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Au-delà des mots et des images, bases neurophysiologiques d'un système sémantique commun à la compréhension des phrases et des scènes visuelles

Abstract : Certain theories of cognitive function postulate a neural system for processing meaning, independent of the stimulus input modality. The objective of this thesis work, in line with the embodied cognition domain, was to study functionalities of such a network involved in both sentence and visual scene comprehension. In the literature, a wide network of fronto-temporo-parietal sensorimotor and associative areas are described as being involved in this process, and while there’s a lack of consensus on the amodal nature of this system, extensive research has focused on identifying distributed cortical systems that participate in meaning representations separately in the visual and language modalities. Moreover, the stimuli used are generally less complex than everyday life situations we meet. However, a significant portion of human mental life is built upon the construction of perceptually and socially rich internal scene representations and these mental models are involved in a large variety of processes for exploring specific memories of the past, planning the future, or understanding current situations. Although diffusion-tensor imagery based techniques makes feasible the visualization of white matter tracts in the human brain, the connectivity of the semantic network has been little studied. Through different experimental protocols involving mainly neuroimaging techniques (fMRI, DTI, EEG), we were able to reveal the neurophysiological basis of this common semantic network involved in the building of representation and comprehension of rich verbal and non-verbal stimuli. With our first experiment, we examined brain activation and connectivity in 19 subjects who read sentences and viewed pictures corresponding to everyday events, in a combined fMRI and DTI study. Conjunction of activity in understanding sentences and pictures revealed a common fronto temporo-parietal network that included inferior frontal gyrus, precentral gyrus, the retrosplenial complex, and medial temporal gyrus extending into the temporo-parietal junction (TPJ) and inferior parietal lobe. DTI tractography revealed a specific architecture of white matter fibers supporting this network which involves principally the pathways described as the ventral semantic route (IFOF, UF, ILF, MdLF). Our second experiment, which is a behavioral protocol, explored interindividual differences in the ability to represent sentences presented in auditory or visual modality. We demonstrated that individuals are not equal in this capacity to represent sentences, these differences were reflected in the effects on behavioral markers including scores of ease of representation (COR) and speed of responses (TR); they are also related to the number of fibers of the MdLF which supposes a role for this fasciculus in capacities of representation. Both the results of this behavioral protocol and results from our third EEG experiment also showed that the contextual effect was significant: the context induced by the presentation of a first stimulus has the ability to influence the representation of a second stimulus when is the second is semantically consistent or not with the first presented stimulus. Our EEG results (ERPs) revealed components influenced by the available semantic information: early attentional effects which could be modality-specific and later semantic integration process common for verbal and non-verbal stimuli... [etc]
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https://tel.archives-ouvertes.fr/tel-02613379
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Anne-Lise Jouen. Au-delà des mots et des images, bases neurophysiologiques d'un système sémantique commun à la compréhension des phrases et des scènes visuelles. Neurosciences [q-bio.NC]. Université Claude Bernard - Lyon I, 2013. Français. ⟨NNT : 2013LYO10322⟩. ⟨tel-02613379⟩

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