Effects of Place of Articulation Changes on Auditory Neural Activity: A Magnetoencephalography Study

In casual speech, phonemic segments often assimilate such that they adopt features from adjacent segments, a typical feature being their place of articulation within the vocal tract (e.g., labial, coronal, velar). Place assimilation (e.g., from coronal /n/ to labial /m/: rainbow→*raimbow) alters the surface form of words. Listeners' ability to perceptually compensate for such changes seems to depend on the phonemic context, on whether the adjacent segment (e.g., the /b/ in “rainbow”) invites the particular change. Also, some assimilations occur frequently (e.g., /n/→/m/), others are rare (e.g., /m/→/n/). We investigated the effects of place assimilation, its contextual dependency, and its frequency on the strength of auditory evoked mismatch negativity (MMN) responses, using pseudowords. Results from magnetoencephalography (MEG) revealed that the MMN was modulated both by the frequency and contextual appropriateness of assimilations

Body representation in infants: Categorical boundaries of body parts as assessed by somatosensory mismatch negativity.

There is growing interest in developing and using novel measures to assess how the body is represented in human infancy. Various lines of evidence with adults and older children show that tactile perception is modulated by a high-level representation of the body. For instance, the distance between two points of tactile stimulation is perceived as being greater when these points cross a joint boundary than when they are within a body part, suggesting that the representation of the body is structured with joints acting as categorical boundaries between body parts. Investigating the developmental origins of this categorical effect has been constrained by infants' inability to verbally report on the properties of tactile stimulation. Here we made novel use of an infant brain measure, the somatosensory mismatch negativity (sMMN), to explore categorical aspects of tactile body processing in infants aged 6-7 months. Amplitude of the sMMN elicited by tactile stimuli across the wrist boundary was significantly greater than for stimuli of equal distance that were within the boundary, suggesting a categorical effect in body processing in infants. We suggest that an early-appearing, structured representation of the body into 'parts' may play a role in mapping correspondences between self and other

Spatiotemporal Convergence of Semantic Processing in Reading and Speech Perception

Retrieval of word meaning from the semantic system and its integration with context are often assumed to be shared by spoken and written words. How is modality-independent semantic processing manifested in the brain, spatially and temporally? Time-sensitive neuroimaging allows tracking of neural activation sequences. Use of semantically related versus unrelated word pairs or sentences ending with a semantically highly or less plausible word, in separate studies of the auditory and visual modality, has associated lexical-semantic analysis with sustained activation at ∼200–800 ms. Magnetoencephalography (MEG) studies have further identified the superior temporal cortex as a main locus of the semantic effect. Nevertheless, a direct comparison of the spatiotemporal neural correlates of visual and auditory word comprehension in the same brain is lacking. We used MEG to compare lexical-semantic analysis in the visual and auditory domain in the same individuals, and contrasted it with phonological analysis that, according to models of language perception, should occur at a different time with respect to semantic analysis in reading and speech perception. The stimuli were lists of four words that were either semantically or phonologically related, or with the final word unrelated to the preceding context. Superior temporal activation reflecting semantic processing occurred similarly in the two modalities, left-lateralized at 300–450 ms and thereafter bilaterally, generated in close-by areas. Effect of phonology preceded the semantic effect in speech perception but not in reading. The present data indicate involvement of the middle superior temporal cortex in semantic processing from ∼300 ms onwards, regardless of input modality.Peer reviewe

Spatiotemporal Dynamics of Word Processing in the Human Brain

We examined the spatiotemporal dynamics of word processing by recording the electrocorticogram (ECoG) from the lateral frontotemporal cortex of neurosurgical patients chronically implanted with subdural electrode grids. Subjects engaged in a target detection task where proper names served as infrequent targets embedded in a stream of task-irrelevant verbs and nonwords. Verbs described actions related to the hand (e.g, throw) or mouth (e.g., blow), while unintelligible nonwords were sounds which matched the verbs in duration, intensity, temporal modulation, and power spectrum. Complex oscillatory dynamics were observed in the delta, theta, alpha, beta, low, and high gamma (HG) bands in response to presentation of all stimulus types. HG activity (80–200 Hz) in the ECoG tracked the spatiotemporal dynamics of word processing and identified a network of cortical structures involved in early word processing. HG was used to determine the relative onset, peak, and offset times of local cortical activation during word processing. Listening to verbs compared to nonwords sequentially activates first the posterior superior temporal gyrus (post-STG), then the middle superior temporal gyrus (mid-STG), followed by the superior temporal sulcus (STS). We also observed strong phase-locking between pairs of electrodes in the theta band, with weaker phase-locking occurring in the delta, alpha, and beta frequency ranges. These results provide details on the first few hundred milliseconds of the spatiotemporal evolution of cortical activity during word processing and provide evidence consistent with the hypothesis that an oscillatory hierarchy coordinates the flow of information between distinct cortical regions during goal-directed behavior

