Differential Entrainment of Neuroelectric Delta Oscillations in Developmental Dyslexia

Oscillatory entrainment to the speech signal is important for language processing, but has not yet been studied in developmental disorders of language. Developmental dyslexia, a difficulty in acquiring efficient reading skills linked to difficulties with phonology (the sound structure of language), has been associated with behavioural entrainment deficits. It has been proposed that the phonological ‘deficit’ that characterises dyslexia across languages is related to impaired auditory entrainment to speech at lower frequencies via neuroelectric oscillations (<10 Hz, ‘temporal sampling theory’). Impaired entrainment to temporal modulations at lower frequencies would affect the recovery of the prosodic and syllabic structure of speech. Here we investigated event-related oscillatory EEG activity and contingent negative variation (CNV) to auditory rhythmic tone streams delivered at frequencies within the delta band (2 Hz, 1.5 Hz), relevant to sampling stressed syllables in speech. Given prior behavioural entrainment findings at these rates, we predicted functionally atypical entrainment of delta oscillations in dyslexia. Participants performed a rhythmic expectancy task, detecting occasional white noise targets interspersed with tones occurring regularly at rates of 2 Hz or 1.5 Hz. Both groups showed significant entrainment of delta oscillations to the rhythmic stimulus stream, however the strength of inter-trial delta phase coherence (ITC, ‘phase locking’) and the CNV were both significantly weaker in dyslexics, suggestive of weaker entrainment and less preparatory brain activity. Both ITC strength and CNV amplitude were significantly related to individual differences in language processing and reading. Additionally, the instantaneous phase of prestimulus delta oscillation predicted behavioural responding (response time) for control participants only.     

Zebra finches are sensitive to prosodic features of human speech

Variation in pitch, amplitude and rhythm adds crucial paralinguistic information to human speech. Such prosodic cues can reveal information about the meaning or emphasis of a sentence or the emotional state of the speaker. To examine the hypothesis that sensitivity to prosodic cues is language independent and not human specific, we tested prosody perception in a controlled experiment with zebra finches. Using a go/no-go procedure, subjects were trained to discriminate between speech syllables arranged in XYXY patterns with prosodic stress on the first syllable and XXYY patterns with prosodic stress on the final syllable. To systematically determine the salience of the various prosodic cues (pitch, duration and amplitude) to the zebra finches, they were subjected to five tests with different combinations of these cues. The zebra finches generalized the prosodic pattern to sequences that consisted of new syllables and used prosodic features over structural ones to discriminate between stimuli. This strong sensitivity to the prosodic pattern was maintained when only a single prosodic cue was available. The change in pitch was treated as more salient than changes in the other prosodic features. These results show that zebra finches are sensitive to the same prosodic cues known to affect human speech perception.     

Speech rhythm: a metaphor?

Is speech rhythmic? In the absence of evidence for a traditional view that languages strive to coordinate either syllables or stress-feet with regular time intervals, we consider the alternative that languages exhibit contrastive rhythm subsisting merely in the alternation of stronger and weaker elements. This is initially plausible, particularly for languages with a steep ‘prominence gradient’, i.e. a large disparity between stronger and weaker elements; but we point out that alternation is poorly achieved even by a ‘stress-timed’ language such as English, and, historically, languages have conspicuously failed to adopt simple phonological remedies that would ensure alternation. Languages seem more concerned to allow ‘syntagmatic contrast’ between successive units and to use durational effects to support linguistic functions than to facilitate rhythm. Furthermore, some languages (e.g. Tamil, Korean) lack the lexical prominence which would most straightforwardly underpin prominence of alternation. We conclude that speech is not incontestibly rhythmic, and may even be antirhythmic. However, its linguistic structure and patterning allow the metaphorical extension of rhythm in varying degrees and in different ways depending on the language, and it is this analogical process which allows speech to be matched to external rhythms.     

