Understanding the neural mechanisms for infants' perception of native and non-native speech.

Though perceptual narrowing has been widely recognized as a process guiding cognitive development and category learning in infancy and early childhood, its neural mechanisms and traits at a cortical level remain unclear. Using an electroencephalography (EEG) abstract mismatch negativity (MMN) paradigm, Australian infants' neural sensitivity to (native) English and (non-native) Nuu-Chah-Nulth speech contrasts was examined in a cross-sectional design at the onset (5-6 months) and offset (11-12 months) of perceptual narrowing. Immature mismatch responses (MMR) were observed among younger infants for both contrasts, while older infants showed MMR response to the non-native contrast, and both MMR and MMN to the native contrast. Sensitivity to the Nuu-Chah-Nulth contrast at perceptual narrowing offset was retained yet stayed immature. Findings conform to perceptual assimilation theories, reflecting plasticity in early speech perception and development. Compared to behavioural paradigms, neural examination effectively reveals experience-induced processing differences to subtle contrasts at the offset of perceptual narrowing.

Impaired neural entrainment to low frequency amplitude modulations in English-speaking children with dyslexia or dyslexia and DLD.

Neural synchronization to amplitude-modulated noise at three frequencies (2 Hz, 5 Hz, 8 Hz) thought to be important for syllable perception was investigated in English-speaking school-aged children. The theoretically-important delta-band (∼2Hz, stressed syllable level) was included along with two syllable-level rates. The auditory steady state response (ASSR) was recorded using EEG in 36 7-to-12-year-old children. Half of the sample had either dyslexia or dyslexia and DLD (developmental language disorder). In comparison to typically-developing children, children with dyslexia or with dyslexia and DLD showed reduced ASSRs for 2 Hz stimulation but similar ASSRs at 5 Hz and 8 Hz. These novel data for English ASSRs converge with prior data suggesting that children with dyslexia have atypical synchrony between brain oscillations and incoming auditory stimulation at âˆ¼ 2 Hz, the rate of stressed syllable production across languages. This atypical synchronization likely impairs speech processing, phonological processing, and possibly syntactic processing, as predicted by Temporal Sampling theory.

Infants show enhanced neural responses to musical meter frequencies beyond low-level features.

Music listening often entails spontaneous perception and body movement to a periodic pulse-like meter. There is increasing evidence that this cross-cultural ability relates to neural processes that selectively enhance metric periodicities, even when these periodicities are not prominent in the acoustic stimulus. However, whether these neural processes emerge early in development remains largely unknown. Here, we recorded the electroencephalogram (EEG) of 20 healthy 5- to 6-month-old infants, while they were exposed to two rhythms known to induce the perception of meter consistently across Western adults. One rhythm contained prominent acoustic periodicities corresponding to the meter, whereas the other rhythm did not. Infants showed significantly enhanced representations of meter periodicities in their EEG responses to both rhythms. This effect is unlikely to reflect the tracking of salient acoustic features in the stimulus, as it was observed irrespective of the prominence of meter periodicities in the audio signals. Moreover, as previously observed in adults, the neural enhancement of meter was greater when the rhythm was delivered by low-pitched sounds. Together, these findings indicate that the endogenous enhancement of metric periodicities beyond low-level acoustic features is a neural property that is already present soon after birth. These high-level neural processes could set the stage for internal representations of musical meter that are critical for human movement coordination during rhythmic musical behavior. RESEARCH HIGHLIGHTS: 5- to 6-month-old infants were presented with auditory rhythms that induce the perception of a periodic pulse-like meter in adults. Infants showed selective enhancement of EEG activity at meter-related frequencies irrespective of the prominence of these frequencies in the stimulus. Responses at meter-related frequencies were boosted when the rhythm was conveyed by bass sounds. High-level neural processes that transform rhythmic auditory stimuli into internal meter templates emerge early after birth.

Language specificity in cortical tracking of speech rhythm at the mora, syllable, and foot levels.

