Language-specific memory traces of consonants in the brain

The tone atlas of perceptual discriminability and perceptual distance: Four tone languages and five language groups

Some prior investigations suggest that tone perception is flexible, reasonably independent of native phonology, whereas others suggest it is constrained by native phonology. We address this issue in a systematic and comprehensive investigation of adult tone perception. Sampling from diverse tone and non-tone speaking communities, we tested discrimination of the three major tone systems (Cantonese, Thai, Mandarin) that dominate the tone perception literature, in relation to native language and language experience as well as stimulus variation (tone properties, presentation order, pitch cues) using linear mixed effect modelling and multidimensional scaling. There was an overall discrimination advantage for tone language speakers and for native tones. However, language- and tone-specific effects, and presentation order effects also emerged. Thus, over and above native phonology, stimulus variation exerts a powerful influence on tone discrimination. This study provides a tone atlas, a reference guide to inform empirical studies of tone sensitivity, both retrospectively and prospectively.

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.

Neural Representation of the English Vowel Feature [High]: Evidence From /ε/ vs. /ɪ/

Many studies have observed modulation of the amplitude of the neural index mismatch negativity (MMN) related to which member of a phoneme contrast [phoneme A, phoneme B] serves as the frequent (standard) and which serves as the infrequent (deviant) stimulus (i.e., AAAB vs. BBBA) in an oddball paradigm. Explanations for this amplitude modulation range from acoustic to linguistic factors. We tested whether exchanging the role of the mid vowel /ε/ vs. high vowel /ɪ/ of English modulated MMN amplitude and whether the pattern of modulation was compatible with an underspecification account, in which the underspecified height values are [−high] and [−low]. MMN was larger for /ε/ as the deviant, but only when compared across conditions to itself as the standard. For the within-condition comparison, MMN was larger to /ɪ/ deviant minus /ε/ standard than to the reverse. A condition order effect was also observed. MMN amplitude was smaller to the deviant stimulus if it had previously served as the standard. In addition, the amplitudes of late discriminative negativity (LDN) showed similar asymmetry. LDN was larger for deviant /ε/ than deviant /ɪ/ when compared to themselves as the standard. These findings were compatible with an underspecification account, but also with other accounts, such as the Natural Referent Vowel model and a prototype model; we also suggest that non-linguistic factors need to be carefully considered as additional sources of speech processing asymmetries.

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.

The Duration of Auditory Sensory Memory for Vowel Processing: Neurophysiological and Behavioral Measures

Speech perception behavioral research suggests that rates of sensory memory decay are dependent on stimulus properties at more than one level (e.g., acoustic level, phonemic level). The neurophysiology of sensory memory decay rate has rarely been examined in the context of speech processing. In a lexical tone study, we showed that long-term memory representation of lexical tone slows the decay rate of sensory memory for these tones. Here, we tested the hypothesis that long-term memory representation of vowels slows the rate of auditory sensory memory decay in a similar way to that of lexical tone. Event-related potential (ERP) responses were recorded to Mandarin non-words contrasting the vowels /i/ vs. /u/ and /y/ vs. /u/ from first-language (L1) Mandarin and L1 American English participants under short and long interstimulus interval (ISI) conditions (short ISI: an average of 575 ms, long ISI: an average of 2675 ms). Results revealed poorer discrimination of the vowel contrasts for English listeners than Mandarin listeners, but with different patterns for behavioral perception and neural discrimination. As predicted, English listeners showed the poorest discrimination and identification for the vowel contrast /y/ vs. /u/, and poorer performance in the long ISI condition. In contrast to Yu et al. (2017), however, we found no effect of ISI reflected in the neural responses, specifically the mismatch negativity (MMN), P3a and late negativity ERP amplitudes. We did see a language group effect, with Mandarin listeners generally showing larger MMN and English listeners showing larger P3a. The behavioral results revealed that native language experience plays a role in echoic sensory memory trace maintenance, but the failure to find an effect of ISI on the ERP results suggests that vowel and lexical tone memory traces decay at different rates.

