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.     

Phonetic learning as a pathway to language: new data and native language magnet theory expanded (NLM-e)

Infants' speech perception skills show a dual change towards the end of the first year of life. Not only does non-native speech perception decline, as often shown, but native language speech perception skills show improvement, reflecting a facilitative effect of experience with native language. The mechanism underlying change at this point in development, and the relationship between the change in native and non-native speech perception, is of theoretical interest. As shown in new data presented here, at the cusp of this developmental change, infants' native and non-native phonetic perception skills predict later language ability, but in opposite directions. Better native language skill at 7.5 months of age predicts faster language advancement, whereas better non-native language skill predicts slower advancement. We suggest that native language phonetic performance is indicative of neural commitment to the native language, while non-native phonetic performance reveals uncommitted neural circuitry. This paper has three goals: (i) to review existing models of phonetic perception development, (ii) to present new event-related potential data showing that native and non-native phonetic perception at 7.5 months of age predicts language growth over the next 2 years, and (iii) to describe a revised version of our previous model, the native language magnet model, expanded (NLM-e). NLM-e incorporates five new principles. Specific testable predictions for future research programmes are described.     

Speech and non-speech audio-visual illusions: a developmental study

It is well known that simultaneous presentation of incongruent audio and visual stimuli can lead to illusory percepts. Recent data suggest that distinct processes underlie non-specific intersensory speech as opposed to non-speech perception. However, the development of both speech and non-speech intersensory perception across childhood and adolescence remains poorly defined. Thirty-eight observers aged 5 to 19 were tested on the McGurk effect (an audio-visual illusion involving speech), the Illusory Flash effect and the Fusion effect (two audio-visual illusions not involving speech) to investigate the development of audio-visual interactions and contrast speech vs. non-speech developmental patterns. Whereas the strength of audio-visual speech illusions varied as a direct function of maturational level, performance on non-speech illusory tasks appeared to be homogeneous across all ages. These data support the existence of independent maturational processes underlying speech and non-speech audio-visual illusory effects.     

Basic auditory processes involved in the analysis of speech sounds

This paper reviews the basic aspects of auditory processing that play a role in the perception of speech. The frequency selectivity of the auditory system, as measured using masking experiments, is described and used to derive the internal representation of the spectrum (the excitation pattern) of speech sounds. The perception of timbre and distinctions in quality between vowels are related to both static and dynamic aspects of the spectra of sounds. The perception of pitch and its role in speech perception are described. Measures of the temporal resolution of the auditory system are described and a model of temporal resolution based on a sliding temporal integrator is outlined. The combined effects of frequency and temporal resolution can be modelled by calculation of the spectro-temporal excitation pattern, which gives good insight into the internal representation of speech sounds. For speech presented in quiet, the resolution of the auditory system in frequency and time usually markedly exceeds the resolution necessary for the identification or discrimination of speech sounds, which partly accounts for the robust nature of speech perception. However, for people with impaired hearing, speech perception is often much less robust.     

Speech Misperception: Speaking and Seeing Interfere Differently with Hearing

Speech perception is thought to be linked to speech motor production. This linkage is considered to mediate multimodal aspects of speech perception, such as audio-visual and audio-tactile integration. However, direct coupling between articulatory movement and auditory perception has been little studied. The present study reveals a clear dissociation between the effects of a listener’s own speech action and the effects of viewing another’s speech movements on the perception of auditory phonemes. We assessed the intelligibility of the syllables [pa], [ta], and [ka] when listeners silently and simultaneously articulated syllables that were congruent/incongruent with the syllables they heard. The intelligibility was compared with a condition where the listeners simultaneously watched another’s mouth producing congruent/incongruent syllables, but did not articulate. The intelligibility of [ta] and [ka] were degraded by articulating [ka] and [ta] respectively, which are associated with the same primary articulator (tongue) as the heard syllables. But they were not affected by articulating [pa], which is associated with a different primary articulator (lips) from the heard syllables. In contrast, the intelligibility of [ta] and [ka] was degraded by watching the production of [pa]. These results indicate that the articulatory-induced distortion of speech perception occurs in an articulator-specific manner while visually induced distortion does not. The articulator-specific nature of the auditory-motor interaction in speech perception suggests that speech motor processing directly contributes to our ability to hear speech.     

