Auditory event-related potentials in the assessment of auditory processing disorders: a pilot study

Relationship Between Temporal Pattern Perception Test and Mismatch Negativity in Children With Auditory Processing Disorder and Dyslexia

BACKGROUND AND OBJECTIVES

Mismatch negativity (MMN) is an objective test for assessing auditory function. The central auditory nervous system processes different stimuli in various ways. This can be assessed using MMN elicited with different stimuli in an "oddball" paradigm. This study evaluated temporal ordering skills using MMN with different durations of stimuli. This study aimed to determine the correlation between the results of the behavioral duration pattern test (DPT) with MMN in typically developing children versus children with dyslexia and auditory processing disorder (APD). Subjects and.

METHODS

Two groups of children participated in the study. The experimental group included 16 children with APD and dyslexia who had scored below the age-matched scores in the DPT. The control group consisted of 16 typically developing children with age-matched scores in the DPT. MMN was elicited using the same stimuli (250 ms and 500 ms) as that of the DPT in both groups. MMN latency, MMN amplitude, and area under the curve were measured in both groups.

RESULTS

Compared to the control group, children with APD and dyslexia showed increased MMN latency, reduced amplitude, and decreased area under the curve. There was a low correlation (r= -0.293, p<0.05) between MMN latency and DPT scores. The correlation between MMN amplitude and DPT scores was moderate (0.472, p<0.001). Furthermore, a strong correlation (0.536, p<0.001) between area under the curve and DPT scores was demonstrated.

CONCLUSIONS

MMN amplitude and MMN area under the curve could serve as valid indicators during assessment of temporal ordering in children with APD and dyslexia.

Subcortical and Cortical Electrophysiological Measures in Children With Speech-in-Noise Deficits Associated With Auditory Processing Disorders

PURPOSE

The aim of this study was to analyze the subcortical and cortical auditory evoked potentials for speech stimuli in children with speech-in-noise (SIN) deficits associated with auditory processing disorder (APD) without any reading or language deficits.

METHOD

The study included 20 children in the age range of 9-13 years. Ten children were recruited to the APD group; they had below-normal scores on the speech-perception-in-noise test and were diagnosed as having APD. The remaining 10 were typically developing (TD) children and were recruited to the TD group. Speech-evoked subcortical (brainstem) and cortical (auditory late latency) responses were recorded and compared across both groups.

RESULTS

The results showed a statistically significant reduction in the amplitudes of the subcortical potentials (both for stimulus in quiet and in noise) and the magnitudes of the spectral components (fundamental frequency and the second formant) in children with SIN deficits in the APD group compared to the TD group. In addition, the APD group displayed enhanced amplitudes of the cortical potentials compared to the TD group.

CONCLUSION

Children with SIN deficits associated with APD exhibited impaired coding/processing of the auditory information at the level of the brainstem and the auditory cortex.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.21357735.

Long Latency Auditory Evoked Responses in the Identification of Children With Central Auditory Processing Disorders: A Scoping Review

PURPOSE

The long latency auditory evoked responses (LLAERs), originating in the auditory cortex, are often considered a biomarker for maturity in the central auditory system and may therefore be useful in the evaluation of children with central auditory processing disorder (CAPD). However, the characteristics of the LLAERs elicited in this population have not been widely described, and clinical applications remain unclear. The goal of this scoping review was to investigate if LLAERs can be used to identify children with CAPD.

METHOD

A systematic search strategy was used to identify studies that analyzed the latencies and amplitudes of P1, N1, P2, and N2 waveforms of the LLAERs. The online databases, including Embase, Web of Science, MEDLINE, PubMed, ProQuest, and CINAHL, as well as the gray literature were searched for papers published in English and French between January 1980 and May 2021.

RESULTS

Seventeen papers met the eligibility criteria and were included in the study. Four papers had pre- and posttraining study designs, and the remaining studies were cross-sectional. Several studies reported significant differences in LLAERs between children with CAPD and their normal-hearing peers, and the results tended toward longer latencies and smaller amplitudes regardless of LLAER waves considered. N1 and/or N2 results were most likely to reveal significant differences between children with CAPD and normal-hearing controls and could potentially be considered a biomarker for CAPD.

CONCLUSIONS

It seems that LLAER assessments, especially waves N1 and N2, might assist in better identification of CAPD children. However, considering heterogeneity in the methodology among the included studies, the results should be interpreted with caution. Well-designed studies on children with confirmed CAPD using standard diagnostic and assessment protocols are suggested.