Highlights:

We examined the interaction between auditory sensory memory decay and language experience.

We compared MMN, P3a, LN and behavioral responses in short vs. long interstimulus intervals.

We found that different from lexical tone contrast, MMN, P3a, and LN changes to vowel contrasts are not influenced by lengthening the ISI to 2.6 s.

We also found that the English listeners discriminated the non-native vowel contrast with lower accuracy under the long ISI condition.

One Way or Another: Evidence for Perceptual Asymmetry in Pre-attentive Learning of Non-native Contrasts

Research investigating listeners' neural sensitivity to speech sounds has largely focused on segmental features. We examined Australian English listeners' perception and learning of a supra-segmental feature, pitch direction in a non-native tonal contrast, using a passive oddball paradigm and electroencephalography. The stimuli were two contours generated from naturally produced high-level and high-falling tones in Mandarin Chinese, differing only in pitch direction (Liu and Kager, 2014). While both contours had similar pitch onsets, the pitch offset of the falling contour was lower than that of the level one. The contrast was presented in two orientations (standard and deviant reversed) and tested in two blocks with the order of block presentation counterbalanced. Mismatch negativity (MMN) responses showed that listeners discriminated the non-native tonal contrast only in the second block, reflecting indications of learning through exposure during the first block. In addition, listeners showed a later MMN peak for their second block of test relative to listeners who did the same block first, suggesting linguistic (as opposed to acoustic) processing or a misapplication of perceptual strategies from the first to the second block. The results also showed a perceptual asymmetry for change in pitch direction: listeners who encountered a falling tone deviant in the first block had larger frontal MMN amplitudes than listeners who encountered a level tone deviant in the first block. The implications of our findings for second language speech and the developmental trajectory for tone perception are discussed.

Perception of American English vowels by sequential Spanish-English bilinguals

Research on American-English (AE) vowel perception by Spanish-English bilinguals has focused on the vowels /i/-/ɪ/ (e.g., in sheep/ship). Other AE vowel contrasts may present perceptual challenges for this population, especially those requiring both spectral and durational discrimination. We used Event-Related Potentials (ERPs), MMN (Mismatch Negativity) and P300, to index discrimination of AE vowels /ɑ/-/ʌ/ by sequential adult Spanish-English bilingual listeners compared to AE monolinguals. Listening tasks were non-attended and attended, and vowels were presented with natural and neutralized durations. Regardless of vowel duration, bilingual listeners showed no MMN to unattended sounds, and P300 responses were elicited to /ɑ/ but not /ʌ/ in the attended condition. Monolingual listeners showed pre-attentive discrimination (MMN) for /ɑ/ only; while both vowels elicited P300 responses when attended. Findings suggest that Spanish-English bilinguals recruit attentional and cognitive resources enabling native-like use of both spectral and durational cues to discriminate between AE vowels /ɑ/ and /ʌ/.

Neurophysiological and Behavioral Responses of Mandarin Lexical Tone Processing

Language experience enhances discrimination of speech contrasts at a behavioral- perceptual level, as well as at a pre-attentive level, as indexed by event-related potential (ERP) mismatch negativity (MMN) responses. The enhanced sensitivity could be the result of changes in acoustic resolution and/or long-term memory representations of the relevant information in the auditory cortex. To examine these possibilities, we used a short (ca. 600 ms) vs. long (ca. 2,600 ms) interstimulus interval (ISI) in a passive, oddball discrimination task while obtaining ERPs. These ISI differences were used to test whether cross-linguistic differences in processing Mandarin lexical tone are a function of differences in acoustic resolution and/or differences in long-term memory representations. Bisyllabic nonword tokens that differed in lexical tone categories were presented using a passive listening multiple oddball paradigm. Behavioral discrimination and identification data were also collected. The ERP results revealed robust MMNs to both easy and difficult lexical tone differences for both groups at short ISIs. At long ISIs, there was either no change or an enhanced MMN amplitude for the Mandarin group, but reduced MMN amplitude for the English group. In addition, the Mandarin listeners showed a larger late negativity (LN) discriminative response than the English listeners for lexical tone contrasts in the long ISI condition. Mandarin speakers outperformed English speakers in the behavioral tasks, especially under the long ISI conditions with the more similar lexical tone pair. These results suggest that the acoustic correlates of lexical tone are fairly robust and easily discriminated at short ISIs, when the auditory sensory memory trace is strong. At longer ISIs beyond 2.5 s language-specific experience is necessary for robust discrimination.