Endogenous cortical rhythms determine cerebral specialization for speech perception and production

Across multiple timescales, acoustic regularities of speech match rhythmic properties of both the auditory and motor systems. Syllabic rate corresponds to natural jaw-associated oscillatory rhythms, and phonemic length could reflect endogenous oscillatory auditory cortical properties. Hemispheric lateralization for speech could result from an asymmetry of cortical tuning, with left and right auditory areas differentially sensitive to spectro-temporal features of speech. Using simultaneous electroencephalographic (EEG) and functional magnetic resonance imaging (fMRI) recordings from humans, we show that spontaneous EEG power variations within the gamma range (phonemic rate) correlate best with left auditory cortical synaptic activity, while fluctuations within the theta range correlate best with that in the right. Power fluctuations in both ranges correlate with activity in the mouth premotor region, indicating coupling between temporal properties of speech perception and production. These data show that endogenous cortical rhythms provide temporal and spatial constraints on the neuronal mechanisms underlying speech perception and production.     

The mismatch negativity as an index of the perception of speech sounds by the human brain

The present article outlines the contribution of the mismatch negativity (MMN), and its magnetic equivalent MMNm, to our understanding of the perception of speech sounds in the human brain. MMN data indicate that each sound, both speech and non-speech, develops its neural representation corresponding to the percept of this sound in the neurophysiological substrate of auditory sensory memory. The accuracy of this representation, determining the accuracy of the discrimination between different sounds, can be probed with MMN separately for any auditory feature or stimulus type such as phonemes. Furthermore, MMN data show that the perception of phonemes, and probably also of larger linguistic units (syllables and words), is based on language-specific phonetic traces developed in the posterior part of the left-hemisphere auditory cortex. These traces serve as recognition models for the corresponding speech sounds in listening to speech.     

Speech perception at the interface of neurobiology and linguistics

Speech perception consists of a set of computations that take continuously varying acoustic waveforms as input and generate discrete representations that make contact with the lexical representations stored in long-term memory as output. Because the perceptual objects that are recognized by the speech perception enter into subsequent linguistic computation, the format that is used for lexical representation and processing fundamentally constrains the speech perceptual processes. Consequently, theories of speech perception must, at some level, be tightly linked to theories of lexical representation. Minimally, speech perception must yield representations that smoothly and rapidly interface with stored lexical items. Adopting the perspective of Marr, we argue and provide neurobiological and psychophysical evidence for the following research programme. First, at the implementational level, speech perception is a multi-time resolution process, with perceptual analyses occurring concurrently on at least two time scales (approx. 20-80 ms, approx. 150-300 ms), commensurate with (sub)segmental and syllabic analyses, respectively. Second, at the algorithmic level, we suggest that perception proceeds on the basis of internal forward models, or uses an 'analysis-by-synthesis' approach. Third, at the computational level (in the sense of Marr), the theory of lexical representation that we adopt is principally informed by phonological research and assumes that words are represented in the mental lexicon in terms of sequences of discrete segments composed of distinctive features. One important goal of the research programme is to develop linking hypotheses between putative neurobiological primitives (e.g. temporal primitives) and those primitives derived from linguistic inquiry, to arrive ultimately at a biologically sensible and theoretically satisfying model of representation and computation in speech.     

Nonnative Audiovisual Speech Perception in Noise: Dissociable Effects of the Speaker and Listener

Nonnative speech poses a challenge to speech perception, especially in challenging listening environments. Audiovisual (AV) cues are known to improve native speech perception in noise. The extent to which AV cues benefit nonnative speech perception in noise, however, is much less well-understood. Here, we examined native American English-speaking and native Korean-speaking listeners'' perception of English sentences produced by a native American English speaker and a native Korean speaker across a range of signal-to-noise ratios (SNRs;−4 to −20 dB) in audio-only and audiovisual conditions. We employed psychometric function analyses to characterize the pattern of AV benefit across SNRs. For native English speech, the largest AV benefit occurred at intermediate SNR (i.e. −12 dB); but for nonnative English speech, the largest AV benefit occurred at a higher SNR (−4 dB). The psychometric function analyses demonstrated that the AV benefit patterns were different between native and nonnative English speech. The nativeness of the listener exerted negligible effects on the AV benefit across SNRs. However, the nonnative listeners'' ability to gain AV benefit in native English speech was related to their proficiency in English. These findings suggest that the native language background of both the speaker and listener clearly modulate the optimal use of AV cues in speech recognition.     