Cortical auditory evoked potentials with different acoustic stimuli: Evidence of differences and similarities in coding in auditory processing disorders

OBJECTIVES

The use of cortical auditory evoked potentials allows for the study of the processing of acoustic signals at the cortical level, an important step in the diagnostic evaluation process, and for the monitoring of the therapeutic process associated with auditory processing disorders (APD). The differences and similarities in the acoustic coding between different types of stimuli in the context of APD remain unknown to this date.

METHODS

A total of 37 children aged between 7 and 11 years, with and without APDs (identified based on verbal and non-verbal tests), all with a suitable intelligence quotient with respect to their chronological age, were assessed. Components P1 and N1 were studied using verbal and non-verbal stimuli.

RESULTS

The comparison between stimuli in each group revealed that the control group had higher latency and amplitude values for speech stimuli, except for the P1 amplitude, while the group with APDs had different results with respect to the amplitudes of P1 and N1, yielding higher values for speech sounds. The differences between the groups varied according to the type of stimulus: the difference was in amplitude for the verbal stimulus and latency for the non-verbal stimulus.

CONCLUSION

The records of components P1 and N1 revealed that the children with APDs performed the coding underlying the detection and identification of acoustic signals, whether verbal and non-verbal, according to a different pattern than the children in the control group.

Speech Perception in Noise Predicts Oral Narrative Comprehension in Children With Developmental Language Disorder

We examined the relative contribution of auditory processing abilities (tone perception and speech perception in noise) after controlling for short-term memory capacity and vocabulary, to narrative language comprehension in children with developmental language disorder. Two hundred and sixteen children with developmental language disorder, ages 6 to 9 years (Mean = 7; 6), were administered multiple measures. The dependent variable was children's score on the narrative comprehension scale of the Test of Narrative Language. Predictors were auditory processing abilities, phonological short-term memory capacity, and language (vocabulary) factors, with age, speech perception in quiet, and non-verbal IQ as covariates. Results showed that narrative comprehension was positively correlated with the majority of the predictors. Regression analysis suggested that speech perception in noise contributed uniquely to narrative comprehension in children with developmental language disorder, over and above all other predictors; however, tone perception tasks failed to explain unique variance. The relative importance of speech perception in noise over tone-perception measures for language comprehension reinforces the need for the assessment and management of listening in noise deficits and makes a compelling case for the functional implications of complex listening situations for children with developmental language disorder.

Electrophysiological Screening for Children With Suspected Auditory Processing Disorder: A Systematic Review

Objective: This research aimed to provide evidence for the early identification and intervention of children at risk for auditory processing disorder (APD). Electrophysiological studies on children with suspected APDs were systematically reviewed to understand the different electrophysiological characteristics of children with suspected APDs. Methods: Computerized databases such as PubMed, Cochrane, MEDLINE, Web of Science, and EMBASE were searched for retrieval of articles since the establishment of the database through May 18, 2020. Cohort, case-control, and cross-sectional studies that evaluated the literature for the electrophysiological assessment of children with suspected APD were independently reviewed by two researchers for literature screening, literature quality assessment, and data extraction. The Newcastle-Ottawa Scale and 11 entries recommended by the Agency for Healthcare Research and Quality were used to evaluate the quality of the literature. Results: In accordance with the inclusion criteria, 14 articles were included. These articles involved 7 electrophysiological testing techniques: click-evoked auditory brainstem responses, frequency-following responses, the binaural interaction component of the auditory brainstem responses, the middle-latency response, cortical auditory evoked potential, mismatch negativity, and P300. The literature quality was considered moderate. Conclusions: Auditory electrophysiological testing can be used for the characteristic identification of children with suspected APD; however, the value of various electrophysiological testing methods for screening children with suspected APD requires further study.

Mismatch Negativity in children with Phonological Disorders

OBJECTIVE

to characterize the latency, amplitude and area variables of the Mismatch Negativity (MMN) elicited with verbal stimuli in children with PD, in addition to assessing whether this potential can be a useful tool in capturing auditory perception and discrimination deficits related to this disorder.

METHODS

MMN was recorded using a combination of speech contrast consisting of acoustic syllables [da vs ta], as the standard and deviant stimuli, in 34 children aged between 5 and 8 years. 14 children of the sample were already diagnosed with Phonological Disorder (PD) while 19 were characterized with typical development.