A Neurophysiological Investigation of Non-native Phoneme Perception by Dutch and German Listeners

The Mismatch Negativity (MMN) response has often been used to measure memory traces for phonological representations and to show effects of long-term native language (L1) experience on neural organization. We know little about whether phonological representations of non-native (L2) phonemes are modulated by experience with distinct non-native accents. We used MMN to examine effects of experience with L2-accented speech on auditory brain responses. Specifically, we tested whether it is long-term experience with language-specific L2 pronunciations or instead acoustic similarity between L2 speech sounds that modulates non-native phoneme perception. We registered MMN responses of Dutch and German proficient L2 speakers of English to the English interdental fricative /𝜃/ and compared it to its non-native pronunciations /s/ (typical pronunciation of /𝜃/ for German speakers) and /t/ (typical pronunciation of /𝜃/ for Dutch speakers). Dutch and German listeners heard the English pseudoword thond and its pronunciation deviants sond and tond. We computed the identity Mismatch Negativity (iMMN) by analyzing the difference in ERPs when the deviants were the frequent vs. the infrequent stimulus for the respective group of L2 listeners. For both groups, tond and sond elicited mismatch effects of comparable size. Overall, the results suggest that experience with deviant pronunciations of L2 speech sounds in foreign-accented speech does not alter auditory memory traces. Instead, non-native phoneme perception seems to be modulated by acoustic similarity between speech sounds rather than by experience with typical L2 pronunciation patterns.

Representation of spectro-temporal features of spoken words within the P1-N1-P2 and T-complex of the auditory evoked potentials (AEP)

The purpose of the study was to determine whether P1-N1-P2 and T-complex morphology reflect spectro-temporal features within spoken words that approximate the natural variation of a speaker and whether waveform morphology is reliable at group and individual levels, necessary for probing auditory deficits. The P1-N1-P2 and T-complex to the syllables /pət/ and /sət/ within 70 natural word productions each were examined. EEG was recorded while participants heard nonsense word pairs and performed a syllable identification task to the second word in the pairs. Single trial auditory evoked potentials (AEP) to the first words were analyzed. Results found P1-N1-P2 and T-complex to reflect spectral and temporal feature processing. Also, results identified preliminary benchmarks for single trial response variability for individual subjects for sensory processing between 50 and 600ms. P1-N1-P2 and T-complex, at least at group level, may serve as phenotypic signatures to identify deficits in spectro-temporal feature recognition and to determine area of deficit, the superior temporal plane or lateral superior temporal gyrus.

Neural measures of a Japanese consonant length discrimination by Japanese and American English listeners: Effects of attention

This study examined automaticity of discrimination of a Japanese length contrast for consonants (miʃi vs. miʃʃi) in native (Japanese) and non-native (American-English) listeners using behavioral measures and the event-related potential (ERP) mismatch negativity (MMN). Attention to the auditory input was manipulated either away from the auditory input via a visual oddball task (Visual Attend), or to the input by asking the listeners to count auditory deviants (Auditory Attend). Results showed a larger MMN when attention was focused on the consonant contrast than away from it for both groups. The MMN was larger for consonant duration increments than decrements. No difference in MMN between the language groups was observed, but the Japanese listeners did show better behavioral discrimination than the American English listeners. In addition, behavioral responses showed a weak, but significant correlation with MMN amplitude. These findings suggest that both acoustic-phonetic properties and phonological experience affects automaticity of speech processing. This article is part of a Special Issue entitled SI: Prediction and Attention.

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.

