Attenuated auditory event-related potential (mismatch negativity) in children with developmental dysphasia

Mismatch Negativity Responses to Different Auditory Attributes in Normally Developing Infants and Children

Introduction Mismatch negativity (MMN) is a change-specific component of the event-related potentials that is elicited by an irregularity in repetitive auditory stimulation. As it is developmentally stable and can be measured in the absence of the participant's attention, it can be a valuable method for assessing auditory discrimination in infants and young children. The classic MMN paradigm involves tone frequency as the mismatching attribute. Multi-feature MMN paradigms which involve different auditory attributes can assess discrimination abilities in a wider group of disorders. The study aimed to report standardised MMN values obtained with MMN paradigms including several auditory attributes to extend the clinical applicability of the test in infants and young children. Methods MMN responses were recorded in 42 normal infants and young children (2 months to 5 years) with multi-feature MMN paradigms. MMN variables in different trials were compared by one-way ANOVA. Pearson's correlation coefficient and independent sample t-test were performed for finding an association with the age and gender of the participants respectively. P<0.05 was considered as statistically significant. Results MMN amplitude exhibited statistically significant differences in different MMN paradigms (p<0.05). An increase in the degree of standard and deviant differences and double deviant responses also resulted in larger MMN. MMN latency variation in the trials was not statistically significant. The age and gender of the participants did not influence the MMN variables with statistical significance. Conclusion MMN paradigms with different auditory attributes report significant amplitude variations. Multi-feature MMN paradigms can optimize the clinical applicability of the test and can determine the profile of different auditory discrimination abilities.

Auditory Evoked Potentials in Communication Disorders: An Overview of Past, Present, and Future

This article provides a brief overview of auditory evoked potentials (AEPs) and their application in the areas of research and clinics within the field of communication disorders. The article begins with providing a historical perspective within the context of the key scientific developments that led to the emergence of numerous types of AEPs. Furthermore, the article discusses the different AEP techniques in the light of their feasibility in clinics. As AEPs, because of their versatility, find their use across disciplines, this article also discusses some of the research questions that are currently being addressed using AEP techniques in the field of communication disorders and beyond. At the end, this article summarizes the shortcomings of the existing AEP techniques and provides a general perspective toward the future directions. The article is aimed at a broad readership including (but not limited to) students, clinicians, and researchers. Overall, this article may act as a brief primer for the new AEP users, and as an overview of the progress in the field of AEPs along with future directions, for those who already use AEPs on a routine basis.

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.

Mismatch Negativity in Children: Reference Values

Introduction  The Mismatch Negativity (MMN) auditory evoked potential evaluation is a promising procedure to assess objectively the ability of auditory discrimination. Objective  To characterize the latency and amplitude values of MMN in children with normal auditory thresholds and without auditory complaints. Methods  Children between 5 and 11 years old participated in the present study. All participants underwent acoustic immittance measurements and tonal and vocal audiometry. The MMN was recorded with the MASBE ATC Plus system (Contronic, Pelotas, RS, Brazil). The electrodes were fixed in Fz (active electrode), Fpz (ground electrode) and in M2 and M1 (references electrodes). The intensity used was 80 dBHL, the frequent stimulus was 1,000 Hz and the rare stimulus was 2,000 Hz. The stimuli were presented in both ears separately. Results  For the female group, the mean latencies and amplitude of MMN were 177.3 ms and 5.01 μV in the right ear (RE) and 182.4 ms and 5.39 μV in the left ear (LE). In the male group, the mean latencies were 194.4 ms in the RE and 183.6 ms in the LE, with an amplitude of 5.11 μV in the RE and 5.83 μV in the LE. There was no statistically significant difference between ears ( p  = 0.867 - latency and p  = 0.178 - amplitude), age ( p  > 0.20) and the gender of the participants ( p  > 0.05). Conclusion  Using the described protocol, the mean latency value of MMN was 184.0 ms for RE and 182.9 ms for LE, and the amplitude was 5.05 μV and 5.56 μV for the left and right ears, respective.