Timing of Surgical Intervention with Cochlear Implant in Patients with Large Vestibular Aqueduct Syndrome

Objectives

(1) To report the speech perception and intelligibility results of Mandarin-speaking patients with large vestibular aqueduct syndrome (LVAS) after cochlear implantation (CI); (2) to compare their performance with a group of CI users without LVAS; (3) to understand the effects of age at implantation and duration of implant use on the CI outcomes. The obtained data may be used to guide decisions about CI candidacy and surgical timing.

Methods

Forty-two patients with LVAS participating in this study were divided into two groups: the early group received CI before 5 years of age and the late group after 5. Open-set speech perception tests (on Mandarin tones, words and sentences) were administered one year after implantation and at the most recent follow-up visit. Categories of auditory perception (CAP) and Speech Intelligibility Rating (SIR) scale scores were also obtained.

Results

The patients with LVAS with more than 5 years of implant use (18 cases) achieved a mean score higher than 80% on the most recent speech perception tests and reached the highest level on the CAP/SIR scales. The early group developed speech perception and intelligibility steadily over time, while the late group had a rapid improvement during the first year after implantation. The two groups, regardless of their age at implantation, reached a similar performance level at the most recent follow-up visit.

Conclusion

High levels of speech performance are reached after 5 years of implant use in patients with LVAS. These patients do not necessarily need to wait until their hearing thresholds are higher than 90 dB HL or PB word score lower than 40% to receive CI. They can do it “earlier” when their speech perception and/or speech intelligibility do not reach the performance level suggested in this study.     

Contributions of Electric and Acoustic Hearing to Bimodal Speech and Music Perception

Cochlear implant (CI) users have difficulty understanding speech in noisy listening conditions and perceiving music. Aided residual acoustic hearing in the contralateral ear can mitigate these limitations. The present study examined contributions of electric and acoustic hearing to speech understanding in noise and melodic pitch perception. Data was collected with the CI only, the hearing aid (HA) only, and both devices together (CI+HA). Speech reception thresholds (SRTs) were adaptively measured for simple sentences in speech babble. Melodic contour identification (MCI) was measured with and without a masker instrument; the fundamental frequency of the masker was varied to be overlapping or non-overlapping with the target contour. Results showed that the CI contributes primarily to bimodal speech perception and that the HA contributes primarily to bimodal melodic pitch perception. In general, CI+HA performance was slightly improved relative to the better ear alone (CI-only) for SRTs but not for MCI, with some subjects experiencing a decrease in bimodal MCI performance relative to the better ear alone (HA-only). Individual performance was highly variable, and the contribution of either device to bimodal perception was both subject- and task-dependent. The results suggest that individualized mapping of CIs and HAs may further improve bimodal speech and music perception.     

Decoding Speech Perception by Native and Non-Native Speakers Using Single-Trial Electrophysiological Data

Brain-computer interfaces (BCIs) are systems that use real-time analysis of neuroimaging data to determine the mental state of their user for purposes such as providing neurofeedback. Here, we investigate the feasibility of a BCI based on speech perception. Multivariate pattern classification methods were applied to single-trial EEG data collected during speech perception by native and non-native speakers. Two principal questions were asked: 1) Can differences in the perceived categories of pairs of phonemes be decoded at the single-trial level? 2) Can these same categorical differences be decoded across participants, within or between native-language groups? Results indicated that classification performance progressively increased with respect to the categorical status (within, boundary or across) of the stimulus contrast, and was also influenced by the native language of individual participants. Classifier performance showed strong relationships with traditional event-related potential measures and behavioral responses. The results of the cross-participant analysis indicated an overall increase in average classifier performance when trained on data from all participants (native and non-native). A second cross-participant classifier trained only on data from native speakers led to an overall improvement in performance for native speakers, but a reduction in performance for non-native speakers. We also found that the native language of a given participant could be decoded on the basis of EEG data with accuracy above 80%. These results indicate that electrophysiological responses underlying speech perception can be decoded at the single-trial level, and that decoding performance systematically reflects graded changes in the responses related to the phonological status of the stimuli. This approach could be used in extensions of the BCI paradigm to support perceptual learning during second language acquisition.     

