Cortical Dynamics of Language

The human capability for fluent speech profoundly directs inter-personal communication and, by extension, self-expression. Language is lost in millions of people each year due to trauma, stroke, neurodegeneration, and neoplasms with devastating impact to social interaction and quality of life. The following investigations were designed to elucidate the neurobiological foundation of speech production, building towards a universal cognitive model of language in the brain. Understanding the dynamical mechanisms supporting cortical network behavior will significantly advance the understanding of how both focal and disconnection injuries yield neurological deficits, informing the development of therapeutic approaches

Multimodal imaging of language perception

This Thesis draws together several lines of research by examining language perception in the same individuals using three neuroimaging methods: magnetoencephalography (MEG), functional magnetic resonance imaging (fMRI), and electroencephalography (EEG). The MEG experiments conducted in this Thesis demonstrated that neural processing of written and spoken words converges to the superior temporal cortex following initial modality-specific analysis. In both reading and speech perception, the superior temporal cortex is involved in processing word meaning at ∼250-450 ms in the left hemisphere and after ∼450 ms bilaterally. The data thus support a view of a largely shared semantic system in auditory and visual language perception, in line with the assumption that reading acquisition makes use of the neural systems originally developed for speech perception during evolution and in individual language development. The MEG experiments on reading morphologically complex words showed that the left superior temporal activation was enhanced for the morphologically complex words at ∼200-700 ms. The results suggest that the majority of inflected words in the highly inflected Finnish language are represented in a decomposed form and that the decomposition process requires additional neural resources. Only very high-frequency inflected words may acquire full-form representations. The MEG results on parafoveal preview in reading indicated that neural processing of written words in the left hemisphere is affected by a preview of words in the right visual field. The underlying neural mechanism may facilitate reading of connected text in natural conditions. In a direct comparison, MEG and fMRI showed diverging activation patterns in a reading task although the same individuals were performing the same task. Based on the similarity of the EEG responses recorded simultaneously with both MEG and fMRI, the participants were performing the task similarly during the two recordings. The divergent MEG and fMRI results cannot be attributed to differences in the experimental procedures or language since these factors were controlled. Rather, they are likely to reflect actual dissimilarities in the way neural activity in a high-level cognitive task is picked up by MEG evoked responses and fMRI signals

Proper Names and Common Nouns Dissociation: Exploring Differences in Linguistic Processing and Memory Retrieval

Tese de mestrado, Ciência Cognitiva, 2022, Universidade de Lisboa, Faculdade de CiênciasPhilosophy and linguistics suggest that proper names and common nouns are dissociate lexicosemantic categories. Evidence from psychology and neuropsychology honours this distinction as it provides indications that they may activate different neuro-functional systems. Nevertheless, there are still some lacks in the literature that must be filled. There are mixed findings about the temporal pole involvement in proper names retrieval. Furthermore, to our knowledge, no study has yet investigated the dissociation of proper names vs. common nouns in light of the welldocumented oscillatory dissociation of episodic theta and semantic alpha as reflecting the distinct declarative memory requirements. Besides, no study has explored the brain-based dissociation between the two categories using images as a stimulus. Our naming task showed that there is a dissociation in the retrieval of proper names being more demanding and source-consuming compared to common nouns. Also, oscillations patterns revealed a more pronounced evoked theta power in the proper names retrieval condition in comparison to the common nouns condition. For the alpha wave, we did not obtain differences between the categories. These results sustain the claim of the existence of functionally and anatomically distinct retrieval pathways for the categories of proper and common names, and thus, a dissociation between proper names and common nouns

Evoked Potentials during Language Processing as Neurophysiological Phenomena

The evoked, event-related potential of the EEG has been extensively employed to study language processing. But what is the ERP? An extensive discussion of contemporary theories about the neurophysiology underlying late ERPs is given. Then, in a series of experiments, domain-general perspectives on ERP components are tested regarding their applicability for language-related brain activity. A range of analysis methods (some of which have not been previously applied to the study of auditory sentence processing) such as single-trial analyses and independent component decomposition, demonstrate the degree to which domain general mechanisms explain the language-related EEG