Low-level neural auditory discrimination dysfunctions in specific language impairment-A review on mismatch negativity findings

In specific language impairment (SLI), there is a delay in the child’s oral language skills when compared with nonverbal cognitive abilities. The problems typically relate to phonological and morphological processing and word learning. This article reviews studies which have used mismatch negativity (MMN) in investigating low-level neural auditory dysfunctions in this disorder. With MMN, it is possible to tap the accuracy of neural sound discrimination and sensory memory functions. These studies have found smaller response amplitudes and longer latencies for speech and non-speech sound changes in children with SLI than in typically developing children, suggesting impaired and slow auditory discrimination in SLI. Furthermore, they suggest shortened sensory memory duration and vulnerability of the sensory memory to masking effects. Importantly, some studies reported associations between MMN parameters and language test measures. In addition, it was found that language intervention can influence the abnormal MMN in children with SLI, enhancing its amplitude. These results suggest that the MMN can shed light on the neural basis of various auditory and memory impairments in SLI, which are likely to influence speech perception.

Mismatch negativity in children with specific language impairment and auditory processing disorder

Introduction

Mismatch negativity, an electrophysiological measure, evaluates the brain's capacity to discriminate sounds, regardless of attentional and behavioral capacity. Thus, this auditory event-related potential is promising in the study of the neurophysiological basis underlying auditory processing.

Objective

To investigate complex acoustic signals (speech) encoded in the auditory nervous system of children with specific language impairment and compare with children with auditory processing disorders and typical development through the mismatch negativity paradigm.

Methods

It was a prospective study. 75 children (6–12 years) participated in this study: 25 children with specific language impairment, 25 with auditory processing disorders, and 25 with typical development. Mismatch negativity was obtained by subtracting from the waves obtained by the stimuli /ga/ (frequent) and /da/ (rare). Measures of mismatch negativity latency and two amplitude measures were analyzed.

Results

It was possible to verify an absence of mismatch negativity in 16% children with specific language impairment and 24% children with auditory processing disorders. In the comparative analysis, auditory processing disorders and specific language impairment showed higher latency values and lower amplitude values compared to typical development.

Conclusion

These data demonstrate changes in the automatic discrimination of crucial acoustic components of speech sounds in children with specific language impairment and auditory processing disorders. It could indicate problems in physiological processes responsible for ensuring the discrimination of acoustic contrasts in pre-attentional and pre-conscious levels, contributing to poor perception.

Mismatch negativity (MMN) as an index of cognitive dysfunction

Cognition is often affected in a variety of neuropsychiatric, neurological, and neurodevelopmental disorders. The neural discriminative response, reflected in mismatch negativity (MMN) and its magnetoencephalographic equivalent (MMNm), has been used as a tool to study a variety of disorders involving auditory cognition. MMN/MMNm is an involuntary brain response to auditory change or, more generally, to pattern regularity violation. For a number of disorders, MMN/MMNm amplitude to sound deviance has been shown to be attenuated or the peak-latency of the component prolonged compared to controls. This general finding suggests that while not serving as a specific marker to any particular disorder, MMN may be useful for understanding factors of cognition in various disorders, and has potential to serve as an indicator of risk. This review presents a brief history of the MMN, followed by a description of how MMN has been used to index auditory processing capability in a range of neuropsychiatric, neurological, and neurodevelopmental disorders. Finally, we suggest future directions for research to further enhance our understanding of the neural substrate of deviance detection that could lead to improvements in the use of MMN as a clinical tool.