The five myths of MMN: redefining how to use MMN in basic and clinical research

The goal of this review article is to redefine what the mismatch negativity (MMN) component of event-related potentials reflects in auditory scene analysis, and to provide an overview of how the MMN serves as a valuable tool in Cognitive Neuroscience research. In doing so, some of the old beliefs (five common 'myths') about MMN will be dispelled, such as the notion that MMN is a simple feature discriminator and that attention itself modulates MMN elicitation. A revised description of what MMN truly reflects will be provided, which includes a principal focus onto the highly context-dependent nature of MMN elicitation and new terminology to discuss MMN and attention. This revised framework will help clarify what has been a long line of seemingly contradictory results from studies in which behavioral ability to hear differences between sounds and passive elicitation of MMN have been inconsistent. Understanding what MMN is will also benefit clinical research efforts by providing a new picture of how to design appropriate paradigms suited to various clinical populations.

Assessing the double phonemic representation in bilingual speakers of Spanish and English: an electrophysiological study

Event Related Potentials (ERPs) were recorded from Spanish-English bilinguals (N=10) to test pre-attentive speech discrimination in two language contexts. ERPs were recorded while participants silently read magazines in English or Spanish. Two speech contrast conditions were recorded in each language context. In the phonemic in English condition, the speech sounds represented two different phonemic categories in English, but represented the same phonemic category in Spanish. In the phonemic in Spanish condition, the speech sounds represented two different phonemic categories in Spanish, but represented the same phonemic categories in English. Results showed pre-attentive discrimination when the acoustics/phonetics of the speech sounds match the language context (e.g., phonemic in English condition during the English language context). The results suggest that language contexts can affect pre-attentive auditory change detection. Specifically, bilinguals' mental processing of stop consonants relies on contextual linguistic information.

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.

Regional differences in the listener's phonemic inventory affect semantic processing: A mismatch negativity (MMN) study

Using the mismatch negativity (MMN) response, we examined how Standard French and Southern French speakers access the meaning of words ending in /e/ or /ε/ vowels which are contrastive in Standard French but not in Southern French. In Standard French speakers, there was a significant difference in the amplitude of the brain response after the deviant-minus-standard subtraction between the frontocentral (FC) and right lateral (RL) recording sites for the final-/ε/ word but not the final-/e/ word. In contrast, the difference in the amplitude of the brain response between the FC and RL recording sites did not significantly vary as a function of the word's final vowel in Southern French speakers. Our findings provide evidence that access to lexical meaning in spoken word recognition depends on the speaker's native regional accent.

Perception of a Japanese vowel length contrast by Japanese and American English listeners: behavioral and electrophysiological measures

This study examined the role of automatic selective perceptual processes in native and non-native listeners' perception of a Japanese vowel length contrast (tado vs. taado), using multiple, natural-speech tokens of each category as stimuli in a "categorial oddball" design. Mismatch negativity (MMN) was used to index discrimination of the temporally-cued vowel contrast by naïve adult American listeners and by a native Japanese-speaking control group in two experiments in which attention to the auditory input was manipulated: in Exp 1 (Visual-Attend), listeners silently counted deviants in a simultaneously-presented visual categorial oddball shape discrimination task; in Exp 2 (Auditory-Attend), listeners attended to the auditory input and implicitly counted target deviants. MMN results showed effects of language experience and attentional focus: MMN amplitudes were smaller for American compared to Japanese listeners in the Visual-Attend Condition and for the American listeners in the Visual compared to Auditory-Attend Condition. Subtle differences in topography were also seen, specifically in that the Japanese group showed more robust responses than the American listeners at left hemisphere scalp sites that probably index activity from the superior temporal gyrus. Follow-up behavioral discrimination tests showed that Americans discriminated the contrast well above chance, but more poorly than did Japanese listeners. This pattern of electrophysiological and behavioral results supports the conclusion that early experience with phonetic contrasts of a language results in changes in neural representations in the auditory cortex that allow for more robust automatic, phonetic processing of native-language speech input.