Phonological representations are unconsciously used when processing complex, non-speech signals

Neuroimaging studies of speech processing increasingly rely on artificial speech-like sounds whose perceptual status as speech or non-speech is assigned by simple subjective judgments; brain activation patterns are interpreted according to these status assignments. The naïve perceptual status of one such stimulus, spectrally-rotated speech (not consciously perceived as speech by naïve subjects), was evaluated in discrimination and forced identification experiments. Discrimination of variation in spectrally-rotated syllables in one group of naïve subjects was strongly related to the pattern of similarities in phonological identification of the same stimuli provided by a second, independent group of naïve subjects, suggesting either that (1) naïve rotated syllable perception involves phonetic-like processing, or (2) that perception is solely based on physical acoustic similarity, and similar sounds are provided with similar phonetic identities. Analysis of acoustic (Euclidean distances of center frequency values of formants) and phonetic similarities in the perception of the vowel portions of the rotated syllables revealed that discrimination was significantly and independently influenced by both acoustic and phonological information. We conclude that simple subjective assessments of artificial speech-like sounds can be misleading, as perception of such sounds may initially and unconsciously utilize speech-like, phonological processing.     

Visual Speech Perception in Foveal and Extrafoveal Vision: Further Implications for Divisions in Hemispheric Projections

When observing a talking face, it has often been argued that visual speech to the left and right of fixation may produce differences in performance due to divided projections to the two cerebral hemispheres. However, while it seems likely that such a division in hemispheric projections exists for areas away from fixation, the nature and existence of a functional division in visual speech perception at the foveal midline remains to be determined. We investigated this issue by presenting visual speech in matched hemiface displays to the left and right of a central fixation point, either exactly abutting the foveal midline or else located away from the midline in extrafoveal vision. The location of displays relative to the foveal midline was controlled precisely using an automated, gaze-contingent eye-tracking procedure. Visual speech perception showed a clear right hemifield advantage when presented in extrafoveal locations but no hemifield advantage (left or right) when presented abutting the foveal midline. Thus, while visual speech observed in extrafoveal vision appears to benefit from unilateral projections to left-hemisphere processes, no evidence was obtained to indicate that a functional division exists when visual speech is observed around the point of fixation. Implications of these findings for understanding visual speech perception and the nature of functional divisions in hemispheric projection are discussed.     

The purity of auditory memory

Recent evidence from experiments on immediate memory indicates unambiguously that silent speech perception can produce typically 'auditory' effects while there is either active or passive mouthing of the relevant articulatory gestures. This result falsifies previous theories of auditory sensory memory (pre-categorical acoustic store) that insisted on external auditory stimulation as indispensable for access to the system. A resolution is proposed that leaves the properties of pre-categorical acoustic store much as they were assumed to be before but adds the possibility that visual information can affect the selection of auditory features in a pre-categorical stage of speech perception. In common terms, a speaker's facial gestures (or one's own) can influence auditory experience independently of determining what it was that was said. Some results in word perception that encourage this view are discussed.     

The formation of interhemispheric asymmetry in human ontogeny during the perception of emotions in normal speech and in stuttering]

Age peculiarities of functional brain asymmetry in perception of emotional information of speech have been revealed. It was shown that the age of 4-7 years is most important for formation of this asymmetry in emotional perception. It is in this age that functional reorganization of perception in stuttering children is observed. These data indicate that correction of emotional activity in stutterers should be made at early periods of their life.     