Event-related potentials to tones show differences between children with multiple risk factors for dyslexia and control children before the onset of formal reading instruction

Multiple risk factors can affect the development of specific reading problems or dyslexia. In addition to the most prevalent and studied risk factor, phonological processing, auditory discrimination problems have also been found in children and adults with reading difficulties. The present study examined 37 children between the ages of 5 and 6, 11 of which had multiple risk factors for developing reading problems. The children participated in a passive oddball EEG experiment with sinusoidal sounds with changes in sound frequency, duration, or intensity. The responses to the standard stimuli showed a negative voltage shift in children at risk for reading problems compared to control children at 107-215 ms in frontocentral areas corresponding to P1 offset and N250 onset. Source analyses showed that the difference originated from the left and right auditory cortices. Additionally, the children at risk for reading problems had a larger late discriminative negativity (LDN) response in amplitude for sound frequency change than the control children. The amplitudes at the P1-N250 time window showed correlations to letter knowledge and phonological identification whereas the amplitudes at the LDN time window correlated with verbal short-term memory and rapid naming. These results support the view that problems in basic auditory processing abilities precede the onset of reading instruction and can act as one of the risk factors for dyslexia.

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

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

Spectral vs. temporal auditory processing in specific language impairment: a developmental ERP study

Pre-linguistic sensory deficits, especially in "temporal" processing, have been implicated in developmental language impairment (LI). However, recent evidence has been equivocal with data suggesting problems in the spectral domain. The present study examined event-related potential (ERP) measures of auditory sensory temporal and spectral processing, and their interaction, in typical children and those with LI (7-17 years; n=25 per group). The stimuli were three CV syllables and three consonant-to-vowel transitions (spectral sweeps) isolated from the syllables. Each of these six stimuli appeared in three durations (transitions: 20, 50, and 80 ms; syllables: 120, 150, and 180 ms). Behaviorally, the group with LIs showed inferior syllable discrimination both with long and short stimuli. In ERPs, trends were observed in the group with LI for diminished long-latency negativities (the N2-N4 peaks) and a developmentally transient enhancement of the P2 peak. Some, but not all, ERP indices of spectral processing also showed trends to be diminished in the group with LI specifically in responses to syllables. Importantly, measures of the transition N2-N4 peaks correlated with expressive language abilities in the LI children. None of the group differences depended on stimulus duration. Therefore, sound brevity did not account for the diminished spectral resolution in these LI children. Rather, the results suggest a deficit in acoustic feature integration at higher levels of auditory sensory processing. The observed maturational trajectory suggests a non-linear developmental deviance rather than simple delay.

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.

Language impairment is reflected in auditory evoked fields

Specific language impairment (SLI) is diagnosed when a child has problems in producing or understanding language despite having a normal IQ and there being no other obvious explanation. There can be several associated problems, and no single underlying cause has yet been identified. Some theories propose problems in auditory processing, specifically in the discrimination of sound frequency or rapid temporal frequency changes. We compared automatic cortical speech-sound processing and discrimination between a group of children with SLI and control children with normal language development (mean age: 6.6 years; range: 5-7 years). We measured auditory evoked magnetic fields using two sets of CV syllables, one with a changing consonant /da/ba/ga/ and another one with a changing vowel /su/so/sy/ in an oddball paradigm. The P1m responses for onsets of repetitive stimuli were weaker in the SLI group whereas no significant group differences were found in the mismatch responses. The results indicate that the SLI group, having weaker responses to the onsets of sounds, might have slightly depressed sensory encoding.

Abnormal frequency discrimination in children with SLI as indexed by mismatch negativity (MMN)

For several decades, the aetiology of specific language impairment (SLI) has been associated with a central auditory processing deficit disrupting the normal language development of affected children. One important aspect for language acquisition is the discrimination of different acoustic features, such as frequency information. Concerning SLI, studies to date that examined frequency discrimination abilities have been contradictory. We hypothesized that an auditory processing deficit in children with SLI depends on the frequency range and the difference between the tones used. Using a passive mismatch negativity (MMN)-design, 13 boys with SLI and 13 age- and IQ-matched controls (7-11 years) were tested with two sine tones of different frequency (700Hz versus 750Hz). Reversed hemispheric activity between groups indicated abnormal processing in SLI. In a second time window, MMN2 was absent for the children with SLI. It can therefore be assumed that a frequency discrimination deficit in children with SLI becomes particularly apparent for tones below 750Hz and for a frequency difference of 50Hz. This finding may have important implications for future research and integration of various research approaches.

