Sound complexity and 'speechness' effects on pre-attentive auditory discrimination in children

Unified Coding of Spectral and Temporal Phonetic Cues: Electrophysiological Evidence for Abstract Phonological Features

Spoken word recognition models and phonological theory propose that abstract features play a central role in speech processing. It remains unknown, however, whether auditory cortex encodes linguistic features in a manner beyond the phonetic properties of the speech sounds themselves. We took advantage of the fact that English phonology functionally codes stops and fricatives as voiced or voiceless with two distinct phonetic cues: Fricatives use a spectral cue, whereas stops use a temporal cue. Evidence that these cues can be grouped together would indicate the disjunctive coding of distinct phonetic cues into a functionally defined abstract phonological feature. In English, the voicing feature, which distinguishes the consonants [s] and [t] from [z] and [d], respectively, is hypothesized to be specified only for voiceless consonants (e.g., [s t]). Here, participants listened to syllables in a many-to-one oddball design, while their EEG was recorded. In one block, both voiceless stops and fricatives were the standards. In the other block, both voiced stops and fricatives were the standards. A critical design element was the presence of intercategory variation within the standards. Therefore, a many-to-one relationship, which is necessary to elicit an MMN, existed only if the stop and fricative standards were grouped together. In addition to the ERPs, event-related spectral power was also analyzed. Results showed an MMN effect in the voiceless standards block—an asymmetric MMN—in a time window consistent with processing in auditory cortex, as well as increased prestimulus beta-band oscillatory power to voiceless standards. These findings suggest that (i) there is an auditory memory trace of the standards based on the shared (voiceless) feature, which is only functionally defined; (ii) voiced consonants are underspecified; and (iii) features can serve as a basis for predictive processing. Taken together, these results point toward auditory cortex's ability to functionally code distinct phonetic cues together and suggest that abstract features can be used to parse the continuous acoustic signal.

Extracting Phonetic Features From Natural Classes: A Mismatch Negativity Study of Mandarin Chinese Retroflex Consonants

How speech sounds are represented in the brain is not fully understood. The mismatch negativity (MMN) has proven to be a powerful tool in this regard. The MMN event-related potential is elicited by a deviant stimulus embedded within a series of repeating standard stimuli. Listeners construct auditory memory representations of these standards despite acoustic variability. In most designs that test speech sounds, however, this variation is typically intra-category: All standards belong to the same phonetic category. In the current paper, inter-category variation is presented in the standards. These standards vary in manner of articulation but share a common phonetic feature. In the standard retroflex experimental block, Mandarin Chinese speaking participants are presented with a series of "standard" consonants that share the feature [retroflex], interrupted by infrequent non-retroflex deviants. In the non-retroflex standard experimental block, non-retroflex standards are interrupted by infrequent retroflex deviants. The within-block MMN was calculated, as was the identity MMN (iMMN) to account for intrinsic differences in responses to the stimuli. We only observed a within-block MMN to the non-retroflex deviant embedded in the standard retroflex block. This suggests that listeners extract [retroflex] despite significant inter-category variation. In the non-retroflex standard block, because there is little on which to base a coherent auditory memory representation, no within-block MMN was observed. The iMMN to the retroflex was observed in a late time-window at centro-parieto-occipital electrode sites instead of fronto-central electrodes, where the MMN is typically observed, potentially reflecting the increased difficulty posed by the added variation in the standards. In short, participants can construct auditory memory representations despite significant acoustic and inter-category phonological variation so long as a shared phonetic feature binds them together.

Brain responses to change in phonological structures of varying complexity in children and adults

Language-related change-detection processes are often investigated using syllables that are very simple in terms of phonological structure. However, phonological complexity is known to be challenging for young typically developing children and pathological populations. We investigated brain correlates of phonological processing and their age-related changes with a passive change-detection protocol including stimuli of varying phonological complexity, which allowed comparing responses to simple and complex phonological deviancies. Mismatch Negativity (MMN) and Late Discriminative Negativity (LDN) responses were recorded in both school-age children (n = 22) and adults (n = 24). MMN was similar for simple and complex phonological deviancy in both groups, whereas LDN appeared to be modulated by phonological complexity, albeit with different patterns according to age. In response to complex phonological change, children displayed a larger LDN response with a typical fronto-central scalp distribution, while adults showed an additional right-posterior activity but no larger amplitude than for simple change. Thus, LDN appears to be a good electrophysiological index of phonological complexity processing. This study validated the use of the LDN through this protocol for the investigation of phonological complexity processing throughout the development.