Recent research shows that adults' neural oscillations track the rhythm of the speech signal. However, the extent to which this tracking is driven by the acoustics of the signal, or by language-specific processing remains unknown. Here adult native listeners of three rhythmically different languages (English, French, Japanese) were compared on their cortical tracking of speech envelopes synthesized in their three native languages, which allowed for coding at each of the three language's dominant rhythmic unit, respectively the foot (2.5 Hz), syllable (5 Hz), or mora (10 Hz) level. The three language groups were also tested with a sequence in a non-native language, Polish, and a non-speech vocoded equivalent, to investigate possible differential speech/nonspeech processing. The results first showed that cortical tracking was most prominent at 5 Hz (syllable rate) for all three groups, but the French listeners showed enhanced tracking at 5 Hz compared to the English and the Japanese groups. Second, across groups, there were no differences in responses for speech versus non-speech at 5 Hz (syllable rate), but there was better tracking for speech than for non-speech at 10 Hz (not the syllable rate). Together these results provide evidence for both language-general and language-specific influences on cortical tracking.

English and Mandarin native speakers' cue-weighting of lexical stress: Results from MMN and LDN.

Past research on how listeners weight stress cues such as pitch, duration and intensity has reported two inconsistent patternss: listeners' weighting conforms to 1) their native language experience (e.g., language rhythmicity, lexical tone), and 2) a general "iambic-trochaic law" (ITL), favouring innate sound groupings in cue perception. This study aims to tease apart the above effects by investigating the weighting of pitch, duration and intensity cues in stress-timed (Australian English) and non-stress-timed and tonal (Taiwan Mandarin) language speaking adults using a mismatch negativity (MMN) multi-feature paradigm. Results show effects that can be explained by language-specific rhythmic influence, but only partially by the ITL. Moreover, these findings revealed cross-linguistic differences indexed by both MMN and late discriminative negativity (LDN) responses at cue and syllable position levels, and thus call for more sophisticated perspectives for existing cue-weighting models.

A prime-masked ERP investigation on phonology in visual word processing among bilingual speakers of alphasyllabic and alphabetic orthographies.

In this study, we experimentally manipulated the phonology of the cross-script prime-target dyads in an ERP-coupled masked priming paradigm to explore the role phonology plays in visual word processing. The written characters of certain bilingual dyads seldom show any visual/orthographic similarity, yet have the same phonological representation. While the Bilingual Interactive Activation (BIA) model relies on the orthographic similarity between the languages in a bilingual dyad, its revised version (BIA + model) additionally banks on the phonological (and semantic) similarity between the words in such dyads. Thus, there exists the need to investigate the role of phonological (and semantic) similarity between the words of a bilingual dyad, especially in the absence of orthographic similarity. Borrowed words from one language to another provide a suitable avenue to explore this question. Cross-orthographic (or cross-script) bilingual participants of this study performed the semantic judgment of visually presented words in a masked priming paradigm in each of their languages while we simultaneously collected the event-related potentials (ERPs). The primes were either translations (different phonology & orthography: P-O-; phonologically incongruent) or transliterations (same phonology & different orthography: P + O-; phonologically congruent) of the target. Overall, the results showed no difference between the two prime conditions. We discuss our findings in light of the BIA and BIA + models of bilingual visual word processing and discuss the relevance of the former model in orthographically distinct bilingual language dyads.

Babies detect when the timing is right: Evidence from event-related potentials to a contingent mother-infant conversation.

Social interactions are vital for healthy brain development. Burgeoning behavioural evidence indicates that a caregiver who provides contingently timed vocal responses to infant vocalisations provides key support for early language development. Understanding how contingently timed vocal responses relate to neurodevelopment in early infancy is lacking. This study compares event-related potentials (ERPs) to contingent and non-contingently timed vocalisations in 6- and 9-month-old infants (n = 36), and adults (n = 24). ERPs were recorded from each age group while listening to a naturalistic 21-minute recording of a mother playing and conversing with her baby. At 6-months, infants showed a significant positive ERP response to contingent vocalisations by the mother and infant. At 9-months infants showed negative ERP response to the mother's contingent speech. Adults showed no differences in ERPs between contingent and non-contingent speech regardless of the talker. We interpret the increased positivity in response to contingent speech as suggesting that infants show an attentional response at 6-months, and the increased negativity at 9-months relates to lexical-semantic processing. Further work is necessary to confirm the development of distinct ERPs shown in response to natural speech.