The Role of Early Auditory Discrimination Deficits in Language Disorders

Language impairments can have a devastating effect on the individual’s life. Brain damage such as stroke may cause varying degrees of impaired language. Even milder language problems, such as developmental dyslexia or specific language impairment, can have long-lasting detrimental effects on the individual’s life, affecting both success at school as well as motivation and even self-esteem. In recent years, the mismatch negativity (MMN) has been intensively applied to study the neural basis of language impairments. These studies have shown that the MMN, which reflects the early stages of cortical sound discrimination, is abnormal in a large variety of language impairments. Furthermore, a close relationship between the MMN and some language disorders is suggested by significant correlations between the MMN and language test results. Further support is provided by follow-up studies suggesting that the MMN parameters may predict future language problems in children and by investigations indicating that intervention programs with an ameliorating effect also concurrently change the MMN. However, when interpreting the implications of MMN results it is important to acknowledge that this response specifically reflects early stages of auditory discrimination and should, therefore, be combined with measures probing the further steps of auditory processing for a more complete picture of the underlying deficits of language. The current review addresses how the MMN can be used in determining auditory impairments in language disorders such as aphasia, dyslexia, autism spectrum, and specific language impairment.

The contribution of AERPs (MMN and LDN) to studying temporal vs. linguistic processing deficits in children with reading difficulties

One of the factors responsible for the appearance of reading problems seems to be a difficulty in discriminating auditory stimuli presented in rapid succession, known as the 'temporal processing hypothesis'. In this study automatic discrimination processes were evaluated in 31 children with reading difficulties and 24 control children between 4 and 8 years of age, using a passive oddball paradigm, in which syllables (/ba/ and /da/) and complex tones were presented. Analysis of the MMN component revealed significant differences between the groups only in the task involving linguistic stimuli, detecting longer latency of the component in the experimental group. The LDN component showed lower amplitudes and delayed latencies in the experimental group during the processing of both types of stimuli. These differences, however, were more marked in the task involving syllables, where a higher mean amplitude was observed in the experimental group than in the control group in the right hemisphere. The task involving complex tones also revealed differences between the groups at the frontal electrodes, indicating different maturative courses of the potential. The findings demonstrate the existence of a strongly pronounced preattentional auditory deficit during phonological processing, and also reveal important differences between the various stages of automatic information processing in children with and without reading disabilities.

Individual differences in auditory processing in specific language impairment: a follow-up study using event-related potentials and behavioural thresholds

It has frequently been claimed that children with specific language impairment (SLI) have impaired auditory perception, but there is much controversy about the role of such deficits in causing their language problems, and it has been difficult to establish solid, replicable findings in this area. Discrepancies in this field may arise because (a) a focus on mean results obscures the heterogeneity in the population and (b) insufficient attention has been paid to maturational aspects of auditory processing. We conducted a study of 16 young people with specific language impairment (SLI) and 16 control participants, 24 of whom had had auditory event-related potentials (ERPs) and frequency discrimination thresholds assessed 18 months previously. When originally assessed, around one third of the listeners with SLI had poor behavioural frequency discrimination thresholds, and these tended to be the younger participants. However, most of the SLI group had age-inappropriate late components of the auditory ERP, regardless of their frequency discrimination. At follow-up, the behavioural thresholds of those with poor frequency discrimination improved, though some remained outside the control range. At follow-up, ERPs for many of the individuals in the SLI group were still not age-appropriate. In several cases, waveforms of individuals in the SLI group resembled those of younger typically-developing children, though in other cases the waveform was unlike that of control cases at any age. Electrophysiological methods may reveal underlying immaturity or other abnormality of auditory processing even when behavioural thresholds look normal. This study emphasises the variability seen in SLI, and the importance of studying individual cases rather than focusing on group means.