RESULTS

No statistically significant differences were observed for the MMN responses recorded between children with PD and their typically developed peers.

CONCLUSION

The results suggest that the MMN may not be the most suitable procedure to assess auditory perception and discrimination deficits that could potentially be related to PD.

Feasibility of objective assessment of difference limen for intensity using acoustic change complex in children with central auditory processing disorder

INTRODUCTION

Acoustic change complex (ACC) shows brain's ability to discriminate between acoustic features in an ongoing stimulus. It is this nature of ACC that has generated interest in studying the usefulness of ACC as an objective tool for evaluating difference limens for various stimulus parameters. The present study therefore aimed at investigating the utility of ACC as an objective measure of difference limen for intensity (DLI) in normal hearing children with and without (C)APD.

METHODS

Fifteen children with (C)APD and 15 normal hearing children in whom (C)APD was ruled out (comparison group) in the age range of 8-12 years underwent ACC for 6 intensity differences (+1, +3, +4, +5, +10 & +20 dB) and a standard stimulus using a 1000 Hz stimulus.

RESULTS

Behavioral DLI (DLI_b) as well as DLI found using ACC (DLI_o) were both significantly larger in children with (C)APD than the comparison group (p < 0.05). Further, there was a significantly strong positive correlation between DLI_b and DLI_o (p < 0.001].

CONCLUSION

Outcome of the study provides evidence for the clinical use of ACC as an objective tool for examining DLI in children with (C)APD.

Electrophysiological characteristics in children with listening difficulties, with or without auditory processing disorder

Objective: To determine if the auditory middle latency responses (AMLR), auditory late latency response (ALLR) and auditory P300 were sensitive to auditory processing disorder (APD) and listening difficulties in children, and further to elucidate mechanisms regarding level of neurobiological problems in the central auditory nervous system. Design: Three-group, repeated measure design. Study sample: Forty-six children aged 8-14 years were divided into three groups: children with reported listening difficulties fulfilling APD diagnostic criteria, children with reported listening difficulties not fulfilling APD diagnostic criteria and normally hearing children. Results: AMLR Na latency and P300 latency and amplitude were sensitive to listening difficulties. No other auditory evoked potential (AEP) measures were sensitive to listening difficulties, and no AEP measures were sensitive to APD only. Moderate correlations were observed between P300 latency and amplitude and the behavioural AP measures of competing words, frequency patterns, duration patterns and dichotic digits. Conclusions: Impaired thalamo-cortical (bottom up) and neurocognitive function (top-down) may contribute to difficulties discriminating speech and non-speech sounds. Cognitive processes involved in conscious recognition, attention and discrimination of the acoustic characteristics of the stimuli could contribute to listening difficulties in general, and to APD in particular.

Auditory event-related potentials and function of the medial olivocochlear efferent system in children with auditory processing disorders

OBJECTIVE

The objectives were to investigate the function of central auditory pathways and of the medial efferent olivocochlear system (MOCS).

DESIGN

Event-related potentials (ERP) were recorded following the delivery of the stimulus /da/ in quiet and in ipsilateral, contralateral, and binaural noise conditions and correlated to the results of the auditory processing disorders (APD) diagnostic test battery. MOCS function was investigated by adding ipsilateral, contralateral, and binaural noise to transient evoked otoacoustic emission recordings. Auditory brainstem responses and pure tone audiogram were also evaluated.

STUDY SAMPLE

Nineteen children (7 to 12 years old) with APD were compared with 24 age-matched controls.

RESULTS

Otoacoustic emissions and ABR characteristics did not differ between groups, whereas ERP latencies were significantly longer and of higher amplitudes in APD children than in controls, in both quiet and noise conditions. The MOCS suppression was higher in APD children.

CONCLUSIONS

Findings indicate that children with APD present with neural deficiencies in both challenging and nonchallenging environments with an increase in the timing of several central auditory processes correlated to their behavioural performances. Meanwhile, their modulation of the auditory periphery under noisy conditions differs from control children with higher suppression.