Teadvuse neuronaalsete korrelaatide uurimismetoodika edasiarendusi

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Küsimust selle kohta, mis on teadvus, peetakse kaasaegse teaduse viimaseks tõeliselt suureks probleemiks, sest senini pole mitte keegi suutnud selgitada, miks ja kuidas aju töö on seotud teadvuselamustega. Tänapäeval on üldiselt aktsepteeritud, et teadvuse mõistmiseks on esimese sammuna tarvis täpsemalt määratleda ja tundma õppida teadvuse neuronaalseid korrelaate – neid ajuprotsesse, mis on minimaalselt tarvilikud mingi kindla teadvuselamuse jaoks. Antud väitekirjas on sellele eesmärgile kaasa aidatud nägemistajuga kaasnevate teadvuselamuste neuronaalsete korrelaatide ning nende markerite uurimise kaudu. Kuna on tõenäoline, et varasemate uurimuste tulemused ei peegelda mitte ainult teadvuse neurokorrelaate, vaid ka neile süstemaatiliselt eelnevate või järgnevate protsesside korrelaate, püüti käesolevas töös neid kaasnevaid protsesse täpsemalt uurida ning osades katsetes metodoloogilistel eesmärkidel hoopis vältida. Selleks kasutati varasemast hoolikamalt planeeritud katseparadigmasid, tulemuste töötlemise uusi võtteid ning mitmekesisemat loomulikku pildimaterjali. Lisaks võeti arvesse neurovõrgustike pidevalt muutuvat dünaamilist seisundit ja selle mõju teadvustamise protsessidele. Kokkuvõtvalt võib öelda, et väitekirjas kajastatud uurimustööde tulemuste järgi hakkavad visuaalsete teadvuselamuste vahetud neuromarkerid ilmnema umbes 200 ms jooksul pärast visuaalse stimulatsiooni jõudmist võrkkestale. Samas võib teadvuselamuste kujunemine aga olla hoopis järkjärguline protsess, sest teadvusega korreleerub usaldusväärselt ka umbes 100 ms hilisem neuromarker. Lisaks viitavad tulemused sellele, et visuaalse süsteemi keeruline dünaamika tuleb kõige paremini esile realistliku pildimaterjaliga, mitte lihtsate ja kunstlike geomeetriliste kujunditega. Inimajus on talletunud ohtralt eelteadmisi reaalse visuaalse maailma ning selle reeglipärasuste kohta. See informatsioon mõjutab juba väga varajases faasis nägemistaju ja teadvustamise protsesse, neid täiendades ning parandades.Consciousness is the biggest unsolved problem of modern science because no one has successfully explained how the concerted firing of brain cells is able to produce our subjective experience of the world. It has been argued that in order to understand this phenomenon better we must first identify the neural correlates of consciousness – those neural events which are jointly sufficient for producing a specific conscious experience. The present thesis was set to contribute to this research effort by investigating the neural correlates and markers of conscious visual perception. It is likely that previous studies have failed to identify the true correlates of consciousness because their results also contain processes that systematically precede or follow conscious experience, but do not directly reflect consciousness itself. Thus, the current aim was to study these additional processes in more detail or to even avoid their contribution is some studies. To that end more carefully designed experimental paradigms and more realistic stimulus material was employed. Furthermore, the ongoing state of more global neural networks and its influence on conscious perception was taken into account. Together the results demonstrate that neural markers of conscious visual perception begin to arise about 200 ms after the visual image reaches our eyes. It is however possible that conscious perception is a gradual phenomenon proceeding step-by-step, because another marker also reliably correlates with conscious visual perception around 100 ms later. Furthermore, some results indicate that the complex dynamics of our visual system are best observable with realistic images and not to the same extent with simple and artificial figures. The brain retains a lot of prior knowledge about the natural visual world and its regularities. This information influences the processes of conscious perception early on by complementing and correcting them

Whispers: Cognitive Process in Inter-semiotic Translation

The research uses Whispers, a graduate student theater project as the case study to analyze the cognitive process of inter-semiotic translation from different media/semiotic pairs. The study adopts the Interpretive Theory of Translation proposed by Danica Seleskovitch and Marianne Lederer as a point of reference to examine artists\u27 thought processes when translating across sign systems. Spontaneous reflection of the artists, retrospective interviews, and written statements of the artists used during the performance have been collected along with copies of the source and target media. The paper begins with an introduction to the Whispers and the Interpretive Model proposed by Seleskovitch and Lederer, then proceeds with six section analysis, discussing Sylvia Skok’s paintings as the source media, Neva Derewelzky’s translation from painting to music composition, Marielle Zuccolo’s translation from poetry to American Sign Language, the cast’s collective translation from paintings to poetry, René Neville’s translation from painting and poetry to choreography, and the dancers’ translation of their names into choreography. The study concludes with a discussion session, summarizing the inquiry, reviewing the strength and limitations of the project, and proposing directions for further investigation

Independent Component Analysis of Event-Related Electroencephalography During Speech and Non-Speech Discrimination: : Implications for the Sensorimotor ∆∞ Rhythm in Speech Processing

