Relations entre conscience et représentations sémantiques verbales : approche comportementale et neurophysiologique chez le sujet sain et le patient cérébro-lésé

The study of cognitive functions so complex such as language and consciousness, and of their interactions, is a challenge at the boundaries between medicine (intensive care, anesthesia, neurology) and cognitive neuroscience. Semantic processing provides our perceptual experiences with a level of abstraction allowing a variety of conceptual functions such as object recognition, social cognition, or language. In this thesis, we explored the relationships between verbal semantic processing and consciousness using a double approach: first, by studying healthy subjects in conscious and unconscious condition (using visual masking), and secondly by studying patients with disorders of consciousness. Through this work we provided empirical evidence of unconscious semantic representations. We then proposed that the two main brain signatures of semantic processing observed in ERPs (N400 and LPC / P600) could be integrated in a two stages model: a first unconscious stage (corresponding to the N400), followed or not by a second stage of processing corresponding to conscious semantics (LPC / P600). Exploring the differences between conscious and nonconscious processing, we showed that nonconscious semantic processing is sensitive to conscious top-down influences. These results refute a strictly automatic conception of unconscious cognition. Our results also shed new light on the respective roles of the two hemispheres in the resolution of semantic ambiguity. The exploration of high-level cognitive abilities, - such a verbal semantic processing - in patients affected with disorder of consciousness should enable significant advancements in their medical management.L'étude de fonctions cognitives telles que le langage, la conscience et a fortiori leurs relations, constitue un défi aux confins de la médecine et des neurosciences cognitives. Le traitement sémantique procure à nos expériences perceptuelles un niveau de représentation abstrait, permettant une variété de fonctions conceptuelles. Dans ce travail, nous avons voulu explorer les relations entre le traitement sémantique verbal et la conscience en adoptant une double approche : d'une part en étudiant des sujets sains en condition de perception consciente et inconsciente (en utilisant une technique de masquage visuel), et d'autre part en étudiant des patients présentant un trouble de la conscience. Au travers de ce travail, nous apportons des arguments en faveur de l'existence de représentations sémantiques verbales inconscientes. Nous proposons également que les deux signatures cérébrales observées en potentiels évoqués (N400 puis LPC/P600) puissent s'intégrer dans un modèle à deux temps : premier temps inconscient (correspondant à la N400), puis second temps conscient (correspondant à la LPC/P600). En explorant les différences entre traitement conscient et non conscient, nous montrons que le traitement sémantique non conscient est sensible aux influences descendantes conscientes, ce qui réfute une conception strictement automatique de la cognition inconsciente. Nos résultats apportent également un nouveau regard sur les mécanismes de résolution d'ambiguïté sémantique. L'exploration des capacités cognitives telles que le traitement sémantique verbal, chez des patients présentant un trouble de la conscience, devrait permettre des avancées notables dans leur prise en charge

Head-Driven Phrase Structure Grammar

Head-Driven Phrase Structure Grammar (HPSG) is a constraint-based or declarative approach to linguistic knowledge, which analyses all descriptive levels (phonology, morphology, syntax, semantics, pragmatics) with feature value pairs, structure sharing, and relational constraints. In syntax it assumes that expressions have a single relatively simple constituent structure. This volume provides a state-of-the-art introduction to the framework. Various chapters discuss basic assumptions and formal foundations, describe the evolution of the framework, and go into the details of the main syntactic phenomena. Further chapters are devoted to non-syntactic levels of description. The book also considers related fields and research areas (gesture, sign languages, computational linguistics) and includes chapters comparing HPSG with other frameworks (Lexical Functional Grammar, Categorial Grammar, Construction Grammar, Dependency Grammar, and Minimalism)

Head-Driven Phrase Structure Grammar

Head-Driven Phrase Structure Grammar (HPSG) is a constraint-based or declarative approach to linguistic knowledge, which analyses all descriptive levels (phonology, morphology, syntax, semantics, pragmatics) with feature value pairs, structure sharing, and relational constraints. In syntax it assumes that expressions have a single relatively simple constituent structure. This volume provides a state-of-the-art introduction to the framework. Various chapters discuss basic assumptions and formal foundations, describe the evolution of the framework, and go into the details of the main syntactic phenomena. Further chapters are devoted to non-syntactic levels of description. The book also considers related fields and research areas (gesture, sign languages, computational linguistics) and includes chapters comparing HPSG with other frameworks (Lexical Functional Grammar, Categorial Grammar, Construction Grammar, Dependency Grammar, and Minimalism)

Consequences of bi-literacy in bilingual individuals: in the healthy and neurologically impaired