Abnormal Resting-State Quantitative Electroencephalogram in Children With Central Auditory Processing Disorder: A Pilot Study

In this study, we showed an abnormal resting-state quantitative electroencephalogram (QEEG) pattern in children with central auditory processing disorder (CAPD). Twenty-seven children (16 male, 11 female; mean age = 10.7 years) with CAPD and no symptoms of other developmental disorders, as well as 23 age- and sex-matched, typically developing children (TDC, 11 male, 13 female; mean age = 11.8 years) underwent examination of central auditory processes (CAPs) and QEEG evaluation consisting of two randomly presented blocks of “Eyes Open” (EO) or “Eyes Closed” (EC) recordings. Significant correlations between individual frequency band powers and CAP tests performance were found. The QEEG studies revealed that in CAPD relative to TDC there was no effect of decreased delta absolute power (1.5–4 Hz) in EO compared to the EC condition. Furthermore, children with CAPD showed increased theta power (4–8 Hz) in the frontal area, a tendency toward elevated theta power in EO block, and reduced low-frequency beta power (12–15 Hz) in the bilateral occipital and the left temporo-occipital regions for both EO and EC conditions. Decreased middle-frequency beta power (15–18 Hz) in children with CAPD was observed only in the EC block. The findings of the present study suggest that QEEG could be an adequate tool to discriminate children with CAPD from normally developing children. Correlation analysis shows relationship between the individual EEG resting frequency bands and the CAPs. Increased power of slow waves and decreased power of fast rhythms could indicate abnormal functioning (hypoarousal of the cortex and/or an immaturity) of brain areas not specialized in auditory information processing.

Abnormalities in cortical auditory responses in children with central auditory processing disorder

The main objective of the present study was to identify markers of neural deficits in children with central auditory processing disorder (CAPD) by measuring latency and amplitude of the auditory cortical responses and mismatch negativity (MMN) responses. Passive oddball paradigms were used with nonverbal and verbal stimuli to record cortical auditory-evoked potentials and MMN. Twenty-three children aged 9-12 participated in the study: 10 with normal hearing acuity as well as CAPD and 13 with normal hearing without CAPD. No significant group differences were observed for P1 latency and amplitude. Children with CAPD were observed to have significant N2 latency prolongation and amplitude reduction with nonverbal and verbal stimuli compared to children without CAPD. No significant group differences were observed for the MMN conditions. Moreover, electrode position affected the results in the same manner for both groups of children. The findings of the present study suggest that the N2 response could be a marker of neural deficits in children with CAPD. N2 results suggest that maturational factors or a different mechanism could be involved in processing auditory information at the central level for these children.

Electrophysiological assessment of auditory processing disorder in children with non-syndromic cleft lip and/or palate

Objectives

Cleft lip and/or palate is a common congenital craniofacial malformation found worldwide. A frequently associated disorder is conductive hearing loss, and this disorder has been thoroughly investigated in children with non-syndromic cleft lip and/or palate (NSCL/P). However, analysis of auditory processing function is rarely reported for this population, although this issue should not be ignored since abnormal auditory cortical structures have been found in populations with cleft disorders. The present study utilized electrophysiological tests to assess the auditory status of a large group of children with NSCL/P, and investigated whether this group had less robust central auditory processing abilities compared to craniofacially normal children.

Methods

146 children with NSCL/P who had normal peripheral hearing thresholds, and 60 craniofacially normal children aged from 6 to 15 years, were recruited. Electrophysiological tests, including auditory brainstem response (ABR), P1-N1-P2 complex, and P300 component recording, were conducted.

Results

ABR and N1 wave latencies were significantly prolonged in children with NSCL/P. An atypical developmental trend was found for long latency potentials in children with cleft compared to control group children. Children with unilateral cleft lip and palate showed a greater level of abnormal results compared with other cleft subgroups, whereas the cleft lip subgroup had the most robust responses for all tests.

Conclusion

Children with NSCL/P may have slower than normal neural transmission times between the peripheral auditory nerve and brainstem. Possible delayed development of myelination and synaptogenesis may also influence auditory processing function in this population. Present research outcomes were consistent with previous, smaller sample size, electrophysiological studies on infants and children with cleft lip/palate disorders. In view of the these findings, and reports of educational disadvantage associated with cleft disorders, further research that focuses on the auditory processing abilities of children with cleft lip/palate disorder is warranted.

Characteristics of Auditory Processing Disorders: A Systematic Review

PURPOSE

The purpose of this review article is to describe characteristics of auditory processing disorders (APD) by evaluating the literature in which children with suspected or diagnosed APD were compared with typically developing children and to determine whether APD must be regarded as a deficit specific to the auditory modality or as a multimodal deficit.