Background: The functional significance of sensorimotor integration in acoustic speech processing is unclear despite more than three decades of neuroimaging research. Constructivist theories have long speculated that listeners make predictions about articulatory goals functioning to weight sensory analysis toward expected acoustic features (e.g. analysis-by-synthesis; internal models). Direct-realist accounts posit that sensorimotor integration is achieved via a direct match between incoming acoustic cues and articulatory gestures. A method capable of favoring one account over the other requires an ongoing, high-temporal resolution measure of sensorimotor cortical activity prior to and following acoustic input. Although scalp-recorded electroencephalography (EEG) provides a measure of cortical activity on a millisecond time scale, it has low-spatial resolution due to the blurring or mixing of cortical signals on the scalp surface. Recently proposed solutions to the low-spatial resolution of EEG known as blind source separation algorithms (BSS) have made the identification of distinct cortical signals possible. The µ rhythm of the EEG is known to briefly suppress (i.e., decrease in spectral power) over the sensorimotor cortex during the performance, imagination, and observation of biological movements, suggesting that it may provide a sensitive index of sensorimotor integration during speech processing. Neuroimaging studies have traditionally investigated speech perception in two-forced choice designs in which participants discriminate between pairs of speech and nonspeech control stimuli. As such, this classical design was employed in the current dissertation work to address the following specific aims to: 1) isolate independent components with traditional EEG signatures within the dorsal sensorimotor stream network; 2) identify components with features of the sensorimotor µ rhythm and; 3) investigate changes in timefrequency activation of the µ rhythm relative to stimulus type, onset, and discriminability (i.e., perceptual performance). In light of constructivist predictions, it was hypothesized that the µ rhythm would show significant suppression for syllable stimuli prior to and following stimulus onset, with significant differences between correct discrimination trials and those discriminated at chance levels. Methods: The current study employed millisecond temporal resolution EEG to measure ongoing decreases and increases in spectral power (event-related spectral perturbations; ERSPs) prior to, during, and after the onset of acoustic speech and tone-sweep stimuli embedded in white-noise. Sixteen participants were asked to passively listen to or actively identify speech and tone signals in a two-force choice same/different discrimination task. To investigate the role of ERSPs in perceptual identification performance, high signal-to-noise ratios (SNRs) in which speech and tone identification was significantly better than chance (+4dB) and low SNRs in which performance was below chance (-6dB and -18dB) were compared to a baseline of passive noise. Independent component analysis (ICA) of the EEG was used to reduce artifact and source mixing due to volume conduction. Independent components were clustered using measure product methods and cortical source modeling, including spectra, scalp distribution, equivalent current dipole estimation (ECD), and standardized low-resolution tomography (sLORETA). Results: Data analysis revealed six component clusters consistent with a bilateral dorsal-stream sensorimotor network, including component clusters localized to the precentral and postcentral gyrus, cingulate cortex, supplemental motor area, and posterior temporal regions. Timefrequency analysis of the left and right lateralized µ component clusters revealed significant (pFDR\u3c.05) suppression in the traditional beta frequency range (13-30Hz) prior to, during, and following stimulus onset. No significant differences from baseline were found for passive listening conditions. Tone discrimination was different from passive noise in the time period following stimulus onset only. No significant differences were found for correct relative to chance tone stimuli. For both left and right lateralized clusters, early suppression (i.e., prior to stimulus onset) compared to the passive noise baseline was found for the syllable discrimination task only. Significant differences between correct trials and trials identified at chance level were found for the time period following stimulus offset for the syllable discrimination task in left lateralized cluster. Conclusions: As this is the first study to employ BSS methods to isolate components of the EEG during acoustic speech and non-speech discrimination, findings have important implications for the functional role of sensorimotor integration in speech processing. Consistent with expectations, the current study revealed component clusters associated with source models within the sensorimotor dorsal stream network. Beta suppression of the µ component clusters in both the left and right hemispheres is consistent with activity in the precentral gyrus prior to and following acoustic input. As early suppression of the µ was found prior the syllable discrimination task, the present findings favor internal model concepts of speech processing over mechanisms proposed by direct-realists. Significant differences between correct and chance syllable discrimination trials are also consistent with internal model concepts suggesting that sensorimotor integration is related to perceptual performance at the point in time when initial articulatory hypotheses are compared with acoustic input. The relatively inexpensive, noninvasive EEG methodology used in this study may have translational value in the future as a brain computer interface (BCI) approach. As deficits in sensorimotor integration are thought to underlie cognitive-communication impairments in a number of communication disorders, the development of neuromodulatory feedback approaches may provide a novel avenue for augmenting current therapeutic protocols