Maturation of Speech-Sound ERPs in 5-6-Year-Old Children: A Longitudinal Study

The maturation of 5-6-year-old children's auditory discrimination - indicated by the development of the auditory event-related-potentials (ERPs) - has not been previously studied in longitudinal settings. For the first time, we present here the results based on extensive dataset collected from 75 children. We followed the 5- to 6-year-olds for 20 months and measured their ERPs four times with the same multifeature paradigm with phonemic stimuli. The amplitude of the mismatch negativity (MMN) response increased during this time for vowel, vowel duration and frequency changes. Furthermore, the P3a component started to mature toward adult-like positivity for the vowel, intensity and frequency deviants and the late discriminative negativity (LDN) component decreased with age for vowel and intensity deviants. All the changes in the components seemed to happen during the second follow-up year, when Finnish children are taught letter symbols and other preliminary academic skills before going to school at the age of seven. Therefore, further studies are needed to clarify if these changes in the auditory discrimination are purely age-related or due to increasing linguistic knowledge of the children.

Developmental changes in automatic rule-learning mechanisms across early childhood

Infants' ability to learn complex linguistic regularities from early on has been revealed by electrophysiological studies indicating that 3-month-olds, but not adults, can automatically detect non-adjacent dependencies between syllables. While different ERP responses in adults and infants suggest that both linguistic rule learning and its link to basic auditory processing undergo developmental changes, systematic investigations of the developmental trajectories are scarce. In the present study, we assessed 2- and 4-year-olds' ERP indicators of pitch discrimination and linguistic rule learning in a syllable-based oddball design. To test for the relation between auditory discrimination and rule learning, ERP responses to pitch changes were used as predictor for potential linguistic rule-learning effects. Results revealed that 2-year-olds, but not 4-year-olds, showed ERP markers of rule learning. Although, 2-year-olds' rule learning was not dependent on differences in pitch perception, 4-year-old children demonstrated a dependency, such that those children who showed more pronounced responses to pitch changes still showed an effect of rule learning. These results narrow down the developmental decline of the ability for automatic linguistic rule learning to the age between 2 and 4 years, and, moreover, point towards a strong modification of this change by auditory processes. At an age when the ability of automatic linguistic rule learning phases out, rule learning can still be observed in children with enhanced auditory responses. The observed interrelations are plausible causes for age-of-acquisition effects and inter-individual differences in language learning.

Converging evidence for [coronal] underspecification in English-speaking adults

The goal of this study was to test the predictions of the Featurally Underspecified Lexicon (FUL) theory by examining event-related potential (ERP) indices of phonological representation. Two English consonants differing in place of articulation were selected: [labial] /b/ and [coronal] /d/. It was assumed that the phonological representation of /d/ contained less distinctive feature information due to its [coronal] place of articulation, as compared to /b/. English-speaking adults were presented with two syllables, /bɑ/ and /dɑ/, in an ERP oddball paradigm where both syllables served as the standard and deviant stimulus in opposite stimulus sets. Three types of analyses were conducted: traditional mean amplitude measurements, cluster-based permutation tests, and single-trial general linear model (GLM) analyses of group-level and single-subject data. The less specified /dɑ/ deviant elicited a large MMN while no MMN was elicited by the more specified deviant /bɑ/. Additionally, the /dɑ/ standard syllable elicited larger responses than did the /bɑ/ standard, while deviant syllables did not differ. This implies that the MMN was driven by responses elicited by the standards rather than the deviants. At the single-subject level, not all participants demonstrated significant MMN responses, though all had measurable differences between the standard syllables. Thus, to continue to propose that [coronal] underspecification is a language universal phenomenon, ERP indices other than the MMN should be examined.

Phoneme processing skills are reflected in children's MMN responses

Phonological awareness (PA), the core contributor in phoneme processing abilities, has a link to later reading skills in children. However, the associations between PA and neural auditory discrimination are not clear. We used event-related potential (ERP) methodology and neuropsychological testing to monitor the neurocognitive basis of phonological awareness in typically developing children. We measured 5-6-year-old children's (N=70) phoneme processing, word completion and perceptual reasoning skills and compared their test results to their brain responses to phonemic changes, separately for each test. We found that children performing better in Phoneme processing test showed larger mismatch negativity (MMN) responses than children scoring lower in the same test. In contrast, no correspondence between test scores and brain responses was found for Auditory closure. Thus, the results suggest that automatic auditory change detection is linked to phoneme awareness in preschool children.