Temporal evolution of gamma activity in human cortex during an overt and covert word repetition task

Several scientists have proposed different models for cortical processing of speech. Classically, the regions participating in language were thought to be modular with a linear sequence of activations. More recently, modern theoretical models have posited a more hierarchical and distributed interaction of anatomic areas for the various stages of speech processing. Traditional imaging techniques can only define the location or time of cortical activation, which impedes the further evaluation and refinement of these models. In this study, we take advantage of recordings from the surface of the brain [electrocorticography (ECoG)], which can accurately detect the location and timing of cortical activations, to study the time course of ECoG high gamma (HG) modulations during an overt and covert word repetition task for different cortical areas. For overt word production, our results show substantial perisylvian cortical activations early in the perceptual phase of the task that were maintained through word articulation. However, this broad activation is attenuated during the expressive phase of covert word repetition. Across the different repetition tasks, the utilization of the different cortical sites within the perisylvian region varied in the degree of activation dependent on which stimulus was provided (auditory or visual cue) and whether the word was to be spoken or imagined. Taken together, the data support current models of speech that have been previously described with functional imaging. Moreover, this study demonstrates that the broad perisylvian speech network activates early and maintains suprathreshold activation throughout the word repetition task that appears to be modulated by the demands of different conditions

Neural dynamics of inflectional and derivational processing in spoken word comprehension: laterality and automaticity.

Rapid and automatic processing of grammatical complexity is argued to take place during speech comprehension, engaging a left-lateralized fronto-temporal language network. Here we address how neural activity in these regions is modulated by the grammatical properties of spoken words. We used combined magneto- and electroencephalography to delineate the spatiotemporal patterns of activity that support the recognition of morphologically complex words in English with inflectional (-s) and derivational (-er) affixes (e.g., bakes, baker). The mismatch negativity, an index of linguistic memory traces elicited in a passive listening paradigm, was used to examine the neural dynamics elicited by morphologically complex words. Results revealed an initial peak 130-180 ms after the deviation point with a major source in left superior temporal cortex. The localization of this early activation showed a sensitivity to two grammatical properties of the stimuli: (1) the presence of morphological complexity, with affixed words showing increased left-laterality compared to non-affixed words; and (2) the grammatical category, with affixed verbs showing greater left-lateralization in inferior frontal gyrus compared to affixed nouns (bakes vs. beaks). This automatic brain response was additionally sensitive to semantic coherence (the meaning of the stem vs. the meaning of the whole form) in left middle temporal cortex. These results demonstrate that the spatiotemporal pattern of neural activity in spoken word processing is modulated by the presence of morphological structure, predominantly engaging the left-hemisphere's fronto-temporal language network, and does not require focused attention on the linguistic input

On the context-dependent nature of the contribution of the ventral premotor cortex to speech perception

What is the nature of the interface between speech perception and production, where auditory and motor representations converge? One set of explanations suggests that during perception, the motor circuits involved in producing a perceived action are in some way enacting the action without actually causing movement (covert simulation) or sending along the motor information to be used to predict its sensory consequences (i.e., efference copy). Other accounts either reject entirely the involvement of motor representations in perception, or explain their role as being more supportive than integral, and not employing the identical circuits used in production. Using fMRI, we investigated whether there are brain regions that are conjointly active for both speech perception and production, and whether these regions are sensitive to articulatory (syllabic) complexity during both processes, which is predicted by a covert simulation account. A group of healthy young adults (1) observed a female speaker produce a set of familiar words (perception), and (2) observed and then repeated the words (production). There were two types of words, varying in articulatory complexity, as measured by the presence or absence of consonant clusters. The simple words contained no consonant cluster (e.g. “palace”), while the complex words contained one to three consonant clusters (e.g. “planet”). Results indicate that the left ventral premotor cortex (PMv) was significantly active during speech perception and speech production but that activation in this region was scaled to articulatory complexity only during speech production, revealing an incompletely specified efferent motor signal during speech perception. The right planum temporal (PT) was also active during speech perception and speech production, and activation in this region was scaled to articulatory complexity during both production and perception. These findings are discussed in the context of current theories of speech perception, with particular attention to accounts that include an explanatory role for mirror neurons