METHOD

Six electronic databases were searched for peer-reviewed studies investigating children with (suspected) APD in comparison with typically developing peers. Relevant studies were independently reviewed and appraised by 2 reviewers. Methodological quality was quantified using the American Speech-Language-Hearing Association's levels of evidence.

RESULTS

Fifty-three relevant studies were identified. Five studies were excluded because of weak internal validity. In total, 48 studies were included, of which only 1 was classified as having strong methodological quality. Significant dissimilarities were found between children referred with listening difficulties and controls. These differences relate to auditory and visual functioning, cognition, language, reading, and physiological and neuroimaging measures.

CONCLUSIONS

Methodological quality of most of the incorporated studies was rated moderate due to the heterogeneous groups of participants, inadequate descriptions of participants, and the omission of valid and reliable measurements. The listening difficulties of children with APD may be a consequence of cognitive, language, and attention issues rather than bottom-up auditory processing.

Auditory temporal-organization abilities in school-age children with peripheral hearing loss

PURPOSE

The objective was to assess auditory sequential organization (ASO) ability in children with and without hearing loss.

METHOD

Forty children 9 to 12 years old participated in the study: 12 with sensory hearing loss (HL), 12 with central auditory processing disorder (CAPD), and 16 with normal hearing. They performed an ASO task in which they were asked to recall 2, 3, and 5 verbal and nonverbal stimuli with an interstimulus interval (ISI) of 425 ms as well as sequences of 2 elements with an ISI of 20 or 1,000 ms.

RESULTS

No significant difference was found between the group of children with HL and the 2 other groups on nonverbal stimuli in all testing conditions. Regardless of ISI duration or number of elements in the sequence, children with HL had significantly fewer correct responses than children with normal hearing and children with CAPD for the verbal stimuli /ba/-/da/. Children with HL had significantly better performance than children with CAPD for the verbal a/-/da/ when the number of elements in the sequence varied.

CONCLUSIONS

Children with sensory HL showed impaired ASO ability when recalling verbal /ba/-/da/. Results suggest that hearing loss can induce a specific signature when processing these verbal stimuli.

Speech perception in noise: exploring the effect of linguistic context in children with and without auditory processing disorder

OBJECTIVE

The objective of this study was to investigate whether the speech perception problems in noise of children with auditory processing disorder (APD) stem from an auditory or a higher order dysfunction.

DESIGN

A repeated measures design comparing the sentence key word recognition scores of children with APD and a control group was used. Four sentence lists from the Test de phrases dans le bruit (TPB) were presented with a babble masker at four different signal-to-noise ratios. The TPB is a Canadian French adaptation of the speech perception in noise test.

STUDY SAMPLE

Ten participants between 9-12 years with APD participated in this study, as well as ten age- and gender-matched children with no sign of APD.

RESULTS

Group analyses revealed that children with APD had poorer overall sentence key word recognition scores than the control group. Analysis of the difference scores between the high and low predictability sentences indicated that the benefit derived from linguistic context is similar between the groups. However, individual patterns of results revealed different profiles within the APD group.

CONCLUSION

Further study using a larger sample is warranted to deepen our understanding of the nature of APD and identify characteristic profiles to enable better tailoring of therapeutic programs.

Protocol to collect late latency auditory evoked potentials

Long Latency Auditory Evoked Potentials (LLAEP) represents a number of electrical changes occurring in the central nervous system, resulting from stimulation of the auditory sensorial pathways. Many studies approach the use of these potentials controlling the artifact created by eye movement with the use of equipment with a large number of channels. However, what happens is very different in Brazilian clinical practice, where the equipment used has a very limited number of channels.

Aim

to compare the two methods used to control the artifacts created by eye movements during LLAEP capture using two recording channels.

Materials and Methods

this is a prospective study with the application of two LLAEP capturing methods (eye artifact subtraction and rejection limit control) in 10 normal hearing individuals.

Results

we did not observe statistically significant differences concerning the latency values obtained with the use of both methods, only concerning amplitude values.

Conclusion

both methods were efficient to capture the LLAEP and to control the eye movement artifact. The rejection limit control method produced greater amplitude values.

Central hearing system maturation in normally hearing children

BACKGROUND

the long latency auditory evoked potentials (LLAEP) provide objective data about the function of hearing cortical structures.