Phonological abilities in literacy-impaired children: Brain potentials reveal deficient phoneme discrimination, but intact prosodic processing

Intact phonological processing is crucial for successful literacy acquisition. While individuals with difficulties in reading and spelling (i.e., developmental dyslexia) are known to experience deficient phoneme discrimination (i.e., segmental phonology), findings concerning their prosodic processing (i.e., suprasegmental phonology) are controversial. Because there are no behavior-independent studies on the underlying neural correlates of prosodic processing in dyslexia, these controversial findings might be explained by different task demands. To provide an objective behavior-independent picture of segmental and suprasegmental phonological processing in impaired literacy acquisition, we investigated event-related brain potentials during passive listening in typically and poor-spelling German school children. For segmental phonology, we analyzed the Mismatch Negativity (MMN) during vowel length discrimination, capturing automatic auditory deviancy detection in repetitive contexts. For suprasegmental phonology, we analyzed the Closure Positive Shift (CPS) that automatically occurs in response to prosodic boundaries. Our results revealed spelling group differences for the MMN, but not for the CPS, indicating deficient segmental, but intact suprasegmental phonological processing in poor spellers. The present findings point towards a differential role of segmental and suprasegmental phonology in literacy disorders and call for interventions that invigorate impaired literacy by utilizing intact prosody in addition to training deficient phonemic awareness.

Effects of Presentation Rate and Attention on Auditory Discrimination: A Comparison of Long-Latency Auditory Evoked Potentials in School-Aged Children and Adults

Decoding human speech requires both perception and integration of brief, successive auditory stimuli that enter the central nervous system as well as the allocation of attention to language-relevant signals. This study assesses the role of attention on processing rapid transient stimuli in adults and children. Cortical responses (EEG/ERPs), specifically mismatch negativity (MMN) responses, to paired tones (standard 100-100 Hz; deviant 100-300 Hz) separated by a 300, 70 or 10 ms silent gap (ISI) were recorded under Ignore and Attend conditions in 21 adults and 23 children (6-11 years old). In adults, an attention-related enhancement was found for all rate conditions and laterality effects (L>R) were observed. In children, 2 auditory discrimination-related peaks were identified from the difference wave (deviant-standard): an early peak (eMMN) at about 100-300 ms indexing sensory processing, and a later peak (LDN), at about 400-600 ms, thought to reflect reorientation to the deviant stimuli or "second-look" processing. Results revealed differing patterns of activation and attention modulation for the eMMN in children as compared to the MMN in adults: The eMMN had a more frontal topography as compared to adults and attention played a significantly greater role in childrens' rate processing. The pattern of findings for the LDN was consistent with hypothesized mechanisms related to further processing of complex stimuli. The differences between eMMN and LDN observed here support the premise that separate cognitive processes and mechanisms underlie these ERP peaks. These findings are the first to show that the eMMN and LDN differ under different temporal and attentional conditions, and that a more complete understanding of children's responses to rapid successive auditory stimulation requires an examination of both peaks.

Differences in sensory processing of German vowels and physically matched non-speech sounds as revealed by the mismatch negativity (MMN) of the human event-related brain potential (ERP)

We compared processing of speech and non-speech by means of the mismatch negativity (MMN). For this purpose, the MMN elicited by vowels was compared to those elicited by two non-speech stimulus types: spectrally rotated vowels, having the same stimulus complexity as the speech stimuli, and sounds based on the bands of formants of the vowels, representing non-speech stimuli of lower complexity as compared to the other stimulus types. This design allows controlling for effects of stimulus complexity when comparing neural correlates of processing speech to non-speech. Deviants within a modified multi-feature design differed either in duration or spectral property. Moreover, the difficulty to discriminate between the standard and the two deviants was controlled for each stimulus type by means of an additional active discrimination task. Vowels elicited a larger MMN compared to both non-speech stimulus types, supporting the concept of language-specific phoneme representations and the role of the participants' prior experience.

Developmental changes in mismatch responses to mandarin consonants and lexical tones from early to middle childhood

The purpose of this study was to use mismatch responses (MMRs) to explore the dynamic changes of Mandarin speech perception abilities from early to middle childhood. Twenty preschoolers, 18 school-aged children, and 26 adults participated in this study. Two sets of synthesized speech stimuli varying in Mandarin consonant (alveolo-palatal affricate vs. fricative) and lexical tone features (rising vs. contour tone) were used to examine the developmental course of speech perception abilities. The results indicated that only the adult group demonstrated typical early mismatch negativity (MMN) responses, suggesting that the ability to discriminate specific speech cues in Mandarin consonant and lexical tone is a continuing process in preschool- and school-aged children. Additionally, distinct MMR patterns provided evidence indicating diverse developmental courses to different speech characteristics. By incorporating data from the two speech conditions, we propose using MMR profiles consisting of mismatch negativity (MMN), positive mismatch response (p-MMR), and late discriminative negativity (LDN) as possible brain indices to investigate speech perception development.