Neural mechanisms of foreign language phoneme acquisition in early adulthood : MEG study

Tämän tutkimuksen tavoitteena on selvittää omaan äidinkieleen kuulumattomien foneemikontrastien oppimisen mekanismeja nuorilla aikuisilla neurofysiologisten ja behavioraalisten menetelmien avulla. Perinteisesti kielen foneettisen avaruuden omaksumisen on ajateltu tapahtuvan ensisijaisesti varhaislapsuuden kielellisten herkkyyskausien aikana, jonka jälkeen uusien foneemien oppiminen on haastavaa. Myöhemmät tutkimukset ovat kuitenkin osoittaneet, että vieraiden foneemien omaksuminen on mahdollista myös aikuisiällä. Uusien foneemikategorioiden muodostuminen vaatii aivoissa solutason plastisia muutoksia. Aivojen kykyä erotella läheisesti toisiaan muistuttavia foneemikategorioita kielenprosessoinnin varhaisella tasolla on tutkittu neurofysiologisin menetelmin esimerkiksi tapahtumasidonnaisen poikkeavuusnegatiivisuusvasteen (eng. mismatch negativity, MMN) avulla. MMN-vaste, tai sen magneettinen vastine MMNm, syntyy seurauksena muutoksiin sensorisessa havaintoympäristössä. Tutkimuksissa lyhyenkin auditiivisen harjoittelujakson on havaittu vahvistavan aivojen kykyä erotella läheisesti toisiaan muistuttavia vieraita foneemeja ja voimistavan MMN- ja MMNm-vasteita. Tässä tutkimuksessa vieraan kielen foneettisen oppimisen neuraalista perustaa ja oppimisen aiheuttamia plastisia muutoksia aivoissa tutkittiin magnetoenkefalografialla (MEG) neuromagneettisten tapahtumasidonnaisten vasteiden (erityisesti MMNm) avulla. Tutkimuksessa mitattiin 20 suomalaista koehenkilöä, joiden tehtävänä oli oppia erottelemaan akustisesti toisiaan läheisesti muistuttavia venäjän kielen frikatiiveja Ш /ʂ/ ja Щ /ɕ(ː)/. Erottelukykyä mitattiin ensin behavioraalisella tehtävällä, jossa koehenkilöille toistettiin nauhoitettuja venäjänkielisiä epäsanaminimipareja, jossa sanan ensimmäistä foneemia varioitiin. Koehenkilöiden tehtävänä oli vastata, kuulivatko he sanoissa eroa. Samoja kuuloärsykkeitä toistettiin koehenkilöille sen jälkeen passiivisessa MEG-tehtävässä, jossa testattiin aivojen kykyä havaita ero ärsykkeissä ilman, että niihin kiinnitetään huomiota (koehenkilöt katselivat samalla äänetöntä elokuvaa). Mittauksen jälkeen koehenkilöt harjoittelivat foneemien erottelua kotona noin viikon ajan tietokoneavusteisen oppimispelin avulla, jonka jälkeen heidät mitattiin uudelleen. MEG-signaalien lähdemallinnusta varten koehenkilöiden aivoista otettiin myös rakenteelliset magneettikuvat. Tutkittavien foneemien behavioraalinen erottelukyky oli selvästi tuttuja kontrollifoneemeita heikompaa. Erottelukyky vaikutti paranevan harjoittelun seurauksena hieman, mutta ero ei ollut tilastollisesti merkitsevä. Hypoteesien vastaisesti tilastollisesti merkitseviä MMNm-vasteita ei löydetty ennen eikä jälkeen harjoittelun, eikä muissakaan auditorisissa MEG-vasteissa tai niiden neuraalisten lähdevirtojen voimakkuuksissa tai jakaumassa ollut tilastollisesti merkitsevää eroa mittauskertojen välillä. Yksilölliset erot oppimisessa olivat kuitenkin suuria. Koehenkilöillä, joilla behavioraalinen erottelukyky parani harjoittelun myötä, oli silmämääräisesti havaittavissa hypoteesien mukaista vahvistumista auditorisissa vasteissa. Vaikka efekti oli erittäin pieni eikä tilastollisesti merkitsevä, vastaavaa ei havaittu epäoppijoilla eikä kontrollitilanteessa. Tässä tutkimuksessa ei kyetty replikoimaan aiempien tutkimusten tuloksia foneemien omaksumisesta aikuisiällä. Vaikka on todennäköistä, että tietyt metodologiset heikkoudet (mm. vähäinen ärsykkeiden määrä MEG-tehtävässä, haastavat ärsykkeet) vaikuttivat tulosten merkitsevyyteen, voidaan tämän tutkimuksen valossa aiempien tutkimustulosten yleistettävyyttä kyseenalaistaa.The aim of this study is to examine the learning mechanisms and acquisition of non-native phoneme contrasts in young adults using neurophysiological and behavioral methods. According to the traditional view, acquiring novel phonemes after the sensitive periods in the early childhood is very difficult. However, later findings have shown that foreign phoneme contrasts can be learned at a later age, too. Acquiring new phonemic categories requires neuroplastic changes in the brain. Neurophysiological