Stress “Deafness” Reveals Absence of Lexical Marking of Stress or Tone in the Adult Grammar

A Sequence Recall Task with disyllabic stimuli contrasting either for the location of prosodic prominence or for the medial consonant was administered to 150 subjects equally divided over five language groups. Scores showed a significant interaction between type of contrast and language group, such that groups did not differ on their performance on the consonant contrast, while two language groups, Dutch and Japanese, significantly outperformed the three other language groups (French, Indonesian and Persian) on the prosodic contrast. Since only Dutch and Japanese words have unpredictable stress or accent locations, the results are interpreted to mean that stress “deafness” is a property of speakers of languages without lexical stress or tone markings, as opposed to the presence of stress or accent contrasts in phrasal (post-lexical) constructions. Moreover, the degree of transparency between the locations of stress/tone and word boundaries did not appear to affect our results, despite earlier claims that this should have an effect. This finding is of significance for speech processing, language acquisition and phonological theory.     

Beat gestures influence which speech sounds you hear

Beat gestures—spontaneously produced biphasic movements of the hand—are among the most frequently encountered co-speech gestures in human communication. They are closely temporally aligned to the prosodic characteristics of the speech signal, typically occurring on lexically stressed syllables. Despite their prevalence across speakers of the world''s languages, how beat gestures impact spoken word recognition is unclear. Can these simple ‘flicks of the hand'' influence speech perception? Across a range of experiments, we demonstrate that beat gestures influence the explicit and implicit perception of lexical stress (e.g. distinguishing OBject from obJECT), and in turn can influence what vowels listeners hear. Thus, we provide converging evidence for a manual McGurk effect: relatively simple and widely occurring hand movements influence which speech sounds we hear.     

Temporal resolution of the Florida manatee (<Emphasis Type="Italic">Trichechus manatus latirostris</Emphasis>) auditory system

Auditory evoked potential (AEP) measurements of two Florida manatees (Trichechus manatus latirostris) were measured in response to amplitude modulated tones. The AEP measurements showed weak responses to test stimuli from 4 kHz to 40 kHz. The manatee modulation rate transfer function (MRTF) is maximally sensitive to 150 and 600 Hz amplitude modulation (AM) rates. The 600 Hz AM rate is midway between the AM sensitivities of terrestrial mammals (chinchillas, gerbils, and humans) (80–150 Hz) and dolphins (1,000–1,200 Hz). Audiograms estimated from the input–output functions of the EPs greatly underestimate behavioral hearing thresholds measured in two other manatees. This underestimation is probably due to the electrodes being located several centimeters from the brain.     

Effect of bilingualism on lexical stress pattern discrimination in French-learning infants

Monolingual infants start learning the prosodic properties of their native language around 6 to 9 months of age, a fact marked by the development of preferences for predominant prosodic patterns and a decrease in sensitivity to non-native prosodic properties. The present study evaluates the effects of bilingual acquisition on speech perception by exploring how stress pattern perception may differ in French-learning 10-month-olds raised in bilingual as opposed to monolingual environments. Experiment 1 shows that monolinguals can discriminate stress patterns following a long familiarization to one of two patterns, but not after a short familiarization. In Experiment 2, two subgroups of bilingual infants growing up learning both French and another language (varying across infants) in which stress is used lexically were tested under the more difficult short familiarization condition: one with balanced input, and one receiving more input in the language other than French. Discrimination was clearly found for the other-language-dominant subgroup, establishing heightened sensitivity to stress pattern contrasts in these bilinguals as compared to monolinguals. However, the balanced bilinguals' performance was not better than that of monolinguals, establishing an effect of the relative balance of the language input. This pattern of results is compatible with the proposal that sensitivity to prosodic contrasts is maintained or enhanced in a bilingual population compared to a monolingual population in which these contrasts are non-native, provided that this dimension is used in one of the two languages in acquisition, and that infants receive enough input from that language.     

The Proximate Phonological Unit of Chinese-English Bilinguals: Proficiency Matters

An essential step to create phonology according to the language production model by Levelt, Roelofs and Meyer is to assemble phonemes into a metrical frame. However, recently, it has been proposed that different languages may rely on different grain sizes of phonological units to construct phonology. For instance, it has been proposed that, instead of phonemes, Mandarin Chinese uses syllables and Japanese uses moras to fill the metrical frame. In this study, we used a masked priming-naming task to investigate how bilinguals assemble their phonology for each language when the two languages differ in grain size. Highly proficient Mandarin Chinese-English bilinguals showed a significant masked onset priming effect in English (L2), and a significant masked syllabic priming effect in Mandarin Chinese (L1). These results suggest that their proximate unit is phonemic in L2 (English), and that bilinguals may use different phonological units depending on the language that is being processed. Additionally, under some conditions, a significant sub-syllabic priming effect was observed even in Mandarin Chinese, which indicates that L2 phonology exerts influences on L1 target processing as a consequence of having a good command of English.     