Effect of maturation on suprasegmental speech processing in full- and preterm infants: a mismatch negativity study

Infants born prematurely are at higher risk for later linguistic deficits present in delayed or atypical processing of phonetic and prosodic information. In order to be able to specify the nature of this atypical development, it is important to investigate the role of early experience in language perception. According to the concept of Gonzalez-Gomez and Nazzi (2012) there is a special intrauterine sensitivity to the prosodic features of languages that should have a special role in language acquisition. Therefore, we may also assume that pre- and full-term infants having months difference in intrauterine experience show different maturation patterns of processing prosodic and phonetic information present at word level. The aim of our study was to investigate the effect of these differences on word stress pattern vs. phoneme information processing. Two age groups of infants (6 and 10 month-olds) were included in our study. 21 of 46 of the total of infants investigated were prematurely born with low birth weight. We used the mismatch negativity (MMN) event related brain potential (ERP) component, a widely used electrophysiological correlate of acoustic change detection, for testing the assumed developmental changes of phoneme and word stress discrimination. In a passive oddball paradigm we used a word as standard, a pseudo-word as phoneme deviant, and an illegally uttered word as stress deviant. Our results showed no differences in MMN responses in the phoneme deviant condition between the groups, meaning a relatively intact maturation of phoneme processing of preterm infants as compared to their contemporaries. However, the mismatch responses measured in the stress condition revealed significant between-group differences. These results strengthen the view that the total length of intrauterine experience influences the time of emergence of prosodic processing.

Separating acoustic deviance from novelty during the first year of life: a review of event-related potential evidence

Orienting to salient events in the environment is a first step in the development of attention in young infants. Electrophysiological studies have indicated that in newborns and young infants, sounds with widely distributed spectral energy, such as noise and various environmental sounds, as well as sounds widely deviating from their context elicit an event-related potential (ERP) similar to the adult P3a response. We discuss how the maturation of event-related potentials parallels the process of the development of passive auditory attention during the first year of life. Behavioral studies have indicated that the neonatal orientation to high-energy stimuli gradually changes to attending to genuine novelty and other significant events by approximately 9 months of age. In accordance with these changes, in newborns, the ERP response to large acoustic deviance is dramatically larger than that to small and moderate deviations. This ERP difference, however, rapidly decreases within first months of life and the differentiation of the ERP response to genuine novelty from that to spectrally rich but repeatedly presented sounds commences during the same period. The relative decrease of the response amplitudes elicited by high-energy stimuli may reflect development of an inhibitory brain network suppressing the processing of uninformative stimuli. Based on data obtained from healthy full-term and pre-term infants as well as from infants at risk for various developmental problems, we suggest that the electrophysiological indices of the processing of acoustic and contextual deviance may be indicative of the functioning of auditory attention, a crucial prerequisite of learning and language development.

Evidence for the late MMN as a neurophysiological endophenotype for dyslexia

Dyslexia affects 5–10% of school-aged children and is therefore one of the most common learning disorders. Research on auditory event related potentials (AERP), particularly the mismatch negativity (MMN) component, has revealed anomalies in individuals with dyslexia to speech stimuli. Furthermore, candidate genes for this disorder were found through molecular genetic studies. A current challenge for dyslexia research is to understand the interaction between molecular genetics and brain function, and to promote the identification of relevant endophenotypes for dyslexia. The present study examines MMN, a neurophysiological correlate of speech perception, and its potential as an endophenotype for dyslexia in three groups of children. The first group of children was clinically diagnosed with dyslexia, whereas the second group of children was comprised of their siblings who had average reading and spelling skills and were therefore “unaffected” despite having a genetic risk for dyslexia. The third group consisted of control children who were not related to the other groups and were also unaffected. In total, 225 children were included in the study. All children showed clear MMN activity to/da/−/ba/contrasts that could be separated into three distinct MMN components. Whilst the first two MMN components did not differentiate the groups, the late MMN component (300–700 ms) revealed significant group differences. The mean area of the late MMN was attenuated in both the dyslexic children and their unaffected siblings in comparison to the control children. This finding is indicative of analogous alterations of neurophysiological processes in children with dyslexia and those with a genetic risk for dyslexia, without a manifestation of the disorder. The present results therefore further suggest that the late MMN might be a potential endophenotype for dyslexia.

