Valerie L. Shafer

Maturation of mismatch negativity in typically developing infants and preschool children.

Objective 1) To determine whether an adult-like mismatch negativity (MMN) can be reliably elicited in typically developing awake infants and preschool children, and if so 2) to examine whether maturational changes exist in MMN latency and amplitude. Design Two experiments were designed to elicit MMN using an “oddball” paradigm. In Experiment 1, a 1000-Hz tone served as the standard stimulus and a 1200-Hz tone as the deviant. In Experiment 2, a 1000-Hz standard stimulus and a 2000-Hz deviant were presented. Infants’ ages ranged from 2 to 47 and 3 to 44 mo in Experiments 1 and 2, respectively. Results In Experiment 1, a negativity was not elicited in the majority of the infants and preschoolers tested. In Experiment 2, a negativity was reliably elicited in the infants and preschoolers across all ages. A significant negative correlation was observed between age and latency, but not for age and amplitude for this negativity. This negativity was found to decrease at a rate of 1 msec/mo. Infants younger than 12 mo of age showed a significantly larger positivity to the deviant than to the standard between 150–300 and 200–300 msec in Experiments 1 and 2, respectively. Conclusions The discriminative processes indexed by MMN in response to frequency changes are immature in infants and preschool children. Although there is convincing evidence that the negativity elicited in Experiment 2 is an immature MMN, the possibility that it may be an “obligatory effect” indexing recovery from refractoriness cannot be ruled out at this time. The results from these experiments suggest that the MMN component has limited use as a clinical tool at this time for infants and young children.

Maturation of mismatch negativity in school-age children.

Objective: Event‐related potentials were recorded to investigate the maturation of auditory processing in school‐age children. Design: The mismatch negativity (MMN) was obtained in an oddball tone discrimination paradigm in 66 school‐age children and 12 adults. In the childrens data, a prominent negativity to both the standard and deviant tone, peaking around 200 msec, was observed, and compared with the N1 auditory evoked potential component. Results: The MMN was found to decrease with latency by 11 msec/yr from 4 to 10 yr of age. No developmental change in MMN amplitude was seen from 4 to 10 yr of age. However, the MMN amplitude was significantly smaller in adults than in children. The prominent negativity in children was significantly later than the adult N1 component, and did not change in latency from 4 to 10 yr of age. This finding adds to a body of evidence suggesting that this prominent negativity and the adult N1 are not the same component. The magnitude of the prominent negativity in children decreased slightly with age. Conclusion: Changes in the timing of the brain discriminative response, MMN, suggest systematic maturational changes in auditory processing.

Neurophysiological Indexes of Speech Processing Deficits in Children with Specific Language Impairment

We used neurophysiological and behavioral measures to examine whether children with specific language impairment (SLI) have deficits in automatic processing of brief, phonetically similar vowels, and whether attention plays a role in such deficits. The neurophysiological measure mismatch negativity (MMN) was used as an index of discrimination in two tasks; one in which children ignored the auditory stimuli and watched a silent video and a second in which they attended to the auditory modality. Children with SLI showed good behavioral discrimination, but significantly poorer behavioral identification of the brief vowels than the children with typical language development (TLD). For the TLD children, two neurophysiological measures (MMN and a later negativity, LN) indexed discrimination of the vowels in both tasks. In contrast, only the LN was elicited in either task for the SLI group. We did not see a direct correspondence between the absence of MMN and poor behavioral performance in the children with SLI. This pattern of findings indicates that children with SLI have speech perception deficiencies, although the underlying cause may vary.

Maturation of speech discrimination in 4- to 7-yr-old children as indexed by event-related potential mismatch responses.

Objectives: This study examined maturation of mismatch responses (MMRs) to an English vowel contrast (/I/ versus /&egr;/) in 4- to 7-yr-old children. Design: Event-related potentials were recorded to a standard [&egr;] and deviant [I] vowel presented in trains of 10 stimuli at a rate of 1/650 msecs and with an intertrain interval of 1.5 secs. Each train contained two deviant vowels. Averaged responses were calculated for the infrequent (deviant) and the frequent (standard) trials for each child and compared across age groups. Results: Significantly greater negativity, consistent with the adult mismatch negativity (MMN), was observed to the deviants between 300 and 400 msecs for both younger (4- and 5-yr-old) and older (6- and 7-yr-old) children. This MMN-like negativity shifted earlier in latency by 25 msecs/yr with increasing age. Most of the children younger than 5.5 yrs and some of the older children also showed a positive MMR (p-MMR) peaking between 100 and 300 msecs. The p-MMR diminished in amplitude with increasing age. Conclusions: Maturation of speech discrimination, as indexed by MMN, occurs more rapidly between 4 and 7 yrs of age for vowels than for tones. A p-MMR preceding the MMN also reflects discrimination in younger children and declines in amplitude with age.

Maturation of mismatch negativity: A scalp current density analysis

Objective Auditory evoked potentials provide the opportunity to better understand the central processing of auditory stimuli, which is the basis of speech and language perception. The purpose of this study was to examine maturational changes in the topography of one of these auditory evoked potentials, the mismatch negativity (MMN), using scalp current density (SCD) analysis. Design Subjects were children ages 4 to 11 yr (N = 53), and adults (N = 12). Stimuli were 85 dB peSPL 1000 Hz standard tones and 1200 Hz deviant tones (deviant probability = 0.15). Auditory evoked potentials were recorded using surface electrodes placed at 32 locations on the head while subjects ignored the stimuli by watching a silent video. Results Significant maturational changes in topography of MMN were seen over frontal and left lateral sites. Conclusions Differences in MMN for the children compared to adults indicate that the MMN generators or their orientation, and thus the neural processes underlying discrimination of simple tones, are not yet mature by 11 yr of age.