Acoustic versus phonetic representation of speech as reflected by the mismatch negativity event-related potential

The concept of categorical perception of speech and speech-like sounds has been central to models of speech perception for decades. Event-related potentials (ERPs) provide a neurophysiologic perspective of this important phenomenon. In the present experiment the mismatch negativity (MMN) event-related potential, which is sensitive to fine acoustic differences, was recorded in adults. Of interest was whether the MMN reflects the acoustic or categorical perception of speech.The MMN was elicited by stimulus pairs (along a continuum varying in place of articulation from /da/ to /ga/) which had been identified as the same phoneme /da/ (within category condition) and as different phonemes /da/ and /ga/ (across categories condition). The acoustic differences between these two pairs of stimuli were equivalent.The MMN was observed in all subjects both in the within and across category conditions. Furthermore, the MMN did not differ in latency, amplitude or area within and across categories. That is, the MMN indicated equal discrimination both across and within categories. These results suggest that the MMN appears to reflect the processing of acoustic aspects of the speech stimulus, but not phonetic processing into categories. The MMN appears to be an extremely sensitive electrophysiologic index of minimal acoustic differences in speech stimuli.     

Sensorimotor integration in speech processing: computational basis and neural organization

Sensorimotor integration is an active domain of speech research and is characterized by two main ideas, that the auditory system is critically involved in speech production and that the motor system is critically involved in speech perception. Despite the complementarity of these ideas, there is little crosstalk between these literatures. We propose an integrative model of the speech-related "dorsal stream" in which sensorimotor interaction primarily supports speech production, in the form of a state feedback control architecture. A critical component of this control system is forward sensory prediction, which affords a natural mechanism for limited motor influence on perception, as recent perceptual research has suggested. Evidence shows that this influence is modulatory but not necessary for speech perception. The neuroanatomy of the proposed circuit is discussed as well as some probable clinical correlates including conduction aphasia, stuttering, and aspects of schizophrenia.     

Enhanced Syllable Discrimination Thresholds in Musicians

Speech processing inherently relies on the perception of specific, rapidly changing spectral and temporal acoustic features. Advanced acoustic perception is also integral to musical expertise, and accordingly several studies have demonstrated a significant relationship between musical training and superior processing of various aspects of speech. Speech and music appear to overlap in spectral and temporal features; however, it remains unclear which of these acoustic features, crucial for speech processing, are most closely associated with musical training. The present study examined the perceptual acuity of musicians to the acoustic components of speech necessary for intra-phonemic discrimination of synthetic syllables. We compared musicians and non-musicians on discrimination thresholds of three synthetic speech syllable continua that varied in their spectral and temporal discrimination demands, specifically voice onset time (VOT) and amplitude envelope cues in the temporal domain. Musicians demonstrated superior discrimination only for syllables that required resolution of temporal cues. Furthermore, performance on the temporal syllable continua positively correlated with the length and intensity of musical training. These findings support one potential mechanism by which musical training may selectively enhance speech perception, namely by reinforcing temporal acuity and/or perception of amplitude rise time, and implications for the translation of musical training to long-term linguistic abilities.     

Sustained neural rhythms reveal endogenous oscillations supporting speech perception

Rhythmic sensory or electrical stimulation will produce rhythmic brain responses. These rhythmic responses are often interpreted as endogenous neural oscillations aligned (or “entrained”) to the stimulus rhythm. However, stimulus-aligned brain responses can also be explained as a sequence of evoked responses, which only appear regular due to the rhythmicity of the stimulus, without necessarily involving underlying neural oscillations. To distinguish evoked responses from true oscillatory activity, we tested whether rhythmic stimulation produces oscillatory responses which continue after the end of the stimulus. Such sustained effects provide evidence for true involvement of neural oscillations. In Experiment 1, we found that rhythmic intelligible, but not unintelligible speech produces oscillatory responses in magnetoencephalography (MEG) which outlast the stimulus at parietal sensors. In Experiment 2, we found that transcranial alternating current stimulation (tACS) leads to rhythmic fluctuations in speech perception outcomes after the end of electrical stimulation. We further report that the phase relation between electroencephalography (EEG) responses and rhythmic intelligible speech can predict the tACS phase that leads to most accurate speech perception. Together, we provide fundamental results for several lines of research—including neural entrainment and tACS—and reveal endogenous neural oscillations as a key underlying principle for speech perception.

Just as a child on a swing continues to move after the pushing stops, this study reveals similar entrained rhythmic echoes in brain activity after hearing speech and electrical brain stimulation; perturbation with tACS shows that these brain oscillations help listeners to understand speech.