Event-related potentials to an english/spanish syllabic contrast in mexican 10-13-month-old infants

We report brain electrophysiological responses from 10- to 13-month-old Mexican infants while listening to native and foreign CV-syllable contrasts differing in Voice Onset Time (VOT). All infants showed normal auditory event-related potential (ERP) components. Our analyses showed ERP evidence that Mexican infants are capable of discriminating their native sounds as well as the acoustically salient (aspiration) foreign contrast. The study showed that experience with native language influences VOT perception in Spanish learning infants. The acoustic salience of aspiration is perceived by both Spanish and English learning infants, but exposure provides additional phonetic status to this native-language feature for English learning infants. The effects of early experience and neural commitment as well as the impact of acoustic salience are further discussed.

First genome-wide association scan on neurophysiological endophenotypes points to trans-regulation effects on SLC2A3 in dyslexic children

Dyslexia is one of the most common learning disorders affecting about 5% of all school-aged children. It has been shown that event-related potential measurements reveal differences between dyslexic children and age-matched controls. This holds particularly true for mismatch negativity (MMN), which reflects automatic speech deviance processing and is altered in dyslexic children. We performed a whole-genome association analysis in 200 dyslexic children, focusing on MMN measurements. We identified rs4234898, a marker located on chromosome 4q32.1, to be significantly associated with the late MMN component. This association could be replicated in an independent second sample of 186 dyslexic children, reaching genome-wide significance in the combined sample (P = 5.14e-08). We also found an association between the late MMN component and a two-marker haplotype of rs4234898 and rs11100040, one of its neighboring single nucleotide polymorphisms (SNPs). In the combined sample, this marker combination withstands correction for multiple testing (P = 6.71e-08). Both SNPs lie in a region devoid of any protein-coding genes; however, they both show significant association with mRNA-expression levels of SLC2A3 on chromosome 12, the predominant facilitative glucose transporter in neurons. Our results suggest a possible trans-regulation effect on SLC2A3, which might lead to glucose deficits in dyslexic children and could explain their attenuated MMN in passive listening tasks.

Auditory and visual novelty processing in normally-developing Kenyan children

OBJECTIVE

The aim of this study was to describe the normative development of the electrophysiological response to auditory and visual novelty in children living in rural Kenya.

METHODS

We examined event-related potentials (ERPs) elicited by novel auditory and visual stimuli in 178 normally-developing children aged 4-12 years (86 boys, mean 6.7 years, SD 1.8 years and 92 girls, mean 6.6 years, SD 1.5 years) who were living in rural Kenya.

RESULTS

The latency of early components (auditory P1 and visual N170) decreased with age and their amplitudes also tended to decrease with age. The changes in longer-latency components (Auditory N2, P3a and visual Nc, P3a) were more modality-specific; the N2 amplitude to novel stimuli decreased with age and the auditory P3a increased in both latency and amplitude with age. The Nc amplitude decreased with age while visual P3a amplitude tended to increase, though not linearly.

CONCLUSIONS

The changes in the timing and magnitude of early-latency ERPs likely reflect brain maturational processes. The age-related changes to auditory stimuli generally occurred later than those to visual stimuli suggesting that visual processing matures faster than auditory processing.

SIGNIFICANCE

ERPs may be used to assess children's cognitive development in rural areas of Africa.

Mismatch response to polysyllabic nonwords: a neurophysiological signature of language learning capacity

Background

The ability to repeat polysyllabic nonwords such as “blonterstaping” has frequently been shown to correlate with language learning ability but it is not clear why such a correlation should exist. Three alternative explanations have been offered, stated in terms of differences in: (a) perceptual ability; (b) efficiency of phonological loop functioning; (c) pre-existing vocabulary knowledge and/or articulatory skills. In the present study, we used event-related potentials to assess the contributions from these three factors to explaining individual variation in nonword repetition ability.

Methodology/Principal Findings

59 adults who were subdivided according to whether they were good or poor nonword-repeaters participated. Electrophysiologically measured mismatch responses were recorded to changes in consonants as participants passively listened to a repeating four syllable CV-string. The consonant change could occur in one of four positions along the CV-string and we predicted that: (a) if nonword repetition depended purely on auditory discrimination ability, then reduced mismatch responses to all four consonant changes would be observed in the poor nonword-repeaters, (b) if it depended on encoding or decay of information in a capacity-limited phonological store, then a position specific decrease in mismatch response would be observed, (c) if neither cognitive capacity was involved, then the two groups of participants would provide equivalent mismatch responses. Consistent with our second hypothesis, a position specific difference located on the third syllable was observed in the late discriminative negativity (LDN) window (230–630 ms post-syllable onset).

