strongly affected by magnitude and also substantially by rate and direction of the change. These stimulus dependencies should be considered in choosing stimuli for ACCs as objective clinical measure of hearing performance.

The impact of hearing aids and age-related hearing loss on auditory plasticity across three months - An electrical neuroimaging study

The present study investigates behavioral and electrophysiological auditory and cognitive-related plasticity in three groups of healthy older adults (60-77 years). Group 1 was moderately hearing-impaired, experienced hearing aid users, and fitted with new hearing aids using non-linear frequency compression (NLFC on); Group 2, also moderately hearing-impaired, used the same type of hearing aids but NLFC was switched off during the entire period of study duration (NLFC off); Group 3 represented individuals with age-appropriate hearing (NHO) as controls, who were not different in IQ, gender, or age from Group 1 and 2. At five measurement time points (M1-M5) across three months, a series of active oddball tasks were administered while EEG was recorded. The stimuli comprised syllables consisting of naturally high-pitched fricatives (/sh/, /s/, and /f/), which are hard to distinguish for individuals with presbycusis. By applying a data-driven microstate approach to obtain global field power (GFP) as a measure of processing effort, the modulations of perceptual (P50, N1, P2) and cognitive-related (N2b, P3b) auditory evoked potentials were calculated and subsequently related to behavioral changes (accuracy and reaction time) across time. All groups improved their performance across time, but NHO showed consistently higher accuracy and faster reaction times than the hearing-impaired groups, especially under difficult conditions. Electrophysiological results complemented this finding by demonstrating longer latencies in the P50 and the N1 peak in hearing aid users. Furthermore, the GFP of cognitive-related evoked potentials decreased from M1 to M2 in the NHO group, while a comparable decrease in the hearing-impaired group was only evident at M5. After twelve weeks of hearing aid use of eight hours each day, we found a significantly lower GFP in the P3b of the group with NLFC on as compared to the group with NLFC off. These findings suggest higher processing effort, as evidenced by higher GFP, in hearing-impaired individuals when compared to those with normal hearing, although the hearing-impaired show a decrease of processing effort after repeated stimulus exposure. In addition, our findings indicate that the acclimatization to a new hearing aid algorithm may take several weeks.

Musicians Are Better than Non-musicians in Frequency Change Detection: Behavioral and Electrophysiological Evidence

Objective: The objectives of this study were: (1) to determine if musicians have a better ability to detect frequency changes under quiet and noisy conditions; (2) to use the acoustic change complex (ACC), a type of electroencephalographic (EEG) response, to understand the neural substrates of musician vs. non-musician difference in frequency change detection abilities.

Methods: Twenty-four young normal hearing listeners (12 musicians and 12 non-musicians) participated. All participants underwent psychoacoustic frequency detection tests with three types of stimuli: tones (base frequency at 160 Hz) containing frequency changes (Stim 1), tones containing frequency changes masked by low-level noise (Stim 2), and tones containing frequency changes masked by high-level noise (Stim 3). The EEG data were recorded using tones (base frequency at 160 and 1200 Hz, respectively) containing different magnitudes of frequency changes (0, 5, and 50% changes, respectively). The late-latency evoked potential evoked by the onset of the tones (onset LAEP or N1-P2 complex) and that evoked by the frequency change contained in the tone (the acoustic change complex or ACC or N1′-P2′ complex) were analyzed.

Results: Musicians significantly outperformed non-musicians in all stimulus conditions. The ACC and onset LAEP showed similarities and differences. Increasing the magnitude of frequency change resulted in increased ACC amplitudes. ACC measures were found to be significantly different between musicians (larger P2′ amplitude) and non-musicians for the base frequency of 160 Hz but not 1200 Hz. Although the peak amplitude in the onset LAEP appeared to be larger and latency shorter in musicians than in non-musicians, the difference did not reach statistical significance. The amplitude of the onset LAEP is significantly correlated with that of the ACC for the base frequency of 160 Hz.

Conclusion: The present study demonstrated that musicians do perform better than non-musicians in detecting frequency changes in quiet and noisy conditions. The ACC and onset LAEP may involve different but overlapping neural mechanisms.

Significance: This is the first study using the ACC to examine music-training effects. The ACC measures provide an objective tool for documenting musical training effects on frequency detection.