Electrophysiological and behavioural study of localisation in presence of noise.

OBJECTIVE: The ability to determine the location of the sound source is often important for effective communication. However, it is not clear how the localisation is affected by background noise. In the current study, localisation in quiet versus noise was evaluated in adults both behaviourally, and using MMN and P3b. DESIGN: The speech token/da/was presented in a multi-deviant oddball paradigm in quiet and in presence of speech babble at +5 dB SNR. The deviants were presented at locations that differed from the standard by 30°, 60° and 90°. STUDY SAMPLE: Sixteen normal hearing adults between the age range of 18-35 years participated in the study. RESULTS: The results showed that participants were significantly faster and more accurate at identifying deviants presented at 60° and 90° as compared to 30°. Neither reaction times nor electrophysiological measures (MMN/P3b) were affected by the background noise. The deviance magnitude (30°, 60° and 90°) did not affect the MMN amplitude, but the smaller deviant (30°) generated P3b with smaller amplitude. CONCLUSIONS: Under the stimulus paradigm and measures employed in this study, localisation ability as effectively sampled appeared resistant to speech babble interference.

Infant-directed speech facilitates seven-month-old infants' cortical tracking of speech.

This study assessed cortical tracking of temporal information in incoming natural speech in seven-month-old infants. Cortical tracking refers to the process by which neural activity follows the dynamic patterns of the speech input. In adults, it has been shown to involve attentional mechanisms and to facilitate effective speech encoding. However, in infants, cortical tracking or its effects on speech processing have not been investigated. This study measured cortical tracking of speech in infants and, given the involvement of attentional mechanisms in this process, cortical tracking of both infant-directed speech (IDS), which is highly attractive to infants, and the less captivating adult-directed speech (ADS), were compared. IDS is the speech register parents use when addressing young infants. In comparison to ADS, it is characterised by several acoustic qualities that capture infants' attention to linguistic input and assist language learning. Seven-month-old infants' cortical responses were recorded via electroencephalography as they listened to IDS or ADS recordings. Results showed stronger low-frequency cortical tracking of the speech envelope in IDS than in ADS. This suggests that IDS has a privileged status in facilitating successful cortical tracking of incoming speech which may, in turn, augment infants' early speech processing and even later language development.

Weighting of Amplitude and Formant Rise Time Cues by School-Aged Children: A Mismatch Negativity Study.

Purpose: An important skill in the development of speech perception is to apply optimal weights to acoustic cues so that phonemic information is recovered from speech with minimum effort. Here, we investigated the development of acoustic cue weighting of amplitude rise time (ART) and formant rise time (FRT) cues in children as measured by mismatch negativity (MMN). Method: Twelve adults and 36 children aged 6-12 years listened to a /ba/-/wa/ contrast in an oddball paradigm in which the standard stimulus had the ART and FRT cues of /ba/. In different blocks, the deviant stimulus had either the ART or FRT cues of /wa/. Results: The results revealed that children younger than 10 years were sensitive to both ART and FRT cues whereas 10- to 12-year-old children and adults were sensitive only to FRT cues. Moreover, children younger than 10 years generated a positive mismatch response, whereas older children and adults generated MMN. Conclusion: These results suggest that preattentive adultlike weighting of ART and FRT cues is attained only by 10 years of age and accompanies the change from mismatch response to the more mature MMN response. Supplemental Material: https://doi.org/10.23641/asha.6207608.

Are lexical tones musical? Native language's influence on neural response to pitch in different domains.