Conclusions/Significance

Our data thus confirm that people who are poorer at nonword repetition are less efficient in early processing of polysyllabic speech materials, but this impairment is not attributable to deficits in low level auditory discrimination. We conclude by discussing the significance of the observed relationship between LDN amplitude and nonword repetition ability and describe how this relatively little understood ERP component provides a biological window onto processes required for successful language learning.

Effect of inverting electrode on mismatch negativity presence for perceptible/imperceptible tonal frequency contrasts

The effect of inverting electrode location and stimulus perceptibility on the presence of the mismatch negativity (MMN) evoked response was investigated in 20 normal-hearing adult females. Perceptible and imperceptible frequency contrasts were employed in an oddball paradigm. The perceptible contrast consisted of an 1122 Hz standard and a 1000 Hz target, while the imperceptible contrast consisted of an 1122 Hz standard and an 1120 Hz target. Data were referenced separately to the tip of the nose, the ipsilateral mastoid, and the mathematical average of the two mastoids. Presence of a response was determined according to strict criteria established a priori. The correspondence between MMN findings and parallel behavioral discrimination data was not systematic. Inverting electrode had an effect of MMN presence. MMNs were more likely to be present for mastoid-referenced data than nose-referenced data. Thus, when using the current paradigm, a mastoid reference is suggested to optimize the detection of the MMN response.

Ereigniskorrelierte Potenziale und auditives sensorisches Gedächtnis

Fragestellung: Defizite im auditiven Kurzzeitgedächtnis werden als Ursache u. a. für Sprachentwicklungs- und Lese-Rechtschreibstörungen diskutiert. Für die ersten Lebensjahre fehlen bislang jedoch aussagefähige Untersuchungen zum Kurzzeitgedächtnis. Ziel der vorliegenden Studie war es, bei jüngeren Kindern die Dauer des auditiven sensorischen Gedächtnisses mit objektiven Methoden zu bestimmen. Methodik: In Gruppen unauffällig entwickelter, zwei- (n = 37) bzw. sechsjähriger (n = 52) Kinder wurden mit einem passiven auditiven Oddball-Paradigma und variablem Interstimulusintervall (ISI: 0.5–5 s, je nach Gruppe) ereigniskorrelierte Potenziale (EKP) abgeleitet. Ergebnisse: Bei kurzem ISI waren eine Mismatch Negativity (MMN) und eine Late Discriminative Negativity (LDN) und bei langem ISI eine P3a zu beobachten. Eine ISI-Abhängigkeit war für die MMN und LDN statistisch zu belegen. Die Änderung der EKP-Komponentenstruktur trat bei den sechsjährigen Kindern bei einem deutlich längeren ISI als bei den zweijährigen ein. Schlussfolgerungen: Die Punkte des Verschwindens von MMN und LDN bei ISI–Verlängerung sprechen dafür, dass die Dauer des auditiven sensorischen Gedächtnisses bei zweijährigen Kindern etwa 1–2 s und bei sechsjährigen 3–5 s beträgt. Allerdings scheinen an der Kurzzeitspeicherung akustischer Signale verschiedene Mechanismen mit unterschiedlicher Dauer der Speicherung beteiligt zu sein, da eine P3a auch nach Verschwinden von MMN und LDN noch ableitbar ist.

Topography of syllable change-detection electrophysiological indices in children and adults with reading disabilities

INTRODUCTION

Developmental dyslexia (DD) is a frequent language-based learning disorder. The predominant etiological view postulates that reading problems originate from a phonological impairment.

METHOD

We studied mismatch negativity (MMN) and Late Discriminative Negativity (LDN) to syllables change in both children (n=12; 8-12 years) and young adults (n=15; 14-23 years) with DD compared with controls.

RESULTS/DISCUSSION

The present study confirmed abnormal automatic discrimination of syllable changes in both children and adults with developmental dyslexia. MMN topographic, amplitude and latency group differences were evidenced, suggesting different brain mechanisms involved in elementary auditory stimulus change-detection in DD, especially in the left hemisphere. The LDN results demonstrated that the auditory disorder of temporal processing in DD children becomes more serious at late stages of information processing and that the apparent cerebral hypo reactivity to speech changes in DD actually may correspond to additional processes. The age-related differences observed in both MMN and LDN topographies, amplitudes and latency between subjects with DD and controls could indicate different developmental courses in the neural representation of basic speech sounds in good and poor readers, with a tendency to normalization with increasing age.