studies have examined the brain’s ability to differentiate between closely related phonemic categories at the early stage of spoken language processing by measuring, for example, event-related mismatch negativity responses (MMN). MMN, or its magnetic equivalent MMNm, is elicited when the brain registers a difference in a repetitive sensory stimulus. Studies have shown that even a moderate amount of auditory training with closely related foreign phonemes improves the brain’s ability to discriminate between them resulting in enhanced MMN or MMNm responses. In this experiment the neural mechanisms of foreign language phoneme acquisition and the learning-related neuroplastic changes were studied using magnetoencephalography (MEG) and neuromagnetic evoked responses (MMNm in particular). 20 Finnish subjects were measured in the experiment. Their task was to learn to differentiate between acoustically closely related Russian fricatives Ш /ʂ/ and Щ /ɕ(ː)/. The subjects’ differentiation skills were first tested in a behavioral task where Russian pseudoword minimal pairs were presented to them auditorily. The first phoneme in the word pairs was varied and the subjects had to report whether they heard a difference between the words or not. The same stimuli were then presented in a passive MEG task where the brain’s change detection responses were tested in an unattended situation as the subjects were watching a silent film. After the measurement the subjects practiced the phonemes at home for approximately one week by playing a learning game by computer. After training they were measured again. Structural magnetic resonance images of the subjects’ brain were also measured for MEG source localization purposes. Behavioral discrimination ability of the experimental phonemes was considerably worse than with familiar control phonemes. The discrimination skills seemed to improve by training, but the difference was not statistically significant. Contrary to the hypotheses, statistically significant MMNm responses were not found before or after training. No significant differences were found in other auditory MEG responses or their neural source current distributions between the measurements either. However, individual differences in learning were sizeable. For the subjects who improved their performance in the behavioral task a modest training-related boost in the auditory responses supporting the hypotheses could be observed. Although very small and statistically insignificant, the effect was opposite for control stimuli and did not exist in the non-learner group suggesting some sort of change in neural processing in the learner group. This study was not able to replicate the findings from various previous studies on phoneme acquisition in adulthood. Although it is likely that certain methodological limitations (e.g. small number of stimulus repetitions, challenging stimuli) affected the significance of the results, based on this study the generalizability of some of the previous findings can be called into question

Role of medial premotor areas in action language processing in relation to motor skills

The literature reports that the supplementary motor area (SMA) and pre-supplementary motor area (pre-SMA) are involved in motor planning and execution, and in motor-related cognitive functions such as motor imagery. However, their specific role in action language processing remains unclear. In the present study, we investigated the impact of repetitive transcranial magnetic stimulation (rTMS) over SMA and pre-SMA during an action semantic analogy task (SAT) in relation with fine motor skills (i.e., manual dexterity) and motor imagery abilities in healthy non-expert adults. The impact of rTMS over SMA (but not pre-SMA) on reaction times (RT) during SAT was correlated with manual dexterity. Specifically, results show that rTMS over SMA modulated RT for those with lower dexterity skills. Our results therefore demonstrate a causal involvement of SMA in action language processing, as well as the existence of inter-individual differences in this involvement. We discuss these findings in light of neurolinguistic theories of language processing