The Role of Phoneme in Mandarin Chinese Production: Evidence from ERPs

Established linguistic theoretical frameworks propose that alphabetic language speakers use phonemes as phonological encoding units during speech production whereas Mandarin Chinese speakers use syllables. This framework was challenged by recent neural evidence of facilitation induced by overlapping initial phonemes, raising the possibility that phonemes also contribute to the phonological encoding process in Chinese. However, there is no evidence of non-initial phoneme involvement in Chinese phonological encoding among representative Chinese speakers, rendering the functional role of phonemes in spoken Chinese controversial. Here, we addressed this issue by systematically investigating the word-initial and non-initial phoneme repetition effect on the electrophysiological signal using a picture-naming priming task in which native Chinese speakers produced disyllabic word pairs. We found that overlapping phonemes in both the initial and non-initial position evoked more positive ERPs in the 180- to 300-ms interval, indicating position-invariant repetition facilitation effect during phonological encoding. Our findings thus revealed the fundamental role of phonemes as independent phonological encoding units in Mandarin Chinese.     

Tuning of Human Modulation Filters Is Carrier-Frequency Dependent

Recent studies employing speech stimuli to investigate ‘cocktail-party’ listening have focused on entrainment of cortical activity to modulations at syllabic (5 Hz) and phonemic (20 Hz) rates. The data suggest that cortical modulation filters (CMFs) are dependent on the sound-frequency channel in which modulations are conveyed, potentially underpinning a strategy for separating speech from background noise. Here, we characterize modulation filters in human listeners using a novel behavioral method. Within an ‘inverted’ adaptive forced-choice increment detection task, listening level was varied whilst contrast was held constant for ramped increments with effective modulation rates between 0.5 and 33 Hz. Our data suggest that modulation filters are tonotopically organized (i.e., vary along the primary, frequency-organized, dimension). This suggests that the human auditory system is optimized to track rapid (phonemic) modulations at high sound-frequencies and slow (prosodic/syllabic) modulations at low frequencies.     

Iconicity as structure mapping

Linguistic and psycholinguistic evidence is presented to support the use of structure-mapping theory as a framework for understanding effects of iconicity on sign language grammar and processing. The existence of structured mappings between phonological form and semantic mental representations has been shown to explain the nature of metaphor and pronominal anaphora in sign languages. With respect to processing, it is argued that psycholinguistic effects of iconicity may only be observed when the task specifically taps into such structured mappings. In addition, language acquisition effects may only be observed when the relevant cognitive abilities are in place (e.g. the ability to make structural comparisons) and when the relevant conceptual knowledge has been acquired (i.e. information key to processing the iconic mapping). Finally, it is suggested that iconicity is better understood as a structured mapping between two mental representations than as a link between linguistic form and human experience.     

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.     

Ethanol induces oxidative stress in alveolar macrophages via upregulation of NADPH oxidases

Chronic alcohol abuse is a comorbid variable of acute respiratory distress syndrome. Previous studies showed that, in the lung, chronic alcohol consumption increased oxidative stress and impaired alveolar macrophage (AM) function. NADPH oxidases (Noxes) are the main source of reactive oxygen species in AMs. Therefore, we hypothesized that chronic alcohol consumption increases AM oxidant stress through modulation of Nox1, Nox2, and Nox4 expression. AMs were isolated from male C57BL/6J mice, aged 8-10 wk, which were treated with or without ethanol in drinking water (20% w/v, 12 wk). MH-S cells, a mouse AM cell line, were treated with or without ethanol (0.08%, 3 d) for in vitro studies. Selected cells were treated with apocynin (300 μM), a Nox1 and Nox2 complex formation inhibitor, or were transfected with Nox small interfering RNAs (20-35 nM), before ethanol exposure. Human AMs were isolated from alcoholic and control patients' bronchoalveolar lavage fluid. Nox mRNA levels (quantitative RT-PCR), protein levels (Western blot and immunostaining), oxidative stress (2',7'-dichlorofluorescein-diacetate and Amplex Red analysis), and phagocytosis (Staphylococcus aureus internalization) were measured. Chronic alcohol increased Nox expression and oxidative stress in mouse AMs in vivo and in vitro. Experiments using apocynin and Nox small interfering RNAs demonstrated that ethanol-induced Nox4 expression, oxidative stress, and AM dysfunction were modulated through Nox1 and Nox2 upregulation. Further, Nox1, Nox2, and Nox4 protein levels were augmented in human AMs from alcoholic patients compared with control subjects. Ethanol induces AM oxidative stress initially through upregulation of Nox1 and Nox2 with downstream Nox4 upregulation and subsequent impairment of AM function.     

