Hemispheres cerebraux et traitement phonologique et semantique des mots isoles

Ever since the nineteenth century, many studies have attempted to determine the existence and/or the nature of the two cerebral hemispheres' contribution to various aspects of language. The work in this thesis studies two aspects of word processing in the same participants, using behavioral data and functional neuroimaging. The exploration of the neurobiological correlates underlying the phonological and semantic processing of isolated words should lead to a better understanding of interhemispheric cooperation in distinct language components.; The participants were young French-speaking, right-handed and well-educated women. They had to perform two tasks: a grapheme-phoneme matching task for phonological processing and a category judgment task for semantic processing. In both tasks, the stimuli were visually presented French words with two levels of difficulty according to their graphophonemic transparency or semantic prototypicality. Divided visual field and functional magnetic resonance imaging (fMRI) methods were used for the data acquisition.; After a brief review of the literature (chapter 1), chapter 2 presents the two studies which were necessary to specify the methodological choices for both tasks and stimuli. More specifically, these studies allowed us to affirm the existence of the transparency and prototypicality effects. The results of study 3 (chapter 3), carried out in a divided visual field condition, highlight the left hemisphere's (LH) involvement in both phonological and semantic word processing, whereas the right hemisphere (RH) contributes only to semantic processing. Chapter 4 (studies 4 and 5) presents the fMRI results. The phonological task activated regions of the LH whereas the semantic task implicated both the LH and the RH, in the frontal, temporal and cerebellar regions. The different difficulty levels of the stimuli affected the behavioral data but not the fMRI data. Thus, it seems that both cerebral hemispheres have different abilities for the phonological and/or semantic processing of isolated words. The use of varied methods supports a better understanding of their contributions and their potential cooperation to process language.