CONCLUSION

Our results showing atypical electrophysiological concomitants of speech auditory perception in DD strongly support the hypothesis of deviant cortical organization in DD.

Reduced mismatch negativity in posttraumatic stress disorder: a compensatory mechanism for chronic hyperarousal?

Mismatch Negativity (MMN) is yet poorly understood in the context of Posttraumatic Stress Disorder (PTSD, e.g. [Morgan 3rd, C.A., Grillon, C., 1999. Abnormal mismatch negativity in women with sexual assault-related posttraumatic stress disorder. Biol. Psychiatry 45, 827-832.]). PTSD symptoms like hyperarousal, emotional pressure and avoidance may interfere with pre-attentive sensory processing. We tested this in an optimized MMN design [Näätänen, R., Pakarinen, S., Rinne, T., Takegata, R. (2004) The mismatch negativity (MMN): towards the optimal paradigm. Clin. Neurophysiol. 115: 140-144.] with PTSD victims and a control group without PTSD. A group of PTSD subjects was compared with gender and age-matched, healthy comparison subjects without PTSD. A "memory trace" was elicited by frequently presented "standard" auditory stimuli (50% occurrence) of 1 kHz, 75 ms duration, intermittently with 8 rare "deviants", which differed in frequency (higher/lower), intensity (louder/softer), duration (shorter), direction (left/right) or by the presence of a gap in the sound. During presentation of tones a silent film was shown. Psychometric data were collected by SCID, BSI, Attentiveness Inventory, Edinburgh Handedness Questionnaire, and the PTSD Screening Scale by Breslau et al. [Breslau, N., Peterson, E.L., Kessler, R.C., Schultz, L.R. (1999) Short screening scale for DSM-IV posttraumatic stress disorder. Am. J. Psychiatry 156: 908-911.]. Group comparisons of the MMN were performed for left/right-frontal/temporal, and for midline electrode sites. A good differentiation of both groups was found in psychometric and electrophysiological data. The PTSD group revealed on most BSI scales enhanced values of psychic aberration. The amplitude of the MMN was significantly reduced in the PTSD compared to non-PTSD subjects. MMN was significantly correlated with the total PTSD score. The data suggest a reduction in pre-attentive auditory sensory memory in PTSD due to specific symptom variables such as hyperarousal, sleeplessness, impaired concentration and a general enhanced excitation of the nervous system. This protective inhibition is thought to be a fine-tuning process in PTSD in order to prevent arousal overload.

Effects of Breast Milk and Milk Formula Diets on Synthesized Speech Sound-Induced Event-Related Potentials in 3- and 6-Month-Old Infants

Effects of breast milk and milk formula supplemented with docosahexaenoic acid and arachidonic acid on speech processing were investigated by recording event-related potentials (ERPs) to synthesized /pa/ and /ba/ (oddball paradigm, 80%:20%) at 3 and 6 months of age. Behavioral assessment was also obtained. A major positive component (P200) was elicited by both types of sounds. It had a maximal scalp distribution in the fronto-central areas in both groups of infants. The mean latencies did not differ between the groups or between the stimulus types. However, the latencies decreased across age in both groups. The mean P200 amplitude in the formula-fed infants was lower than that in the breast-fed infants, but the difference was not significant. The between-stimulus differences in frontal P200 amplitudes were positively correlated with the behavioral scores of Bayley Index of Infant Development. These data suggest that the processing of the present speech stimuli is not affected by the investigated diets in the early infancy.

Extracting rules: early and late mismatch negativity to tone patterns

The auditory processing of physical stimulus features can be measured by the mismatch negativity. Past studies have shown that higher-order stimulus features also elicit a mismatch negativity. In some studies, a second component, termed late mismatch negativity, has been observed; yet the functional significance of this component remains unclear. We tested two-tone-pattern stimuli following an abstract rule in healthy adults. As expected, the tone pattern elicited a significant mismatch negativity peaking at 146 ms but a significant late mismatch negativity at around 340 ms was also observed. These findings show that the violation of an abstract rule elicits an early and late mismatch negativity. The late mismatch negativity might be triggered on the basis of auditory rule extraction processes and reflect a transfer of rules to the long-term memory.

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.

Phonological categorization of vowels: a mismatch negativity study

There is electrophysiological evidence that phonological categorization has occurred within 100-200 ms post stimulus onset for the syllables /tae/ and /dae/, which vary in voice onset time. Using a similar paradigm, this study investigated when phonological categorization occurred for the contrast between /I/ and /epsilon/, using synthesized speech tokens that differed in the frequency of the first formant. Here we show that phonological categorization of these tokens has not occurred 100-200 ms after stimulus onset. However, the presence of a late mismatch negativity (350 ms after stimulus onset) indicated that phonological categorization had taken place by this time.