Neurophysiologic correlates of deficient phonological representations and object naming in prematurely born children

OBJECTIVE

The aim of this follow-up study was to evaluate the development of object naming ability and auditory processing in prematurely born children. Furthermore, we investigated whether the mismatch negativity (MMN) parameters at the age of 4 years correlate with the MMN parameters and naming ability at the age of 6 years.

METHODS

Twelve very low birth weight (VLBW) preterm children (mean age 5 years 7 months) and matched controls were studied. Object naming was measured by the Boston naming test. Auditory event-related potentials (ERPs), especially the MMN, were recorded for Finnish syllables (standard /taa/; deviants /ta/ and /kaa/) in an oddball paradigm.

RESULTS

VLBW preterm children scored significantly lower in the object naming test than their controls. The MMN amplitude for consonant change was significantly smaller in the preterm group compared to the controls. The MMN amplitude at the age of 4 years correlated with the MMN amplitude at the age of 6 years. Furthermore, absence of the MMN at the age of 4 years predicted naming difficulties at the age of 6 years.

CONCLUSIONS

VLBW preterm children with a difficulty to preattentively discriminate changes in syllables, as indexed by the diminished change detection response, MMN, seem to have sustained naming difficulty. Therefore, it is reasonable to record the MMN along with the language development from infancy, in order to identify the children at risk for language deficiencies and to provide appropriate rehabilitation.

Development of the automatic mismatch response: from frontal positivity in kindergarten children to the mismatch negativity

OBJECTIVE

The automatic event-related potential (ERP) response to auditory deviance typically consists of a frontocentral mismatch negativity (MMN), which has been shown to be quite stable during development. Whereas in some infant studies, positive frontal mismatch responses have been reported instead of a MMN; to date, such positivities have not been reported for older children.

METHODS

Oddball sequences with small frequency and phoneme deviance (standard: 1000 Hz, 'ba'; larger deviance: 1060 Hz, 'ta'; smaller deviance: 1030 Hz, 'da') and short intervals (every 0.38 s) were presented to 6-7-year-old children and adults during 43-channel ERP recordings.

RESULTS

Children showed a consistent frontal positive mismatch response with posterior negativity (179-207 ms), and adults a frontocentral MMN with mastoid positivity (129-199 ms). This map polarity reversal was reflected by significantly different 3D centroid distributions. Low-resolution electromagnetic tomography (LORETA) revealed temporal mismatch response sources for both age groups and conditions.

CONCLUSIONS

Major developmental changes characterise the automatic mismatch response for the small deviances and short intervals used. Source localisation suggests that children's and adults' mismatch responses originated from superior temporal plane generators with similar localisation but opposite polarity. This indicates qualitatively different neurophysiological functioning of the automatic bi-temporal auditory change detectors in children and adults.

Neural plasticity following auditory training in children with learning problems

OBJECTIVE

This study examined the plasticity of the central auditory pathway and accompanying cognitive changes in children with learning problems.

METHODS

Children diagnosed with a learning disability and/or attention deficit disorder worked with commercial auditory processing training software for 8 weeks; control groups consisted of normal-learning and learning-impaired children who did not participate in any remedial programs. Auditory brainstem function was evaluated in response to click and speech stimuli in quiet; cortical responses to speech stimuli were obtained in quiet and noise. Academic achievement and cognitive abilities were assessed with standardized measures.

RESULTS

Compared to controls, the trained group improved on measures of auditory processing and exhibited changes in cortical responses in quiet and in noise. In quiet, cortical responses reflected an accelerated maturational pattern; in background noise, cortical responses became more resistant to degradation. Brainstem responses did not change with training.