Background. In the current global, cross-cultural scenario, being bilingual or multilingual is a norm rather than an exception. In such an environment an individual may be actively involved in reading and writing in all their languages in addition to speaking them. Regular use of two or more languages is termed as bilingualism and being able to read and write in both of them is referred to as bi-literacy. Research indicates that bilingualism has an impact on language production and cognition, specifically executive functions. Given the impact of literacy and bilingualism, the reasonable question that arises, is whether bi-literacy would offer an additional impact on language production and cognition. This becomes even more relevant in a multilingual, multi-cultural society such as India. We examined the impact of bi-literacy on oral language production (at word and connected speech level), comprehension and on non-verbal executive function measures in bi-literate bilingual healthy adults in an immigrant diaspora living in the UK. In addition to English, they were speakers of one of the South Indian languages (Kannada, Malayalam, Tamil and Telugu). The significance of bi-literacy among bilinguals assumes further importance in aphasia (language impairment due to brain damage). For those who have aphasia in one or more languages due to brain damage, the severity of impairment maybe different in both languages, also the modalities of language may be differentially affected. In particular, reading and writing maybe impaired differently in the languages used by a bi/multilingual. Manifestation of reading impairments are also dependent on the nature of the script of the language being read [e.g., Raman & Weekes (2005) report differential dyslexia in a Turkish-English speaker who exhibited surface dyslexia in English and deep dysgraphia in Turkish]. Our study contributes to the field of bilingual aphasia by focusing specifically on reading differing from the existing literature of aphasia in bilinguals, where the focus has predominantly been on language production and comprehension. Studying reading impairments provides a better understanding of how the reading impairments are manifested in the two languages, which will aid appropriate assessment and intervention. This research investigated the impact of bi-literacy in both populations (healthy adults and neurologically impaired) in two phases: Phase I (in UK) and Phase II (in India). Aim. Phase I investigated the impact of bi-literacy on oral language production (at word level and connected speech), comprehension and non-verbal executive function in bi-literate bilingual healthy adults. Phase II examined the reading impairments in two languages of bilingual persons with aphasia (BPWA). Methods. For Phase I, participants were thirty-four bi-literate bilingual healthy adults with English as their L2 and one of the Dravidian languages (Kannada, Malayalam, Tamil and Telugu) as their L1. We have used the term ‘print exposure’ as a proxy for literacy. They were divided into a high print exposure (HPE, n=22) and a low print exposure (LPE, n=12) group based on their performance on two tasks measuring L2 print exposure- grammaticality judgement task and sentence verification task. We also quantified their bilingual characteristics- proficiency, reading and writing characteristics and dominance. The groups were matched on years of education, age and gender. Participants completed a set of oral language production tasks in L2 (at word level) namely -verbal fluency, word and non-word repetition; comprehension tasks in L2 namely synonymy triplets task and sentence comprehension task (Chapter 2); oral narrative task in L2 (at connected speech level) (Chapter 3) followed by non-verbal executive function tasks tapping into inhibitory control (Spatial Stroop and Flanker tasks), working memory (visual n-back and auditory n-back) and task switching (colour-shape task) (Chapter 4). For Phase II, we characterized the reading abilities of four BPWA who spoke one of the Dravidian languages (Kannada, Tamil, Telugu) (alpha-syllabic) as their L1 and English (alphabetic) as their L2. We quantified their bilingual characteristics- proficiency, reading and writing characteristics and dominance. Subtests from the Psycholinguistic Assessment of Language Processing in Aphasia (PALPA; Kay, Lesser & Coltheart, 1992) were used to document the reading profile of BPWA in English and reading subtests from Reading Acquisition Profile (RAP-K; Rao, 1997) and words from Bilingual Aphasia test -Hindi (BAT; Paradis & Libben, 1987) were used to document the reading profile of BPWA in Kannada and Hindi respectively. Findings. Based on the findings of Phase I (i.e., results from Chapter 2-4), we found prominent differences between HPE and LPE on comprehension measures (synonymy triplets and sentence comprehension tasks). This is in contrast to the results observed in monolingual adults, were semantics is less impacted by print exposure. Moreover, our predictions that HPE will result in better oral language production skills were borne out in specific conditions-semantic fluency and non-word repetition task (at word level) and higher number of words in the narrative, higher verbs per utterance and fewer repetitions (at connected speech level). In addition, the non-verbal executive functions, we found no direct link between print exposure (in L2) and non-verbal executive functions in bi-literate bilinguals excepting working memory (auditory N-back task). Additionally, another consistency in our findings is that there seems to be a strong link between print exposure and semantic processing in our research. The findings on the semantic tasks have been consistent across comprehension (synonymy triplets task and sentence comprehension task) and production (semantic fluency) favouring HPE. The findings from Phase II (Chapter 5) reveal differences of reading characteristics in the two languages (with different scripts) of the four BPWA. This research provides preliminary evidence that a script related difference exists in the manifestation of dyslexia in bi-scriptal BPWA speaking a combination of alphabetic and alpha-syllabic languages. Conclusions. Our research contributes to the existing literature by highlighting the relationship between bi-literacy and language production, comprehension and non-verbal cognition where bi-literacy seems to have a higher impact on language than cognition. The contrary findings from the monolinguals and children literature, highlight the importance for considering nuances of bilingual research and specifically challenges the notion that semantic comprehension is not significantly affected by literacy. In the neurologically impaired population, our research provides a comprehensive profiling of reading abilities in BPWA in the Indian population with languages having different scripts. Using this profiling and classification, we are able to affirm the findings previously found in literature emphasizing the importance of script in the assessment of reading abilities in BPWA. Such profiling and classification assist in the development of bilingual models of reading aloud and classifying different types of reading impairments