Language experience shapes musical and speech pitch processing. We investigated whether speaking a lexical tone language natively modulates neural processing of pitch in language and music as well as their correlation. We tested tone language (Mandarin Chinese), and non-tone language (Dutch) listeners in a passive oddball paradigm measuring mismatch negativity (MMN) for (i) Chinese lexical tones and (ii) three-note musical melodies with similar pitch contours. For lexical tones, Chinese listeners showed a later MMN peak than the non-tone language listeners, whereas for MMN amplitude there were no significant differences between groups. Dutch participants also showed a late discriminative negativity (LDN). In the music condition two MMNs, corresponding to the two notes that differed between the standard and the deviant were found for both groups, and an LDN were found for both the Dutch and the Chinese listeners. The music MMNs were significantly right lateralized. Importantly, significant correlations were found between the lexical tone and the music MMNs for the Dutch but not the Chinese participants. The results suggest that speaking a tone language natively does not necessarily enhance neural responses to pitch either in language or in music, but that it does change the nature of neural pitch processing: non-tone language speakers appear to perceive lexical tones as musical, whereas for tone language speakers, lexical tones and music may activate different neural networks. Neural resources seem to be assigned differently for the lexical tones and for musical melodies, presumably depending on the presence or absence of long-term phonological memory traces.

Atypical cortical entrainment to speech in the right hemisphere underpins phonemic deficits in dyslexia.

Developmental dyslexia is a multifaceted disorder of learning primarily manifested by difficulties in reading, spelling, and phonological processing. Neural studies suggest that phonological difficulties may reflect impairments in fundamental cortical oscillatory mechanisms. Here we examine cortical mechanisms in children (6-12 years of age) with or without dyslexia (utilising both age- and reading-level-matched controls) using electroencephalography (EEG). EEG data were recorded as participants listened to an audio-story. Novel electrophysiological measures of phonemic processing were derived by quantifying how well the EEG responses tracked phonetic features of speech. Our results provide, for the first time, evidence for impaired low-frequency cortical tracking to phonetic features during natural speech perception in dyslexia. Atypical phonological tracking was focused on the right hemisphere, and correlated with traditional psychometric measures of phonological skills used in diagnostic dyslexia assessments. Accordingly, the novel indices developed here may provide objective metrics to investigate language development and language impairment across languages.

Effect of EEG Referencing Methods on Auditory Mismatch Negativity.

Auditory event-related potentials (ERPs) have consistently been used in the investigation of auditory and cognitive processing in the research and clinical laboratories. There is currently no consensus on the choice of appropriate reference for auditory ERPs. The most commonly used references in auditory ERP research are the mathematically linked-mastoids (LM) and average referencing (AVG). Since LM and AVG referencing procedures do not solve the issue of electrically-neutral reference, Reference Electrode Standardization Technique (REST) was developed to create a neutral reference for EEG recordings. The aim of the current research is to compare the influence of the reference on amplitude and latency of auditory mismatch negativity (MMN) as a function of magnitude of frequency deviance across three commonly used electrode montages (16, 32, and 64-channel) using REST, LM, and AVG reference procedures. The current study was designed to determine if the three reference methods capture the variation in amplitude and latency of MMN with the deviance magnitude. We recorded MMN from 12 normal hearing young adults in an auditory oddball paradigm with 1,000 Hz pure tone as standard and 1,030, 1,100, and 1,200 Hz as small, medium and large frequency deviants, respectively. The EEG data recorded to these sounds was re-referenced using REST, LM, and AVG methods across 16-, 32-, and 64-channel EEG electrode montages. Results revealed that while the latency of MMN decreased with increment in frequency of deviant sounds, no effect of frequency deviance was present for amplitude of MMN. There was no effect of referencing procedure on the experimental effect tested. The amplitude of MMN was largest when the ERP was computed using LM referencing and the REST referencing produced the largest amplitude of MMN for 64-channel montage. There was no effect of electrode-montage on AVG referencing induced ERPs. Contrary to our predictions, the results suggest that the auditory MMN elicited as a function of increments in frequency deviance does not depend on the choice of referencing procedure. The results also suggest that auditory ERPs generated using REST referencing is contingent on the electrode arrays more than the AVG referencing.

When speaker identity is unavoidable: Neural processing of speaker identity cues in natural speech.