Deviant neurophysiological asymmetry in children with language impairment.

Deviant anatomical asymmetry of perisylvian cortex is argued to be linked to specific language impairment (SLI). However, no studies have examined whether deviant functional asymmetry underlies the processing of spoken language. In the current study, brain-electrical activity was recorded from 31 scalp sites to the function word ‘the’ embedded in auditorally presented stories and nonsense contexts. The SLI children showed reversed asymmetry at electrode sites over temporal cortex compared to control children in processing this word in all contexts. They also appear to lack some contribution from a deep neural generator in processing ‘the’ in the story. This investigation is the first to demonstrate a direct link between deviant neurophysiological asymmetry and the processing of spoken language in children with SLI.

Neurophysiological Indices of Attention to Speech in Children with Specific Language Impairment

OBJECTIVE The aim was to determine whether children with specific language impairment (SLI) differed from children with typical language development (TLD) in their allocation of attention to speech sounds. METHODS Event-related potentials were recorded to non-target speech sounds in two tasks (passive-watch a video and attend to target tones among speech sounds) in two experiments, one using 50-ms duration vowels and the second using 250-ms vowels. The difference in ERPs across tasks was examined in the latency range of the early negative difference wave (Nd) found in adults. Analyses of the data using selected superior and inferior sites were compared to those using electrical field power (i.e., global field power or GFP). The topography of the ERP at the maximum GFP was also examined. RESULTS A negative difference, comparable to the adult Nd, was observed in the attend compared to the passive task for both types of analysis, suggesting allocation of attentional resources to processing the speech stimuli in the attend task. Children with TLD also showed greater negativity than those with SLI in the passive task for the long vowels, suggesting that they allocated more attentional resources to processing the speech in this task than the SLI group. This effect was only significant using the GFP analysis and was seen as smaller GFP for the TLD than SLI group. The SLI group also showed significantly later latency than the TLD group in reaching the maximum GFP. In addition, a significantly greater proportion of children with SLI compared to those with typical language showed left-greater-than-right frontocentral amplitude at the latency determined from each childs maximum GFP peak. CONCLUSIONS Children generally showed greater attention to speech sounds when attention is directed to the auditory modality compared to the visual modality. However, children with TLD, unlike SLI, also appear to devote some attentional resources to speech even in a task in which they are instructed to attend to visual information and ignore the speech. SIGNIFICANCE These findings suggest that children with SLI have limited attentional resources, that they are poorer at dividing attention, or that they are less automatic in allocating resources to speech compared to children with typically developing language skills.

The Development of English Vowel Perception in Monolingual and Bilingual Infants: Neurophysiological Correlates

The goal of this paper was to examine intrinsic and extrinsic factors contributing to the development of speech perception in monolingual and bilingual infants and toddlers. A substantial number of behavioral studies have characterized when infants show changes in behavior towards speech sounds in relation to amount of experience with these sounds. However, these studies cannot explain to what extent the developmental timeline is influenced by experience with the language versus constraints imposed by cortical maturation. Studies using electrophysiological measures to examine the development of auditory and speech processing have shown great differences in infant and adult electrophysiological correlates of processing. Many of these differences are a function of immature cortex in the infant. In this paper, we examined the maturation of infant and child event-related-potential (ERP) electrophysiological components in processing an English vowel contrast and explored to what extent these components are influenced by intrinsic (e.g., sex) versus extrinsic factors, such as language experience (monolingual vs. bilingual). Our findings demonstrate differences in the pattern of ERP responses related to age and sex, as well as language experience. These differences make it clear that general maturational factors need to be taken into consideration in examining the effect of language experience on the neurodevelopment of speech perception.

Evidence of deficient central speech processing in children with specific language impairment: the T-complex.

OBJECTIVE This paper examined neurophysiological correlates of speech in children with language impairment (LI) and typical language development (TLD) across four experiments using different speech stimuli and tasks. METHODS The T-complex event-related potential (ERP) components and other ERP components (e.g., mismatch negativity [MMN]; N400) were examined. A subset of the children participated in more than one of the experiments. RESULTS 73% of the children with LI had poor T-complex measures compared to only 13% of children with TLD. The T-complex measures were more comparable, in terms of indicating typical versus deviant processing, to neurophysiological measures of language processing, such as lexical discrimination, than to other measures of auditory and speech processing, such as the MMN. Only one LI child showed no poor measures and 64% showed three or more poor neurophysiological measures. However, 50% of children with TLD showed no poor neurophysiological measures, and 82% of the TLD children showed no more than two poor measures. CONCLUSIONS These results suggest that poor auditory processing, as measured by the T-complex, is a marker for LI and that multiple deficits serve to mark LI. SIGNIFICANCE The T-complex measures, indexing secondary auditory cortex, reflect an important aspect of processing in speech and language development.

Brain responses to filled gaps

An unresolved issue in the study of sentence comprehension is whether the process of gap-filling is mediated by the construction of empty categories (traces), or whether the parser relates fillers directly to the associated verbs argument structure. We conducted an event-related potentials (ERP) study that used the violation paradigm to examine the time course and spatial distribution of brain responses to ungrammatically filled gaps. The results indicate that the earliest brain response to the violation is an early left anterior negativity (eLAN). This ERP indexes an early phase of pure syntactic structure building, temporally preceding ERPs that reflect semantic integration and argument structure satisfaction. The finding is interpreted as evidence that gap-filling is mediated by structurally predicted empty categories, rather than directly by argument structure operations.