Selective sensitivity of hearing to amplitude modulation of speech in man]

Studies on the sensitivity of man's hearing to the reception of amplitude modulation (AM) of the sound reveal statistically reliable threshold minimum in the region of 4-6 c. p. s. It is suggested that this phenomenon is evolutionary conditioned by tuning of human auditory system on the perception of speech, in which AM results from articulation of the syllables. The acoustical analysis of several speech extracts demonstrated statistically reliable maximum of AM of the sound flow just within 4-6 c. p. s. Therefore, the selective sensitivity of hearing to perception of these AM frequencies increases the safety and interference resistance of the system "speech-hearing".     

The Integration of Prosodic Speech in High Functioning Autism: A Preliminary fMRI Study

Background

Autism is a neurodevelopmental disorder characterized by a specific triad of symptoms such as abnormalities in social interaction, abnormalities in communication and restricted activities and interests. While verbal autistic subjects may present a correct mastery of the formal aspects of speech, they have difficulties in prosody (music of speech), leading to communication disorders. Few behavioural studies have revealed a prosodic impairment in children with autism, and among the few fMRI studies aiming at assessing the neural network involved in language, none has specifically studied prosodic speech. The aim of the present study was to characterize specific prosodic components such as linguistic prosody (intonation, rhythm and emphasis) and emotional prosody and to correlate them with the neural network underlying them.

Methodology/Principal Findings

We used a behavioural test (Profiling Elements of the Prosodic System, PEPS) and fMRI to characterize prosodic deficits and investigate the neural network underlying prosodic processing. Results revealed the existence of a link between perceptive and productive prosodic deficits for some prosodic components (rhythm, emphasis and affect) in HFA and also revealed that the neural network involved in prosodic speech perception exhibits abnormal activation in the left SMG as compared to controls (activation positively correlated with intonation and emphasis) and an absence of deactivation patterns in regions involved in the default mode.

Conclusions/Significance

These prosodic impairments could not only result from activation patterns abnormalities but also from an inability to adequately use the strategy of the default network inhibition, both mechanisms that have to be considered for decreasing task performance in High Functioning Autism.     

Hearing and seeing meaning in speech and gesture: insights from brain and behaviour

As we speak, we use not only the arbitrary form–meaning mappings of the speech channel but also motivated form–meaning correspondences, i.e. iconic gestures that accompany speech (e.g. inverted V-shaped hand wiggling across gesture space to demonstrate walking). This article reviews what we know about processing of semantic information from speech and iconic gestures in spoken languages during comprehension of such composite utterances. Several studies have shown that comprehension of iconic gestures involves brain activations known to be involved in semantic processing of speech: i.e. modulation of the electrophysiological recording component N400, which is sensitive to the ease of semantic integration of a word to previous context, and recruitment of the left-lateralized frontal–posterior temporal network (left inferior frontal gyrus (IFG), medial temporal gyrus (MTG) and superior temporal gyrus/sulcus (STG/S)). Furthermore, we integrate the information coming from both channels recruiting brain areas such as left IFG, posterior superior temporal sulcus (STS)/MTG and even motor cortex. Finally, this integration is flexible: the temporal synchrony between the iconic gesture and the speech segment, as well as the perceived communicative intent of the speaker, modulate the integration process. Whether these findings are special to gestures or are shared with actions or other visual accompaniments to speech (e.g. lips) or other visual symbols such as pictures are discussed, as well as the implications for a multimodal view of language.     