Speech sound acoustic properties vary largely across speakers and accents. When perceiving speech, adult listeners normally disregard non-linguistic variation caused by speaker or accent differences, in order to comprehend the linguistic message, e.g. to correctly identify a speech sound or a word. Here we tested whether the process of normalizing speaker and accent differences, facilitating the recognition of linguistic information, is found at the level of neural processing, and whether it is modulated by the listeners' native language. In a multi-deviant oddball paradigm, native and nonnative speakers of Dutch were exposed to naturally-produced Dutch vowels varying in speaker, sex, accent, and phoneme identity. Unexpectedly, the analysis of mismatch negativity (MMN) amplitudes elicited by each type of change shows a large degree of early perceptual sensitivity to non-linguistic cues. This finding on perception of naturally-produced stimuli contrasts with previous studies examining the perception of synthetic stimuli wherein adult listeners automatically disregard acoustic cues to speaker identity. The present finding bears relevance to speech normalization theories, suggesting that at an unattended level of processing, listeners are indeed sensitive to changes in fundamental frequency in natural speech tokens.

Mature neural responses to Infant-Directed Speech but not Adult-Directed Speech in Pre-Verbal Infants.

Infant directed speech (IDS), the speech register adults use when talking to infants, has been shown to have positive effects on attracting infants' attention, language learning, and emotional communication. Here event related potentials (ERPs) are used to investigate the neural coding of IDS and ADS (adult directed speech) as well as their discrimination by both infants and adults. Two instances of the vowel /i/, one extracted from ADS and one from IDS, were presented to 9-month-old infants and adults in two oddball conditions: ADS standard/IDS deviant and IDS standard/ADS deviant. In Experiment 1 with adults, the obligatory ERPs that code acoustic information were different for ADS and IDS; and discrimination, indexed by mismatch negativity (MMN) responses, showed that IDS and ADS deviants were discriminated equally well; although, the P3a response was larger for IDS suggesting it captured adults' attention more than did ADS. In infants the obligatory responses did not differ for IDS and ADS, but for discrimination, while IDS deviants generated both a slow-positive mismatch response (MMR) as well as an adult-like MMN, the ADS deviants generated only an MMR. The presence of a mature adult-like MMN suggests that the IDS stimulus is easier to discriminate for infants.

Effects of Type of Agreement Violation and Utterance Position on the Auditory Processing of Subject-Verb Agreement: An ERP Study.

Previous ERP studies have often reported two ERP components-LAN and P600-in response to subject-verb (S-V) agreement violations (e.g., the boys (*) runs). However, the latency, amplitude and scalp distribution of these components have been shown to vary depending on various experiment-related factors. One factor that has not received attention is the extent to which the relative perceptual salience related to either the utterance position (verbal inflection in utterance-medial vs. utterance-final contexts) or the type of agreement violation (errors of omission vs. errors of commission) may influence the auditory processing of S-V agreement. The lack of reports on these effects in ERP studies may be due to the fact that most studies have used the visual modality, which does not reveal acoustic information. To address this gap, we used ERPs to measure the brain activity of Australian English-speaking adults while they listened to sentences in which the S-V agreement differed by type of agreement violation and utterance position. We observed early negative and positive clusters (AN/P600 effects) for the overall grammaticality effect. Further analysis revealed that the mean amplitude and distribution of the P600 effect was only significant in contexts where the S-V agreement violation occurred utterance-finally, regardless of type of agreement violation. The mean amplitude and distribution of the negativity did not differ significantly across types of agreement violation and utterance position. These findings suggest that the increased perceptual salience of the violation in utterance final position (due to phrase-final lengthening) influenced how S-V agreement violations were processed during sentence comprehension. Implications for the functional interpretation of language-related ERPs and experimental design are discussed.

Neural processing of amplitude and formant rise time in dyslexia.

This study aimed to investigate how children with dyslexia weight amplitude rise time (ART) and formant rise time (FRT) cues in phonetic discrimination. Passive mismatch responses (MMR) were recorded for a/ba/-/wa/contrast in a multiple deviant odd-ball paradigm to identify the neural response to cue weighting in 17 children with dyslexia and 17 age-matched control children. The deviant stimuli had either partial or full ART or FRT cues. The results showed that ART did not generate an MMR in either group, whereas both partial and full FRT cues generated MMR in control children while only full FRT cues generated MMR in children with dyslexia. These findings suggest that children, both controls and those with dyslexia, discriminate speech based on FRT cues and not ART cues. However, control children have greater sensitivity to FRT cues in speech compared to children with dyslexia.

