Alina Leminen

Spatiotemporal Dynamics of the Processing of Spoken Inflected and Derived Words: A Combined EEG and MEG Study

The spatiotemporal dynamics of the neural processing of spoken morphologically complex words are still an open issue. In the current study, we investigated the time course and neural sources of spoken inflected and derived words using simultaneously recorded electroencephalography (EEG) and magnetoencephalography (MEG) responses. Ten participants (native speakers) listened to inflected, derived, and monomorphemic Finnish words and judged their acceptability. EEG and MEG responses were time-locked to both the stimulus onset and the critical point (suffix onset for complex words, uniqueness point for monomorphemic words). The ERP results showed that inflected words elicited a larger left-lateralized negativity than derived and monomorphemic words approximately 200 ms after the critical point. Source modeling of MEG responses showed one bilateral source in the superior temporal area ∼100 ms after the critical point, with derived words eliciting stronger source amplitudes than inflected and monomorphemic words in the right hemisphere. Source modeling also showed two sources in the temporal cortex approximately 200 ms after the critical point. There, inflected words showed a more systematic pattern in source locations and elicited temporally distinct source activity in comparison to the derived word condition. The current results provide electrophysiological evidence for at least partially distinct cortical processing of spoken inflected and derived words. In general, the results support models of morphological processing stating that during the recognition of inflected words, the constituent morphemes are accessed separately. With regard to derived words, stem and suffix morphemes might be at least initially activated along with the whole word representation.

Neural dynamics of inflectional and derivational morphology processing in the human brain.

We investigated neural distinctions between inflectional and derivational morphology and their interaction with lexical frequency using the mismatch negativity (MMN), an established neurophysiological index of experience-dependent linguistic memory traces and automatic syntactic processing. We presented our electroencephalography (EEG) study participants with derived and inflected words of variable lexical frequencies against their monomorphemic base forms in a passive oddball paradigm, along with acoustically matched pseudowords. Sensor space and distributed source modelling results showed that at 100-150 msec after the suffix onset, derived words elicited larger responses than inflected words. Furthermore, real derived words showed advantage over pseudo-derivations and frequent derivations elicited larger activation than less frequent ones. This pattern of results is fully in line with previous research that explained lexical MMN enhancement by an activation of strongly connected word-specific long-term memory circuits, and thus suggests stronger lexicalisation for frequently used complex words. At the same time, a strikingly different pattern was found for inflectional forms: higher response amplitude for pseudo-inflections than for real inflected words, with no clear frequency effects. This is fully in line with previous MMN results on combinatorial processing of (morpho)syntactic stimuli: higher response to ungrammatical morpheme strings than grammatical ones, which does not depend on the strings surface frequency. This pattern suggests that, for inflectional forms, combinatorial processing route dominates over whole-form storage and access. In sum, our results suggest that derivations are more likely to form unitary representations than inflections which are likely to be processed combinatorially, and imply at least partially distinct brain mechanisms for the processing and representation of these two types of morphology. These dynamic mechanisms, underpinned by perisylvian networks, are activated rapidly, at 100-150 msec after the information arrives at the input, and in a largely automatic fashion, possibly providing neural basis for the first-pass morphological processing of spoken words.

Two Distinct Auditory-Motor Circuits for Monitoring Speech Production as Revealed by Content-Specific Suppression of Auditory Cortex

Speech production, both overt and covert, down-regulates the activation of auditory cortex. This is thought to be due to forward prediction of the sensory consequences of speech, contributing to a feedback control mechanism for speech production. Critically, however, these regulatory effects should be specific to speech content to enable accurate speech monitoring. To determine the extent to which such forward prediction is content-specific, we recorded the brains neuromagnetic responses to heard multisyllabic pseudowords during covert rehearsal in working memory, contrasted with a control task. The cortical auditory processing of target syllables was significantly suppressed during rehearsal compared with control, but only when they matched the rehearsed items. This critical specificity to speech content enables accurate speech monitoring by forward prediction, as proposed by current models of speech production. The one-to-one phonological motor-to-auditory mappings also appear to serve the maintenance of information in phonological working memory. Further findings of right-hemispheric suppression in the case of whole-item matches and left-hemispheric enhancement for last-syllable mismatches suggest that speech production is monitored by 2 auditory-motor circuits operating on different timescales: Finer grain in the left versus coarser grain in the right hemisphere. Taken together, our findings provide hemisphere-specific evidence of the interface between inner and heard speech.