CONCLUSIONS

Children with learning problems who practiced with auditory training software exhibited plasticity of neural encoding of speech sounds at the cortical, but not subcortical, level of the auditory pathway. This plasticity was accompanied by improvement in behavioral performance.

SIGNIFICANCE

This study demonstrates that in learning-impaired children working with commercial auditory processing training programs affects both the perception and the cortical representation of sound.

Auditory sensory impairment in children with oral clefts as indexed by auditory event-related potentials

Children with nonsyndromic oral clefts and with the CATCH 22 syndrome (acronym for cardiac defects, abnormal faces, thymus hypoplasia, clefts, and hypocalcemia) display a range of language and learning disabilities, the neurofunctional bases of which are not yet understood. This review summarizes recent event-related brain potential (ERP) studies on central auditory processing in infants and children with different cleft types and presents an effort to integrate these ERP and earlier behavioral findings into a workable hypothesis on the mechanisms of cognitive impairment in the oral cleft population. The encoding of the acoustic sound features and the functioning of auditory sensory memory (ASM) were studied by recording cortical auditory ERPs. Tapped were two ASM functions: tone pitch discrimination and the duration of sensory memory for tone pitch. In infants with cleft palate, tone pitch discrimination was impaired at birth and at 6 months of age. In infants with cleft lip and palate, no ASM impairment was detected at either age. In school-aged children with clefts and CATCH 22 syndrome, the discrimination of tone pitch was intact under optimal stimulation conditions. However, in these children, shortened duration of ASM was observed, with the magnitude of its shortening covarying with cleft type and being most pronounced in children with CATCH 22 syndrome. The different types of ASM dysfunction found in children with different cleft types could not be accounted for by the peripheral hearing deficits. The relation between ASM dysfunction and known behavioral cognitive disability profiles in children with different cleft types suggests that ASM is implicated in language disabilities of children with oral clefts. Furthermore, it appears that the ASM impairment and oral clefting are linked in a comorbid fashion.

Cognitive functions of adolescent childhood cancer survivors assessed by event-related potentials

BACKGROUND

Neurophysiological methods were applied to examine subtle central nervous system (CNS) adverse effects for adolescent childhood cancer survivors. We analyzed auditory event-related potentials (ERPs)-P300 and MMN/P3a complex-to find out whether there was impaired attention orientation in asymptomatic cancer survivors, and whether these ERP methods could be used as more objective tools in detecting those survivors who might need academic testing. Previous clinical studies of P300 have focused on leukemia survivors. MMN for cancer survivors has not been reported.

PROCEDURE

The subjects were survivors of childhood leukemia (n=11) and solid tumors (n=8), as well as healthy controls (n=10). The mean age was 15.5 years for survivors and 15.9 years for controls. Pure sine-wave tones (500 and 553 Hz, 100 ms) were used as stimuli in an oddball paradigm. The ERPs to frequency change were measured. MMN recordings were performed in a passive non-attended situation where the subject was watching a voiceless video cartoon. P300 was produced thereafter, but in an active attend situation, by the same auditory oddball paradigm as MMN.

RESULTS

A significant difference was detected between the groups for the latency of P300 at electrodes Cz (P = 0.03) and C4 (P = 0.05). The cancer survivors had prolonged P300 latencies as an indication of prolonged short-term memory processing. The area and latency parameters of MMN did not differ significantly between the study groups, but in cancer survivors, the area and the mean amplitude of the subsequent P3a wave were diminished. The results indicate that the discrimination process was not as easy for the survivors as for the controls. However, it seems that in cancer survivors the basic mechanism starting attention shift to novel stimuli is not impaired.

CONCLUSIONS

These results indicate that it is important to carefully evaluate the proper methods for the teaching of children who are survivors of malignancies. The auditory information may not always lead to the best possible learning results.