Word production and executive control in bilingual aphasia

Word production is an essential feature of successful communication where semantic information (meaning) of a word is activated first, and this representation then activates the corresponding phonological form followed by the articulation of the target word. However, the production of words becomes effortful and impaired following neurological impairments (e.g., aphasia). The nature of word production impairments in aphasia is poorly understood and inadequately treated. In healthy monolingual speakers, word production involves selection of target word from competing lexical items within the target language. The situation becomes complicated for bilinguals with two sets of lexical systems leading to enhanced lexical competition. Research has shown different executive control processes are involved while resolving lexical competition. There is currently not a consensus in the literature as to whether this lexical competition is resolved in the same way by monolingual and bilingual speakers. Moreover, research on the nature of word production deficits in bilinguals with aphasia (BWA) and their relationship to executive control mechanism is not established in the literature, especially in Indian languages. In this project, we investigate the relationship between word production and executive control in a systematic and stepwise exploration in two phases (Phase I in UK and Phase II in India) by using different participant groups, wide range of linguistic measures, and separate executive control measures. Participants in Phase I were 25 healthy Bengali-English bilinguals and English monolinguals who were matched on age, gender, years of education, non-verbal intelligence, and vocabulary. Participants completed two linguistic experimental tasks (verbal fluency in Chapter 2 and blockedcyclic naming in Chapter 3) in English and three executive control tasks (inhibitory control: Stroop task, mental-set shifting: colour-shape switch task, working memory: backward digit span test). Results revealed bilinguals performed at par with the monolinguals in some linguistic measures (semantic fluency and heterogenous context in blocked-cyclic naming) and outperformed monolinguals in certain linguistic measures (e.g. letter fluency and homogenous context in blockedcyclic naming). Therefore, bilingual disadvantage in the linguistic domain can be negated if vocabulary is controlled for. Also, bilingual advantage in the non-linguistic domain can be extended to the linguistic domain if the linguistic tasks were made more challenging by increasing the executive control demands. Bilingual Participants in Phase II were eight Bengali-English BWA and eight Bengali-English bilingual healthy adults (BHA) who were matched on age, gender, years of education, and measures of bilingualism. Participants completed two linguistic tasks (verbal fluency in Chapter 4 and picture naming involving cognates and non-cognates in Chapter 5) in both languages and same executive control tasks as in Phase I, except for mental-set shifting (Trail Making Test). As expected, we found evidence of linguistic and executive control impairments at the group level for BWA individuals. Similar to the monolingual group in Phase I, we found BWA had more difficulty in the linguistic measures (e.g. fluency difference score, number of switches, between-cluster pause) where executive control demands were higher. However, the underlying executive control deficits in the linguistic tasks may not be visible with the usual analysis techniques. Therefore, we argued in favor of including a more fine-grained analysis of linguistic tasks. In terms of cross-linguistic impairment following a stroke, our results showed similar impairment in both the languages and the post-stroke language ability (e.g. better performance in Bengali) mirrored their pre-stroke language ability (Bengali dominant). Findings from the linguistic tasks revealed that despite showing deficits in lexical access, BWA still mirrored the BHA in terms of the underlying language processing mechanism which is required to perform in the linguistic tasks. In summary, performance differences on the linguistic measures were mediated by various factors such as the participant groups, nature of the task, language proficiency, and executive control abilities. We emphasise the importance of characterising the BWA participants in terms of their linguistic impairments in both languages, bilingualism related variables, separate linguistic and executive control measures and involved analysis approaches. We provide a foundation for future research on understanding the interplay of linguistic and executive control processes during word production in healthy bilinguals as well as in BWA population