Bilingualism modulates the white matter structure of language-related pathways

ABSTRACT Learning and speaking a second language (L2) may result in profound changes in the human brain. Here, we investigated local structural differences along two language‐related white matter trajectories, the arcuate fasciculus and the inferior fronto‐occipital fasciculus (IFOF), between early simultaneous bilinguals and late sequential bilinguals. We also examined whether early exposure to two languages might lead to a more bilateral structural organization of the arcuate fasciculus. Fractional anisotropy, mean and radial diffusivities (FA, MD, and RD respectively) were extracted to analyse tract‐specific changes. Additionally, global voxel‐wise effects were investigated with Tract‐Based Spatial Statistics (TBSS). We found that relative to late exposure, early exposure to L2 leads to increased FA along a phonology‐related segment of the arcuate fasciculus, but induces no modulations along the IFOF, associated to semantic processing. Late sequential bilingualism, however, was associated with decreased MD along the bilateral IFOF. Our results suggest that early vs. late bilingualism may lead to qualitatively different kind of changes in the structural language‐related network. Furthermore, we show that early bilingualism contributes to the structural laterality of the arcuate fasciculus, leading to a more bilateral organization of these perisylvian language‐related tracts.

The role of attention in processing morphologically complex spoken words: an EEG/MEG study.

This study determined to what extent morphological processing of spoken inflected and derived words is attention-independent. To answer these questions EEG and MEG responses were recorded from healthy participants while they were presented with spoken Finnish inflected, derived, and monomorphemic words. In the non-attended task, the participants were instructed to ignore the incoming auditory stimuli and concentrate on the silent cartoon. In the attended task, previously reported by Leminen et al. (2011), the participants were to judge the acceptability of each stimulus. Importantly, EEG and MEG responses were time-locked to the onset of critical information [suffix onset for the complex words and uniqueness point (UP) for the monomorphemic words]. Early after the critical point, word type did not interact with task: in both attended and non-attended tasks, the event-related potentials (ERPs) showed larger negativity to derived than inflected or monomorphemic words ~100 ms after the critical point. MEG source waveforms showed a similar pattern. Later than 100 ms after the critical point, there were no differences between word types in the non-attended task either in the ERP or source modeling data. However, in the attended task inflected words elicited larger responses than other words ~200 ms after the critical point. The results suggest different brain representations for derived and inflected words. The early activation after the critical point was elicited both in the non-attended and attended tasks. As this stage of word recognition was not modulated by attention, it can be concluded to reflect an automatic mapping of incoming acoustic information onto stored representations. In contrast, the later differences between word types in the attended task were not observed in the non-attended task. This indicates that later compositional processes at the (morpho)syntactic-semantic level require focused attention.

Time course of the neural processing of spoken derived words: an event-related potential study.

Event-related potentials were recorded to examine the time course of the neural processing of spoken (i) existing derived words, (ii) morphologically legal, and (iii) illegal pseudowords in the Finnish language. The stimuli were matched by (complex) uniqueness/deviation points and event-related potentials were time-locked to stimulus onset and suffix onset. Illegal pseudowords elicited a larger negativity than existing words approximately 300 ms after suffix onset, suggesting a difficulty to semantically integrate morphemes. The magnitude of the negativity effect was similar for legal pseudowords and existing words, reflecting successful licensing and integration of morphemes for legal pseudowords. The results suggest parallel full-form and morpheme-based processing of spoken derived stimuli and emphasize the role of semantic interpretability in morphological parsing.

Flexible, rapid and automatic neocortical word form acquisition mechanism in children as revealed by neuromagnetic brain response dynamics

