Hia Datta

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.

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.

The development of the length of the temporal window of integration for rapidly presented auditory information as indexed by MMN.

OBJECTIVE The length of the temporal window integrating successive auditory stimuli into unitary percepts has been estimated to be less than 200 ms in adults. The aim of the study was to investigate the development of the integrating window in children to determine whether it is similar to young adults. METHODS A modified auditory oddball paradigm was presented at a rapid (150-400 ms) onset-to-onset pace during recording of electroencephalogram in two groups of children (aged 5-8 and 9-11 years) and one group of adults. Latencies and amplitudes of the P1, N1, and the mismatch negativity (MMN) components of event-related brain potentials (ERPs) were measured. RESULTS The length of the temporal window of integration (TWI) was shorter in adults (<200 ms) than older children (<300 ms in 9-11-year-olds) and younger children (<350 ms in the 5-8-year-olds). In addition, age-related changes were found in the latency and amplitude of the ERP components. CONCLUSIONS The results demonstrate a general maturational development of the auditory evoked potentials and also a specific maturational process for temporal encoding of information in auditory cortex. SIGNIFICANCE Rapid stimulus presentation rates can be successfully used in school-aged children to study neural mechanisms of auditory processes.

Native language experience influences the topography of the mismatch negativity to speech.

The ability to learn second language speech sound categories declines during development. We examined this phenomenon by studying the mismatch negativity (MMN) to the /r/ – /l/ distinction in native English speakers and learners of English as a second language who are native speakers of Japanese. Previous studies have suggested that the MMN is remarkably plastic when evaluated as a waveform at a central electrode. We replicated this finding: analyses of the MMN at a typical electrode location (Fz) revealed only small, non-significant differences between groups, despite large behavioral differences in the ability to discriminate these sounds from one another. Topographic analyses, however, revealed reliable differences in lateralization of the MMN, such that native English speakers’ responses were left-lateralized relative to native Japanese speakers’ responses.

ERP indices of vowel processing in Spanish–English bilinguals

This study examined behavioral and neurophysiological indices of discrimination of an English vowel contrast [[ɪ–ɛ] by early and late bilingual Spanish-English speakers, compared to monolingual English speakers. Electrophysiological measures (Mismatched Negativity - MMN) and behavioral measures (AX discrimination and forced-choice identification) were employed to examine perception of a nine-step vowel continuum, re-synthesized from natural tokens. Results revealed that (i) both monolingual and early bilinguals showed similar behavioral perception while late bilinguals performed more poorly on all behavioral tasks; and (ii) monolinguals showed robust evidence of discrimination (MMN) at a pre-attentive level that was significantly larger than found for either early or late bilinguals. These findings suggested that early input of English vowels to bilinguals did not necessarily lead to robust, automatic processing, as measured at a more attention-independent neural level; but earlier experience with a second language allowed for native-like speech perception measured with behavioral tasks.

Sensitive periods for language and recovery from stroke: Conceptual and practical parallels

In this review, we consider the literature on sensitive periods for language acquisition from the perspective of the stroke recovery literature treated in this Special Issue. Conceptually, the two areas of study are linked in a number of ways. For example, the fact that learning itself can set the stage for future failures to learn (in second language learning) or to remediate (as described in constraint therapy) is an important insight in both areas, as is the increasing awareness that limits on learning can be overcome by creating the appropriate environmental context. Similar practical issues, such as distinguishing native-like language acquisition or recovery of function from compensatory mechanisms, arise in both areas as well.

Discrimination and identification of long vowels in children with typical language development and specific language impairment

Researchers have claimed that children with specific language impairment (SLI) have particular difficulties in discriminating and identifying phonetically similar and brief speech sounds (Stark and Heinz, 1966; Studdert‐Kennedy and Bradley, 1997; Sussman, 1993). In a recent study (Shafer et al., 2004), children with SLI were reported to have difficulty in processing brief (50 ms), phonetically similar vowels (/I‐E/). The current study investigated perception of long (250 ms), phonetically similar vowels (/I‐E/) in 8‐ to 10‐year‐old children with SLI and typical language development (TLD). The purpose was to examine whether phonetic similarity in vowels leads to poorer speech‐perception in the SLI group. Behavioral and electrophysiological methods were employed to examine discrimination and identification of a nine‐step vowel continuum from /I/ to /E/. Similar performances in discrimination were found for both groups, indicating that lengthening vowel duration indeed improves discrimination of phonetically...

English vowel contrast perception on monolingual and bilingual 4‐ to 7‐year olds: Behavioral and neurophysiological evidence.

The role of simultaneous bilingual language exposure on speech perception development has been far from definitive. Behavioral literature has been controversial in terms of whether bilingual children keep pace with their monolingual peers [Burns et al. (2007); Sundara et al. (2006)]. The purpose of the current study is to: (1) investigate whether bilingual exposure to Spanish and English affects processing of speech stimuli that are phonemic only in English in children from 4–7 years of age; (2) whether the event‐related potential (ERP) measures correlate with the behavioral measure (e.g., phoneme identification). Phonetically similar vowel contrasts (I versus E) were presented in an oddball paradigm while ERPs were collected from 65 scalp sites. Vowel discrimination and vowel identification were carried out using I‐E vowel continuum. Preliminary analyses suggest that there is no difference in how monolingual and bilingual children behaviorally identify this vowel contrast. In terms of the ERP responses, ...