Early and late mismatch negativity elicited by words and speech-like stimuli in children

In auditory perception the brain's attentional and preattentional mechanisms select certain stimuli for preferential processing and filter out irrelevant input. This study investigated nonattentive auditory processing in children. Event-related potentials (ERPs) provide a means to study neural correlates related to language and speech-sound processing. Mismatch negativity (MMN) is an ERP wave that indicates attention-independent perceptual change detection. In this study cortical ERPs were elicited by complex tones, naturally spoken words, and pseudowords, with each stimulus type containing equal acoustical elements. Tones elicited a bifurcated mismatch negativity (MMN), with early MMN (peaking at 150-200 ms) being more dominant. On the other hand, words elicited a strong late MMN, peaking at about 400-450 ms after stimulus onset. The MMN wave form was significantly weaker for pseudowords than for words. The late MMN wave, especially for word differences, was found to reflect summating MMN generators and memory trace formation on gestalt bases. Results suggest that the auditory processing, even nonattended, is highly associated with the cognitive meaning of the stimuli.

Electrophysiological dissociation between verbal and nonverbal semantic processing in learning disabled adults

Event-related potentials (ERPs) were recorded as 16 adults with learning disabilities (LD) and 16 controls were presented with two sets of stimuli. The first set comprised pairs of line drawings and environmental sounds (nonverbal condition); the second consisted of printed and spoken words (verbal condition). In the controls, semantically related items elicited smaller N400s than unrelated items in both conditions, with opposing hemispheric asymmetries for spoken words and environmental sounds. The LD group did not show a significant difference between related and unrelated words, despite a robust context effect for nonspeech sounds. The results suggest anomalous processing limited to the verbal domain in a simple semantic association task in the LD group. Semantic deficits in this group may reflect a relatively specific deficit in forming verbal associations rather than a more general difficulty that spans both verbal and nonverbal domains.

Mismatch negativity (MMN) as a tool for investigating auditory discrimination and sensory memory in infants and children

For decades behavioral methods, such as the head-turning or sucking paradigms, have been the primary methods to investigate auditory discrimination, learning and the function of sensory memory in infancy and early childhood. During recent years, however, a new method for investigating these issues in children has emerged. This method makes use of the mismatch negativity (MMN), the brain's automatic change-detection response, which has been used intensively in both basic and clinical studies in adults for twenty years. This review demonstrates that, unlike many other components of event-related potentials, the MMN is developmentally quite stable and can be obtained even from pre-term infants. Further, MMN amplitude is only slightly smaller in infants than is usually reported in school-age children and it does not seem to differ much from that obtained in adults. MMN latency has been reported to be slightly longer in infants than in adults but reaches adult values by the early school-age years. Child MMN does not seem to be analogous to adult MMN, however. For example, contrary to the results of adult studies, a prominent MMN can be obtained from in all waking- and sleep states in infants. Moreover, MMN scalp distribution seems to be broader and more central in children than in adults.

Stability of mismatch negativities in children

OBJECTIVES AND METHODS

Mismatch negativities (MMN) to frequency and duration changes in a series of repetitive tones and to two different consonant-vowel syllables (ba and ga, standard da) were recorded in a test and retest session in 15 children aged 7-11 years. Reliability within one session and stability between the sessions of MMN amplitudes and the ERP-components P1 and N1 were determined by correlation coefficients.

RESULTS

Mean amplitudes of the grand averages showed a decrease of MMN during the second test session in a late latency window (400-500 ms) for the frequency MMN and of the MMN elicited by speech stimuli. The individual stability reached significance only for the duration deviant and one of the syllables. Compared to results found in adults with similar stimulus conditions the stability of the MMN in children seems to be somewhat lower. The components P1 and N1 to both stimulus types (tone and speech), however, showed a high reliability and individual stability.

CONCLUSION

While MMN is a useful tool to study processing deficits in groups of children, as e.g. in language-impaired children, MMN as a individual diagnostic measure should be interpreted very cautiously.