ABSTRACT Children learn new words and word forms with ease, often acquiring a new word after very few repetitions. Recent neurophysiological research on word form acquisition in adults indicates that novel words can be acquired within minutes of repetitive exposure to them, regardless of the individuals focused attention on the speech input. Although it is well‐known that children surpass adults in language acquisition, the developmental aspects of such rapid and automatic neural acquisition mechanisms remain unexplored. To address this open question, we used magnetoencephalography (MEG) to scrutinise brain dynamics elicited by spoken words and word‐like sounds in healthy monolingual (Danish) children throughout a 20‐min repetitive passive exposure session. We found rapid neural dynamics manifested as an enhancement of early (˜100 ms) brain activity over the short exposure session, with distinct spatiotemporal patterns for different novel sounds. For novel Danish word forms, signs of such enhancement were seen in the left temporal regions only, suggesting reliance on pre‐existing language circuits for acquisition of novel word forms with native phonology. In contrast, exposure both to novel word forms with non‐native phonology and to novel non‐speech sounds led to activity enhancement in both left and right hemispheres, suggesting that more wide‐spread cortical networks contribute to the build‐up of memory traces for non‐native and non‐speech sounds. Similar studies in adults have previously reported more sluggish (˜15–25 min, as opposed to 4 min in the present study) or non‐existent neural dynamics for non‐native sound acquisition, which might be indicative of a higher degree of plasticity in the childrens brain. Overall, the results indicate a rapid and highly plastic mechanism for a dynamic build‐up of memory traces for novel acoustic information in the childrens brain that operates automatically and recruits bilateral temporal cortical circuits. HIGHLIGHTSChildren acquire novel word forms in an automatic fashion after mere 4 min.To acquire new native‐language word forms, the left perisylvian neural network is used.Bilataral hemispheric structures support acquisition of non‐native language word forms.

Auditory evoked potentials to speech and nonspeech stimuli are associated with verbal skills in preschoolers

Highlights • ERPs to speech and matched nonspeech sounds were recorded in 63 preschoolers.• P1 and N2 were larger for nonspeech than speech sounds, the opposite being true for N4.• Differences between speech and nonspeech ERPs were associated with verbal skills.• ERP lateralization was associated with phonological and naming abilities.• The results suggest that ERPs are useful measures of children’s cortical functioning.

Language control mechanisms differ for native languages: neuromagnetic evidence from trilingual language switching

ABSTRACT How does the brain process and control languages that are learned at a different age, when proficiency in all these languages is high? Early acquired strong languages are likely to have higher baseline activation levels than later learned less‐dominant languages. However, it is still largely unknown how the activation levels of these different languages are controlled, and how interference from an irrelevant language is prevented. In this magnetoencephalography (MEG) study on language switching during auditory perception, early Finnish‐Swedish bilinguals (N = 18) who mastered English with high proficiency after childhood were presented with spoken words in each of the three languages, while performing a simple semantic categorisation task. Switches from the later learned English to either of the native languages resulted in increased neural activation in the superior temporal gyrus (STG) 400–600 ms after word onset (N400m response), whereas such increase was not detected for switches from native languages to English or between the native languages. In an earlier time window of 350–450 ms, English non‐switch trials showed higher activation levels in the inferior frontal gyrus (IFG), pointing to ongoing inhibition of the native languages during the use of English. Taken together, these asymmetric switch costs suggest that native languages are suppressed during the use of a non‐native language, despite the receptive nature of the language task. This effect seems to be driven mostly by age of acquisition or language exposure, rather than proficiency. Our results indicate that mechanisms of control between two native languages differ from those of a later learned language, as upbringing in an early bilingual environment has likely promoted automatiation of language control specifically for the native languages. HIGHLIGHTSNo switching costs were incurred between early acquired native languages.Increasedsource strength in IFG may indicate ongoing inhibition of native languages.AoA and/or everyday language exposure affect language control mechanisms.

The time-course of morphosyntactic and semantic priming in late bilinguals: A study of German adjectives

How do late proficient bilinguals process morphosyntactic and lexical-semantic information in their non-native language (L2)? How is this information represented in the L2 mental lexicon? And what are the neural signatures of L2 morphosyntactic and lexical-semantic processing? We addressed these questions in one behavioral and two ERP priming experiments on inflected German adjectives testing a group of advanced late Russian learners of German in comparison to native speaker (L1) controls. While in the behavioral experiment, the L2 learners performed native-like, the ERP data revealed clear L1/L2 differences with respect to the temporal dynamics of grammatical processing. Specifically, our results show that L2 morphosyntactic processing yielded temporally and spatially extended brain responses relative to L1 processing, indicating that grammatical processing of inflected words in an L2 is more demanding and less automatic than in the L1. However, this group of advanced L2 learners showed native-like lexical-semantic processing.