Alpha power decreases associated with prediction in written and spoken sentence comprehension

Alpha and beta power decreases have been associated with prediction in a variety of cognitive domains. Recent studies in sentence comprehension have also reported alpha and/or beta power decreases preceding contextually predictable words, albeit with remarkable spatiotemporal variability across reports. To contribute to the understanding of the mechanisms underlying this phenomenon, and the sources of variability, the present study explored to what extent these prediction-related alpha and beta power decreases might be common across different modalities of comprehension. To address this, we re-analysed the data of two EEG experiments that employed the same materials in written and in spoken comprehension. Sentence contexts were weakly or strongly constraining about a sentence-final word, which was presented after a 1 s delay, either matching or mismatching the expectation. In written comprehension, alpha power (8-12 Hz) decreased before final words appearing in strongly (relative to weakly) constraining contexts, in line with previous reports. Furthermore, a similar oscillatory phenomenon was evidenced in spoken comprehension, although with relevant spatiotemporal differences. Altogether, the findings agree with the involvement of both modality-specific and general-domain mechanisms in the elicitation of prediction-related alpha power decreases in sentence comprehension. Specifically, we propose that this phenomenon might partly reflect richer and more precise information representation when linguistic contexts afford prediction

Alpha power decreases associated with prediction in written and spoken sentence comprehension

Alpha and beta power decreases have been associated with prediction in a variety of cognitive domains. Recent studies in sentence comprehension have also reported alpha and/or beta power decreases preceding contextually predictable words, albeit with remarkable spatiotemporal variability across reports. To contribute to the understanding of the mechanisms underlying this phenomenon, and the sources of variability, the present study explored to what extent these prediction-related alpha and beta power decreases might be common across different modalities of comprehension. To address this, we re-analysed the data of two EEG experiments that employed the same materials in written and in spoken comprehension. Sentence contexts were weakly or strongly constraining about a sentence-final word, which was presented after a 1 s delay, either matching or mismatching the expectation. In written comprehension, alpha power (8–12 Hz) decreased before final words appearing in strongly (relative to weakly) constraining contexts, in line with previous reports. Furthermore, a similar oscillatory phenomenon was evidenced in spoken comprehension, although with relevant spatiotemporal differences. Altogether, the findings agree with the involvement of both modality-specific and general-domain mechanisms in the elicitation of prediction-related alpha power decreases in sentence comprehension. Specifically, we propose that this phenomenon might partly reflect richer and more precise information representation when linguistic contexts afford prediction.pre-doctoral grant (FPU "Ayudas para la Formacion de Profesorado Universitario") of the Spanish Ministry of Education, Culture and Sport FPU15/0555

Perceptual facilitation of word recognition through motor activation during sentence comprehension

Published online 29 July 2018Despite the growing literature on anticipatory language processing, the brain dynamics of this high-level predictive process are still unclear. In the present MEG study, we analyzed pre- and post-stimulus oscillatory activity time-locked to the reading of a target word. We experimentally contrasted the processing of the same target word following two highly constraining sentence contexts, in which the constraint was driven either by the semantic content or by the lexical association between words. Previous research suggests the presence of sensory facilitation for expected words in the latter condition but not in the former. We observed a dissociation between beta (∼20 Hz) and gamma (>50 Hz) band activity in pre- and post-stimulus time intervals respectively. Both the beta and gamma effects were evident in occipital brain regions, and only the pre-stimulus beta effect additionally involved left pre-articulatory motor regions. Lexically constrained (vs. semantically constrained) words elicited reduced beta power around 400 msec before the target word in motor regions and a functionally related gamma enhancement in occipital regions around 200 msec post-target. The present findings highlight the role of the motor network in word-form prediction and support proposals claiming that low-level perceptual representations can be pre-activated during language prediction.This work was partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO), the Agencia Estatal de Investigación (AEI) and the (Fondo Europeo de Desarrollo Regional FEDER) (grant PSI2015-65694-P, “Severo Ochoa” programme SEV-2015-490 for Centres of Excellence in R&D), and by the Basque government (grant PI_2016_1_0014). Further support derived from the AThEME project funded by the European Commission 7th Framework Programme, the ERC- 2011-ADG-295362 from the European Research Council

Language prediction is reflected by coupling between frontal gamma and posterior alpha oscillations

Readers and listeners actively predict upcoming words during language processing. These predictions might serve to support the unification of incoming words into sentence context and thus rely on interactions between areas in the language network. In the current magnetoencephalography study, participants read sentences that varied in contextual constraints so that the predictability of the sentence-final words was either high or low. Before the sentence-final words, we observed stronger alpha power suppression for the highly compared with low constraining sentences in the left inferior frontal cortex, left posterior temporal region, and visual word form area. Importantly, the temporal and visual word form area alpha power correlated negatively with left frontal gamma power for the highly constraining sentences. We suggest that the correlation between alpha power decrease in temporal language areas and left prefrontal gamma power reflects the initiation of an anticipatory unification process in the language network