AIM

to characterize the maturation of the central hearing system in normally hearing children.

METHOD

record of LLAEP of fifty-six subjects with hearing tresholds within normal limits, of both genders, being 46 children and 10 adults. With the availability of two recording channels, one was directed to register the LLAEP and the other, to record the artifact generated by ocular movement, aiming at its control. The potentials were recorded with subjects in an alert state, through electrodes positioned in Cz (active) and A2 (reference), and the ocular movements, through electrodes in the left supra and infra-orbital positions; the ground electrode was placed in A1. The morphology and the values of latency and of amplitude for components P1, N1 and P2, according to age, were analyzed. In order to verify the reproducibility of the recorded potentials, a double blind study was carried out, by introducing the analysis of another evaluator.

RESULTS

the double blind study did not present statistically significant differences between the analyses. With the increase in age there was an improvement in the morphology and a decrease in the latency values of components P1, N1 and P2. Also there was a decrease in the amplitude of component P1 and no variation in the amplitude values was observed for components N1 and P2. No statistically significant difference was observed between genders.

CONCLUSION

the maturational process of the central hearing system occurs gradually, being the greatest changes observed when comparing children and adults.

Mismatch negativity in patients with (central) auditory processing disorders

Mismatch Negativity (MMN) is a long-latency auditory evoked potential that provides an objective index of discrimination skills and auditory sensorial memory. It may, therefore, be used as an electrophysiological evaluation of central auditory processing.

Aim

To study MMN in patients with Central Auditory Processing Disorder - CAPD.

Study Method

A prospective clinical study.

Material and Method

Eight individuals with CAPD, aged between nine and 14 years, were evaluated; there was also a control group. MMN was elicited for tone stimuli (tone bursts), differing in terms of frequency (MMNf - standard stimulus: 750 Hz and deviant stimulus: 1,000 Hz), as well as duration (MMNd - standard stimulus: 100 ms and deviant stimulus: 50 ms; at 1,000 Hz).

Results

The presence of MMNf and of MMNd was statistically demonstrated in both groups. No significant statistical differences, however, were observed between MMNf and MMNd latencies and amplitude values in the two groups. Also, no significant statistical differences were observed between the MMNf and the MMNd among the groups.

Conclusion

The CAPD individuals that were evaluated showed no changes in MMNf or MMNd.

Clinical use of AEVP- and AERP-measures in childhood speech disorders

It has long been recognized that from the first months of life auditory perception plays a crucial role in speech and language development. Only in recent years, however, is the precise mechanism of auditory development and its interaction with the acquisition of speech and language beginning to be systematically revealed. This paper presents the results of a series of studies exploring the relevance of electrophysiological measurements for the objective diagnosis of children with language and speech disorders. In the first, retrospective, study, an inventory was made of clinical neurological, neuropsychological, logopedic and neurophysiological findings obtained from 43 children referred to the Paediatric Neurology Centre for the diagnosis of their speech and language deficits. Neurophysiological abnormalities were found in 95% of these children, among these deviant auditory evoked potentials (AEVPs). The second study demonstrated developmental trends in the waveform of the cortical AEVPs up to age 6 years; the implications for longitudinal studies are discussed. Preliminary results from the third study show emerging differences in auditory event-related potentials (AERPs) for young children who are at risk for developmental dyslexia based on their family history. These findings underscore the clinical usefulness of neurophysiological measures for the diagnosis of speech-language disorders. Clinical protocols are further developed and tested.

ERPs differentiate syllable and nonphonetic sound processing in children and adults

We examined maturation of speech-sound-related indices of auditory event-related brain potentials (ERPs). ERPs were elicited by syllables and nonphonetic correlates in children and adults. Compared with syllables, nonphonetic stimuli elicited larger N1 and P2 in adults and P1 in children. Because the nonphonetics were more perceptually salient, this N1 effect was consistent with known N1 sensitivity to sound onset features. Based on stimulus dependence and independent component structure, children's P1 appeared to contain overlapping P2-like activity. In both subject groups, syllables elicited larger N2/N4 peaks. This might reflect sound content feature processing, more extensive for speech than nonspeech sounds. Therefore, sound detection mechanisms (N1, P2) still develop whereas sound content processing (N2, N4) is largely mature during mid-childhood; in children and adults, speech sounds are processed more extensively than nonspeech sounds 200-400 ms poststimulus.