Electrophysiological indices of discrimination of long-duration, phonetically similar vowels in children with typical and atypical language development

PURPOSE

The authors investigated the neurophysiological bases of vowel perception in children with specific language impairment (SLI) compared with typical language development (TLD) controls using 250-ms phonetically similar vowels. In a previous study, children with SLI showed a poor neurophysiological response (the mismatch negativity [MMN]) to 50-ms versions of these vowels, regardless of whether attention was directed to (attend) or away (passive) from the auditory modality (V. Shafer, M. Morr, H. Datta, D. Kurtzberg, & R. Schwartz, 2005). They hypothesized that longer vowels would allow for improved speech perception.

METHOD

Brain responses were elicited to the vowel contrast in 2 conditions: (a) attend and (b) passive. Behavioral discrimination and identification responses were also examined.

RESULTS

Both SLI and TLD groups showed evidence of discrimination (MMN) of the vowels in the attend and passive conditions. Only subtle differences in the scalp topography of a late negative (LN) brain component were observed between groups. The SLI compared with the TLD group showed significantly poorer identification of these long vowels, as found previously with the shorter vowels.

CONCLUSIONS

Increased vowel duration can improve discrimination in children with SLI. However, poor identification of these longer vowels by some children with SLI suggests a deficit in long-term phonological representations or accessing these representations.

The mismatch negativity (MMN) in basic research of central auditory processing: a review

In the present article, the basic research using the mismatch negativity (MMN) and analogous results obtained by using the magnetoencephalography (MEG) and other brain-imaging technologies is reviewed. This response is elicited by any discriminable change in auditory stimulation but recent studies extended the notion of the MMN even to higher-order cognitive processes such as those involving grammar and semantic meaning. Moreover, MMN data also show the presence of automatic intelligent processes such as stimulus anticipation at the level of auditory cortex. In addition, the MMN enables one to establish the brain processes underlying the initiation of attention switch to, conscious perception of, sound change in an unattended stimulus stream.

Cortical auditory evoked potentials to acoustic changes in speech stimuli in children

OBJECTIVE

To compare the maturation of speech-evoked N170 components of cortical auditory evoked potentials with that of tone-evoked N1 components.

PATIENTS AND METHODS

Cortical auditory evoked potentials to speech and tone stimuli were derived in 42 children from age 4 to 14 years. The N170 was derived from the difference curve of responses to monosyllabic words with initial consonant-to-vowel transitions and their intensity-equivalent noise signals.

RESULTS

The incidence of N1 increased from 71% below age 9 to 91% above, that of N170 tended to increase from 40 to 67% above. From age 9, adult-like morphologies of the difference waveforms were found and the time constants of N1 and N170 latency maturation were nearly identical.

CONCLUSION

The N170 component is interpreted as a response to speech-specific acoustic changes such as the consonant-vowel transition. The late appearance of N170 indicates an electrophysiological correlate of speech perception that continues to develop into adolescence. Its clinical application, however, is limited due to the low incidence of N170.

Auditory sensory memory and working memory processes in children with normal hearing and cochlear implants

There can be wide variation in the level of oral/aural language ability that prelingually hearing-impaired children develop after cochlear implantation. Automatic perceptual processing mechanisms have come under increasing scrutiny in attempts to explain this variation. Using mismatch negativity methods, this study explored associations between auditory sensory memory mechanisms and verbal working memory function in children with cochlear implants and a group of hearing controls of similar age. Whilst clear relationships were observed in the hearing children between mismatch activation and working memory measures, this association appeared to be disrupted in the implant children. These findings would fit with the proposal that early auditory deprivation and a degraded auditory signal can cause changes in the processes underpinning the development of oral/aural language skills in prelingually hearing-impaired children with cochlear implants and thus alter their developmental trajectory.

Electrophysiological evidence implicates automatic low-level feature detectors in perceptual asymmetry

Perceptual asymmetry has been demonstrated behaviorally using frequency modulated (FM) stimuli: a modulated tone is easier to detect among unmodulated distracters than the converse. We demonstrate perceptual asymmetry for FM tones in the mismatch negativity (MMN) component of the event-related potential, regardless of whether the participant attends to the tones. These results suggest that perceptual asymmetry reflects the automatic activation of low-level feature detectors in the auditory system.

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.