MMN to natural Arabic CV syllables: 1-normative data

Mismatch negativity response parameters; latency, amplitude, and duration to natural Arabic CV syllables differing in durational change (Baa-Waa) and in spectrotemporal change (Gaa-Daa) were obtained from normal hearing young adult Egyptians. The aim was to get normative data for MMN response parameters and to find any differences between both primary and non-primary auditory pathways in encoding and processing speech signals. Statistically significant differences between durational and spectrotemporal contrasts for latency and duration were found. This was attributed to acoustic differences and to physiological differences between primary and non-primary auditory pathways.

Event-related potentials associated with sound discrimination versus novelty detection in children

In children, deviant sounds in an oddball paradigm elicit a mismatch negativity (MMN) indexing discrimination of sound change and late difference negativity (LDN) with unknown functional significance. Salient sounds elicit an ERP index if orienting, P3a, and a late negative component, Nc. We compared children's responses elicited by moderate sound changes and novel sounds to examine the relationships between MMN and LDN, and LDN and Nc. Two components of the Nc, the Nc1 and Nc2, were identified. The scalp topography of LDN differed from those of the MMN and Nc1. Children's early P3a appeared mature but late P3a lacked frontal predominance. The findings suggested that LDN is not linked with either the sensory or attentional processing. It might reflect cognitive, albeit preattentive, processing of sound change. The Nc1 appears to reflect cognitive attentive processing of salient stimuli and the Nc2 might reflect reorienting after distraction.

Event-related potentials associated with second language learning in children

OBJECTIVE

In this study, we investigated learning-related changes in auditory event-related potentials (ERPs) of Finnish-speaking 3-6-year-old children caused by learning French language.

METHODS

Using an oddball paradigm, ERPs to sounds of French language were recorded in the two groups of healthy children: those who were learning French (experimental group) and those who were not learning any foreign language (control peers).

RESULTS

When the children from the experimental group were exposed to the foreign language, they automatically developed French-specific memory traces that helped them to discriminate, categorize, and pronounce utterances of the new language as indicated by the mismatch negativity (MMN) component of the ERPs in a previous study. We found that the learning process was also reflected by changes in P3a and late difference negativity (LDN) responses. Unlike MMN and P3a, the LDN has been discovered relatively recently and its functional role remains unclear. Similarly, as the MMN magnitude increased during the learning process, an increase of the P3a (known to reflect the involuntary attention switching toward deviant stimuli) and LDN amplitudes was observed. The ERPs of the control peers did not change significantly over the test period.

CONCLUSIONS

When phonemes of a foreign language are learned, this process is accompanied with the increase in the MMN, P3a, and LDN amplitudes in children. Though the functional significance of LDN remains to be further investigated, our results support its possible link to reorienting processes following distraction.

Event-related potential indices of auditory vowel processing in 3-year-old children

OBJECTIVE

To determine the ERP characteristics and ERP indices of central speech sound encoding and discrimination in young children.

METHODS

Auditory sensory event-related potentials (ERPs) and the ERP index of auditory sensory discrimination (the mismatch negativity, MMN) were elicited by vowel stimuli in 3-year-old children. In an oddball paradigm, the standard stimulus was vowel /a/, one deviant stimulus was vowel /o/ (the across-category change), and the other was nasalized vowel /a/ (within-category change). In addition, the ERP changes occurring during the 14 min uninterrupted recording were examined.

RESULTS

As indexed by the sensory P1, N2, and N4 peaks, the 3-year-old children's transient neural encoding of vowels was comparable to that earlier registered in 1-year-old children but also showed vowel-specific characteristics observed in school-age children. The 3-year-old's MMN was comparable in amplitude to the school-age children's MMN and appeared to be sensitive to the across-category aspects of vowel changes. However, its latency was longer in the 3-year-olds than in school-age children. Among the sensory ERPs, only the N4 peak showed significant diminution during the experiment. The across-category change MMN diminished after 10 min of the recording, however, over the frontal areas only.

CONCLUSIONS

In the 3-year-old children, the sensory processing of vowels exhibited transitional characteristics between those observed in infants and school-age children. The auditory sensory discrimination in the 3-year-olds appeared to be sensitive to the phonemic aspects of stimulus change. The frontally-predominant MMN diminution during the experiment might indicate the greater refractoriness of its frontal-lobe generators. In general, the auditory sensory ERPs show distinct maturational profiles from that of the MMN.