Auditory ERP response to successive stimuli in infancy.

Background. Auditory Event-Related Potentials (ERPs) are useful for understanding early auditory development among infants, as it allows the collection of a relatively large amount of data in a short time. So far, studies that have investigated development in auditory ERPs in infancy have mainly used single sounds as stimuli. Yet in real life, infants must decode successive rather than single acoustic events. In the present study, we tested 4-, 8-, and 12-month-old infants' auditory ERPs to musical melodies comprising three piano notes, and examined ERPs to each individual note in the melody. Methods. Infants were presented with 360 repetitions of a three-note melody while EEG was recorded from 128 channels on the scalp through a Geodesic Sensor Net. For each infant, both latency and amplitude of auditory components P1 and N2 were measured from averaged ERPs for each individual note. Results. Analysis was restricted to response collected at frontal central site. For all three notes, there was an overall reduction in latency for both P1 and N2 over age. For P1, latency reduction was significant from 4 to 8 months, but not from 8 to 12 months. N2 latency, on the other hand, decreased significantly from 4 to 8 to 12 months. With regard to amplitude, no significant change was found for either P1 or N2. Nevertheless, the waveforms of the three age groups were qualitatively different: for the 4-month-olds, the P1-N2 deflection was attenuated for the second and the third notes; for the 8-month-olds, such attenuation was observed only for the middle note; for the 12-month-olds, the P1 and N2 peaks show relatively equivalent amplitude and peak width across all three notes. Conclusion. Our findings indicate that the infant brain is able to register successive acoustic events in a stream, and ERPs become better time-locked to each composite event over age. Younger infants may have difficulties in responding to late occurring events in a stream, and the onset response to the late events may overlap with the incomplete response to preceding events.

Using event-related potentials to measure phrase boundary perception in English.

BACKGROUND: The closure positive shift (CPS) event related potential (ERP) is commonly used as a neural measure of phrase boundary perception in speech. The present study investigated whether the CPS was elicited by acoustic cues at phrase boundaries in English. ERPs were recorded when participants listened passively to sentences with either early or late phrase boundaries. RESULTS: The closure positive shift (CPS) ERP was elicited at both early and late phrase boundaries. However, the latency, amplitude, and scalp distribution of these passive CPS ERPs in English sentences differed to active CPS ERPs measured in non-English sentences in previous studies. CONCLUSIONS: These results show that acoustic cues at the phrase boundaries in English are sufficient to elicit the CPS, and suggest that different processes might be involved in the generation of the CPS in active and passive conditions.

Assessing spectral and temporal processing in children and adults using temporal modulation transfer function (TMTF), Iterated Ripple Noise (IRN) perception, and spectral ripple discrimination (SRD).

BACKGROUND: There are many clinically available tests for the assessment of auditory processing skills in children and adults. However, there is limited data available on the maturational effects on the performance on these tests. PURPOSE: The current study investigated maturational effects on auditory processing abilities using three psychophysical measures: temporal modulation transfer function (TMTF), iterated ripple noise (IRN) perception, and spectral ripple discrimination (SRD). RESEARCH DESIGN: A cross-sectional study. Three groups of subjects were tested: 10 adults (18-30 yr), 10 older children (12-18 yr), and 10 young children (8-11 yr) DATA COLLECTION AND ANALYSIS: Temporal envelope processing was measured by obtaining thresholds for amplitude modulation detection as a function of modulation frequency (TMTF; 4, 8, 16, 32, 64, and 128 Hz). Temporal fine structure processing was measured using IRN, and spectral processing was measured using SRD. RESULTS: The results showed that young children had significantly higher modulation thresholds at 4 Hz (TMTF) compared to the other two groups and poorer SRD scores compared to adults. The results on IRN did not differ across groups. CONCLUSIONS: The results suggest that different aspects of auditory processing mature at different age periods and these maturational effects need to be considered while assessing auditory processing in children.