Language Universals Engage Broca's Area

It is well known that natural languages share certain aspects of their design. For example, across languages, syllables like blif are preferred to lbif. But whether language universals are myths or mentally active constraints—linguistic or otherwise—remains controversial. To address this question, we used fMRI to investigate brain response to four syllable types, arrayed on their linguistic well-formedness (e.g., blif≻bnif≻bdif≻lbif, where ≻ indicates preference). Results showed that syllable structure monotonically modulated hemodynamic response in Broca''s area, and its pattern mirrored participants'' behavioral preferences. In contrast, ill-formed syllables did not systematically tax sensorimotor regions—while such syllables engaged primary auditory cortex, they tended to deactivate (rather than engage) articulatory motor regions. The convergence between the cross-linguistic preferences and English participants'' hemodynamic and behavioral responses is remarkable given that most of these syllables are unattested in their language. We conclude that human brains encode broad restrictions on syllable structure.     

Speech-evoked activity in primary auditory cortex: effects of voice onset time

Neural encoding of temporal speech features is a key component of acoustic and phonetic analyses. We examined the temporal encoding of the syllables /da/ and /ta/, which differ along the temporally based, phonetic parameter of voice onset time (VOT), in primary auditory cortex (A1) of awake monkeys using concurrent multilaminar recordings of auditory evoked potentials (AEP), the derived current source density, and multiunit activity. A general sequence of A1 activation consisting of a lamina-specific profile of parallel and sequential excitatory and inhibitory processes is described. VOT is encoded in the temporal response patterns of phase-locked activity to the periodic speech segments and by “on” responses to stimulus and voicing onset. A transformation occurs between responses in the thalamocortical (TC) fiber input and A1 cells. TC fibers are more likely to encode VOT with “on” responses to stimulus onset followed by phase-locked responses during the voiced segment, whereas A1 responses are more likely to exhibit transient responses both to stimulus and voicing onset. Relevance to subcortical speech processing, the human AEP and speech psychoacoustics are discussed. A mechanism for categorical differentiation of voiced and unvoiced consonants is proposed.     

Stochastic Time Models of Syllable Structure

Drawing on phonology research within the generative linguistics tradition, stochastic methods, and notions from complex systems, we develop a modelling paradigm linking phonological structure, expressed in terms of syllables, to speech movement data acquired with 3D electromagnetic articulography and X-ray microbeam methods. The essential variable in the models is syllable structure. When mapped to discrete coordination topologies, syllabic organization imposes systematic patterns of variability on the temporal dynamics of speech articulation. We simulated these dynamics under different syllabic parses and evaluated simulations against experimental data from Arabic and English, two languages claimed to parse similar strings of segments into different syllabic structures. Model simulations replicated several key experimental results, including the fallibility of past phonetic heuristics for syllable structure, and exposed the range of conditions under which such heuristics remain valid. More importantly, the modelling approach consistently diagnosed syllable structure proving resilient to multiple sources of variability in experimental data including measurement variability, speaker variability, and contextual variability. Prospects for extensions of our modelling paradigm to acoustic data are also discussed.     

Vocal modulation during courtship increases proceptivity even in naive listeners

Speakers modulate their voice when talking to infants, but we know little about subtle variation in acoustic parameters during speech in adult social interactions. Because tests of perception of such variation are hampered by listeners' understanding of semantic content, studies often confine speech to enunciation of standard sentences, restricting ecological validity. Furthermore, apparent paralinguistic modulation in one language may be underpinned by specific parameters of that language. Here we circumvent these problems by recording speech directed to attractive or unattractive potential partners or competitors, and testing responses to these recordings by naive listeners, across both a Germanic (English) and a Slavic (Czech) language. Analysis of acoustic parameters indicates that men's voices varied F₀ most in speech towards potential attractive versus unattractive mates, while modulation of women's F₀ variability was more sensitive to competitors, with higher variability when those competitors were relatively attractive. There was striking similarity in patterns of social context-dependent F₀ variation across the two model languages, with both men's and women's voices varying most when responding to attractive individuals. Men's minimum pitch was lower when responding to attractive than unattractive women. For vocal modulation to be effective, however, it must be sufficiently detectable to promote proceptivity towards the speaker. We showed that speech directed towards attractive individuals was preferred by naive listeners of either language over speech by the same speaker to unattractive individuals, even when voices were stripped of several acoustic properties by low-pass filtering, which renders speech unintelligible. Our results suggest that modulating F₀ may be a critical parameter in human courtship, independently of semantic content.