A predictive coding model of the N400

The N400 event-related component has been widely used to investigate the neural mechanisms underlying real-time language comprehension. However, despite decades of research, there is still no unifying theory that can explain both its temporal dynamics and functional properties. In this work, we show that predictive coding – a biologically plausible algorithm for approximating Bayesian inference – offers a promising framework for characterizing the N400. Using an implemented predictive coding computational model, we demonstrate how the N400 can be formalized as the lexico-semantic prediction error produced as the brain infers meaning from the linguistic form of incoming words. We show that the magnitude of lexico-semantic prediction error mirrors the functional sensitivity of the N400 to various lexical variables, priming, contextual effects, as well as their higher-order interactions. We further show that the dynamics of the predictive coding algorithm provides a natural explanation for the temporal dynamics of the N400, and a biologically plausible link to neural activity. Together, these findings directly situate the N400 within the broader context of predictive coding research. More generally, they raise the possibility that the brain may use the same computational mechanism for inference across linguistic and non-linguistic domains.</p

Using sentence context and mouth cues to aid speech comprehension: an electroencephalographic study on Cochlear Implant users

The research project presented in the thesis explores the electrophysiological correlates of linguistic prediction and audio-visual speech processing in deaf people with Cochlear Implant (CI) and people with normal hearing, in order to explore possible group differences. We implement an experimental paradigm in which participants observe audio-visual speech stimuli that vary for predictability of the last word of the sentence (i.e. the target) and visibility of mouth articulatory movements. During the procedure, we record the electroencephalographic signal (EEG) in order to compare the different experimental conditions in terms of neural oscillations and Event Related Potential (ERP) response to the target word. We also administrate linguistic tests to participants in order to relate behavioural performance to the electrophysiological results. The thesis presents a theoretical overview on prediction in language comprehension, the neural correlates of prediction and audio-visual speech integration and previous studies exploring these processes in CI users. Then, it presents the methods used in the experiment and preliminary data from a subgroup of participants with CI

The effects of DMT and associated psychedelics on the human mind and brain

This work presents seven investigations conducted with the aim to determine the effects of DMT (a compound which is able to cause remarkable effects in consciousness) and associated psychedelic drugs on the human brain and mind. Including a variety of neuroimaging (EEG, MEG and fMRI), phenomenological, psychometric and naturalistic research methods, these are the first controlled investigations of the impact of DMT in the human resting brain. Results revealed that DMT disrupted several brain mechanisms associated with top-down control (alpha power, integrity of high-level networks, modularity), increased measures related to entropy, or disorder (Lempel-Ziv complexity, novel pairwise connectivity) and immersive states of consciousness (delta/theta power), with some of these effects following the experiential trajectories of the DMT state. We also observed a significant temporal correlation between some of these effects (alpha power and default-mode network integrity fluctuations), which were supported by LSD effects of reduced feedback connectivity and neural adaption mechanisms. suggesting that the psychedelic brain state is one of reduced modularity, increased integration and functional plasticity. These findings were complemented by psychological studies showing that the DMT state is one of immersive visual imagery, intense somatic experiences and partial disconnection from the environment, which we found shared significant overlap with near- death experiences. DMT administration also resulted in positive mental health outcomes in healthy volunteers providing evidence for the first time that DMT may provide a useful alternative to currently- investigated psychedelic treatments. Finally, results from our last study performed in naturalistic environments revealed that psychedelics are able to have a transformative potential on core beliefs concerning the fundamental nature of reality and consciousness for up to 6 months, with important social and bioethical implications. Collectively these results attest to the strong impact that psychedelics have on varied human domains, which range experience, brain activity, mental health, intersubjectivity and beliefs.Open Acces

Syntactic and lexical processing in healthy ageing

Successful sentence production requires rapid word retrieval and the generation of an appropriate grammatical structure. In this thesis, I investigated how these lexical and syntactic processes are affected by healthy ageing. In Chapter 2, using a structural priming paradigm, I found evidence that the nature of syntactic representations is unaffected by healthy ageing and that global, not internal, structure determined syntactic choices in young and older adults. In Chapters 3-4, using adaptations of the planning scope paradigm, I found that young and older adults engaged in a similar phrasal scope of advanced planning. However, I also found evidence of age-related differences in lexical processing in that older adults were less able to manage the temporal activation of lexical items and their integration into syntactic structures. In Chapter 5, I investigated sentence comprehension using the neuroimaging technique of MEG. In young adults, I found that the binding of words into a minimal sentence structure was associated with a modulation in alpha power. Overall, the findings of this thesis demonstrate that there is a complex relationship between healthy ageing and language, such that certain features of language may be preserved with age, while others decline